source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-1444 | human-biology, evolution
Humans are off the charts in the amount of resources we invest in our children - our lives are 1/4 to 1/3 over before we sometimes leave our parents household (in some societies of course they never leave the house, but step into an extended family). This may be one of the reasons we are so successful as a species - we live in practically every place we possibly could and have no danger of competition from any other living thing excepting ourselves.
The grandmother effect is essentially the idea that if women, who are more attached to the offspring in more cases than fathers, continue to live and help support the grandchildren and make them more successful, then this will allow post menopausal women to have a longer lifespan (which they do).
The evolutionary biologist Sara Hrdy, emeritus UC Davis, has written quite a bit about the nuances of the evolution of the role of motherhood - reading some of her articles or books might give you a deeper sense of how profoundly filial love has shaped human beings.
--- more answer this stuff may or may not be worth reading depending on how broadly you want to understand this question...
Its important to say that many of the expansions of human average human lifespan have not been genetic. Its commonly cited that sewer systems, clean water, antibiotics and plentiful food are the three most important factors in human lifespan - and before modern developed world nations, the average lifespan of human beings was somewhere in the 30s. And there are significant lifespan differences in regions where these factors and others (education of women, access to prenatal and early care etc) are available.
Studies continue to be published that examine environmental and lifestyle factors compared to genetics and it seems that environment and lifestyle can make an astounding difference.
But genetics undoubtedly has a role to play here too. There are probably some individual humans and animals which have evolved to live longer. This has been found to be genetically related in some humans by demographics and family lines.
The following is multiple choice question (with options) to answer.
Microevolution occuring and taking place over many generations results in? | [
"fission",
"microinjection",
"recalibration",
"macroevolution"
] | D | Macroevolution occurs over geologic time above the level of the species. The fossil record reflects this level of evolution. It results from microevolution taking place over many generations. |
SciQ | SciQ-1445 | mineralogy, hydrogeology, mars
Despite active transport into Earth’s mantle, water has been present on our planet’s surface for most of geological time. Yet water disappeared from the Martian surface soon after its formation. Although some of the water on Mars was lost to space via photolysis following the collapse of the planet’s magnetic field, the widespread serpentinization of Martian crust suggests that metamorphic hydration reactions played a critical part in the sequestration of the crust. Here we quantify the relative volumes of water that could be removed from each planet’s surface via the burial and metamorphism of hydrated mafic crusts, and calculate mineral transition-induced bulk-density changes at conditions of elevated pressure and temperature for each. The metamorphic mineral assemblages in relatively FeO-rich Martian lavas can hold about 25 per cent more structurally bound water than those in metamorphosed terrestrial basalts, and can retain it at greater depths within Mars. Our calculations suggest that in excess of 9 per cent by volume of the Martian mantle may contain hydrous mineral species as a consequence of surface reactions, compared to about 4 per cent by volume of Earth’s mantle. Furthermore, neither primitive nor evolved hydrated Martian crust show noticeably different bulk densities compared to their anhydrous equivalents, in contrast to hydrous mafic terrestrial crust, which transforms to denser eclogite upon dehydration. This would have allowed efficient overplating and burial of early Martian crust in a stagnant-lid tectonic regime, in which the lithosphere comprised a single tectonic plate, with only the warmer, lower crust involved in mantle convection. This provided an important sink for hydrospheric water and a mechanism for oxidizing the Martian mantle. Conversely, relatively buoyant mafic crust and hotter geothermal gradients on Earth reduced the potential for upper-mantle hydration early in its geological history, leading to water being retained close to its surface, and thus creating conditions conducive for the evolution of complex multicellular life.
does serpentinization just refer to the formation of some hydrated minerals that happen to be of a class that is historically been referred to as serpentinite or it's subgroup
The following is multiple choice question (with options) to answer.
What do craters and rifts become when they fill with water? | [
"streams",
"seas",
"rivers",
"lakes"
] | D | Left: Indrik myneur; Right: Courtesy of UNEP/GRID. Craters and rifts become lakes when they fill with water . Left: CC BY 2.0; Right: Non-copyrighted and available for free use. |
SciQ | SciQ-1446 | neuroscience
Title: Nervous system : Nerve signals If the electrical signals from all the various organs throughout the body eventually connect to the nerves in the spinal column traveling up to the brain, how does the brain differentiate the different signals. Is the nerve in the spinal column like an electrical conduit with many wires inside? Yes is the simple answer. A nerve will go up to a specific part of the brain which the brain knows corresponds to a certain region of the body. It isn't perfect though e.g. pain in the diaphragm confuses the brain which doesn't recognise that pain must be coming from there so instead tells the body there is shoulder pain, however this is useful in medicine. Another infamous example is pain from heart disease (angina) which causes pain in the jaw and arm. Perhaps even more interestingly, if a nerve is cut and then grows back linking to the wrong nerve it may lead to the completely wrong part of the body being identified when touched. Also if the brain itself is stimulated in these corresponding areas, a person will feel he or she is indeed being touched in a certain part of the body.
The following is multiple choice question (with options) to answer.
What system carries messages from sense organs and internal organs to the central nervous system? | [
"sensitive nervous system",
"peripheral nervous system",
"auxiliary nervous system",
"respiratory system"
] | B | The sensory division of the peripheral nervous system carries messages from sense organs and internal organs to the central nervous system. For example, it carries messages about images from the eyes to the brain. Once the messages reach the brain, the brain interprets the information. |
SciQ | SciQ-1447 | human-biology, physiology, respiration, breathing, lungs
Title: Why does hyperventilation make you feel like you need to breathe more? Calm Clinic claims:
"The problem is that hyperventilation makes your body feel like you're not getting enough oxygen. Essentially, it makes you feel like you need to take deeper breaths and take in as much air as possible. This makes all of the symptoms of hyperventilation worse."
As far as I know, the brain controls breathing rate by measuring the amount of carbon dioxide in the blood. So is this true? If so, why? Hyperventilation alone does not cause you to feel that you're not getting enough oxygen. Rather, it's what causes hyperventilation that does that (thus resulting in hyperventilation.)
The Calm Clinic explains this quite well (while only mildly contradicting your quote):
During periods of intense anxiety, the body is sent into a state of fight or flight, when the brain signals to the body that danger is afoot. When this happens, you automatically start breathing quickly, as this oxygenates your blood and prepares your body to respond to a threat by fighting or fleeing. If the threat that has triggered your fight or flight response (whether real or imagined) persists, you’re likely to continue hyperventilating until you start to experience other unpleasant physical symptoms.
The focus of your question is
"...This makes all of the symptoms of hyperventilation worse." [emphasis mine]
You can hyperventilate by breathing too quickly or too deeply; either way, in people without underlying medical disorders, hyperventilation is usually caused by stress/anxiety. Anxiety makes your heart rate increase, and causes a perception of the need for more air (not the actual hyperventilation). It is often accompanied by some degree of chest tightness, which many people reasonable attribute to a problem with their heart. These things tend to cause more stress, so it's a cycle. The symptoms of hyperventilation are dizziness/lightheadedness, tingling in your hands/feet and around your mouth, and more but less common symptoms.
Under normal circumstances, hyperventilation leads to a period of decreased respiratory rate to allow for arterial blood to build up that critical buffer, HCO3.
Dealing with Anxiety Symptoms: Hyperventilation
(written for laypersons)
The following is multiple choice question (with options) to answer.
What disease is described as a respiratory disorder characterized by wheezing, coughing, and a feeling of constriction in the chest? | [
"asthma",
"inflammation",
"dementia",
"indigestion"
] | A | Respiratory system disorders are directly related to air pollution. These disorders have severe effects on human health, some leading to death directly related to air pollution. Air pollution related respiratory disorders include asthma, bronchitis, and emphysema. Asthma is a respiratory disorder characterized by wheezing, coughing, and a feeling of constriction in the chest. Bronchitis is inflammation of the membrane lining of the bronchial tubes of the lungs. Emphysema is a deadly lung disease characterized by abnormal enlargement of air spaces in the lungs and destruction of the lung tissue. Additional lung and heart diseases are also related to air pollution, as are respiratory allergies. |
SciQ | SciQ-1448 | observational-astronomy, telescope, amateur-observing, optics, deep-sky-observing
Use the brightest stars on your journey to guide your way. Look for shapes: triangles of stars of a similar brightness make great signposts.
If you find that you can see more stars in the eyepiece than the star map is showing you, then you might want to change to one of the other applications. SkEye is free and has a limited catalogue. The other two are not free but have more extensive catalogues.
A great desktop application for this is KStars: it has a star hopping tool which will generate set of instructions, given a start point, and end point, and an eyepiece.
I find star hopping to be a fun way to hunt down targets in the sky. For me it makes the sense of discovery even sweeter. Other people find it dull and would rather use a Go-To mount to do the work for them.
Give it a try and find out which type of person you are - either way is perfectly valid :-)
Filters
In a comment, D.Halsey suggests using a light pollution filter. Unfortunately these are less useful than they were. These days many cities have 'upgraded' to LED lighting, which has the unfortunate side-effect of casting light which covers the full visible spectrum. Light pollution filters worked by filtering out the yellow light given off by the old sodium street lights. Against modern LED lights they don't do very much. If you're fortunate then you might live in an area which hasn't yet changed the street lighting over from sodium to LED - in which case go ahead with the light pollution filter!
Filters which do work - on certain nebulae at least - are the O-III (doubly ionised oxygen) and Ha (hydrogen alpha) filters, or one of the several "nebula filters" which allow both of these bands through.
They don't make the objects brighter - they work by making everything else darker. But they do work. I've seen several nebulae from the city which were impossible to see without them.
Just bear in mind that, because they work by dimming everything except the nebula, they're best used with your lowest power eyepiece: the one that gives the biggest exit pupil, and therefore the brightest view.
Aperture and/or darker skies
The following is multiple choice question (with options) to answer.
What is used to darken images of the sky? | [
"uv filter",
"neutral density filter",
"close-up filter",
"polarizing filters"
] | D | Photographs of the sky can be darkened by polarizing filters, a trick used by many photographers to make clouds brighter by contrast. Scattering from other particles, such as smoke or dust, can also polarize light. Detecting polarization in scattered EM waves can be a useful analytical tool in determining the scattering source. There is a range of optical effects used in sunglasses. Besides being Polaroid, other sunglasses have colored pigments embedded in them, while others use non-reflective or even reflective coatings. A recent development is photochromic lenses, which darken in the sunlight and become clear indoors. Photochromic lenses are embedded with organic microcrystalline molecules that change their properties when exposed to UV in sunlight, but become clear in artificial lighting with no UV. Take-Home Experiment: Polarization Find Polaroid sunglasses and rotate one while holding the other still and look at different surfaces and objects. Explain your observations. What is the difference in angle from when you see a maximum intensity to when you see a minimum intensity? Find a reflective glass surface and do the same. At what angle does the glass need to be oriented to give minimum glare?. |
SciQ | SciQ-1449 | endocrinology, pathology, experimental, diabetes-mellitus
Title: Growth Hormone and diabetes Growth hormone and insulin like growth factors are diabetogenic, so I assume that people with high growth hormone (say due to pituitary tumor) may be at high risk for diabetes. Has any correlation been established between these two? I know that diabetes is a multifactorial disorder and so only a correlation may be established. Yes:
That GH has an effect on glycaemic control is most evident from the abnormal glucose tolerance seen in acromegalics...
acromegaly is defined as abnormal growth of the hands, feet, and face, caused by overproduction of growth hormone by the pituitary gland.
Such an effect has been known for decades, which makes sense given how interrelated the axes are. Although I think the best evidence is the fact that the side effects of growth hormone therapy says that Some patients have developed diabetes mellitus...
The following is multiple choice question (with options) to answer.
A tumor of what gland can cause hypersecretion of growth hormone? | [
"Pancreas",
"Parathyroid",
"pituitary gland",
"tissues gland"
] | C | Hypersecretion by an endocrine gland is often caused by a tumor. For example, a tumor of the pituitary gland can cause hypersecretion of growth hormone. If this occurs in childhood, it results in very long arms and legs and abnormally tall stature by adulthood. The condition is commonly known as gigantism (see Figure below ). |
SciQ | SciQ-1450 | homework, cell-membrane, human-physiology, lungs
Title: How many cell membranes are oxygen and carbon dioxide diffuse through in the lungs? In the lungs, oxygen and carbon dioxide pass through cell membranes by diffusion.
Which row is correct?
The correct answer is D, but I think it should be B. I can only think about three layers as maximum which are; epithelium of alveolus, endothelium of capillaries and the membrane of red blood cell. I don't know what are remainings.
Any help would be much appreciated! Oxigen goes from the alveolar's lumen to the cytoplasm of the erythrocyte, and that's 5 membranes:
the "top" of the alveolar epithelial cell
the "bottom" of such cell
the "top" of the endothelial cell (capillary)
the "bottom" of such cell
the erythrocyte membrane
You got all the cells right, but your only problem was this: oxygen diffuses through the cell membrane entering the cell, moves through the cytoplasm, and diffuses through the membrane again exiting the cell. So, for each cell, you have to count 2 membranes. For the last one, the erythrocyte, you have only 1 membrane (because it is $\ce{O2}$ final destination).
For the $\ce{CO2}$ the situation is a little bit more tricky. We have the same 4 membranes (2x epithelial cell and 2x capillary), but $\ce{CO2}$ can come from 2 locations:
from the erythrocyte, where it is formed from $\ce{H2CO3}$ (by the reaction $\ce{H2CO3 -> H2O + CO2}$) or released from the N-terminal group of proteins, like haemoglobin (where it has previously bound)
from the plasma (around 9% of the $\ce{CO2}$).
In the first case we have 5 membranes, and in the second case just 4.
So, the correct answer is D.
The following is multiple choice question (with options) to answer.
After the blood in the pulmonary capillaries becomes saturated with oxygen, it leaves the lungs and travels where? | [
"to the lungs",
"to the kidneys",
"to the brain",
"to the heart"
] | D | After the blood in the pulmonary capillaries becomes saturated with oxygen, it leaves the lungs and travels to the heart. The heart pumps the oxygen-rich blood into arteries, which carry it throughout the body. Eventually, the blood travels into capillaries that supply body tissues. These capillaries are called peripheral capillaries . |
SciQ | SciQ-1451 | thermodynamics, material-science, phase-transition, states-of-matter
Title: Why does matter exist in 3 states (liquids, solid, gas)? Why does matter on the earth exist in three states? Why cannot all matter exist in only one state (i.e. solid/liquid/gas)? The premise is wrong. Not all materials exist in exactly three different states; this is just the simplest schema and is applicable for some simple molecular or ionic substances.
Let's picture what happens to a substance if you start at low temperature, and add ever more heat.
Solid
At very low temperatures, there is virtually no thermal motion that prevents the molecules sticking together. And they stick together because of various forces (the simplest: opposite-charged ions attract each other electrostatically). If you picture this with something like lots of small magnets, it's evident enough that you get a solid phase, i.e. a rigid structure where nothing moves.
Actually though:
Helium won't freeze at any temperature: its ground state in the low-temperature limit at atmospheric pressure is a superfluid. The reason is that microscopically, matter does not behave like discrete magnets or something, but according to quantum mechanics.
There is generally not just one solid state. In the magnet analogy, you can build completely different structures from the same components. Likewise, what we just call “ice” is actually just one possible crystal structure for solid water, more precisely called Ice Ih. There are quite a lot of other solid phases.
Liquid
Now, if you increase temperature, that's like thoroughly vibrating your magnet sculpture. Because these bonds aren't infinitely strong, some of them will release every once in a while, allowing the whole to deform without actually falling apart. This is something like a liquid state.
Actually though:
The following is multiple choice question (with options) to answer.
Depending on the surrounding conditions, normal matter usually exists as one of three phases: solid, liquid, or this? | [
"gas",
"fluid",
"ice",
"crystal"
] | A | Depending on the surrounding conditions, normal matter usually exists as one of three phases: solid, liquid, or gas. A phase change is a physical process in which a substance goes from one phase to another. Usually the change occurs when adding or removing heat at a particular temperature, known as the melting point or the boiling point of the substance. The melting point is the temperature at which the substance goes from a solid to a liquid (or from a liquid to a solid). The boiling point is the temperature at which a substance goes from a liquid to a gas (or from a gas to a liquid). The nature of the phase change depends on the direction of the heat transfer. Heat going into a substance changes it from a solid to a liquid or a liquid to a gas. Removing heat from a substance changes a gas to a liquid or a liquid to a solid. Two key points are worth emphasizing. First, at a substance’s melting point or boiling point, two phases can exist simultaneously. Take water (H2O) as an example. On the Saylor URL: http://www. saylor. org/books. |
SciQ | SciQ-1452 | star, astrophysics
Title: Why are blue stars the hottest? I know that blue stars are the hottest and youngest (according to Universe Today). But what makes them blue, instead of other colors like purple? Our eyes and brains make them blue.
Stars are (close to) a black body, they emit a broad band of radiation. The hottest stars will emit most of their radiation in the ultraviolet but they will still be very bright in visible light.
As they get hotter, they emit even more ultraviolet, and more visible light but the mixture of wavelengths in visible light doesn't change much.
This mixture is interpreted by our brains as being a sort of light blue. No matter how hot the star gets, it will still be emitting lots of visible light in a mixture that looks "light blue". It will never look purple.
Purple can only be seen if either a single short-wavelength visible light is being emitted, or a mixture of short and long wavelengths (red and blue). Neither of the mixtures can occur in light emitted from a black body.
So stars can appear red, orange, yellow, white or light blue, but never green or purple.
The following is multiple choice question (with options) to answer.
What celestial bodies are classified by color and temperature, ranging from blue to red and hottest to coolest? | [
"astroids",
"stars",
"planets",
"galaxies"
] | B | Stars are classified by color and temperature. The most common system uses the letters O (blue), B (blue-white), A (white), F (yellow-white), G (yellow), K (orange), and M (red), from hottest to coolest. |
SciQ | SciQ-1453 | botany, mathematical-models, statistics, biostatistics, migration
Title: Biostatistics: Pollen dispersal directionality What Information am I looking for?
Think about a tree that is sending pollen all over the place. Because of wind, most pollen grain will go toward one direction. Imagine, we split the 2D area around the tree where pollen grains fall into two half disks of equal size. We chose the disks so that the number of pollen grains falling into one half-disk is minimized and the quantity of pollen falling in the other half-disk is maximized.
The information I need is what proportion of pollen grain falls into each disk? Is it $\frac{0.5}{0.5}$ (in which case the wind would have no effect) or is it something like $\frac{0.8}{0.2}$?
Where to get the information from?
I was reading this paper about pollen dispersal directionality and was trying to extract the info I need.
On pages 4 and 5 they explain their analysis under the section statistical procedure. More specifically, in the first paragraph of the 5th page, they seem to describe the meaning of the parameters that are trying to estimate. One of them is the so-called directionality parameter $\delta$. I don't understand how to interpret this parameter $\delta$. This parameter is part of a logistic regression I think (although the authors do not characterize it as such) of "mating success" $y$ against variables $d$ ("distance") and $h$ ("height") and an angular variable $a = \cos(\alpha_0 - \alpha)$. ($\alpha_0$ is the "presumed prevailing direction of effective pollen dispersal," which apparently is not estimated from these data.) The corresponding parameters of the model are $\beta$, $\gamma$, and $\delta$, respectively, hence
$$\phi_j = \Pr(y_j = 1) = \frac{\exp\left(\beta d_j + \gamma h_j + \delta a_j\right)}{\sum_{k=1}^r \exp\left(\beta d_k + \gamma h_k + \delta a_k\right)}$$
The following is multiple choice question (with options) to answer.
What carries small pollen grains farther than they otherwise would go? | [
"birds",
"wind",
"humidity",
"steam"
] | B | |
SciQ | SciQ-1454 | homework-and-exercises, rocket-science, estimation, satellites, propulsion
Title: Launch small satellite? I want to build a small satilite and launch it into low space orbit. Nothing 'too fancy' a Raspberry Pi to power the systems, camera which'all transmit video and also a radio reviver and transmitter, maybe a small power bank to power the Pi and solar panels to charge that and gyro for stability in space instead of multiple thrusters. Hopefully it should last a few weeks before it burns up. The weight of the satilite would be under 5Kg. Also would radiation cause any short term harm to the electronics?
I was also thinking if I could first launch it with a weather balloon, have a small chemical rocket fire just before the weather balloon pops and then once it's reached micro gravity the rocket falls away and a canister of compressed air can accelerate it from there to a distance where should last a couple weeks.
I was also thinking about ion thrusters but they use a lot of electricity
Would this be possible at all? @antlersoft is right. You'd still need a powerful rocket to get moving fast enough to enter into orbit around the Earth, so probably not, unless it's a really really big balloon holding a really big rocket!
The term "microgravity" might be a bit misleading. The gravity up there is almost as strong as it is on the surface. The key is to go fast enough so that your "fall" towards earth actually ends up being an orbit. That's about 7.7 kilometers per second!!
If you are inside a spacecraft, in an orbit, moving at such an orbital velocity, you would also be in orbit around the earth. If you just look at how your body moves with respect to the spacecraft, you could call it "microgravity" (lots of people do, even astronauts) but maybe it should be called micro-acceleration with respect to the spacecraft.
The following is multiple choice question (with options) to answer.
What do rocket-based systems use to propel itself into space? | [
"nuclear reactions",
"water reactions",
"hydrogen reactions",
"chemical reactions"
] | D | The space shuttle—and any other rocket-based system—uses chemical reactions to propel itself into space and maneuver itself when it gets into orbit. The rockets that lift the orbiter are of two different types. The three main engines are powered by reacting liquid hydrogen with liquid oxygen to generate water. Then there are the two solid rocket boosters, which use a solid fuel mixture that contains mainly ammonium perchlorate and powdered aluminum. The chemical reaction between these substances produces aluminum oxide, water, nitrogen gas, and hydrogen chloride. Although the solid rocket boosters each have a significantly lower mass than the liquid oxygen and liquid hydrogen tanks, they provide over 80% of the lift needed to put the shuttle into orbit—all because of chemical reactions. |
SciQ | SciQ-1455 | Next: Order and rate of Up: Preliminaries Previous: Preliminaries
## Sensitivity and Conditioning
In numerical methods, it is important to know how reliable the numerical results produced by some algorithm are, and how sensitive the algorithm is with respect to the inevitable noise in the input variables and system parameters, due possibly to some observational error and truncation error. We need to know how sensitive the output of a given method is with respect to the various perturbations that may occur in computational process. In general, if a large difference in the output may be caused by a small change in the input, then the result is not reliable. How sensitive a problem is and whether the numerical solution is reliable or not depends on whether the problem is well behaved or ill behaved:
• If a small change in the input causes a small change in the output, the system is well conditioned or well behaved.
• If a small change in the input can cause a large change in the output, the system is ill conditioned or ill behaved.
How well or ill conditioned a system is can be measured quantitatively by the absolute or relative condition numbers:
• The absolute condition number is the upper bound of the ratio between the change in output and change in input:
• The relative condition number is the upper bound of the ratio between the relative change in output and relative change in input:
Here is the norm (representing size'') of any variable (scalar, vector, matrix, function, etc.). In the following, we will use mostly the norm for vectors and the corresponding spectral norm for matrices.
As the relative condition number compares the normalized changes in both the input and output, its value is invariant to the specific units used to measure them. Also the change in input can also be equivalently normalized by the input plus change as well as in input. The same is true for the change in the output.
Obviously, the smaller the condition number, the better conditioned the problem is, the less sensitive the solution is with respect to the perturbation of the data (error, noise, approximation, etc.); and the larger the condition number, the more ill conditioned the problem is. In the following, we specifically consider the condition numbers defined for some different systems.
System with single input and output variables
The following is multiple choice question (with options) to answer.
What term simply means sensitive beyond normal levels of activation? | [
"hypersensitivity",
"isosensitivity",
"monosensitivity",
"hyposensitivity"
] | A | Hypersensitivities The word “hypersensitivity” simply means sensitive beyond normal levels of activation. Allergies and inflammatory responses to nonpathogenic environmental substances have been observed since the dawn of history. Hypersensitivity is a medical term describing symptoms that are now known to be caused by unrelated mechanisms of immunity. Still, it is useful for this discussion to use the four types of hypersensitivities as a guide to understand these mechanisms (Figure 21.28). |
SciQ | SciQ-1456 | endocrinology, glucose, homeostasis, insulin, hypothalamus
Title: Role of the Hypothalmus in the control of Blood Sugar In homeostatic regulation of blood glucose, the receptor and effector is the Pancreas, but how does the control centre — the Hypothalamus — connect and link into this process? Your question doesn’t make it clear whether you think that the pancreas must be under the control of the hypothalmus, or whether you are asking whether it has an influence on the pancreas in relation to the secretion of insulin and glucagon, which control the concentration of blood glucose.
First, it has been long known that secretion of insulin can be influenced by the concentration of glucose in isolated pancreatic islets in vitro, so it can not be true that the effects must involve the hypothalmus. This is implicit in most book or general information articles you might find on the web, but for an original reference a review by W.J. Malaisse in Diabetologia 9, 167–173 (1973) seems highly cited.
I know almost nothing about physiology, but on searching the web for the role of the hypothalmus in glucose homeostasis, found a most readable prize-winning postgraduate essay on the topic by Syed Hussein of Imperial College London. I trust that it is in order to append an edited extract of this:
The following is multiple choice question (with options) to answer.
The hypothalamic releasing and inhibiting hormones are secreted near capillaries at the base of the what? | [
"hippocampus",
"lungs",
"pancreas",
"hypothalamus"
] | D | |
SciQ | SciQ-1457 | telescope, amateur-observing, diy
Title: Challenges when trying to build a telescope using two lenses I have some lenses - a 10 cm and 7 cm convex lense and a 4 cm and 1 cm concave lenses. I am trying to make a telescope by combining one of convex and concave lenses, but I am struggeling to do so. The picture that is created using these two lenses doesn't show anything other than the thing that can be seen by eyes. Is it possible to make simple telescope using these lenses?
PS: All of numbers are lense diameters. Diameter is important, but if you're trying to get any magnification out of that system, you need to look at the focal length.
If you have a very distant light source, like the Sun, focused through a convex lens, until the image of the source is as small and as clear as possible, then the focal length is the distance between the lens and the image you're creating. Like when you burn paper with the lens, focal length is the lens-paper distance.
For concave lenses focal length is a little more tricky to define, but they do have a focal length anyway.
If F is the focal length of the forward lens (the objective), and f is the focal length of the lens near your eye (the ocular, or the eyepiece), then the magnification of the instrument is:
M = F / f
So you need an objective with a long focal length, and an eyepiece with a short focal length.
Both the objective and the eyepiece could be convex actually. It's just that the image will be reversed. If the eyepiece is concave, the image will be straight-up, but the field of view of the telescope will be narrow (like looking through a peephole).
If you use both convex lenses, the distance between them need to be close to the sum of their focal lengths, F + f. Start there and adjust it slightly for best results.
If you use a concave lens for the eyepiece, then the distance between lenses needs to be the difference of their focal lengths, F - f.
The following is multiple choice question (with options) to answer.
A microscope can be made from two of what kind of lenses? | [
"inner",
"outer",
"convex",
"angular"
] | C | 26.4 Microscopes Although the eye is marvelous in its ability to see objects large and small, it obviously has limitations to the smallest details it can detect. Human desire to see beyond what is possible with the naked eye led to the use of optical instruments. In this section we will examine microscopes, instruments for enlarging the detail that we cannot see with the unaided eye. The microscope is a multiple-element system having more than a single lens or mirror. (See Figure 26.15) A microscope can be made from two convex lenses. The image formed by the first element becomes the object for the second element. The second element forms its own image, which is the object for the third element, and so on. Ray tracing helps to visualize the image formed. If the device is composed of thin lenses and mirrors that obey the thin lens equations, then it is not difficult to describe their behavior numerically. |
SciQ | SciQ-1458 | microbiology, bacteriology, photosynthesis
2H+ + 2e– → H2
So that the overall reaction becomes:
2H2O + hν → 2H2 + O2
(Of course, this will be at the expense of energy and reducing power for carbohydrate synthesis.)
Using Hydrogenase for the Catalysis
The enzyme, hydrogenase, can catalyse the reduction of hydrogen ions shown above. This enzyme is rare in eukaryotes and absent from higher plants. It is thought to be very ancient, and may have originally been involved in energy generation from hydrogen in early evolution. One of the roles it plays in contemporary organisms is in reoxidizing NADH generated during certain fermentations in bacteria such as the Clostridium family — hydrogen is the gas produced in gas gangrene caused by Clostridium perfringens.
Certain photosynthetic organisms — notably the microalga, Chlamydomonas reinhardtii, and the photosynthetic cyanobacteria — also contain a hydrogenase in their chloroplasts. The activity of this is generally low, but appears to be coupled to photosynthesis in certain circumstances. This is through the reduced ferredoxin produced at PSI transferring its electron to the iron or iron–nickel centre of the hydrogenase:
The following is multiple choice question (with options) to answer.
What produces almost one-half of the earth's oxygen through photosynthesis? | [
"protists",
"prokaryotes",
"algae",
"arthropods"
] | A | Humans could not live on Earth if it were not for protists. Why? Plant-like protists produce almost one-half of the oxygen on the planet through photosynthesis. Other protists decompose and recycle nutrients that humans need to live. All protists make up a huge part of the food chain. |
SciQ | SciQ-1459 | population-genetics, allele
$h$
Dominance Type
Scenario
0<h<1
Incomplete dominance
The heterozygote ($A_1A_2$) more fit than $A_2A_2$ and less fit than $A_1A_1$
h<0
Overdominance
The heterozygote ($A_1A_2$) more fit than homozygotes ($A_1A_1$ and $A_2A_2$)
h>1
Underdominance
The heterozygote ($A_1A_2$) less fit than homozygotes ($A_1A_1$ and $A_2A_2$)
In each of these cases, the phenotype of the heterozygote is something different than either of the homozygotes (hence the term incomplete dominance). What the value $h$ is measuring here is not the difference in phenotypes, it's the effect it has on fitness- which might be different in different contexts.
Let's think about the classic example of overdominance, sickle cell disease. In terms of fitness, individuals with one copy of the sickle cell allele have the sickle cell trait. The sickle cell trait offers resistance to malaria, and therefore higher fitness in regions with endemic malaria. An individual with two copies of the sickle cell allele are less fit because they have sickle cell disease. An individual with no copies of the sickle cell allele is less fit because they don't have resistance to malaria infection.
But this measure of dominance, where we define dominance as the fitness associated with a the expression of a characteristic, is context-dependent- individuals with the sickle cell trait are prone to other diseases, and in the absence of endemic malaria it might be they have lower fitness than an individual with no copies of the sickle cell allele ($0<h<1$).
If we think about dominance as simply the expression of a characteristic, we would actually describe the sickle cell heterozygote as co-dominant- when you look at the blood of individuals with sickle cell trait (heterozygotes), they have a mix of normal-shaped red blood cells and sickle-shaped red blood cells.
So to conclude:
The following is multiple choice question (with options) to answer.
What is said to occur when both traits appear in a heterozygous offspring? | [
"identical twins",
"pollenation",
"xenophobia",
"codominance"
] | D | What happens when there are two alleles in a heterozygote and neither allele is completely dominant nor completely recessive? Can both traits appear in the phenotype? Essentially, yes they can. Can there be two dominant alleles for the same gene? Codominance occurs when both traits appear in a heterozygous offspring. For example, roan shorthorn cattle have codominant genes for hair color. The coat has both red and white hairs; not pink hairs, but red AND white hairs. The letter R indicates red hair color, and R’ white hair color. In cases of codominance, the genotype of the organism can be determined from its phenotype. The heifer in Figure below shows both coat colors and therefore is RR’ heterozygous for coat color. The flower in Figure below also has two codominant alleles; it has red and white petals, not pink petals. Both colors appear in the phenotype. |
SciQ | SciQ-1460 | molecular-biology, book-recommendation, cell-signaling
Title: What are some good books on basics of Cell signaling? I think the title says it all.
(self answered, although others' answers requested)
Cellular Signal Processing (an introduction to the molecular mechanisms of signal transduction), by Frederich Marks, Ursula Klingmuler, Karin Muller-Decker;
Garland/Taylor-Francis.
Link: CRC book, Google books
.............
Structure and function in Cell signaling by John Nelson, Wiley.
Link: Wiley, Google books
The following is multiple choice question (with options) to answer.
What type of response do signal transductions within target cells bring about? | [
"physiological",
"resporatory",
"psychological",
"bacterial"
] | A | |
SciQ | SciQ-1461 | solar-system, comets
But the blatant errors in my assumptions undoubtedly swamp any such effects, and I'm only looking for a rough estimate.
So yes, the Earth's passage through a meteor stream will effectively punch a hole in it, but it's a very small hole relative to the size of the entire stream. It could have a significant effect over millions of years.
I'm making a lot of simplifying assumptions here, but the conclusion seems about right if I've gotten the result within one or two orders of magnitude.
Reference: http://www.amsmeteors.org/meteor-showers/meteor-faq/#5, plus some of my own extremely rough back-of-the-envelope calculations.
The following is multiple choice question (with options) to answer.
What happens to meteors as they fall through the mesosphere? | [
"they burn",
"they grow",
"they stop suddenly",
"they bounce"
] | A | Did you ever see a meteor shower, like the one in Figure below ? Meteors burn as they fall through the mesosphere. The space rocks experience friction with the gas molecules. The friction makes the meteors get very hot. Many meteors burn up completely in the mesosphere. |
SciQ | SciQ-1462 | mineralogy, petrology
Title: How do you use the streckeisen (QAPF) classification ternary diagram to identify igneous rocks based on chemical rock composition? I have been given the following diagrams:
and
and a database that is structured like this:
ROCK NAME |SIO2 |TIO2| AL2O3| CR2O3| FEOT| CAO| MGO| MNO| K2O| NA2O| P2O5|
WEHRLITE |45.42| 0.17| 2.57| 0.32| 11.3384| 7.54| 31.93| 0.17| 0.01| 0.24| 0.01|
I want to know how to normalize the data and use these diagrams to identify the rock name based on the IUGS specification. I then am tasked to write a program that will do this automatically meaning that I have to come up with some semi-mathematically-based process to identify these rocks. Any ideas? Why you should not do it
The QAPF and related diagrams are intended for classification of rocks in the field, or preliminary classification with modal proportions as seen in the optical microscope. They are not designed with the chemical composition of the rocks in the mind. Furthermore, these diagrams are merely descriptive and not genetic. They do not take into account many factors affecting the various characteristics of the rocks. While doing something like this may be interesting for homework exercise, it is not something I would expect to see in a recent research article.
If you want to do it anyway
Your solution should consist of two steps.
The following is multiple choice question (with options) to answer.
What are the three main types of rocks? | [
"limestone , igneous and metamorphic",
"sedimentary, igneous and metamorphic",
"plutonic, igneous and metmorphic",
"crystalline , igneous and metamorphic"
] | B | A geologic map shows the different rocks that are exposed at the surface of a region. Rock units are shown in a color identified in a key. On the geologic map of the Grand Canyon, for example, different rock types are shown in different colors. Some people call the Grand Canyon “layer cake geology“ because most of the rock units are in layers. Rock units show up on both sides of a stream valley. |
SciQ | SciQ-1463 | entomology, reptile
Title: Had there been a non-flying pterosaur? Since there are non-flying birds and secondary non-flying insects, it is reasonable to assume there were also non-flying pterosaurs. Well, according to this source there are no flightless bats, so it isn't an absolute that all flying clades have flightless members:
https://pterosaurheresies.wordpress.com/2011/07/21/meet-the-first-flightless-pterosaur-sos-2428/
Everyone knows about the various flightless birds: the penguin, the dodo, the ostrich… the list goes on. There are no flightless bats. And no one has ever discovered a flightless pterosaur… until now.
But the short answer to your question is: no confirmed flightless pterosaur fossil seems to have been discovered so far.
The longer answer is: from what I can tell no pterosaur has been found that was clearly flightless, but pterosaur flight isn't well-understood in the first place so there is debate as to how and whether some specimens could have flown. It seems to be the consensus so far that they did fly however (based on the lack of mention of flightlessness on the Wikipedia page, and the last paper I link to in this answer is fairly convincing).
As far as not finding flightless specimen, the above link claims to have found one but the source is not reputable and I found no confirmation of it elsewhere (Wikipedia confirms, and I'm usually all about Wikipedia but here the page has all the hallmarks of having been written by the same person who wrote the blog). The same author argues a large pterosaur is flightless here, but their arguments are quite poor compared to others made in the field and they seem again to be the only ones making them.
Here is a post from Tetrapod Zoology in 2008 imagining what a flightless pterosaur might be like, and also claiming none have been found:
The following is multiple choice question (with options) to answer.
What is the only continent without amphibians? | [
"Europe",
"antarctica",
"Africa",
"Australia"
] | B | Amphibians can be found in freshwater and moist terrestrial habitats throughout the world. The only continent without amphibians is Antarctica. Amphibians are especially numerous in temperate lakes and ponds and in tropical rainforests. |
SciQ | SciQ-1464 | zoology
Title: What is right below skin? I was skinning a gopher so my cat can eat it (it was a pest and we didn't want to waste it). I thought its organs would fall out and make a mess, but that didn't happen. There was this sticky, transparent substance that surrounded its insides. What is this casing called? My dad said it was mucus but that isn't specific enough since there is mucus inside the stomach so I don't think they are the same.
I think this casing is found in all multicellular animals but I couldn't be sure. Based on your reference to organs falling out and the overall description, I presume you're thinking of the abdominal cavity primarily, so there you'd be looking at the peritoneum or possibly the serous membranes of other organs (e.g., pleura, pericardium). These are membranous (in the general sense, not as a cell membrane) connective tissues covering the organs found in the abdomen and chest.
Other things you'll find underneath skin would include layers of fat, other connective tissues, muscle.
Here's a labeled image of a mouse dissection from Friedrich, L., Schuster, M., de Celis, M. F. R., Berger, I., Bornstein, S. R., & Steenblock, C. (2021). Isolation and in vitro cultivation of adrenal cells from mice. STAR protocols, 2(4), 100999.:
You might also look for dissections of fetal pigs or cats, which are commonly used in laboratory demonstrations for students (more often cats longer ago, more often fetal pigs these days).
The following is multiple choice question (with options) to answer.
A hair grows out of a follicle and passes through what before extending above the skin surface? | [
"epidermis",
"dermis",
"cartilage",
"callus"
] | A | Hair follicles are structures where hairs originate. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. |
SciQ | SciQ-1465 | bacteriology
Saier, MH. & Bogdanov, V. (2013) Membranous Organelles in Bacteria. JOURNAL OF MOLECULAR MICROBIOLOGY AND BIOTECHNOLOGY 23: 5-12 DOI: 10.1159/000346496
Free full text here.
The language used in this review seems to support the existence of mesosomes as some sort of intermediate in the formation of intracellular membranes in prokaryotes. This review is a polemic in favour of the idea that prokaryotes do indeed contain intracellular membrane-bounded compartments. It has no abstract, but the first paragraph gives a flavour of its stance:
The traditional view of life on Earth divides the living world into two major groups, prokaryotes and eukaryotes. These two groups were originally suggested to differ in very basic respects. While eukaryotes had complex cell structures including a cytoskeleton and intracellular membrane-bounded organelles, prokaryotes were believed to lack them. In fact, numerous textbooks and current sources still note this distinction and hold it to be true. For example, in Campbell’s Biology [Campbell, 1993, p. 515] it is stated without equivocation: ‘Prokaryotic cells lack membrane-enclosed organelles.’ In ‘Functional Anatomy of Prokaryotic and Eukaryotic Cells’ [Tortora et al., 2009, chapt. 4] it is similarly claimed that ‘Prokaryotes lack membrane-enclosed organelles, specialized structures that carry on various activities’. In the current Wikipedia, under ‘Prokaryote’ the following statement can be found: ‘The prokaryotes are a group of organisms whose cells lack a cell nucleus (karyon) or any other membrane-bounded organelles’. In the same online compendium under ‘Organelle’, one can read: ‘whilst prokaryotes do not possess organelles per se, some do contain protein-based microcompartments’. Proteinceous microcompartments will be the subject of a forthcoming Journal of Molecular Microbiology and Biotechnology written symposium, but this one will show that these generalizations, suggesting a lack of subcellular compartmentalization in prokaryotes, are blatantly in error [Murat et al., 2010a].
The following is multiple choice question (with options) to answer.
What are the long, thin structures that protrude from the cell membrane and help single-celled organisms move or swim towards food? | [
"microvilli",
"flagella",
"sporangia",
"tentacles"
] | B | Flagella ( flagellum , singular) are long, thin structures that protrude from the cell membrane. Both eukaryotic and prokaryotic cells can have flagella. Flagella help single-celled organisms move or swim towards food. The flagella of eukaryotic cells are normally used for movement too, such as in the movement of sperm cells, which have only a single flagellum. The flagella of either group are very different from each other. Prokaryotic flagella, shown in Figure below , are spiral-shaped and stiff. They spin around in a fixed base much like a screw does, which moves the cell in a tumbling fashion. Eukaryotic flagella are made of microtubules that bend and flex like a whip. |
SciQ | SciQ-1466 | evolution, genetics, molecular-genetics, theoretical-biology, molecular-evolution
Title: Smallest unit on which selection can act Traditionally, the individual was considered to be the smallest unit on which Natural Selection (NS) acts. Today, we usually consider the gene as being the unit of NS. Of course, we should also consider all sequences that affect the fitness even though they are not genes (even though the do not code for polypeptide). And theoretically, any sequence of DNA does have an effect on fitness because it influences the time and energy for DNA replication (although it might be negligible). The decision of considering the gene as the smallest unit of NS seems rather arbitrary to me. We might as well consider a group of genes or a given exon of even a smaller sequence.
Here are my questions:
What factors influence the minimal size of a sequence to be considered as a unit on which NS acts? Mutation rate, generation time, selection differential for this sequence, recombination rate, ...?
Could we consider a nucleotide as a unit of NS? Why?
How does the quasispecies model fit into the question of what is the smallest unit of NS? (for those interested, you will also find a very good explanation of this model in Martin Nowak's book called Evolutionnary Dynamic: exploring the equations of life)
Is it worth talking about that? Is this question biologically relevant? Or is it rather a question based on a choice of definition such as "Is a virus alive?"
As I asked several questions, let me know if I should split my post into several. Otherwise, please do not hesitate to answer only very partially to this post!
UPDATE
Terdon's answer makes sense to me. I should be a bit more accurate in the reas of my question. I read The extended Phenotype from Richard Dawkins quite a long time ago and if I'm not mistaken, Dawkins says the following things
A unit on which selection acts has to be:
active
germ-line
replicator
A replicator has the 3 following properties:
fecundity
longevity
fidelity while being copied
The following is multiple choice question (with options) to answer.
What is the unit of evolution? | [
"dna",
"a phylum",
"the cell",
"the population"
] | D | The population is the unit of evolution. |
SciQ | SciQ-1467 | fluid-dynamics
Title: Are waves affected by an under-water barrier? Given a wave propagating at the surface of still water towards a barrier that is below the surface, but at a distance that is of the order of the dimensions of the wave (such as depicted in the scheme below).
How will the course of the wave be affected ?
Will it be blind to it and pursue its course unaffected ?
Will it only partially pursue and a part of it will bounce back ?
Something else ?
<
wave
/~~~
/~~~~\ ->
~~~~/~~~~~~`~~~~~~~~~~~~~~~~~~~~~~~~ water surface
____
| |
| |
____________________| |__________
barrier Ocean surface waves that are said to 'feel' bottom are known as shallow water waves which are categorically differentiated from deep water waves according to wavelength and depth, and which are not as affected by the depth of the sea floor.
Ocean surface waves are a movement of energy, not a bulk forward motion of water but do result in local circular orbits of the water particles. With depth the circular orbits flatten into elliptical orbits and eventually vanish, and it's at this depth obstacles will no longer influence surface wave motion. For obstacles that do intrude into this space, the circular or elliptical motions are disturbed and energy is dissipated towards the upper water layers, building up wave height. IN very shallow water the build up can get high enough that the wave can no longer sustain its shape and you have a breaking wave.
The property that actually leads to the loss of energy from obstacles is the viscosity of the water, the ability for layers of water to flow over one another.
The following is multiple choice question (with options) to answer.
What occurs where the water motion slows? | [
"deposition",
"vapor",
"erosion",
"diffusion"
] | A | Longshore drift continually moves sand along the shore. Deposition occurs where the water motion slows. The smallest particles, such as silt and clay, are deposited away from shore. This is where the water is calmer. Larger particles are deposited onshore. This is where waves and other motions are strongest. |
SciQ | SciQ-1468 | homework-and-exercises, electromagnetism
Title: Force on a charged particle in a field of an EM wave For example if there is a charge q with mass m travelling with a velocity v "in the field" of a plane electromagnetic wave that is travelling in the z direction (in free space). My question is what would the force and direction (if any) be if the particle was travelling in the same direction as the wave? If it's a positive charge, the particle moves in the direction of the electric field and vice versa for a negative charge.
However, there also exists another force called the Lorentz force. It essentially states that, if a particle is moving with a velocity perpendicular to a magnetic field, a force is produced in a direction mutually perpendicular to the velocity and magnetic field.
To sum up the forces acting on a moving particle by an electric and magnetic field:
$$ {\vec F} = q({\vec E} + {\vec v}\times{\vec B}) $$
Use this image to deduce the motion of a proton and electron that is travelling in the same direction as the propagation of an electromagnetic wave:
The following is multiple choice question (with options) to answer.
The force on a charged particle in a magnetic field is always perpendicular to both its velocity vector and the? | [
"gravity vector",
"field vector",
"position vector",
"track vector"
] | B | Since the force on a charged particle in a magnetic field is always perpendicular to both its velocity vector and the field vector (check this using the second right hand rule above), a constant magnetic field will provide a centripetal force --- that is, a constant force that is always directed perpendicular to the direction of motion. Two such force/velocity combinations are illustrated above. According to our study of rotational motion, this implies that as long as the particle does not leave the region of the magnetic field, it will travel in a circle. To find the radius of the circle, we set the magnitude of the centripetal force equal to the magnitude of the magnetic force and solve for :. |
SciQ | SciQ-1469 | evolution, mammals
Title: Why haven't land animals evolved beyond urination? It occurred to me (while urinating) that this would seem to be selected against because water is a scarce resource. Why are we constantly losing water we don't need to through urination? What is it about the chemistry of urine and the waste products eliminated that make urination necessary as opposed to eliminating them through defecation and recovering the water on the way out? It is probably true that toilets and other resting-ish area are always a great place to think about biology, I agree $\ddot \smile$.
Why do we urinate?
In short, urine contains the waste from our blood while defecation is just the stuff that we haven't digested. Kidneys are the organs responsible for draining wastes (mostly nitrogen-containing, or nitrogenous, wastes) from our blood.
Trade-off: energy cost vs. water loss
You're correct that the loss of water through urination is a considerable cost for an organism (especially those living in dry environments). But the amount of water used to excrete nitrogenous wastes is negatively correlated with the energy it costs to perform this excretion. In other words, there is a trade-off between water and energy loss during nitrogen excretion. Also, the question of toxicity is important.
Three ways to excrete nitrogenous wastes
Animals basically have three choices to excrete nitrogenous wastes:
Uric acid (excreted by uricotelic organisms)
Solid (crystal) with low water solubility
Low toxicity
Little water is needed
Lots of energy is needed
Ammonia (excreted by aminotelic organisms)
Highly soluble in water
High toxicity
Lots of water is needed to dilute it because of the toxicity
Not much energy is needed
Urea (excreted by ureotelic organisms)
Solid but highly soluble in water
"medium" amount of water is needed
"medium" toxicity
"medium" amount of energy is needed
The following is multiple choice question (with options) to answer.
What is the process of removing wastes and excess water from the body called? | [
"ingestion",
"diffusion",
"inspiration",
"excretion"
] | D | Excretion is the process of removing wastes and excess water from the body. It is one of the major ways the body maintains homeostasis. Although the kidneys are the main organs of excretion, several other organs also excrete wastes. They include the large intestine, liver, skin, and lungs. All of these organs of excretion, along with the kidneys, make up the excretory system . The roles of the excretory organs other than the kidney are summarized below:. |
SciQ | SciQ-1470 | cell-biology
Title: Structure of Cell Are cells spheres or ovals/circles bound by phospholipidbilayer?
If they are spherical how are we able to see the nucleus through the phospholipid bilayer under a microscope? Not exactly. That is a stereotype of cells. Muscle cells are not round nor oval, but rather elongated rods. If you were to look up epithelia cells, you can quickly see that cells are grouped based on their physical characteristics; simple (round/oval & single layer), columnar, and cuboidal to name a few. Cells come in many shapes and sizes. As Hans stated, stains are vital in viewing cellular components. There is a diverse amount of stains used - which all carry a purpose and benefit in a specific application.
The following is multiple choice question (with options) to answer.
What is the skeleton of the cell? | [
"cell wall",
"cytoplasm",
"cell membrane",
"cytoskeleton"
] | D | The cytoplasm consists of watery cytosol and cell structures. It has several functions. The cytoskeleton is the “skeleton” of the cell. It helps the cell keep its shape. |
SciQ | SciQ-1471 | oceanography, geochemistry
Title: Why is NaCl so hyper abundant in the ocean? Why is sodium chloride far and away the most abundant salt dissolved in ocean water? Its two constituent ions do have a very high frequency in the crust of the earth, but they are far from the most common. Chlorine is (according to Wikipedia) the 21st most abundant element, and sodium 6th.
I certainly understand that a combination of their solubility and reasonably high frequency would lead one to expect them to be abundant in sea water, but they are hyper abundant, completely dominating all other salt ions. Iron, for example, is twice as abundant, and potassium only a little less abundant, and fluorine more abundant than chlorine.
Moreover, if the salts are deposited in the ocean through weathering of rocks and deposition via rivers, why does the salinity not simply grow and grow? I understand that some is lost due to tectonic activity, but it seems extraordinarily unlikely that these two forces should be equally balanced, and so we would see a significant change in average salinity over time.
(Please note I am migrating this question from the Chemistry SE at their recommendation.) Fluoride salts tend to be not particularly soluble in water. Chloride salts are. The same goes for salts containing sodium versus those containing calcium. Sodium chloride is ridiculously easy to dissolve.
Regarding your second question, it is geological forces that keep salinity more or less constant. People formerly argued that the Earth can't be more than a few hundred million years old because otherwise the river waters running into the oceans would eventually result in an insanely high salinity. It turns out that the Earth's oceans are young (young compared to the 4.5 billion year age of the Earth). The vast majority of oceanic crust is less than 100 million years old. We see huge salt deposits sprinkled across the world because those are the dried up remnants of former seas and oceans. Salt is also drawn into the Earth at subduction zones, where it combines chemically with basalt.
The following is multiple choice question (with options) to answer.
A salt concentration of 32 percent is nearly ten times that of what abundant resource? | [
"seawater",
"algae",
"oxygen",
"fresh water"
] | A | |
SciQ | SciQ-1472 | atoms
Title: Conversion atom to another One child has claimed to have find a solution to all physical problems. On asking for details, he said that all periodic elements has common components, i.e. electrons, protons, neutrons.
The child has suggested a solution: convert atom to another by adding electron. This way one can get substance like $\ce{H2O, Au, He}$ in abundance.
How can it be done? While what you suggest may sound nice on paper, it has some serious problems.
Getting the elements. Let's say that we're talking about purifying water to remove toxic elements such as Hg or Cd. Extracting the elements out of the water is a feat by itself, for example using reverse osmosis methods. This is a method used for seawater desalination - to turn them from salt water filled with all kinds of elements into drinkable water. This process is very expensive, and a very polluting one as well. Desalination just the amount of water you need for drinking water is complicated, so desalinating an entire reservoir is simply not going to happen.
Let's say you did somehow manage to extract the element in question. Now you need nuclear reactions to transmute one element to another. Not all are possible. For some elements, like Tc or Am this is the only way you can produce them. However, you are going to end up with radioactive nuclear waste.
To sum it up, even if it was possible, you would need so much power and to do it and you will produce some much pollution that it's simply not worth it. Just going and mining the gold will be orders of magnitude cheaper (and probably cleaner) than producing it using nuclear reactions.
If you do manage to somehow extract the the polluting elements, you usually do something else with them (aka recycling) and you do not attempt being an alchemist. Another example is soils contaminated with lead. The solution is to just dig it up, put it somewhere where it is not hazardous to anyone and replace it with clean soil.
The following is multiple choice question (with options) to answer.
Atoms of one element can be transformed into another through which process? | [
"magnetic reactions",
"developed reactions",
"nuclear reactions",
"longer reactions"
] | C | Not all atoms of an element must have precisely the same mass. Atoms of one element can be transformed into another through nuclear reactions. The compositions of many solid compounds are somewhat variable. Under certain circumstances, some atoms can be divided (split into smaller particles). These modifications illustrate the effectiveness of the scientific method; later experiments and observations were used to refine Dalton’s original theory. |
SciQ | SciQ-1473 | zoology, circulatory-system, heart-output, amphibians
I would add to this my notes from when I was a biochem student (but studied Zoology), mentioning the arterial cone and a spiral valve. This is better described in Britannica:
The conus arteriosus is muscular and contains a spiral valve. Again, as in lungfishes, this has an important role in directing blood into the correct arterial arches. In the frog, Rana, venous blood is driven into the right atrium of the heart by contraction of the sinus venosus, and it flows into the left atrium from the lungs. A wave of contraction then spreads over the whole atrium and drives blood into the ventricle, where blood from the two sources tends to remain separate. Separation is maintained in the spiral valve, and the result is similar to the situation in lungfishes. Blood from the body, entering the right atrium, tends to pass to the lungs and skin for oxygenation; that from the lungs, entering the left atrium, tends to go to the head. Some mixing does occur, and this blood tends to be directed by the spiral valve into the arterial arch leading to the body.
The following is multiple choice question (with options) to answer.
Blood from the body enters what chamber of the heart before it is pumped to the right ventricle and then to the lungs? | [
"left atrium",
"left ventricle",
"right atrium",
"left bivalve"
] | C | Blood from the body enters the right atrium of the heart. The right atrium pumps the blood to the right ventricle, which pumps it to the lungs. This loop is represented by the blue arrows in Figure above . |
SciQ | SciQ-1474 | cell-biology, meiosis, mitosis
Title: Is the cell cycle applicable to meiosis as well, or just mitosis? All the diagrams I can find, show the cell cycle as having G1 phase (growth 1), S phase (DNA replication), G2 (growth 2) before the Mitotic phase (mitosis + cytokinesis).
Is there an equivalent "cell cycle" for meiosis, since the chromosomes in parent cell in meiosis also having "double" the genetic material prior to cell division (presumably from DNA replication too)?
Is it simply the same cell cycle as mitosis but with a Meiotic phase instead of Mitotic?
If so, would appreciate if anyone had a diagram :) Thanks! The cell cycle is only associated with mitosis. The cell cycle is the normal process of cell division with which cells can indefinitely increase their number by cyclically repeating the process. When a cell goes through the cycle, the result is two cells that are genetically identical.
Meiosis is a special type of cell division (which can occur only in eukaryotes) that produces cells that are not genetically identical to the initiating cell. The number of chromosomes in each of the resulting cells is half the number that were in the initial cell. (These haploid cells can later participate in fertilization, producing a cell with the original number of chromosomes.) Many of the steps of meiosis are similar to the steps involved in mitosis, but overall the process is more complex. Since meiosis reduces the number of chromosomes, it cannot be repeated and so does not take part in a cell division cycle.
The following is multiple choice question (with options) to answer.
Dna replication, chromosome segregation, and the separation into two daughter cells are steps in what process? | [
"binary fission",
"multiple fission",
"reproductive fission",
"nuclear fission"
] | A | Binary fission can be described as a series of steps, although it is actually a continuous process. The steps are described below and also illustrated in Figure below . They include DNA replication, chromosome segregation, and finally the separation into two daughter cells. |
SciQ | SciQ-1475 | energy, waves, superposition
Title: Superposition of waves and energy transferred A wave transfers energy. I was reading about the superposition of two waves, where the amplitudes of the two waves added up to produce a resultant wave.
So I began wondering about the energy that is now being transferred in this resultant wave. Is it the sum of energy being transferred by both waves?
Please help me understand. When two waves, propagating in a linear medium, interfere with each other, the amplitudes of individual points within the region of interference could add or subtract, but this does not affect the flow of energy.
We can show it in a simple example below:
Point A is in the region of interference and its amplitude will be affected by both waves.
Point B is beyond the region of interference and should not be affected by wave S2. This is because the amplitude at B is defined by a superposition of the two waves, i.e., it has to be the sum of S1 and S2 at point B. Since the amplitude of S2 at B is zero (or negligible), the amplitude at B is affected by S1 only.
The same could be said about all point of wave S1 beyond the region of interference. If so, we have to conclude that S2 would not affect S1 beyond the region of interference and therefore will not change the flow of energy of S1.
We could come to a similar conclusion, if we took into account that the waves don't get reflected while propagating in a uniform linear medium, which means that no energy is coming back and, therefore, it should continue moving forward, unaffected by other waves in that medium. The sound wave moving in the air will be reflected by a wall, but not by another sound wave.
The following is multiple choice question (with options) to answer.
In science, what is defined as the transfer of energy from a vibrating object in waves that travel through matter? | [
"photons",
"vibration",
"energy",
"sound"
] | D | In science, sound is defined as the transfer of energy from a vibrating object in waves that travel through matter. Most people commonly use the term sound to mean what they hear when sound waves enter their ears. The tree above generated sound waves when it fell to the ground, so it made sound according to the scientific definition. But the sound wasn’t detected by a person’s ears if there was nobody in the forest. So the answer to the riddle is both yes and no!. |
SciQ | SciQ-1476 | genetics, biochemistry, proteins, rna
Title: Where do amino acids get attached to tRNA and where is it synthesized? Some very basic parts of transcription/translation seem to be left out in various literature. I can't find the answer to this anywhere:
How exactly is tRNA synthesized? I realize that mRNA is synthesized through transcription and I know a lot about that. However tRNA is supposedly synthesized the same way but every time you read about transcription they just talk about how the mRNA then gets this and that...?
Where do the amino acids get attached? Is it in the nucleus or outside the nucleus?
Thanks. A pre-tRNA is transcribed from tRNA genes in DNA by RNA polymerase III. Processing occurs in the nucleus, where a 5' sequence is cleaved by RNase P, the 3's CCA motif is added, and ~10% of the nucleotides are substituted. The tRNA are transported out via the pore complexes. Aminoacyl-tRNA synthetase enzymes attach amino acids in the cytoplasm in a 2-step reaction that requires ATP. You'll find there's a unique splicing mechanism in tRNA that additionally splices out an anticodon intron which is abesnt in mature tRNA's:
The wikipedia article notes RNA Pol III generally recognizes internal control elements rather than upstream control elements as in a normal gene.
Source: Qiagen
Source: Molecular Cell Biology. 4th edition.
Addendum: I said in my post that tRNA is charged in the cytoplasm, this is somewhat true. In mammalian cells, we also see that tRNA are charged in the nucleus as well, and it might aid in the export of some of these charged tRNAs. (Source)
The following is multiple choice question (with options) to answer.
Where in the cell does transcription occur? | [
"epidermis",
"nucleus",
"protoplasm",
"cell wall"
] | B | Transcription is the DNA → RNA part of the central dogma of molecular biology. It occurs in the nucleus. During transcription, a copy of mRNA is made that is complementary to a strand of DNA. In eukaryotes, mRNA may be modified before it leaves the nucleus. |
SciQ | SciQ-1477 | concentration
Title: Why is the concentration of hydrogen peroxide given as a percentage? For example, 3%, 6% Conventionally, the concentration of solutions is given in moldm⁻³ or M, however, I am curious why the concentration of hydrogen peroxide isn't written in the same way. The concentration, if expressed in mol/L, has no meaning for usual people, who do not know what is a mole. That is why the concentration is expressed in percent. The percent unit is understood by everybody.
The following is multiple choice question (with options) to answer.
Hydrogen peroxide is commonly sold as a 3% by volume solution for use as a what? | [
"detergent",
"surfactant",
"disinfectant",
"antiseptic"
] | C | Hydrogen peroxide is commonly sold as a 3% by volume solution for use as a disinfectant. |
SciQ | SciQ-1478 | visible-light
If no electronic transitions happened in the band of visible light, would we still be able to use this band to see? If no, what would be the most efficient ways to see?
Assuming that we had a device to actually detect the light in these frequencies without using electron transitions (this is more a biophysical question and beyond my capabilities): We would be able to use this band, precisely because of what I said in my original answer: Most of the light we see is reflected sunlight, not absorbed and reemitted or just emitted light. Since sunlight is abundand precisely in the visible spectrum (and this has nothing to do with the emission spectra of atoms), we would see very well. However, colours will be problematic: Sunlight is white and the colours result from an absorption of certain parts of this light, while others are simply reflected.
The absorption process is linked to the spectral lines, but I don't feel that I know enough to make this connection more precise. So it might be that the lack of any absorption in this part of the spectrum will make our world rather colourless - we'd see black and white.
The following is multiple choice question (with options) to answer.
In plants, pigment molecules absorb only visible light for photosynthesis. the visible light seen by humans as white light actually exists in a what? | [
"vacuum",
"invisible spectrum",
"transparency",
"rainbow of colors"
] | D | Absorption of Light Light energy enters the process of photosynthesis when pigments absorb the light. In plants, pigment molecules absorb only visible light for photosynthesis. The visible light seen by humans as white light actually exists in a rainbow of colors. Certain objects, such as a prism or a drop of water, disperse white light to reveal these colors to the human eye. The visible light portion of the electromagnetic spectrum is perceived by the human eye as a rainbow of colors, with violet and blue having shorter wavelengths and, therefore, higher energy. At the other end of the spectrum toward red, the wavelengths are longer and have lower energy. |
SciQ | SciQ-1479 | acid-base, aqueous-solution, ionic-compounds
Title: How to solve this contradiction? I am getting confused about this the more problems I do on it. My understanding was that only strong acids and strong bases will react to produce water and a salt. Something like this:
Molecular Eq: $\ce{HCl(aq) + NaOH(aq) \rightarrow H2O(l) + NaCl}$
Net Ionic Eq: $\ce{H+(aq) +OH- (aq) \rightarrow H_2O(l)}$
Makes perfect sense, both the acid and base break apart and combine with each other. But then I ran across something like this:
Molecular Eq: $\ce{2 CH3CO2H (aq) + Ba(OH)2 (aq) → Ba(CH3CO2)2 (aq) + 2 H2O (l)}$
Net Ionic Eq: $\ce{2CH3CO2H (aq) + 2OH- (aq) → 2CH3CO2- (aq) + 2H2O (l)} $
The net ionic eq tells me that $\ce{CH3CO2H}$ will not break apart, but the molecular equation tells me that they will break apart and form a salt with $\ce{Ba}$.
The following is multiple choice question (with options) to answer.
When an acid and base solutions react, they produce water and a neutral ionic compound known as what? | [
"sand",
"dirt",
"pollen",
"salt"
] | D | When acid and base solutions react, they produce water and a neutral ionic compound called a salt. The reaction is called a neutralization reaction. |
SciQ | SciQ-1480 | photosynthesis, respiration, ecosystem, decomposition
Maybe you should study the metabolic processes of plants and life in general to better understand this. All life consists of chemical reactions that build up structures; in order to build them up you need energy (because of the second law of thermodynamics), and all living things create that energy by breaking down complex molecules into simpler ones. (as such it would be more accurate to say that all life consists of chemical reactions that build up and break down various structures). You might be wondering "but what about the difference between autotrophs and heterotrophs I heard about"; the difference between those is where they get the complex molecules from in the first place. Autotrophs use a different source of energy to build them up while heterotrophs get them from their environment. As such, you can think of every living thing as being made of two kind of molecules: those that actually form their structure (in humans, the molecules that make up cell membranes, bones, muscles, etc) and those that are stored in order to be broken down to power the whole system (in humans that's fat, glycogen, glucose, etc). Of course a molecule can do both; if you're starving your body may start to break down structural molecules for power. There are many different ways of breaking down those big molecules for power; the most efficient one, that starts with a big chain of carbon atoms and cuts it down into individual CO2 molecules using O2 molecules, is called aerobic respiration (i.e. respiration that uses oxygen).
Because those complex molecules are required to power all life, autotrophs (the organisms that actually make them) are very important, and the processes they use to make them are very important too. The process that makes almost all of the molecules that power almost all life on earth is photosynthesis, which uses the energy from the sun to power a reaction that converts CO2 from the atmosphere into big carbon-based molecules we'll call carbohydrates. This is called "fixing carbon", since the carbon atom is the most important one; measuring how much photosynthesis is happening is another way of measuring how many carbon atoms move from being part of a CO2 molecule to being part of a plant.
The following is multiple choice question (with options) to answer.
In the body, oxygen is used by cells of the body’s tissues and carbon dioxide is produced as what? | [
"fuel",
"oxygen",
"waste product",
"food"
] | C | Gas Exchange across the Alveoli In the body, oxygen is used by cells of the body’s tissues and carbon dioxide is produced as a waste product. The ratio of carbon dioxide production to oxygen consumption is the respiratory quotient (RQ). RQ varies between 0.7 and 1.0. If just glucose were used to fuel the body, the RQ would equal one. One mole of carbon dioxide would be produced for every mole of oxygen consumed. Glucose, however, is not the only fuel for the body. Protein and fat are also used as fuels for the body. Because of this, less carbon dioxide is produced than oxygen is consumed and the RQ is, on average, about 0.7 for fat and about 0.8 for protein. The RQ is used to calculate the partial pressure of oxygen in the alveolar spaces within the lung, the alveolar PO Above, 2 the partial pressure of oxygen in the lungs was calculated to be 150 mm Hg. However, lungs never fully deflate with an exhalation; therefore, the inspired air mixes with this residual air and lowers the partial pressure of oxygen within the alveoli. This means that there is a lower concentration of oxygen in the lungs than is found in the air outside the body. Knowing the RQ, the partial pressure of oxygen in the alveoli can be calculated:. |
SciQ | SciQ-1481 | zoology, human-physiology, digestive-system
Title: Are intestinal and pancreatic lipases different? For explaining the action pancreatic lipase, my book wrote this equation:-
$$fat\space particles + lipase\rightarrow fatty\space acid + glycerol + lipase$$
But for intestinal lipase, my book has a different equation:-
$$fat\space particles + lipase\rightarrow monoglyceride + fatty\space acid$$
So, did my book make a mistake or are intestinal and pancreatic lipases different? Pancreatic lipase and intestinal lipase are almost same in their functions. In the intestine, the name of the lipase is a triacylglycerol acyl hydrolase it also called colipase dependent lipase or Pancreatic lipase, Free fatty acids, and 2-monoacylglycerol are the primary products of lipid digestion in the jejunum. and Pancreatic Lipase also produces Free fatty acids and 2- monoacylglycerol.
so we can say that both enzymes are almost same and produce the same products.
Sources Lippincott's Illustrated Reviews Biochemistry 5th edition Chapter 15
The following is multiple choice question (with options) to answer.
Chemical digestion in the small intestine cannot occur without the help of the pancreas and what bile-producing organ? | [
"stomach",
"heart",
"kidney",
"liver"
] | D | 23.6 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder Chemical digestion in the small intestine cannot occur without the help of the liver and pancreas. The liver produces bile and delivers it to the common hepatic duct. Bile contains bile salts and phospholipids, which emulsify large lipid globules into tiny lipid droplets, a necessary step in lipid digestion and absorption. The gallbladder stores and concentrates bile, releasing it when it is needed by the small intestine. The pancreas produces the enzyme- and bicarbonate-rich pancreatic juice and delivers it to the small intestine through ducts. Pancreatic juice buffers the acidic gastric juice in chyme, inactivates pepsin from the stomach, and enables the optimal functioning of digestive enzymes in the small intestine. |
SciQ | SciQ-1482 | inorganic-chemistry, reaction-mechanism, ions
Weiss, A. W. Theoretical Electron Affinities for Some of the Alkali and
Alkaline-Earth Elements. Phys. Rev., 1968, 166 (1), 70-74
Tehan, F. J.; Barnett, B. L.; Dye, J. L. Alkali anions. Preparation and Crystal Structure of a Compound which contains the Cryptated Sodium Cation and the Sodium Anion. J. Am. Chem. Soc., 1974, 96 (23), 7203–7208
Dye, J. L. Compounds of Alkali Metal Anions. Angew. Chem., 1979, 18 (8), 587-598
Dye, J. L.; Ceraso, J. M.; Lok, M. T.; Barnett, B. L.; Tehan, F. J. A Crystalline Salt of the Sodium Anion (Na-). J. Am. Chem. Soc., 1974, 96 (2), 608-609
The following is multiple choice question (with options) to answer.
What property are alkali metals at room temperature? | [
"solid",
"liquid",
"solid",
"mixed"
] | A | Alkali metals are all solids at room temperature. They are relatively soft and low in density. |
SciQ | SciQ-1483 | star, planet, exoplanet, distances, mass
Title: Minimum distance between planets In our solar system, MOIDs (minimum orbital intersection distance) of different planets reach a minimum of ~30 million miles (Mercury and Venus). However, other star systems have more compact planets. So I am wondering, what is the absolute minimum for planets of different sizes (list below)
1 Earth mass
5 Earth masses
10 Earth masses (Neptune-sized)
50 Earth masses (Super-Neptune)
100 Earth masses or 0.3 Jupiter mass (Sub-Jupiter)
1 Jupiter mass
5 Jupiter masses
The following is multiple choice question (with options) to answer.
What is the name of the smallest planet in our solar system, which is also nearest to the sun? | [
"jupitor",
"mercury",
"mars",
"earth"
] | B | Mercury is the smallest planet. It has no moon. It is also the planet closest to the Sun. Pictured below is the surface of Mercury covered with craters ( Figure below ), like Earth’s Moon. Many of the impact craters are billions of years old. This means that Mercury hasn’t changed much geologically for billions of years. It has no plate tectonics. With only a trace of an atmosphere, it has no weather to wear down the ancient craters. |
SciQ | SciQ-1484 | botany, terminology, nomenclature
Regnum Animale: the animals;
Regnum Vegetabile: the plants;
Regnum Lapideum: the minerals (you read it right).
Note that, in this classification, "animals" correspond to what nowadays we call animals and protozoans, and "plants" correspond to what nowadays we call plants, algae, fungi and bacteria.
You have to keep in mind that this book was first published in 1735, well before the evolutionary biology being proposed in the XIX century and established in the XX century. Therefore, it is a book published when fixism was the current paradigm, full of mentions to the scala naturae.
So, the plants (as well as the animals) showed a continuum of species, going to the lower plants (the bacteria) to the higher plants (the flowering ones). It's worth mentioning again that, by that time, bacteria were plants: Phylum Schyzophyta, to be more precise.
Thus, we have "lower plants" and "higher plants", "lower animals" and "higher animals", as well as "lower minerals" and "higher minerals"!
Unfortunately, this terminology is so embedded in the biological sciences that even today, as I mentioned, we struggle to get rid of it.
Just drop "higher plants", whatever it means
As your Wikipedia link says, "higher plants" is a synonym of vascular plants. However, there are a lot of problems here:
First, this is a remnant of the scala naturae and, just because of that, should be avoided. Think of it as a meaningless term, just like "more evolved organism".
Second, there is no clear and indisputable definition of what is a "higher" plant. Some authors used to define the "higher plants" as the Angiosperms only, or the seed plants (Angiosperms + Gymnosperms), or the vascular plants (Angiosperms, Gymnosperms and Pteridophyta).
For instance, in lusophone biology books, it was very common a division in three groups:
lower plants: bacteria and algae;
intermediate plants: bryophytes and pteridophytes;
higher plants: gymnosperms and angiosperms.
The following is multiple choice question (with options) to answer.
All gymnosperm species and many eudicot species undergo what? | [
"secondary growth",
"mutations",
"exploitation",
"third growth"
] | A | |
SciQ | SciQ-1485 | metabolism, energy, physiology
Title: Glycolytic non-oxidative pathway I am currently digging in some books to understand the three major metabolic pathways involved in physical training. The most difficult one for me is the glycolytic non-oxidative pathway (also more commonly known as the anaerobic lactic pathway) and I would like some help from people versed in this field.
In this pathway, as far as I understand, glycolysis produces pyruvate. In this process, NADH and H+ ions are produced along the way.
Then, if there is still a high energy demand (i.e. glycolysis is still necessary); NADH binds with pyruvate to form lactate and free up NAD+ which is necessary to sustain the glycolysis (otherwhise, pyruvate would be consumed via an oxidative pathway i.e. oxidative glycosis or slow glycolysis). This can theoretically continue until glycogen is depleted or severely diminished as far as I understand.
The problem comes then from the H+ ions produced during the glycolysis. These ions cause acidosis of the muscles if not removed. However, they can be removed if sufficient oxygen is present to form water. And here is my main question :
Why, during high intensity exercise, would oxygen be insufficient to take care of the H+ ions produced by the glycolysis ? Is it because muscles used during high intensity are not the best ones for using/transporting oxygen? Is it also because these H+ ions cannot be transported towards neighbouring muscles able to oxidise H+ ions ?
I understand this is a difficult question and maybe there is no precise answer at the moment. If you could point me toward a good ressource that deals with this question, I would be glad. I currently base myself on McArdle book on exercise physiology. I am going to try to walk through this problem, in a step-by-step manner in relation to exercise, starting from at rest, and ending at the point in which the body is no longer able to maintain its energy-charge.
At Rest
The following is multiple choice question (with options) to answer.
Slow-twitch or fast-twitch and oxidative or glycolytic describe what type of fibers? | [
"digestion muscle fibers",
"coronary muscle fibers",
"skeletal muscle fibers",
"capillaries"
] | C | |
SciQ | SciQ-1486 | cell-biology, organelle
Title: Univocal identifying of a plant cell We yesterday got our biology-exams back and there's one exercise where I don't agree with my teacher. However, since he is the expert and not me, I need the support of external sources, i.e. experts in order to justify my statement.
Now in the exercise, we first had to identify the parts of a cell (which was shown in form of an image) and then in part b) reason whether it was an animal or plant cell.
I had identified a chloroplast and a vacuole and stated that the only cell with this organelles was the plant cell. My teacher answered that I had missed the fact, that the cell had also a cell wall (which is indeed a difference between plant and animal cells).
My question is
Is the fact that the cell had a cell wall necessary in my argumentation, i.e. are there other cells having chloroplasts and a vacuole without being a plant cell?
Could you provide a source which supports, or doesn't support my statement so that I can show it to my teacher?
Thanks in advance Your teacher is right, chloroplasts and vacuoles are not sufficient to define a plant cell.
Amoeba have both chloroplasts (McFadden et al, PNAS, 1994) and vacuoles (Day, J. Morphology, 1927) but they are not plants - and they do not have a cell wall.
Sea slugs eat algae and can "steal" their plastids and keep them working for weeks/months, effectively becoming photosynthetic animals for a while. This is called kleptoplastidy (Pillet, Mob. Genet. Elements, 2013).
The following is multiple choice question (with options) to answer.
Plants have a touch response known as what? | [
"trichina",
"pollenation",
"photosynthesis",
"thigmotropism"
] | D | |
SciQ | SciQ-1487 | planet, solar-system
Title: Where is the Solar system's barycenter located? Where is the Solar system's barycenter located?
The solar system as a whole, Where is the center of the mass for the combined mass of the Sun, inner planets, and gas giants, is it inside the Sun? Is there an AU measured distance of it? The solar system barycenter (SSB) is sometimes inside the Sun and sometimes outside.
As an observer outside the solar system could detect with Doppler spectroscopy, the Sun is what's wobbling around.
The Sun's offset from the SSB is a vector sum of roughly:
0.00496 au ±5% away from Jupiter
0.00272 au ±6% away from Saturn
0.00083 au ±5% away from Uranus
0.00155 au ±1% away from Neptune
The other planets contribute much smaller amounts to the total.
Each planet's contribution is proportional to the product of its mass and its orbital distance.
When these components add constructively as in 2020-2023, the center of the Sun can be as far as 2 R☉ away from the SSB.
When they cancel as in 2029-2030, the center of the Sun is within 0.5 R☉ of the SSB.
The solar radius R☉ is 0.00465 au, shown here with a dashed line.
The following is multiple choice question (with options) to answer.
What is at the center of our solar system? | [
"the moon",
"the Kuiper Belt",
"the sun",
"earth"
] | C | The Sun is at the center of the solar system. |
SciQ | SciQ-1488 | photosynthesis, respiration, ecosystem, decomposition
Maybe you should study the metabolic processes of plants and life in general to better understand this. All life consists of chemical reactions that build up structures; in order to build them up you need energy (because of the second law of thermodynamics), and all living things create that energy by breaking down complex molecules into simpler ones. (as such it would be more accurate to say that all life consists of chemical reactions that build up and break down various structures). You might be wondering "but what about the difference between autotrophs and heterotrophs I heard about"; the difference between those is where they get the complex molecules from in the first place. Autotrophs use a different source of energy to build them up while heterotrophs get them from their environment. As such, you can think of every living thing as being made of two kind of molecules: those that actually form their structure (in humans, the molecules that make up cell membranes, bones, muscles, etc) and those that are stored in order to be broken down to power the whole system (in humans that's fat, glycogen, glucose, etc). Of course a molecule can do both; if you're starving your body may start to break down structural molecules for power. There are many different ways of breaking down those big molecules for power; the most efficient one, that starts with a big chain of carbon atoms and cuts it down into individual CO2 molecules using O2 molecules, is called aerobic respiration (i.e. respiration that uses oxygen).
Because those complex molecules are required to power all life, autotrophs (the organisms that actually make them) are very important, and the processes they use to make them are very important too. The process that makes almost all of the molecules that power almost all life on earth is photosynthesis, which uses the energy from the sun to power a reaction that converts CO2 from the atmosphere into big carbon-based molecules we'll call carbohydrates. This is called "fixing carbon", since the carbon atom is the most important one; measuring how much photosynthesis is happening is another way of measuring how many carbon atoms move from being part of a CO2 molecule to being part of a plant.
The following is multiple choice question (with options) to answer.
The different types of what systems work together to carry out all the life functions of the individual? | [
"digestive systems",
"organ systems",
"heartbeat systems",
"maturation systems"
] | B | Organ systems are organized into the organism. The different organ systems work together to carry out all the life functions of the individual. For example, cardiovascular and respiratory systems work together to provide the individual with oxygen and rid it of carbon dioxide. |
SciQ | SciQ-1489 | planet, night-sky, uranus
Title: Why wasn't the planet Uranus recognized by ancient cultures? Mercury, Venus, Mars, Jupiter, and Saturn have been identified by ancient astronomers as they are visible with naked eye at night. The planet Uranus, despite being visible during very clear nights, wasn't recognized as such. Why? The source of light that is Uranus was observed as far back as 128 BC. However it was misidentified as star as late as the 1760's. Then it was observed by Herschel in 1781, who also misidentified it, but as a comet. He had a telescope he built himself which would have been an impressive instrument for the day. He contacted another astronomer, one Nevil Maskelyne, who first suggested it was not a comet, but a planet. Further analysis by other astronomers made this more certain. It was essentially the orbit (not very elliptical) which seems to have been the main reason for identifying it as a planet. That and the apparent lack of a tail.
It required advances in observational accuracy and mathematical analysis of the observations to work out the orbit to work out it was a planet. These things simply were not possible to the required accuracy (or theoretical understanding) until Herschel's time.
From comments and by way of comparison, Saturn was considered a planet in ancient times. It has a shorter orbital period and is a great deal brighter than Uranus. It's relatively easy to spot this bright object whose (apparent) motion can be noticed and is easily distinguished from stars (unlike Uranus). Saturn is the 8th brightest natural object in the night sky. Uranus is the 350th. All the objects considered planets in ancient time were easier to see and notice the apparent motion of compared to stars. Uranus was just beyond that "natural" threshold where this could be done without relatively advanced technologies and theory.
The following is multiple choice question (with options) to answer.
Why is uranus so faint? | [
"too cold",
"too small",
"polluted atmosphere",
"far away"
] | D | Uranus is faint because it is very far away. Its distance from the Sun is 2.8 billion kilometers (1.8 billion miles). A photon from the Sun takes about 2 hours and 40 minutes to reach Uranus. Uranus orbits the Sun once about every 84 Earth years. |
SciQ | SciQ-1490 | photosynthesis, respiration, ecosystem, decomposition
Maybe you should study the metabolic processes of plants and life in general to better understand this. All life consists of chemical reactions that build up structures; in order to build them up you need energy (because of the second law of thermodynamics), and all living things create that energy by breaking down complex molecules into simpler ones. (as such it would be more accurate to say that all life consists of chemical reactions that build up and break down various structures). You might be wondering "but what about the difference between autotrophs and heterotrophs I heard about"; the difference between those is where they get the complex molecules from in the first place. Autotrophs use a different source of energy to build them up while heterotrophs get them from their environment. As such, you can think of every living thing as being made of two kind of molecules: those that actually form their structure (in humans, the molecules that make up cell membranes, bones, muscles, etc) and those that are stored in order to be broken down to power the whole system (in humans that's fat, glycogen, glucose, etc). Of course a molecule can do both; if you're starving your body may start to break down structural molecules for power. There are many different ways of breaking down those big molecules for power; the most efficient one, that starts with a big chain of carbon atoms and cuts it down into individual CO2 molecules using O2 molecules, is called aerobic respiration (i.e. respiration that uses oxygen).
Because those complex molecules are required to power all life, autotrophs (the organisms that actually make them) are very important, and the processes they use to make them are very important too. The process that makes almost all of the molecules that power almost all life on earth is photosynthesis, which uses the energy from the sun to power a reaction that converts CO2 from the atmosphere into big carbon-based molecules we'll call carbohydrates. This is called "fixing carbon", since the carbon atom is the most important one; measuring how much photosynthesis is happening is another way of measuring how many carbon atoms move from being part of a CO2 molecule to being part of a plant.
The following is multiple choice question (with options) to answer.
Which systems work together to provide cells with the oxygen they need for cellular respiration? | [
"muscular and lymph systems",
"respiratory and lymph systems",
"circulatory and digestive systems",
"respiratory and circulatory systems"
] | D | The respiratory and circulatory systems work together to provide cells with the oxygen they need for cellular respiration. Cells also need glucose for cellular respiration. Glucose is a simple sugar that comes from the food we eat. To get glucose from food, digestion must occur. This process is carried out by the digestive system. |
SciQ | SciQ-1491 | muscles, lungs, human-physiology
Title: Why is there smooth muscle in our bronchioles? Having muscle tissue in our bronchioles that can constrict seems like a poor choice for tissue. Why would our airway want to ever close up? Wouldn't it be more beneficial for our bronchioles to just remain open? There are at least two things to consider.
First, ability to limit airflow is a defense mechanism for animal. Imagine getting into area of some sort of toxic evaporation, e.g. CO2 cloud near volcano , then it makes sense to decrease delivery of toxin via lungs to minimum. As I understand, that is what an allergic asthma attack. (Sorry for not providing good enough source of that)
Secondly, you are incorrect in assuming that normal state is "dilated". Dilation of branchioles is sympathetic ("fight-and-fly") response of the nervous system to something like danger, that requires short-term boost in energy production. That is, by default, your airflow is limited. Probably, to limit amount of energy you effectively burn via oxygenation. But most importantly, you leave yourself a reserve in terms of oxygen supply for critical moments.
Some more information you might find here.
The following is multiple choice question (with options) to answer.
What organs have tiny tubes leading to and from elastic air sacs that improve airflow and oxygen uptake? | [
"ovaries",
"apendix",
"liver",
"lungs"
] | D | |
SciQ | SciQ-1492 | everyday-chemistry, toxicity
Such oxidation reactions are catalyzed both by soluble metals such as iron and by light. Hydrogen sulfide also can combine with metals such as iron (Fe++) to precipitate as black iron sulfide (Figure 1 bottom; FeS and FeS2).
The following is multiple choice question (with options) to answer.
What is produced when sulfur and oxygen combine? | [
"sulfur oxide",
"Acidic oxides",
"Basic Oxides",
"hydrogen oxide"
] | A | Sulfur oxides are produced when sulfur and oxygen combine. This happens when coal that contains sulfur burns. |
SciQ | SciQ-1493 | ichthyology, vertebrates
Title: If an organism is supported only by cartilage, does it have an endoskeleton? Lamprey and sharks lack bones, but does this mean they are not classified as having an endoskelton? Does an organism need bone to be considered as having an endoskeleton? From wikipedia
An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue.
Cartilage is a mineralized tissue so it counts as a skeleton from this definition. A bit further in the wikipedia article it says
The vertebrate endoskeleton is basically made up of two types of tissues (bone and cartilage)
The following is multiple choice question (with options) to answer.
A skeleton that consists of hard, mineralized structures located within the soft tissue of organisms is called what? | [
"calcium deposits",
"endoskeleton",
"exoskeleton",
"hydrostatic skeleton"
] | B | Endoskeleton An endoskeleton is a skeleton that consists of hard, mineralized structures located within the soft tissue of organisms. An example of a primitive endoskeletal structure is the spicules of sponges. The bones of vertebrates are composed of tissues, whereas sponges have no true tissues (Figure 38.4). Endoskeletons provide support for the body, protect internal organs, and allow for movement through contraction of muscles attached to the skeleton. |
SciQ | SciQ-1494 | evolution, evolutionary-game-theory, altruism
has little explanation. One possible explanation is that the trait itself may correlate well with genetics. One great answer there is that often the cost of altruism is small anyway. It can explain why people vote. Here the expense is small anyway.
Still there seems to be some factors that are even bigger.
Let's take a look at people that die for their ideology. Christian martyrs, Muslim suicide bombers, or Communist guerilla fighters. They seem to get so little and well, die.
And that's pretty common. It seems pretty easy for a leader or pedagogue to rouse men to be soldiers. Of course, becoming a soldier is a pretty shitty job, yet most men don't mind.
These people make a huge sacrifice for the sake of their country, ideology, or people that are not even genetically related to them.
Why? Your question is quite broad and asks for explanations for various behaviours which can lead to self-sacrifice.
Religious reasons: The genetic influence here may be a predisposition to let others influence you. This is what gives rise to culture in the first place, in other words: the predisposition to at some point maybe sacrifice yourself because you are taught to do so can only die out if the basic behaviour which gives rise to culture dies out. Cultures which lead their members to die may decimate their own numbers, but they will not wipe out culture itself because in the bigger scale, those with culture do better than those without. (Plus, those who sacrifice themselves may have children as well, so any genetic influence on their behaviour can be carried on.) This also goes far into the field of memetic evolution, which is disputed but may be interesting to read about.
Political reasons: As in, dying for one's nation or country rather than because of teachings. This probably has a defensive behaviour towards one's own group as the genetic influence. Also, reputation plays a big role: see shigeta's excellent answer.
You also mention willingness to subordinate oneself which is a very common pattern not only in humans. Richard Dawkins touches on this in The Selfish Gene, but there are probably papers more focussed on this particular topic out there as well.
The following is multiple choice question (with options) to answer.
What evolutionary process does not favor altruistic behavior that causes the death of the altruist? | [
"flow selection",
"random selection",
"natural selection",
"characteristic selection"
] | C | |
SciQ | SciQ-1495 | reproduction
Excerpts from the references that lead to the short answer above:
In the developing female fetus, oogonia become primary oocytes that begin the first division of meiosis. However, this division is not completed and the primary oocytes remain “frozen” in the prophase stage of the first meiotic division.
At birth, oogonia are no longer present. Each primary oocyte is surrounded by a single layer of squamous epithelial cells called follicular cells. The primary oocyte together with its follicular cells is called a primordial follicle. There are about two million primordial follicles with their primary oocytes in the ovaries at birth suspended in the first division of meiosis.
As the female grows, primary oocytes begin to die and disappear with their follicular cells. This process continues until puberty when there are only about 400,000 primordial follicles left in the ovaries. The primary oocytes continue the process of oogenesis after puberty begins.[Source]
The total number of primary oocytes at birth is estimated to vary from 700,000 to2 million. During childhood most oocytes become atretic; only approximately400,000 are present by the beginning of puberty, and fewer than 500 will be ovulated.[Source]
Primary oocytes reach their maximum development at ~20[6] weeks of gestational age, when approximately seven million primary oocytes have been created; however, at birth, this number has already been reduced to approximately 1-2 million.Recently, however, two publications have challenged the belief that a finite number of oocytes are set around the time of birth.[Source]
In the human embryo, the thousand or so oogonia divide rapidly from the second to the seventh month of gestation to form roughly 7 million germ cells.[Source]
REFERENCES:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0008772
The following is multiple choice question (with options) to answer.
In seed plants, after fertilization, what will the ovule eventually develop into? | [
"cone",
"flower",
"root",
"seed"
] | D | An ovule is a female reproductive structure in seed plants that contains a tiny female gametophyte. The gametophyte produces an egg cell. After the egg is fertilized by sperm, the ovule develops into a seed. |
SciQ | SciQ-1496 | blast
And the transcript.
Here's the first-frame translation of the transcript which contains the exact polypeptide above:
frame +1
> - 669
PATRNITIVSIYDYH*NNDLKCVFTE*MEILNRIWILLNSHSP*AQRLHAI**MTKDRLAALKAAQSDDDD
NDDVAVTVDSSGFMEEFFEQVDEIREMIDKIASNVDEVKKKHSAILSAPQTDDKMKEELEELMSEIKKNAN
KVRAKLKVIEQNIEQEEHTNKSSADLRIRKTQHATLSRKFVEVMNDYNACQIDYRERCKGRIKRQLAITGK
TTTNEELEDMIESGNPAIFTQGIIMETQQANETLADIEARHNDIMKLETSIRDLHDMFMDMAMLVESQGEM
IDRIEYNVEQAVDYIETAKMDTKKAVKYQSKARRKKIMILVCLAILIIILVGVIGGTLG***PSSLPLVYS
LIQLFYAACTTAASNIWTHHNRNSYYYNSNSNSNSNCYSNYFSNYYSNRKHYYYYHYYYYYYYYYYYYYYY
YYYYYYDYYYYYYYYYYYYYYYYYCYYYYYYYYYHFHYYYHHYYYHYYYYHYYYHYHHHHHYHYHYHYHHH
HHYHYHYHYHYHYYYYYYYYYYYYYYYYYYYYYYCYYYYYYTFSLVISLYGSSEM*MRLLVLSLYTFYGLF
YPLQQKGSFFF*SLQQTGTGFYNFFSYCQLHNLSIPSPSYFF*EWVFSFLKKHLIEFFCFLILLKFVLSFS
PIISLIISVCRKKISRIFYTIYLKMS**NHYLLF
The following is multiple choice question (with options) to answer.
What is the message sent from the nucleus to the ribosome? | [
"dna",
"mitochondria",
"rna",
"mrna"
] | D | The mRNA is the message sent from the nucleus to the ribosome, the organelle of protein synthesis. Like a foreign language, the genetic code of the mRNA message must then be translated so that the ribosomes make the correct protein. The process of reading the code of a mRNA to make a protein is called translation. |
SciQ | SciQ-1497 | human-biology, digestive-system, immune-system, microbiome
The next level of defense comes from the cells of the innate immune system (14). In innate immunity, specialized cells monitor the area they are in for Pathogen-Associated Molecular Patterns (PAMPs). PAMPs can be sugars that make up the cell walls of the microbe or proteins that get expressed on the surface of the organism, such as Flagellin, a protein only found in the flagella of certain pathogen. The innate immune cells have pattern recognition receptors (PRR) that have a general specificity for recognizing and responding to the PAMPs. Our cells even have PRRs for DNA and Double Stranded RNA's, however those are usually found in vesicles on the inside of the cell. These interactions are very general, however once PRRs bind to the PAMP, they are able to signal into the cytoplasm, which can lead to the production of proteins, among other possible responses.
Here you can think of PRRs like a motion detector in a security system; the dog, or your two year old, or an intruder are going to set off the alarm just the same. It is not specific. The motion sensor "knows" that something that it is supposed to recognize, i.e. a moving object larger than a mouse passed by and it triggered the response, but it cannot tell you which moving object triggered it, only that it was triggered.
The innate immune cells are also able to respond by "eating" the pathogen in a process called phagocytosis. Here, they break up the bacteria, yeast, or the remnants of other dead host cells or large pathogens, things like worms, and put the broken up pieces on protein molecules on their surface.
When innate immune cells do this, they are presenting molecules to specialized immune cells (adaptive immune cells (14)), B-Cells and T-Cells, that are highly specific as to what they will react to. These cells can also cause a lot of damage to the host, so they are tightly regulated. Think of the interactions as keys and locks. A protein from a bacteria should turn a few of these cells on, but a protein from the host should not fit the lock.
The following is multiple choice question (with options) to answer.
The phagocytes that are part of the body’s second line of defense attack any of what that they encounter? | [
"vaccines",
"pathogens",
"parasites",
"viruses"
] | B | The phagocytes that are part of the body’s second line of defense attack any pathogens they encounter. They provide a general defense. Some white blood cells attack only certain pathogens. They provide a specific defense. |
SciQ | SciQ-1498 | biochemistry, proteins, enzymes
Title: Is chitin actually protein? Recently insects are featured as a protein rich source for human nutrition. That humans can really digest chitin through chitinase enzym has been only recently confirmed.
But, does the chitin shell of their body actually count to the protein family?
Wikipedia does not state a clear yes or no. It says it is derivative of glucose, and may be compared by function to keratin protein. I'd really like to exclude any ambuguity and undersrand why. Chitin and protein are completely unrelated.
The only common thing is that they are polymers.
Chitin is a polymer of amino sugars while protein is a polymer of amino acids.
Both monomers are very different and are not converted one to the other.
In fact, chitin, like cellulose, is not fragmented by animals, so it is not absorbed.
Moreover, chitin is a homopolymer, so even if it where absorbed and transformed to amino acids, it would yield only one (or maybe a few ones) but all the others would have to be obtained through a different source.
So chitin is not a source of protein or amino acids.
The following is multiple choice question (with options) to answer.
Fungi are no longer classified as what, possessing cell walls made of chitin rather than cellulose? | [
"flowers",
"roots",
"eukaryotes",
"plants"
] | D | Today, fungi are no longer classified as plants. We now know that they have unique physical, chemical, and genetic traits that set them apart from plants and other eukaryotes. For example, the cell walls of fungi are made of chitin , not cellulose. Also, fungi absorb nutrients from other organisms, whereas plants make their own food. These are just a few of the reasons fungi are now placed in their own kingdom. |
SciQ | SciQ-1499 | nomenclature, metal
Title: What is the IUPAC nomenclature for Intermetallic Compounds? IUPAC has a system for naming organic compounds, ionic compounds, and inorganic compounds. I have seen something vaguely suggesting there is one for intermetallic compounds, such as: $$\ce{Fe-Co}$$ What is the system, if it even exists? If it doesn't exist what is the generally accepted way of naming intermetallic compounds? In your example you have given two metals and a bond-indicating symbol.
Grammar
Hyphens, Plus and Minus Signs, 'em'Dashes and Bond Indicators
'em' Dashes (ALT+0151, 'en' dash would be ALT+0150)
a) Used to indicate metal–metal bonds in polynuclear compounds (e.g. "[Mn2(CO)10 bis(pentacarbonylmanganese)(Mn—Mn)").
b) Used to separate the indvidual constituents in names of (formal) addition compounds (e.g. "3CdSO4·8H2O cadmiumsulfate—water")
Alphabetical Order
a) Intermetallic compounds are sorted alphabetically within the group of cations and anions. Deviations are allowed in order to express structural information.
b) In coordination complexes, ligands are sorted alphabetically and the donating atom is put first (e.g. OH2 instead of H2O).
Further Reading
Therefore, I would write your example as "Co—Fe".
There are a lot more rules that you can read here: https://web.archive.org/web/20181005064417/https://www.iupac.org/fileadmin/user_upload/databases/Red_Book_2005.pdf
The following is multiple choice question (with options) to answer.
What kind of compounds are named for their positive metal ion first, followed by their negative nonmetal ion? | [
"horizontal compounds",
"magnetic compounds",
"magnetic compounds",
"ionic compounds"
] | D | Ionic compounds are named for their positive metal ion first, followed by their negative nonmetal ion. |
SciQ | SciQ-1500 | neuroscience, brain, neurology
There are much more complex and functional methods of actually reading brain function and applying it to precise signals within the brain. All of these methods require the use of large equipment such as Positron Emission Tomography (PET) or Magnetic Resonance Imaging (the particular application here is called functional MRI or fMRI). These all require the patient to lie very still inside a large noisy piece of equipment to measure some aspect of the brain interpretable by equipment/software in question. These methods can be quite specific and do show the interior of the brain.
I don't know much about these methods other than general principles. However, fMRI measures blood flow to a particular area of the brain and requires the person being scanned to concentrate on the topic at hand while the scan is being performed. PET and the related technique Single-Photon Emission Computed Tomography (SPECT) often require the use of an injectable material that the scanner can pick up - this is usually (always?) a mildly radioactive one, often conjugated to a specific biological molecule (see here for a list of radioactives and localizations) so that it is trafficked in the body to a specific location.
In conclusion, people are still working on brain function and assigning particular things to particular locations, so we are still a fairly long way from having methods that can be used to natively control devices via brain function.
The following is multiple choice question (with options) to answer.
Endoscopes are used to explore the body through various orifices or these? | [
"minor incisions",
"dermal tears",
"major incisions",
"ocular cavity"
] | A | Bundles of fibers can be used to transmit an image without a lens, as illustrated in Figure 25.15. The output of a device called an endoscope is shown in Figure 25.15(b). Endoscopes are used to explore the body through various orifices or minor incisions. Light is transmitted down one fiber bundle to illuminate internal parts, and the reflected light is transmitted back out through another to be observed. Surgery can be performed, such as arthroscopic surgery on the knee joint, employing cutting tools attached to and observed with the endoscope. Samples can also be obtained, such as by lassoing an intestinal polyp for external examination. Fiber optics has revolutionized surgical techniques and observations within the body. There are a host of medical diagnostic and therapeutic uses. The flexibility of the fiber optic bundle allows it to navigate around difficult and small regions in the body, such as the intestines, the heart, blood vessels, and joints. Transmission of an intense laser beam to burn away obstructing plaques in major arteries as well as delivering light to activate chemotherapy drugs are becoming commonplace. Optical fibers have in fact enabled microsurgery and remote surgery where the incisions are small and the surgeon’s fingers do not need to touch the diseased tissue. |
SciQ | SciQ-1501 | organic-chemistry, everyday-chemistry, experimental-chemistry, biochemistry, food-chemistry
Title: How Bread is made with yeast, sugar and luke warm milk? Materials and Apparatus:
wheat flour
sugar
dry yeast
glass bowl
covering plate
milk
Procedure:
Lukewarm milk is taken in the glass bowl and sugar is added to it. Then, yeast is added to the same.
The mixture is left undisturbed for 10-12 minutes to activate the yeast
3 cups of wheat flour are added to the bowl containing the milk mixture.
The mixture is mixed thoroughly with 100ml of added water and the dough is kneaded well
The dough is placed in a bowl, covered with a plate and left undisturbed for 2 hours.
My query/confusion:
Why is milk needed?
"activated yeast"- what's the difference?
Can yeast work without sugar or milk.
Detail out the stages of the anaerobic oxidative process which takes place as a common first step in both aerobic and anaerobic respiration.
Finally, feel free to share anything I may be missing which should be here.
If you have any confusion regarding what I want to ask, please ask in the comments. Please upvote if you are curious about it too
milk is not needed, 'pure' bread is without milk
yeast is a fungus, therefore, it is alive. Its best to work with fresh yeast, which you find as small cubes in the refrigerated section. This one does not have to be activated. non-fresh yeast is dried, so in order for it to work properly, it has to be undried by adding water, which is called activation.
and 4. As said before, milk is not needed. Sugar however is the food for the yeast, without it, it does nothing. In aerobic breathing, the yeast metabolizes the sugar as we would: sugar + oxygen -> water + CO2. Without oxygen, the yeast resorts to ethanol fermentation: sugar -> alcohol + CO2 (this is, why it is used to make beer or wine). For making bread, we have a mixture of both respirations, which does not really matter, since we are only interested in the CO2, which makes the dough fluffy =) But without sugar, there is no CO2.
The following is multiple choice question (with options) to answer.
Bread has little holes in it from carbon dioxide produced by what? | [
"sugar",
"bacteria",
"yeast",
"water"
] | C | Bread has little holes in it from carbon dioxide produced by yeast. |
SciQ | SciQ-1502 | atoms
Title: Why aren't atomic radii calculated using Schrödinger's equation? The atomic radii are estimated using a variety of methods: most of these involve dividing their bond length by 2. But that is a very crude way of measuring atomic radii. I mean, atoms overlap each other when bonded, surely the actual atomic radius is much more than the one obtained by this method.
Why don't they simply use the Schrodinger's wave equation to calculate atomic radii. If it can predict atomic orbitals to such accuracy, surely it can predict something as simple as atomic radius? Erwin with his psi can do
Calculations quite a few.
But one thing has not been seen:
Just what does psi really mean?
(Erich Hückel, english translation by Felix Bloch)
It is not easy to perform the calculation that you called simple. The Hamilton operator $\hat{H}$ for a multi-body problem of $K$ cores and $N$ electrons
\[
\hat{H} = - \frac{1}{2}\sum_a^K\frac{1}{M_a}\Delta_a - \frac{1}{2}\sum_i^N\frac{1}{M_i}\Delta_i - \sum_i^N\sum_a^K \frac{Z_a}{r_{ai}} + \sum_{i < j}^N\frac{1}{r_{ij}}+ \sum_{a < b}^K\frac{Z_aZ_b}{R_{ab}}
\]
is still a beast for $K=1$ with all the core-electron and electron-electron interactions.
So, while the question is legitimate, the calculation simply cannot be done without a lot of approximations, such as the Hartree-Fock method.
By the way, for the determination of the atomic radii of solid metals, there's x-ray diffraction, which I wouldn't call crude.
The following is multiple choice question (with options) to answer.
What unit are atomic radii typically measured in? | [
"sporozoans",
"radons",
"picometers",
"powers"
] | C | Atomic radii have been measured for elements. The units for atomic radii are picometers, equal to 10 -12 meters. As an example, the internuclear distance between the two hydrogen atoms in an H 2 molecule is measured to be 74 pm. Therefore, the atomic radius of a hydrogen atom is . |
SciQ | SciQ-1503 | species-identification, microbiology, microscopy
Title: Identification of protozoa under microscope I observed maybe Protozoa from standing FRESH water and from slowly flowing FRESH water. I am complete dilettante. Can you tell what these creatures are?
https://www.youtube.com/watch?v=6D5ck3zNJzA&t=474s
Thank you.
Added picture for to be more specific At first glance, the organisms may hold the appearance of protozoans like ciliates. However, I am of the belief that these 'totally tubular' micro organisms are in fact diatoms.
The diatoms are a diverse range of eucaryotic microalgae which comprise a large percentage of the phytoplankton group. (Diatomaceous earth is the residual remains of their calcareous walls)
They are likely diatoms because of their apparent hard membrane, and slight brown-green pigment, typical of heterokont diatoms.
I would be unable to specify the organism to family level. However, you may wish to complete your investigation by looking under the order 'Pennales'.
For general information regarding the Diatoms, you may visit https://en.wikipedia.org/wiki/Diatom
Morphology and description available from: https://books.google.co.uk/books?id=xhLJvNa3hw0C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Good luck
The following is multiple choice question (with options) to answer.
What are fungus like protists? | [
"slime molds and water lilies",
"water molds and mushrooms",
"lichen and kelp",
"slime molds and water molds"
] | D | Examples of fungus-like protists include slime molds and water molds. |
SciQ | SciQ-1504 | particle-physics, nuclear-physics, atomic-physics, radiation, radioactivity
Title: What is the importance of excited states in the emission of gamma radiation during alpha decay? Let's suppose that during a hypothetical alpha decay of a nucleus X, has two excited states (such as 2.3 mEV and 0.9 mEV) are respectively fed.
The question arises here: what would would be the energy of the gamma rays that could be emitted?
My work: Would the alpha decay energy into the superior excited state (2.3 mEV) be equal to the gamma ray de-exitation from the superior excited state to the inferior excited state (0.9 mEV)?
And then,will the energy when the inferior excited state falls into the ground state be equal to 0.9 mEV?
So, I´m not sure if what we are looking for is a distribution of the energies emitted during this decay, which could vary, OR the total energy of the gamma rays that were emitted, which would be a sum of Excited State 2 -> Excited State 1 and Excited State 1 -> Ground State (1,4 + 0,9= 2,3 mEV)
Thanks for your help. Here's a level scheme for cobalt-60 which I decorated recently to answer another question about gamma emission. The 99.9% decay pathway is highlighted. This is a beta emitter instead of an alpha emitter, but I don't think that's a big deal for your question.
The following is multiple choice question (with options) to answer.
Alpha, beta, and gamma emissions are associated with what kind of energy? | [
"electrical",
"radiation",
"potential",
"kinetic"
] | B | Alpha, beta, and gamma emissions have different abilities to penetrate matter. The relatively large alpha particle is easily stopped by matter (although it may impart a significant amount of energy to the matter it contacts). Beta particles penetrate slightly into matter, perhaps a few centimeters at most. Gamma rays can penetrate deeply into matter and can impart a large amount of energy into the surrounding. |
SciQ | SciQ-1505 | thermodynamics, temperature
The approach to take setting up the problem strongly depends on how you want to solve it. The geometry of the human body (or any non-simple geometry) makes an exact analytical solution impossible. Therefore, you have pretty much 2 options:
Simple Method
Simplify the problem A LOT and treat the problem as a simple body with uniform temperature inside. This method is called "Lumped Parameter Analysis", since you're effectively lumping the entire body (over which the PDEs that govern heat transfer apply pointwise) into a single object. This method is valid when the rate of heat conduction inside the body is very large compared to the rate of heat loss to the surroundings. The non-dimensional number that allows you to make this determination is called the "Biot Number" (which has a lovely Wikipedia page of its own that you should read). Since the body has blood pumping around in it to evenly distribute the heat (ignoring the fact that the fingers and skin will actually be a bit colder than the core temperature), it is a reasonable first-order approximation to assume that the body temperature is constant-ish.
By taking this approach, you are left with the following differential equation:
$$
mc_p\frac{dT}{dt} = Vq_{vol} - A_{s}h(T-T_\infty)
$$
In this equation, $m$ is the mass of the body, $c_p$ is the specific heat of the body (you could approximate this with that of water), $V$ is the volume of the body, $q_{vol}$ is the volumetric heating term (due to your body's ability to produce heat), $h$ is the heat transfer coefficient for convection, and $A_s$ is the surface area of the body.
Approximating $h$ is a bit more involved, so I would direct you to the convection chapters of Incropera's book Fundamentals of Heat and Mass Transfer.
http://www.amazon.com/Fundamentals-Heat-Mass-Transfer-Guide/dp/0470055545
Once you have the information you need in that ODE (including your initial conditions), you can solve it any way you'd like and then find how long it takes for the body to reach 77 F.
Harder Method
The following is multiple choice question (with options) to answer.
Transport of nutrients and regulation of body temperature through fluid flow are characteristics of which bodily system? | [
"peripheral",
"cardiovascular",
"reproductive",
"gastrointestinal"
] | B | Two horrific contraptions on frictionless wheels are compressing a spring by compared to its uncompressed (equilibrium) length. Each of the vehicles is stationary and they are connected by a string. The string is cut! Find the speeds of the vehicles once they lose contact with the spring. |
SciQ | SciQ-1506 | thermodynamics, statistical-mechanics, differentiation, mathematics
$$
(\text{# components})-(\text{# phases}) + 2 = 2
$$
This is the number of independent variables we need to describe the intensive properties of the mixture. In principle we can choose any two among $\{p, T, V, U, S \cdots\}$. Pressure and temperature is a very convenient pair because we can easily measure them and control them experimentally. However, any other set can be used. The equation you wrote,
$$
dU =
\left(\frac{\partial U}{\partial S}\bigg)_VdS
+
\right(\frac{\partial U}{\partial V}\bigg)_SdV
$$
is correct and is equivalent to
$$
dU = T dS - p dV
$$
Mixtures
The number of independent variables is always determined by Gibbs's rule. In a two-component one-phase system we have three independent variables. We normally choose the first two to come from $p, T, V, U, S \cdots$ and the third one is the mol fraction of one of the two components. Again, this is the number of variables we need to describe the intensive properties of the mixture. We may also write equations for the extensive properties of mixture but I will not go there unless there is a question about it.
The following is multiple choice question (with options) to answer.
What are the two components of a mixture called? | [
"concentration and a solvent",
"acid and base",
"solute and a solvent",
"nutrients and a solvent"
] | C | Combinations of different substances are called mixtures. |
SciQ | SciQ-1507 | h. Evaluate C.
i. Compute Q(7), the amount of glucose produced during the day.
Exercise 10.3.5 “Based on studies using isolated animal pancreas preparations
maintained in vitro, it has been determined that insulin is secreted in a biphasic manner in response to a marked increase in blood glucose. There is an initial burst of insulin secretion that may last 5-15 minutes, a result of secretion of preformed insulin secretory granules. This is followed by more gradual and sustained insulin secretion that results largely from biosynthesis of new insulin molecules. ” (Rhoades and Tanner, P 710)
a. A student eats a candy bar at 10:20 am. Draw a graph representative of the rate of insulin secretion between 10:00 and 11:00 am.
b. Draw a graph representative of the amount of serum insulin between 10:00 and 11:00. Assume that insulin is degraded throughout 10 to 11 am at a rate equal to insulin production before the candy is eaten, and that serum insulin at 10:00 was Iq.
CHAPTER 10. THE FUNDAMENTAL THEOREM OF CALCULUS
468
c. Write an expression for the amount of serum insulin, I(t), for t between 10:00 and 11:00 am.
Exercise 10.3.6 Equal quantities of gaseous hydrogen and iodine are mixed resulting in the reaction
which runs until I 2 is exhausted [H 2 is also exhausted). The rate at which I 2 disappears is ^°’^ 2 gm/sec. How much I 2 was initially introduced into the mixture?
a. Sketch the graph of the reaction rate, r(t) = jp^yi-
b. Approximately how much I 2 combined with H 2 during the first second?
c. Approximately how much I 2 combined with H 2 during the second second?
d. Let Q(x) be the amount of I 2 that combines with H 2 during time 0 to 2; seconds. Write an integral that is Q(x).
e. What is Q\x)l
f. Compute W'{x) for W(x) = =^.
g. Show that there is a number, C, for which Q(x) = W(x) + C.
h. Show that C = 0.2 so that Q(x) = 0.2 – g.
The following is multiple choice question (with options) to answer.
Insulin is produced by what cells of the pancreas? | [
"platelet",
"alpha",
"gamma",
"beta"
] | D | Regulation of Blood Glucose Levels by Insulin and Glucagon Cells of the body require nutrients in order to function, and these nutrients are obtained through feeding. In order to manage nutrient intake, storing excess intake and utilizing reserves when necessary, the body uses hormones to moderate energy stores. Insulin is produced by the beta cells of the pancreas, which are stimulated to release insulin as blood glucose levels rise (for example, after a meal is consumed). Insulin lowers blood glucose levels by enhancing the rate of glucose uptake and utilization by target cells, which use glucose for ATP production. It also stimulates the liver to convert glucose to glycogen, which is then stored by cells for later use. Insulin also increases glucose transport into certain cells, such as muscle cells and the liver. This results from an insulin-mediated increase in the number of glucose transporter proteins in cell membranes, which remove glucose from circulation by facilitated diffusion. As insulin binds to its target cell via insulin receptors and signal transduction, it triggers the cell to incorporate glucose transport proteins into its membrane. This allows glucose to enter the cell, where it can be used as an energy source. However, this does not occur in all cells: some cells, including those in the kidneys and brain, can access glucose without the use of insulin. Insulin also stimulates the conversion of glucose to fat in adipocytes and the synthesis of proteins. These actions mediated by insulin cause blood glucose concentrations to fall, called a hypoglycemic “low sugar” effect, which inhibits further insulin release from beta cells through a negative feedback loop. |
SciQ | SciQ-1508 | magnetic-fields, astrophysics, sun
Title: How and why do sunspots occur? I am studying sunspot behavior, and the causes for the occurrence sunspots occur. I've come across the phrase 'local magnetic fields of the Sun'. I have no idea what that means.
Can someone please explain to me how/why sunspots form? The sun is a giant turbulent ball of plasma. It has a certain amount of angular momentum that gives rise to currents, and magnetic fields. As the large planets (Jupiter and Uranus) orbit the Sun, they cause the Sun to wobble about the barycenter. This disturbs the magnetic fields and creates local "vortices" that cause magnetic field lines to move in and out of the sun's surface:
Image and inspiration for this answer from this link which I recommend for further reading.
Because plasmas are "confined" by magnetic field lines, the temperature of the surface of the sun as observed from Earth is changed by the presence of these magnetic fields and the associated coronal flares that follow these lines. An explanation for how that creates a sun spot is given by this image (found on this page) :
image source
The following is multiple choice question (with options) to answer.
What is the arch called that forms when plasma of the sun flows along the loop that connects sunspots? | [
"solar prominence",
"large prominence",
"Energy prominence.",
"vertical prominence"
] | A | Another amazing feature on the Sun is solar prominences. Plasma flows along the loop that connects sunspots. This plasma forms a glowing arch. The arch is a solar prominence. Solar prominences can reach thousands of kilometers into the Sun’s atmosphere. Prominences can last for a day to several months. Prominences can be seen during a total solar eclipse. |
SciQ | SciQ-1509 | zoology, ecology, species-distribution, migration
Title: How do animals end up in remote areas? I was thinking specifically about random marshy water holes on farmers fields. It seems that you can visit just about any one of these and you will find frogs if you look hard enough.
They usually don't seem to be connected to each other. If it were any other land animal I would figure they walk from one spot to another, but in the case of frogs, I don't imagine their range is very vast. But often these marshy spots can be separated by fairly large distances to a frog.
So this brings me to my question: how do each of these spots end up with frogs in them? I don't imagine a frog is going to go hopping over a hill to get to a marsh on the other side, is it? This question pertains to organism dispersal, which is a very active field of study with relation to it's impact on conservation efforts. Much of what I will say below has been covered in this wiki.
Definition: From the Wiki
Technically, dispersal is defined as any movement that has the
potential to lead to gene flow.
It can be broadly classified into two categories:
Density dependent dispersal
Density independent dispersal
The question of frogs and fishes both refer to Density independent dispersal, while an example of density independent dispersal can be the competition for habitat space between big cats and humans (this is a WWF pdf)
From the wiki:
Density-independent dispersal
Organisms have evolved adaptations for dispersal that take advantage
of various forms of kinetic energy occurring naturally in the
environment. This is referred to as density independent or passive
dispersal and operates on many groups of organisms (some
invertebrates, fish, insects and sessile organisms such as plants)
that depend on animal vectors, wind, gravity or current for dispersal.
Density-dependent dispersal
Density dependent or active dispersal for many animals largely depends
on factors such as local population size, resource competition,
habitat quality, and habitat size.
Currently, some studies suggest the same.
This study in particular studied the movement and habitat occupancy patterns within ephemeral and permanent water bodies in response to flooding. They found that during flooding these frogs moved out to flooded ephemeral water bodies and later on moved back again to the permanent ones.
Other suggested readings for those highly interested in the subject may include this (a phd thesis) and this (a project report)
The following is multiple choice question (with options) to answer.
What does some amphibians have as juveniles but not as adults living on land? | [
"vertical line system",
"microscopic line system",
"kinetic line system",
"lateral line system"
] | D | |
SciQ | SciQ-1510 | biochemistry, physiology, muscles
Title: How is ATP involved in muscle contraction? The sliding filament mechanism as explained by my text does not elaborate on how ATP is involved in the cross bridge binding and contraction process. How does muscle contraction utilize ATP?
In my text explains this is the procedure for a contraction:
Ach released by motor neuron cross cleft and binds to motor end
plate
AP generated in response to binding of Ach gated channels and propagates down T tuble
T tuble triggers Ca2+ from sarcoplasmic reticulum
Ca2+ binds onto tropinin on actin filament and removes tropomyosin
This opens up sites for myosin to attach to actin using protein heads
Actin filament is pulled toward the center of sarcomere, causing contraction
I see that the action potential definitely needs ATP in order to be generated, aside from that I am surprised that the actual contraction via cross bridge binding does not seem to need ATP.
ATP prepares myosin for binding with actin by moving it to a
higher-energy state and a "cocked" position.
Once the myosin forms a cross-bridge with actin, the Pi disassociates
and the myosin undergoes the power stroke, reaching a lower energy
state when the sarcomere shortens.
ATP must bind to myosin to break the cross-bridge and enable the
myosin to rebind to actin at the next muscle contraction.
The following is multiple choice question (with options) to answer.
Ejaculation occurs when muscle contractions propel sperm from where? | [
"epididymes",
"penis",
"urinary track",
"cervix"
] | A | Sperm are released from the body during ejaculation. Ejaculation occurs when muscle contractions propel sperm from the epididymes. The sperm are forced through the ducts and out of the body through the urethra. As sperm travel through the ducts, they mix with fluids from the glands to form semen. Hundreds of millions of sperm are released with each ejaculation. |
SciQ | SciQ-1511 | star
Title: Are stars rotating? This question may sound silly but I'm really not pretty sure whether stars are rotating or stationary. If they are not rotating what makes them to be stable? Stars rotate due to the angular momentum of the gas they formed from. This angular momentum must be conserved, and remains as the rotation of the star and it's satellites. If a star collapsed from a completely static gas cloud it would not rotate, but would still be stable. The stability is provided by the hydrostatic equilibrium between radiation and thermal pressure with gravitation collapsing the star - not the stars rotation.
I don't know any statistics but I expect all stars rotate to some degree; It is usually the turbulence of gas clouds that leads to overdensities that then collapse in to stars.
The following is multiple choice question (with options) to answer.
Adult sea stars have what kind of symmetry? | [
"hydrological symmetry",
"radial symmetry",
"skeletal symmetry",
"biological symmetry"
] | B | Adult sea stars and other echinoderms have obvious radial symmetry. What evidence supports the claim that echinoderms evolved from an ancestor with bilateral symmetry?. |
SciQ | SciQ-1512 | neuroscience, neurophysiology, vision, human-eye, color
Title: What color does the other cone in Tetrachromacy correspond to? Human with normal vision possesses 3 cones, which correspond to blue (S), green (M) and red (L). What about tetrachromacy, where people have 4 cones in their retinae? What is the fourth cone exactly, and what color does that other cone correspond to? According to Deeb (2005), there are two relatively common types of causes for tetrachromacy in humans:
The common Ser180Ala polymorphism, which results in two spectrally different red pigments in the retina. This mutation also plays an important role in variation in normal color vision. This polymorphism most likely resulted from gene conversion by the green‐pigment gene.
Another common variation are several red/green pigment chimeras with different spectral properties. The red and green‐pigment genes are arranged in a head‐to‐tail tandem array on the X‐chromosome with one red‐pigment gene followed by one or more green‐pigment genes. The high homology between these genes has predisposed the locus to relatively common recombination events that give rise to red/green hybrids and deletions of green‐pigment genes. Such events constitute the most common cause of red‐green color vision defects. Only the first two pigment genes of the red/green array are expressed in the retina and therefore contribute to the color vision phenotype. The severity of red‐green color vision defects is inversely proportional to the difference between the wavelengths of maximal absorption of the photopigments encoded by the first two genes of the array. Women who are heterozygous for red and green pigment genes that encode three spectrally distinct photopigments have the potential for enhanced color vision.
Reference
Smeeb, Clin Gen (2005); 67:(5): 369-3
Further reading
- Color vision across species
The following is multiple choice question (with options) to answer.
The four types of light receptors include different types of cones and what else? | [
"rods",
"quarks",
"joints",
"neutrons"
] | A | 26.3 Color and Color Vision • The eye has four types of light receptors—rods and three types of color-sensitive cones. • The rods are good for night vision, peripheral vision, and motion changes, while the cones are responsible for central vision and color. • We perceive many hues, from light having mixtures of wavelengths. • A simplified theory of color vision states that there are three primary colors, which correspond to the three types of cones, and that various combinations of the primary colors produce all the hues. • The true color of an object is related to its relative absorption of various wavelengths of light. The color of a light source is related to the wavelengths it produces. • Color constancy is the ability of the eye-brain system to discern the true color of an object illuminated by various light sources. • The retinex theory of color vision explains color constancy by postulating the existence of three retinexes or image systems, associated with the three types of cones that are compared to obtain sophisticated information. |
SciQ | SciQ-1513 | organic-chemistry, mixtures
Title: Would Oxygen Gas and Ozone be a pure substance together? If I have oxygen gas and ozone ($\ce{O2 + O3}$) together would it be considered a pure substance or a mixture?
And would pure substances always have the same molecular structure? Ozone is highly reactive and unstable, while dioxygen is stable. There do not combine to form a compound. So, clearly it is a mixture.
To answer the second part of the question, "And would pure substances always have the same molecular structure?", first a Wikipedia definition on substances, to quote:
A chemical substance is a form of matter having constant chemical composition and characteristic properties.[1][2]...
Chemical substances can be simple substances[4], chemical compounds, or alloys. Chemical elements may or may not be included in the definition, depending on expert viewpoint.[4]
Chemical substances are often called 'pure' to set them apart from mixtures. A common example of a chemical substance is pure water...
However, in practice, no substance is entirely pure, and chemical purity is specified according to the intended use of the chemical.
And further:
A chemical substance may well be defined as "any material with a definite chemical composition" in an introductory general chemistry textbook.[5] According to this definition a chemical substance can either be a pure chemical element or a pure chemical compound. But, there are exceptions to this definition; a pure substance can also be defined as a form of matter that has both definite composition and distinct properties.[6] The chemical substance index published by CAS also includes several alloys of uncertain composition.[7] Non-stoichiometric compounds are a special case (in inorganic chemistry) that violates the law of constant composition, and for them, it is sometimes difficult to draw the line between a mixture and a compound, as in the case of palladium hydride. Broader definitions of chemicals or chemical substances can be found, for example: "the term 'chemical substance' means any organic or inorganic substance of a particular molecular identity, including – (i) any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature".[8]
The following is multiple choice question (with options) to answer.
In what do substances combine chemically to form a new substance? | [
"suspension",
"element",
"compound",
"component"
] | C | A mixture is a combination of two or more substances in any proportion. This is different from a compound, which consists of substances in fixed proportions. The substances in a mixture also do not combine chemically to form a new substance, as they do in a compound. Instead, they just intermingle and keep their original properties. The lemonade pictured above is a mixture because it doesn’t have fixed proportions of ingredients. It could have more or less lemon juice, for example, or more or less sugar, and it would still be lemonade. |
SciQ | SciQ-1514 | safety, gas
Title: Rotten Egg Gas Smell Background context for question
When I was young, we'd go fishing. And Dad would put a camper on the back of the truck. One time we came back in after fishing and the camper smelled like rotten eggs. He used that as an opportunity to teach us how some gases are tasteless/odorless. And as a result that sort of rotten egg smell is added as a safety measure.
Question:
My question is this: What are those gases that are odorless that then have that rotten egg smell added to them? Rotten eggs happen much less frequently than 50-60 years ago because of better hen-consumer refrigeration. Most people today have not had the pleasure of smelling them. H2S and low molecular weight mercaptans [AKA thiols] have distinct more or less unpleasant odors tho at low concentrations they can smell sweet, and we can develop tolerances to many at higher concentrations when they can be deadly. H2S is supposedly the active ingredient in rotten eggs; Methylsulfide CH3SH the active gas in human feces, and thioglycolic acid in eau de skunk.
Manufactured gas, no longer used, was a mix of H2 and CO and is toxic. It was flavored with mercaptan at rather high levels; smelling gas then was almost a death sentence, we were trained to open windows and leave immediately. There was also the explosion hazard. Manufactured gas was replaced by "natural", really fossil fuel, gas that is mostly methane CH4. Methane is odorless, not toxic, but it can be soporific, and it can explode. A warning is still necessary tho it seems to me the odorant is now less noxious and less intense than before [It could be my sense of smell has waned.]. It is to protect from explosion, again evacuate and ventilate. Odorants are added to propane and LPG, I do not know about hydrogen. Perfumes are added to many products to overcome odors or enhance odors and Bitrex is added to some drugs to make them less palatable so it works both ways.
The following is multiple choice question (with options) to answer.
What is the colorless gas with a sharp, pungent odor used in smelling salts? | [
"ammonia",
"hydrogen",
"helium",
"nitrogen"
] | A | Ammonia is a colorless gas with a sharp, pungent odor. Smelling salts utilize this powerful odor. Gaseous ammonia readily liquefies to give a colorless liquid that boils at −33 °C. Due to intermolecular hydrogen bonding, the enthalpy of vaporization of liquid ammonia is higher than that of any other liquid except water, so ammonia is useful as a refrigerant. Ammonia is quite soluble in water (658 L at STP dissolves in 1 L H2O). The chemical properties of ammonia are as follows: 1. Ammonia acts as a Brønsted base, as discussed in the chapter on acid-base chemistry. The ammonium ion is. |
SciQ | SciQ-1515 | human-anatomy
Title: Why is a penis an organ? According to Wikipedia an "An organ is a group of tissues with similar functions". I don't know anything about anatomy but it doesn't seem to me that a penis can be delimited somewhere to form a "group". Therefore I do not understand why a penis is considered an organ.
Can you explain it to me ? Frankly, that's a terrible definition by Wikipedia.
Merriam-Webster defines an organ as:
a differentiated structure (such as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism
or
bodily parts performing a function or cooperating in an activity
The important defining feature of an organ is not that the tissues have similar functions but that, together, the tissues comprise a functional whole that achieves some end goal.
For the penis, it consists of multiple tissues with different functions:
(from https://www.ncbi.nlm.nih.gov/books/NBK525966/figure/article-20668.image.f1/ - original from Gray's Anatomy)
The different tissues pictured here: the fibrous envelope, the corpora cavernosa, the septum pectiniforme, the urethra and blood vessels, the nervous tissue in the skin: all of these tissues have different individual functions: structural, erectile, carrying urine or semen, etc.
The key that unifies them into an organ is that the functions of the penis at the organism level (principally sexual function) are not served by any of these tissues alone, but rather by their combination in a full structure: an organ.
Ultimately, organ definitions are somewhat opinion-based: people are lumpers and splitters, so you might find conflicting definitions for which groupings of tissues reflect distinct organs, but I think by most standards you would find the penis to be considered a distinct organ, affiliated with but distinct from the primary sex organs and associated glands.
The following is multiple choice question (with options) to answer.
Groupings of related organs in the human body are referred to as "organ" what? | [
"conditions",
"functions",
"systems",
"bodies"
] | C | Human organ systems work together to carry out many of their functions. The skeletal and muscular systems are no exception. |
SciQ | SciQ-1516 | human-biology, physiology, metabolism
Thus, carbon dioxide (in the form of bicarbonate) is an obligate requiement for mammalian fatty acid biosynthesis, but no CO2-derived carbon is incorporated into fatty acids.
Carbon dioxide is also required for oxaloacetate formation from pyruvate. This reaction may be though of a method of 'filling up' a key Krebs Cycle intermediate (a so-called anapleurotic reaction). The enzyme here is pyruvate carboxylase and the substrates for the reaction are pyruvate, bicarbonate and ATP, with oxaloacetate being a key product. This enzyme also contains biotin and (like acetyl CoA carboxylase), CO2 becomes covalently bound to biotin during the reaction cycle.
Pyruvate-CoA carboxylase was discovered by Harland.G Wood and C. Werkman in bacteria (See here for a good reference on the early work on pyruvate carboxylase). Its discovery was very controversial because at the time it was thought that animal/bacterial cells could not 'fix' CO2; that is it was though that CO2 is only 'fixed' in photosynthesis. This discovery disproved that piece of dogmatism.
A third enzyme that requires CO2 as substrate (in the form of bicarbonate) is propionyl-CoA carboxylase. This enzyme occurs in mitochondria and functions in odd-chain fatty acid metabolism. It also contains biotin.
I have concentrated on some biochemical aspects of your question. The three enzymes mentioned, acety-CoA carboxylase, pyruvate carboxylase and propionyl-CoA carboxylase all require CO2 in the form of bicarbonate as substrate, all contain biotin, and (as far as I am aware) all play very central roles in mammalian metabolism. (They also all require ATP as substrate).
The following is multiple choice question (with options) to answer.
The enzymes that participate in fatty acid catabolism are located in what? | [
"atoms",
"mitochondria",
"nucleus",
"carbohydrates"
] | B | Like glucose, the fatty acids released in the digestion of triglycerides and other lipids are broken down in a series of sequential reactions accompanied by the gradual release of usable energy. Some of these reactions are oxidative and require nicotinamide adenine dinucleotide (NAD+) and flavin adenine dinucleotide (FAD). The enzymes that participate in fatty acid catabolism are located in the mitochondria, along with the enzymes of the citric acid cycle, the electron transport chain, and oxidative phosphorylation. This localization of enzymes in the mitochondria is of the utmost importance because it facilitates efficient utilization of energy stored in fatty acids and other molecules. Fatty acid oxidation is initiated on the outer mitochondrial membrane. There the fatty acids, which like carbohydrates are relatively inert, must first be activated by conversion to an energy-rich fatty acid derivative of coenzyme A called fatty acyl-coenzyme A (CoA). The activation is catalyzed by acyl-CoA synthetase. For each molecule of fatty acid activated, one molecule of coenzyme A and one molecule of adenosine triphosphate Saylor URL: http://www. saylor. org/books. |
SciQ | SciQ-1517 | parasitology
Title: Tapeworms and their effect on humans I've read that some people in some countries actually use tapeworms as a form of losing weight. What are the dangers to these people? I haven't really found much on this topic (besides popular sites) but I can summarize it here:
There are quite some tapeworms (or cestoda), I found numbers of up to 3500 species. They attach to the intestinal wall of the humans and then start to take up predigested food through their skin. With that, they reduce food from their host and start to grow, some get as long as 15 meters!
Some of the worms seem to be relatively harmless (besides stealing food), but this is more true for the first world. In poor countries, where there is not enough food, tapeworms can cause severe malnutrition.
Some tapeworms can migrate into the blood stream and from there into other tissues or organs like muscles, eye and brain. There they can cause cysts which can lead to organ failure and death.
For more information see this CDC webpage and this article: "Biochemistry and physiology of tapeworms.". This popular article is probably also interesting.
The following is multiple choice question (with options) to answer.
Which organ of the body do large tapeworms attack or block? | [
"liver",
"kidneys",
"heart",
"intestines"
] | D | |
SciQ | SciQ-1518 | evolution, zoology, anatomy, species
Title: Examples of animals with 12-28 legs? Many commonly known animals' limbs usually number between 0 and 10. For example, a non-exhaustive list:
snakes have 0
Members of Bipedidae have 2 legs. Birds and humans have 2 legs (but 4 limbs)
Most mammals, reptiles, amphibians have 4 legs
Echinoderms (e.g., sea stars) typically have 5 legs.
Insects typically have 6 legs
Octopi and arachnids have 8 legs
decapods (e.g., crabs) have 10 legs
....But I can't really think of many examples of animals containing more legs until you reach 30+ legs in centipedes and millipedes. Some millipedes even have as many as 750 legs! The lone example I am aware of, the sunflower sea star, typically has 16-24 (though up to 40) limbs.
So my question is: what are some examples of animals with 12-28 legs? As a couple of counterexamples, species in the classes Symphyla (Pseudocentipedes) and Pauropoda within Myriapoda have 8-11 and 12 leg pairs respectively, so between 16 to 24 legs (sometimes with one or two leg pair stronlgy reduced in size).
(species in Symphyla, from wikipedia)
Another common and species-rich group with 14 walking legs (7 leg pairs) is Isopoda.
(Isopod, picture from wikipedia)
You also need to define 'legs' for the discussion to be meaningful. As you say, decapods have 10 legs on their thoracic segments (thoracic appendages), but they can also have appendages on their abdomens (Pleopods/swimming legs), which will place many decapods in the 10-20 leg range.
(Decapod abdominal appendages/legs in yellow, from wikipedia)
So overall, in Arthropoda, having 12-28 legs doesn't seem all that uncommon. There are probably other Arthropod groups besides those mentioned here that also have leg counts in this range.
However, for a general account, the most likely answer (if there is indeed a relative lack of 12-28 legged animals) is probably evolutionary contingencies and strongly conservative body plans within organism groups.
The following is multiple choice question (with options) to answer.
The sternum and 12 pairs of ribs with their costal cartilages make up what? | [
"thoracic cage",
"chest cage",
"heart cage",
"the core"
] | A | Figure 7.32 Thoracic Cage The thoracic cage is formed by the (a) sternum and (b) 12 pairs of ribs with their costal cartilages. The ribs are anchored posteriorly to the 12 thoracic vertebrae. The sternum consists of the manubrium, body, and xiphoid process. The ribs are classified as true ribs (1–7) and false ribs (8–12). The last two pairs of false ribs are also known as floating ribs (11–12). |
SciQ | SciQ-1519 | cholesterol
Some LDL cholesterol circulating through the bloodstream tends to deposit in the walls of arteries. This process starts as early as childhood or adolescence.
White blood cells swallow and try to digest the LDL, possibly in to digest the LDL, possibly in an attempt to protect the blood vessels.
In the process, the white blood cells convert the LDL to a toxic (oxidized) form.
More white blood cells and other cells migrate to the area, creating steady low steady low-grade inflammation in the artery wall.
Over time, more LDL cholesterol and cells collect in the area. The ongoing process creates a bump in the artery wall called a plaque. The plaque is made of cholesterol, cells, and debris.
The process tends to continue, growing the plaque and slowly blocking the artery.
There is a good overview of the general physiology here in Robbins The Pathologic Basis of Disease. Chapter 5, Genetic Disorders, reviews the physiology, and the relevance to disease, in the section on Familial Hypercholesterolemia. The review is relevant to hypercholesterolemia in general.
The following is multiple choice question (with options) to answer.
Which lipid is mainly responsible for narrowing arteries and causing the disease atherosclerosis? | [
"saturated fat",
"monoglyceride",
"cholesterol",
"unsaturated fat"
] | C | Although some lipids in the diet are essential, excess dietary lipids can be harmful. Because lipids are very high in energy, eating too many may lead to unhealthy weight gain. A high-fat diet may also increase lipid levels in the blood. This, in turn, can increase the risk for health problems such as cardiovascular disease. The dietary lipids of most concern are saturated fatty acids, trans fats, and cholesterol. For example, cholesterol is the lipid mainly responsible for narrowing arteries and causing the disease atherosclerosis. |
SciQ | SciQ-1520 | physical-chemistry, thermodynamics, equilibrium
I know that Gibbs free energy change represents the amount of the non-expansionary work that a reaction is capable...
It is not exactly true, it is not a requirement that the process involve a reaction.
In the ligh of getafix commentary:
Take in mind that physical significance most times, in the core, is just an inaccurate idea about a physical theory/model/law. Although it may be useful sometimes from a practical perspective (and many times leads to catastrophic conclusions), it has not an add value. There is the nature. There are good formal descriptions of it obtained through years of hard work from experienced people. There are pictorial interpretations of those formal descriptions used when formalism turns too hard/complex (physical significance). I noticed that it is fashion to say that one get the true understanding of phenomena when one get the physical significance. I think that one truly understand the phenomena when feels natural the formal description and is also aware that it is just a description.
The following is multiple choice question (with options) to answer.
Physical or chemical changes are generally accompanied by a transfer of what? | [
"pressure",
"color",
"energy",
"shape"
] | C | When physical or chemical changes occur, they are generally accompanied by a transfer of energy. The law of conservation of energy states that in any physical or chemical process, energy is neither created nor destroyed. In other words, the entire energy in the universe is conserved. In order to better understand the energy changes taking place during a reaction, we need to define two parts of the universe, called the system and the surroundings. The system is the specific portion of matter in a given space that is being studied during an experiment or an observation. The surroundings is everything in the universe that is not part of the system. In practical terms for a laboratory chemist, the system is the particular chemicals being reacted, while the surroundings is the immediate vicinity within the room. During most processes, energy is exchanged between the system and the surroundings. If the system loses a certain amount of energy, that same amount of energy is gained by the surroundings. If the system gains a certain amount of energy, that energy is supplied by the surroundings. |
SciQ | SciQ-1521 | organs, lifespan
Title: Organs lifespan out of the body What organ can be conserved outside of the body for the longest time and still function when reimplanted? Depends what you consider an organ. Typically though it's the cells which require the most metabolic activity which have the shortest life span. The kidney is the most of the major internal organs with up to 36 hours with liver coming second at up to 16 hours.
The following is multiple choice question (with options) to answer.
What is the term for a dynamic equilibrium that is maintained in body tissues and organs? | [
"homeostasis",
"dormancy",
"homogeneity",
"metabolism"
] | A | 33.3 Homeostasis Homeostasis is a dynamic equilibrium that is maintained in body tissues and organs. It is dynamic because it is constantly adjusting to the changes that the systems encounter. It is in equilibrium because body functions are kept within a normal range, with some fluctuations around a set point for the processes. |
SciQ | SciQ-1522 | evolution, zoology, anatomy
Title: Are the transverse septum in sharks and the diaphragm in mammals homologous structures? Are the transverse septum in sharks and the diaphragm in mammals homologous structures?
I have searched on Google Scholar and Web of Science, but haven't found substantial evidence to prove or falsify the claim. A beginning of answer here below, I hope. Please first consider that many structures are involved in the question here, the diaphragm (UBERON:0001103), the diaphragmaticus muscle (UBERON:0036071) and the septum transversum (UBERON:0004161). At Bgee (bgee.org) we aim annotating relations of similarity between anatomical structures, please have a look at our GitHub
https://github.com/BgeeDB/anatomical-similarity-annotations
We already annotated 'diaphragm' as a mammalian structure, not homologous in Amniota (please see https://raw.githubusercontent.com/BgeeDB/anatomical-similarity-annotations/master/release/similarity.tsv). In our next release, you will see the annotation for the 'diaphragmaticus muscle' which is an analog organ in Crocodylians (and Turtles) but not homologous to the mammalian diaphragm either. See here for more details about this new Uberon class:
https://github.com/obophenotype/uberon/issues/1229.
Based on the comments here above, I would say that currently we can argue that there is no evidence for a homologous relationship between the 'septum transversum' in sharks and the mammalian diaphragm. Please note that UBERON:0004161 septum transversum describes the (mammalian) embryonic structure that will give rise to the central tendon of the diaphragm, while here you are talking about a adult structure closer to a 'diaphragmaticus muscle'-like septum, as far as I understand.
But anyway thank you for your interesting question that points out a very exciting and rapidly evolving evo-devo field, as this recent paper also suggests
The following is multiple choice question (with options) to answer.
What has a pseudocoelom and hydrostatic skeleton? | [
"roundworms",
"gymnosperms",
"omnivores",
"vertebrates"
] | A | Roundworms make up the phylum Nematoda. They have a pseudocoelom and hydrostatic skeleton. Their body is covered with tough cuticle. Free-living roundworms are found mainly in freshwater habitats. Parasitic roundworms have a variety of hosts, including humans. |
SciQ | SciQ-1523 | volcanology, paleontology, volcanic-hazard, archaeology, pyroclastic-flows
Title: Are Pompeii and Herculaneum unique? Has anyone ever found or gone looking for similar locations, i.e. volcanic eruption sites in which unfortunate victims – human and non-human – have been entombed in the volcanic ash, with the possibility of revealing their forms by producing casts from the voids? Such sites, if they exist, could reveal exciting new knowledge about ancient peoples and animals. Probably the best known is more recent, the 1902 eruption of Mt. Pelée on Martinique, where 30,000 people were killed by pyroclastic flows. I don't know the extent of burial - it appears that the city may have been destroyed more by the ash cloud than the dense part of the flow.
The following is multiple choice question (with options) to answer.
In what two ways are volcanic eruptions characterized? | [
"minor and explosive",
"explosive and non-explosive",
"localized and general",
"non-explosive and serious"
] | B | Eruptions can be explosive or non-explosive. Only rarely do gentle and explosive eruptions happen in the same volcano. |
SciQ | SciQ-1524 | genetics, dna, molecular-genetics, gene-expression, gene-regulation
Title: Do DNA repressors exist? I know about enhancers and the mechanism that lead them to increase the gene expression of their targets but I was wondering if similarly DNA repressors exist. I know about protein repressors but I am looking for some kind of anti(or reversed)-enhancer equivalent in the genome which would act like an enhancer but reduce gene expression.
I am aware of repressed/poised enhancers which would kind of be that process, even if not really a pure repression of the target gene but rather a "non-overexpression". I also know about insulators but again this would be a different mechanism.
Some intergenic region binding protein repressors which by a folding mechanism similar to enhancers would repress a gene perhaps? Yes, these sequences exist and they are called "silencers" (surprising, right?). There are different mechanisms by which this silencing of genes can happen.
In the "classical" way the silencer is bound by a transcription factor which either passively suppress the gene by hindering the binding of specific transcription factors or by actively preventing the assembly of the general transcription factors. See the figure from paper 1:
Additionally there are non-classical negative regulatory element (NRE), which are usually elements upstream of the promoter which inhibit the binding regulatory proteins. NRE can also be enhancers depending on the proteins bound on them. Some NRE can induce a bend of the DNA, inhibiting the access to enhancer or promoter elements.
References:
Transcriptional control and the role of silencers in transcriptional
regulation in eukaryotes.
Transcriptional Regulatory Elements in the Human Genome
The following is multiple choice question (with options) to answer.
Each enhancer is made up of short dna sequences called what? | [
"distal control elements",
"fibrous control elements",
"electrolysis control elements",
"pisttal control elements"
] | A | Figure 16.9 An enhancer is a DNA sequence that promotes transcription. Each enhancer is made up of short DNA sequences called distal control elements. Activators bound to the distal control elements interact with mediator proteins and transcription factors. Two different genes may have the same promoter but different distal control elements, enabling differential gene expression. |
SciQ | SciQ-1525 | star-formation, nebulae
What's the explanation? A pointer to a good article for the knowledgeable lay person would be helpful too. Your option #3 is correct; the shape has little to do with the relative motion of the gas and stars.
Giant molecular clouds
The pillars are part of the giant molecular cloud (GMC) which is giving birth to news stars. Stars are formed when some regions inside the cloud meet the Jeans criterion, i.e. are sufficiently dense and cold that gravity overcomes pressure. Because the density of such clouds is largest in the center (see e.g. Chen et al. 2021), stars will tend to form first in the center.
Stars are formed with a distribution of masses. The most massive ones — the so-called O and B stars — emit copious amounts of ultraviolet photons, which heat and ionize the surrounding medium. A hot, ionized bubble inside the otherwise cold, neutral, and dusty cloud called a Strömgren sphere then forms.
The dark pillars are remainders of the neutral gas, whereas the bluish region is the ionized region, containing newborn stars.
The size of the ionized region
In this answer about the Carina Nebula, I calculated the typical size of a Strömgren sphere, which we can write approximately as
$$
R_\mathrm{S} \simeq 10\,\mathrm{lightyears} \times\color{red}{\left(\frac{Q(\mathrm{H}^0)}{10^{50}\,\mathrm{s}^{-1}}\right)^{1/3}}
\color{blue}{\left(\frac{n_\mathrm{H}}{300\,\mathrm{cm}^{-3}}\right)^{-2/3}}
\color{green}{\left(\frac{T}{10^4\,\mathrm{K}}\right)^{0.23}},
$$
The following is multiple choice question (with options) to answer.
For a star to form, what force pulls gas and dust into the center of the nebula? | [
"motion",
"gravity",
"weight",
"centrifugal force"
] | B | For a star to form, gravity pulls gas and dust into the center of the nebula. As the material becomes denser, the pressure and the temperature increase. When the temperature of the center becomes hot enough, nuclear fusion begins. The ball of gas has become a star!. |
SciQ | SciQ-1526 | atoms, phase
Title: What is the physical state of a single atom? Can a single atom on its own be either a solid, liquid, or a gas? Or is it none of them? This answer has been written so it hopefully can be understood by people that do not have a degree. If something is not correct, let me know, but be aware that throwing around fancy words will not help anyone understanding this any better. Consider the other posts here concerning liquids and solids, I don't want to be redundant and repeat what has been said already.
The answer is a bit complicated. One would intuitively say no, but that doesn't tell the whole story.
Take the interstellar medium. We have about 1 atom per cm³ in there and it is called a "gas". Now that's what I would call an isolated atom in the gas phase.
An atom is an object that belongs into the realms of quantum mechanics. A solid, liquid or gas is something that belongs into our classical world. If you zoom in close enough, that means if we look at a problem microscopically, words like "solid" or "liquid" no longer make sense. If you now begin to zoom out, the quantum effects vanish. This is sometimes called quantum decoherence and we enter the world of classical physics where solids and and liquids exist again.
So I would argue it all depends on how closely you look at the problem. Isolated atoms in a large volume? A gas if you ask me. But if you have to zoom in to talk about an individual atom within a larger compound consisting of many more atoms, let's say one atom within a piece of iron, you no longer can say that this single atom is "solid".
Think of it like this:
Can a single person have a political system?
The following is multiple choice question (with options) to answer.
What do you call elements that contain only atoms of one type of element? | [
"native elements",
"typical elements",
"reactive elements",
"noble gases"
] | A | Native elements contain only atoms of one type of element. They are not combined with other elements. There are very few examples of these types of minerals. Some native elements are rare and valuable. Gold, silver, sulfur, and diamond are examples. |
SciQ | SciQ-1527 | organs, lifespan
Title: Organs lifespan out of the body What organ can be conserved outside of the body for the longest time and still function when reimplanted? Depends what you consider an organ. Typically though it's the cells which require the most metabolic activity which have the shortest life span. The kidney is the most of the major internal organs with up to 36 hours with liver coming second at up to 16 hours.
The following is multiple choice question (with options) to answer.
The organ systems of the body work together to carry out life processes and maintain what? | [
"homeostasis",
"consciousness",
"movement",
"freshness"
] | A | The organ systems of the body work together to carry out life processes and maintain homeostasis. |
SciQ | SciQ-1528 | quantum-mechanics, wavefunction, atomic-physics, approximations, orbitals
Title: Why do we multiply in the total wave function but add in the LCAO method? If to particles with wave functions $\psi_a$ and $\psi_b$ are „combined“ their total wave function is given by:
$$\psi(r_1,r_2)= A[\psi_a(r_1)\psi_b(r_2) \pm \psi_b(r_1)\psi_a(r_2)]$$
(+ for bosons and - for fermions, $A$ is a constant, here I‘m ignoring spin.)
But if we combine the wave functions of two atomic orbitals $\psi_c$ and $\psi_d$ it is done by a simple Linear Combination of Atomic Orbitals (LCAO):
$$\psi = C_1\psi_c + C_2\psi_d$$
Where the $C_1$, $C_2$ are constants.
These two processes of generating the total wave function out of existing ones feel to me as if they should be carried out in the same way. And I understand that we do it this way in the first case since we can’t tell the particles apart and the total wave function therefore has either to be symmetric or antisymmetric. So what is the justification that we can simply add them in the second LCAO case? These formulae do different things. The first one takes 2 (or more) single-particle wavefunctions and gives you a multiple-particle wavefunction that can be interpreted as having one particle in one state and another particle in another state. The second one instead produces a single-particle wavefunction that can be interpreted as a single particle in a superposition of the states. Since they do different things, they look different too.
In quantum chemistry, the overall wavefunction of all the electrons together is often assumed to be of the first form (called a Slater determinant), combining $N$ single-electron spin-orbital wavefunctions. (Reduces to your formula for $N=2,$ replace the determinant with the permanent for bosons.) (In general, the wavefunction may be a linear superposition of these.)
The following is multiple choice question (with options) to answer.
This process of combining the wave functions for atomic orbitals is called what? | [
"hydration",
"assimilation",
"activation",
"hybridization"
] | D | Quantum-mechanical calculations suggest why the observed bond angles in H2O differ from those predicted by the overlap of the 1s orbital of the hydrogen atoms with the 2p orbitals of the oxygen atom. The mathematical expression known as the wave function, ψ, contains information about each orbital and the wavelike properties of electrons in an isolated atom. When atoms are bound together in a molecule, the wave functions combine to produce new mathematical descriptions that have different shapes. This process of combining the wave functions for atomic orbitals is called hybridization and is mathematically accomplished by the linear combination of atomic orbitals, LCAO, (a technique that we will encounter again later). The new orbitals that result are called hybrid orbitals. The valence orbitals in an isolated oxygen atom are a 2s orbital and three 2p orbitals. The valence orbitals in an oxygen atom in a water molecule differ; they consist of four equivalent hybrid orbitals that point approximately toward the corners of a tetrahedron (Figure 8.7). Consequently, the overlap of the O and H orbitals should result in a tetrahedral bond angle (109.5°). The observed angle of 104.5° is experimental evidence for which quantummechanical calculations give a useful explanation: Valence bond theory must include a hybridization component to give accurate predictions. Note that orbitals may sometimes be drawn in an elongated “balloon” shape rather than in a more realistic “plump” shape in order to make the geometry easier to visualize. |
SciQ | SciQ-1529 | electronegativity, hyperconjugation
Title: Inductive effect and hyperconjugation - one elephant, different parts? Are the inductive effect and hyperconjugation both different ways of looking at the same phenomenon - i.e. methyl groups donate negative charge for example. Inductively we can argue that carbon is of greater electronegativity than hydrogen, and so carbon withdraws negative charge from hydrogen, and thus negative charge is "donated" to whatever that the methyl is attached to.
From a hyperconjugative effect we can argue that there is some interaction between the C-H orbitals and some antibonding orbital ... how is this supposed to be stabilizing if it involves an antibonding orbital?
Are the inductive effect and hyperconjugation both different ways of
looking at the same phenomenon
I think so, both inductive and resonance (that's what hyperconjugation is after all) effects move electrons around. I tend to separate the two effects as follows:
inductive effects are associated with electron movement through sigma bonds due to electronegativity differences
resonance effects are associated with electron movement through p orbitals due to electronegativity differences
For example, we often say that a methyl group stabilizes a double bond (carbon-carbon or carbonyl) or a carbocation. The methyl group is roughly $\ce{sp^3}$ hybridized while the double bond carbon or carbocation carbon is roughly $\ce{sp^2}$ hybridized. An $\ce{sp^2}$ orbital is generally lower in energy than an $\ce{sp^3}$ orbital because it contains more s-character. Therefore electrons will generally prefer to flow from $\ce{sp^3}$ to $\ce{sp^2}$ orbitals. The direction of this electron flow also indicates that $\ce{sp^2}$ orbitals are more electronegative than $\ce{sp^3}$ orbitals. How can the $\ce{sp^3}$ methyl group shift electrons to the lower energy, more electronegative $\ce{sp^2}$ carbon? It can do it inductively (through sigma bonds) or through resonance (through p orbitals).
I've added a picture showing resonance structures involving hyperconjugation, just to be clear as to what hyperconjugation involves.
The following is multiple choice question (with options) to answer.
Carbon is a nonmetal with a significantly higher electronegativity; it is therefore more likely to accept electrons in what kind of reaction? | [
"catalyst reaction",
"redox reaction",
"reversable reaction",
"isotope reaction"
] | B | a reductant or an oxidant; it is also a Lewis base. The other reactant (Cl2) is an oxidant, so we expect a redox reaction to occur in which the carbon of CO is further oxidized. Because Cl2 is a two-electron oxidant and the carbon atom of CO can be oxidized by two electrons to the +4 oxidation state, the product is phosgene (Cl2C=O). Unlike Cl2, BF3 is not a good oxidant, even though it contains boron in its highest oxidation state (+3). Nor can BF3 behave like a reductant. Like any other species with only six valence electrons, however, it is certainly a Lewis acid. Hence an acid–base reaction is the most likely alternative, especially because we know that CO can use the lone pair of electrons on carbon to act as a Lewis base. The most probable reaction is therefore the formation of a Lewis acid–base adduct. Typically, both reactants behave like reductants. Unless one of them can also behave like an oxidant, no reaction will occur. We know that Sr is an active metal because it lies far to the left in the periodic table and that it is more electropositive than carbon. Carbon is a nonmetal with a significantly higher electronegativity; it is therefore more likely to accept electrons in a redox reaction. We conclude, therefore, that Sr will be oxidized, and C will be reduced. Carbon forms ionic carbides with active metals, so the reaction will produce a species formally containing either C4− or C22−. Those that contain C4− usually involve small, highly charged metal ions, so Sr2+ will produce the acetylide (SrC2) instead. Exercise. |
SciQ | SciQ-1530 | nomenclature
Title: What do numbers in parenthesis after elements respresent? I have seen elements with a number in parentheses after them in literature, but cannot find what it means. What does the number in parentheses after an element represent, such as in W(100) or Mo(110)?
https://aip.scitation.org/doi/abs/10.1063/1.1727919
https://www.sciencedirect.com/science/article/pii/0039602880900886 These are called Miller indices and they identify a particular surface of a crystal. (You can form different faces by cutting the crystal in different ways.) When you see something like "Mo(110)" it means "the 110 surface of a crystal of molybdenum."
The following is multiple choice question (with options) to answer.
What is denoted by the number above the chemical symbol of each element in a modern periodic table? | [
"metallic number",
"atomic number",
"electron count",
"atomic weight"
] | B | In the modern periodic table, each element is represented by its chemical symbol. The number above each symbol is its atomic number. Atomic numbers increase from left to right and from top to bottom in the table. |
SciQ | SciQ-1531 | forces, classical-mechanics, friction, torque
For me, if the force exerted on the tire by the ground is in the direction of motion, static friction will point backwards, opposing the eventual relative motion
If you gun the engine and the tire spins (or if you're on ice or something with minimal friction), it spins in a way where the bottom of the wheel moves backward (to the rear of the car) and the top of the wheel moves forward.
Friction creates forces that oppose relative motion. Since the wheel "wants" to move backward, that means that the friction force (on the tire) points forward. The relative motion we are talking about isn't between the car and the ground, it's between the bottom of the tire and the ground.
The following is multiple choice question (with options) to answer.
What does the tires meeting the road cause when a car accelerates? | [
"erosion",
"thrust",
"friction",
"vibration"
] | C | A bowling ball rolls down a lane at a constant velocity. (e) A car accelerates down the road. There is friction between the tires and the road. |
SciQ | SciQ-1532 | heat, wavelength
Title: Is carbon dioxide a greenhouse gas?
Possible Duplicate:
What experiments prove the greenhouse effect?
I am seeking for a proof that CO2 is a greenhouse gas. I posted this on Skeptic.SE recently but found no help in seeking for proof:
I assisted to a physicist conference in my university a few years ago
against the case that carbon dioxide was a cause of global warming.
The main point was that CO2 is not a greenhouse gas. I did a
research to find evidence for either side and found absolutely
nothing.
So, is carbon dioxide a greenhouse gas? If yes, has it been
demonstrated in a scientific paper?
Here are some discussion articles describing arguments against CO2
being a greenhouse gas:
The following is multiple choice question (with options) to answer.
What gas is contributing to the greenhouse effect? | [
"nitrogen",
"sodium chloride",
"oxygen",
"carbon dioxide"
] | D | Another major problem caused by air pollution is global climate change. Gases such as carbon dioxide from the burning of fossil fuels increase the natural greenhouse effect. This raises the temperature of Earth’s surface. |
SciQ | SciQ-1533 | evolution, botany, development, fruit, seeds
What is the point of fruit if not to be eaten? It’s my understanding that organisms will adapt to survive and thrive. I understand that being eaten can spread seeds, but this just seems like too much of a risky tactic to rely on.
Following on from part one: If being eaten is the best way to spread seed, why do some plants avoid this (such as by being poisonous or thorny)? Seeds are spread by many mechanisms
Wind dispersal: When air currents used to spread seeds. Often these plants have evolved features to facilitate wind catching, for example dandelions. Aka, anemochory.
Propulsion & bursting: When seeds are propelled from the plant in an such as in these videos. This is called Ballochory.
Water: Similarly to wind dispersal plants can spread seeds by water movement/currents, aka Hydrochory. This is used by many algae and water living plants.
Sticky Seeds: There are many ways a seed can attach to the outside of an animal - by using hooks, barbs, sticky excretions, hairs. Seeds then get carried by an animal and fall off later. This is epizoochory.
Fruiting: Plants can use seed-bearing fruit to encourage animals to eat the seeds. They will then be spread when the waste is excreted after digestion. This is a process of endozoochory.
More than one way to spread a seed
The following is multiple choice question (with options) to answer.
A complex interactions of hormones result in an edible fruit that entices animals that help disperse what? | [
"seeds",
"water",
"rocks",
"pests"
] | A | |
SciQ | SciQ-1534 | entomology, parasitology, parasitism
The male (microgametocytes) and female (macrogametocytes) gametocytes are ingested by a female Anopheles mosquito during a blood meal (8) - only female mosquitoes (of pretty much any species) drink blood. The parasites' multiplication in the mosquito is known as the sporogonic cycle (stage C). While in the mosquito's stomach, the microgametes penetrate the macrogametes generating zygotes (9). The zygotes in turn become motile and elongated (ookinetes) (10) which invade the midgut wall of the mosquito where they develop into oocysts (11). The oocysts grow, rupture, and release sporozoites (12), which make their way to the mosquito's salivary glands. Inoculation of the sporozoites into a new human host perpetuates the malaria life cycle (1).
Sources
The following is multiple choice question (with options) to answer.
What are the cells caused that parasites spread through their host? | [
"sporozoites",
"prokaryotes",
"protists",
"fungi spores"
] | A | |
SciQ | SciQ-1535 | genetics, molecular-evolution
Title: gene mutation occurs on two strands of DNA or just one strand? Suppose we have one strand with 3'-AAA-5' and the other strand is 5'-TTT-3'.
So when point mutation occurs, does it happen to two strands at the same time? e.g. 3'-AAA-5' becomes 3'-AGA-5' and 5'-TTT-3' becomes 5'-TCT-3'?
Or the mutation can occur with only one strand? e.g. only 3'-AAA-5' becomes 3'-AGA-5'? but in this case, A would pair up with G.
When transcription starts, the 3'-5' strand is transcribed, if the mutation does no occur in this strand, does it mean this mutation wouldn't affect any downstream products?
Is it same for indel? A "mutation" is a permanent alteration of the genetic composition of an individual. To obey this definition, a base change in one strand must be accompanied by a corresponding change in the opposite strand. Only in this way a mutation can be transmitted to the offspring.
The situation where only one of the strands has undergone a base change constitutes a pre-mutational DNA damage, as the double strand will show a deformation at that site. The enzymes of DNA repair mechanisms recognize and correct many such "deformations", but sometimes they do not know which was the original base, and introduce a change that become fixed in the DNA sequence.
The following is multiple choice question (with options) to answer.
When can mutations occur in genes? | [
"after rna replication",
"during dna replication",
"after dna replication",
"during rna replication"
] | B | The Evolution of Promoters The evolution of genes may be a familiar concept. Mutations can occur in genes during DNA replication, and the result may or may not be beneficial to the cell. By altering an enzyme, structural protein, or some other factor, the process of mutation can transform functions or physical features. However, eukaryotic promoters and other gene regulatory sequences may evolve as well. For instance, consider a gene that, over many generations, becomes more valuable to the cell. Maybe the gene encodes a structural protein that the cell needs to synthesize in abundance for a certain function. If this is the case, it would be beneficial to the cell for that gene’s promoter to recruit transcription factors more efficiently and increase gene expression. Scientists examining the evolution of promoter sequences have reported varying results. In part, this is because it is difficult to infer exactly where a eukaryotic promoter begins and ends. Some promoters occur within genes; others are located very far upstream, or even downstream, of the genes they are regulating. However, when researchers limited their examination to human core promoter sequences that were defined experimentally as sequences that bind the preinitiation complex, they found that promoters evolve even faster than protein-coding genes. It is still unclear how promoter evolution might correspond to the evolution of humans or other higher organisms. However, the evolution of a promoter to effectively make more or less of a given gene product [1] is an intriguing alternative to the evolution of the genes themselves. Promoter Structures for RNA Polymerases I and III In eukaryotes, the conserved promoter elements differ for genes transcribed by RNA polymerases I, II, and III. RNA polymerase I transcribes genes that have two GC-rich promoter sequences in the -45 to +20 region. These sequences alone are sufficient for transcription initiation to occur, but promoters with additional sequences in the region from -180 to -105 upstream of the initiation site will further enhance initiation. Genes that are transcribed by RNA polymerase III have upstream promoters or promoters that occur within the genes themselves. |
SciQ | SciQ-1536 | life, replication
Title: What is the name of the smallest self-replicating thing? Some time last year, I found an article on Wikipedia about the smallest something to be able to reproduce.
I don't remember exactly what it was, but I am fairly certain that after the initial discovery another of the previous organism (this one slightly smaller) was discovered.
I think that the smallest something might have been the smallest self-replicating protein, or smallest self-replicating molecule, or something like that.
It was not mentioned in this thread: Which organism has the smallest genome length?
It had a strange, stand-out name and I believe it was discovered in the 90s. You're probably thinking of the Spiegelman Monster. It was actually discovered in 1965, but it was discovered that it became shorter over time in 1997.
It also wasn't included in that thread, and it has a strange name.
http://en.wikipedia.org/wiki/Spiegelman_Monster
The following is multiple choice question (with options) to answer.
The sites of protein synthesis are tiny structures called? | [
"ribosomes",
"crystals",
"protons",
"prokaryotes"
] | A | |
SciQ | SciQ-1537 | ichthyology, vertebrates
Title: If an organism is supported only by cartilage, does it have an endoskeleton? Lamprey and sharks lack bones, but does this mean they are not classified as having an endoskelton? Does an organism need bone to be considered as having an endoskeleton? From wikipedia
An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue.
Cartilage is a mineralized tissue so it counts as a skeleton from this definition. A bit further in the wikipedia article it says
The vertebrate endoskeleton is basically made up of two types of tissues (bone and cartilage)
The following is multiple choice question (with options) to answer.
Mollusks, annelids, and arthropods are considered what? | [
"protostomes",
"detritivores",
"micelles",
"protisines"
] | A | Mollusks, annelids, and arthropods are protostomes. Echinoderms and chordates are deuterostomes. This distinction is important. Why does it matter? It shows that echinoderms are more closely related to chordates than are the other invertebrate phyla. This is not apparent based on other, more obvious traits. |
SciQ | SciQ-1538 | newtonian-mechanics, classical-mechanics, forces, torque
Title: Why are non-horizontal levers not considered to be in equilibrium? Consider a triple-beam balance, like so:
(source: microscopesamerica.com)
An unknown mass is placed on the left pan, and the provided weights are moved on the right until the lever arm comes to rest at an exactly horizontal position, as indicated by a line on the rightmost tip of the lever arm. Often, when I'm using the device and I'm close to the equilibrium point, the lever arm will come to rest slightly higher or lower than horizontal, so I'll adjust the weights accordingly until the lines align perfectly.
However, I don't see why the arm must be perfectly horizontal to read an accurate value. Isn't a stationary lever -- no matter what the angle -- an indication that there is no net torque on the system? If so, wouldn't that demonstrate that the masses are balanced in an appropriate way?
In other words, why doesn't a lever which is stationary in a non-horizontal position remain stationary when placed horizontally (and vice versa), since the net torque is zero in both cases? On a well designed balance scale, the center of gravity of the beam or lever arm will be just slightly below the center pivot point.
If the beam is not level, the center of gravity will be to one side or the other of the pivot, and will thus create torque as it tries to move directly below the pivot point.
The distance between the pivot point and the center of gravity of the beam will determine the scale's sensitivity, ie.. the closer the CG is to the pivot, the less torque it will apply when it is out of alignment, and the smaller the difference the scale will be able to detect.
There are no springs, or magnets that cause this effect, just gravity at work.
The following is multiple choice question (with options) to answer.
One of the simplest machines is the lever, which is a rigid bar pivoted at a fixed place called what? | [
"sling",
"caliper",
"wheel",
"fulcrum"
] | D | One of the simplest machines is the lever, which is a rigid bar pivoted at a fixed place called the fulcrum. Torques are involved in levers, since there is rotation about a pivot point. Distances from the physical pivot of the lever are crucial, and we can obtain a useful expression for the MA in terms of these distances. |
SciQ | SciQ-1539 | dna, rna, virus, virology, gene
Title: Is there any virus that contains both DNA and RNA in its genome? It is known that viruses contain DNA or RNA- either one and not both.
I came across a question: Which virus contains both DNA and RNA? Here is the results summary of the study that describes the discovery of DNA:RNA hybrid virus:
Results
Bioinformatic analysis of viral metagenomic sequences derived from a hot, acidic lake revealed a circular, putatively single-stranded DNA virus encoding a major capsid protein similar to those found only in single-stranded RNA viruses. The presence and circular configuration of the complete virus genome was confirmed by inverse PCR amplification from native DNA extracted from lake sediment. The virus genome appears to be the result of a RNA-DNA recombination event between two ostensibly unrelated virus groups. Environmental sequence databases were examined for homologous genes arranged in similar configurations and three similar putative virus genomes from marine environments were identified. This result indicates the existence of a widespread but previously undetected group of viruses.
And here is the link to the paper:
https://biologydirect.biomedcentral.com/articles/10.1186/1745-6150-7-13
The following is multiple choice question (with options) to answer.
In essence, a virus is simply a nucleic acid surrounded by what? | [
"a polymer coat",
"a protein coat",
"a membrane coat",
"a polypeptide"
] | B | A virus is a sub-microscopic particle that can infect living cells. Viruses are much smaller than prokaryotic organisms. In essence, a virus is simply a nucleic acid surrounded by a protein coat, as seen in the Figure below . This outer coat is called a capsid . Viruses will be discussed in more detail in the Viruses concepts. |
SciQ | SciQ-1540 | atoms, terminology
Title: What is a neutral atom? I was told that an atom's atomic number is defined as follows:
The number of electrons or protons present in a neutral atom is called atomic number. It is represented by Z.
What does neutral mean here? Why isn't it just "..present in an atom..."? Electrons and protons are charged particles. The electrons have negative charge, while protons have positive charge. A neutral atom is an atom where the charges of the electrons and the protons balance. Luckily, one electron has the same charge (with opposite sign) as a proton.
Example: Carbon has 6 protons. The neutral Carbon atom has 6 electrons. The atomic number is 6 since there are 6 protons.
The following is multiple choice question (with options) to answer.
How does the number of protons compare to the number of electrons in an electrically neutral atom? | [
"they are half",
"they are equal",
"they are triple",
"they are double"
] | B | In an electrically neutral atom, the number of protons equals the number of electrons. |
SciQ | SciQ-1541 | algorithm-analysis, performance
In short: there is no single scientifically accepted method. Instead, think of science as (a) being precise about what claims you are making, and then (b) providing appropriate evidence to support those claims. What constitutes "appropriate evidence" will depend upon your specific situation. You can often look to other publications in your field to see what evaluation method they used, as initially guidance, but ultimately this is a matter of critical thinking: evaluating evidence in a logical, careful, thoughtful manner.
The following is multiple choice question (with options) to answer.
The scientific method is a method of research with defined steps that include experiments and careful what? | [
"observation",
"discovery",
"consideration",
"estimation"
] | A | that have taken place during this time. There are however, areas of knowledge and human experience that the methods of science cannot be applied to. These include such things as answering purely moral questions, aesthetic questions, or what can be generally categorized as spiritual questions. Science has cannot investigate these areas because they are outside the realm of material phenomena, the phenomena of matter and energy, and cannot be observed and measured. The scientific method is a method of research with defined steps that include experiments and careful observation. The steps of the scientific method will be examined in detail later, but one of the most important aspects of this method is the testing of hypotheses. A hypothesis is a suggested explanation for an event, which can be tested. Hypotheses, or tentative explanations, are generally produced within the context of a scientific theory. A scientific theory is a generally accepted, thoroughly tested and confirmed explanation for a set of observations or phenomena. Scientific theory is the foundation of scientific knowledge. In addition, in many scientific disciplines (less so in biology) there are scientific laws, often expressed in mathematical formulas, which describe how elements of nature will behave under certain specific conditions. There is not an evolution of hypotheses through theories to laws as if they represented some increase in certainty about the world. Hypotheses are the day-to-day material that scientists work with and they are developed within the context of theories. Laws are concise descriptions of parts of the world that are amenable to formulaic or mathematical description. Natural Sciences What would you expect to see in a museum of natural sciences? Frogs? Plants? Dinosaur skeletons? Exhibits about how the brain functions? A planetarium? Gems and minerals? Or maybe all of the above? Science includes such diverse fields as astronomy, biology, computer sciences, geology, logic, physics, chemistry, and mathematics (Figure 1.16). However, those fields of science related to the physical world and its phenomena and processes are considered natural sciences. Thus, a museum of natural sciences might contain any of the items listed above. |
SciQ | SciQ-1542 | evolution, biochemistry, mitochondria
Title: Is there any advantage of having mitochondria for aerobic respiration? If we consider the pathway of breakdown of glucose which includes glycolysis, the citric acid cycle and the electron transport chain, all these processes takes place in some prokaryotes and eukaryotes. In prokaryotes all these processes take place in cytoplasm while in eukaryotes the last two processes take place in mitochondria.
So is there any advantage of performing the last two processes in the mitochondria? Does it yield more energy? If there is no advantage, what is the point of having a mitochondria (at least for this process)? From the evolutionary point of view, the eukaryotes acquired these metabolisms (except glycolysis) from their prokaryotic endosymbionts. Not all prokaryotes have the ETC. The free living ancestor of mitohondria is supposed to be the alpha-proteobacterium.
Now, glycolysis is a common pathway in lot of lifeforms perhaps because of abundance of glucose. TCA cycle is coupled with ETC at certain steps which makes it essentially a part of aerobic metabolism.
The reason for having a dedicated organelle for respiration
ATP synthesis is a membrane process. Imagine a large prokaryotic cell- as big as an animal cell. Such a cell cannot take care of its energetic demands which primarily consists of protein synthesis with the given area of membrane i.e it needs much more ATP-synthases than it can have to cope up with the energy demands of maintaining such a huge cell (this index is approximated based on surface to volume ratio). Therefore it is wise to harbor multiple efficient organelles i.e. mitochondria which themselves have just a small essential genome and proteome to maintain.
For a better understanding, please read this article. I just loved it.
There is also a book by the same author about mitochondria called Power, Sex, Suicide.
The following is multiple choice question (with options) to answer.
The protist life cycle benefits by including what forms of reproduction? | [
"atypical and sexual",
"asexual and biological",
"asexual and sexual",
"ideal and sexual"
] | C | Most protists also have a complex life cycle. The life cycle of an organism is the cycle of phases it goes through until it returns to the starting phase. The protist life cycle includes both sexual and asexual reproduction. Why reproduce both ways? Each way has benefits. Asexual reproduction is fast. It allows rapid population growth when conditions are stable. Sexual reproduction increases genetic variation. This helps ensure that some organisms will survive if conditions change. |
SciQ | SciQ-1543 | human-biology, genetics, cell-biology, terminology
and according to Wikipedia,
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis.
What’s the difference between them? I suppose a mitogen specifically refers to mitosis, but if something is stimulating mitosis, isn’t it stimulating growth? Are mitogens all growth factors? Are all growth factors mitogens? There is a lot of confusion and conflicting / imprecise definitions of these terms. It's biology after all :)
A mitogen is an agent that causes a cell to enter mitosis. This definition is pretty clear, and there is a good consensus about it. (Well technically, mitosis is not the same as cell division, but we will gloss over this distinction.)
The term growth factor has at least two different definitions: (1) a factor that causes growth of tissues, organs or entire individuals; or (2) a factor that causes growth of cells (increase in cell size). These two versions are often mixed up, and this causes no end of confusion. Let's consider them both in turn.
Definition (1) is more common and probably older. Since growth of whole tissues usually (but not always) implies both cell growth and division, according to this definition, a growth factor is also a mitogen. But the reverse is not true: there are cases where cells divide without growing, for example the first few cell divisions of a fertilized egg. But note that, since this definition concerns the level of tissues or individuals, it's meaning is not entirely clear in terms of cell growth and division. Muscle growth in the adult stage usually does not involve cell division, for example.
Definition (2) is better suited to cell biology (in my opinion), because it actually concerns cells, not tissues. This definition is more common when studying cell growth and division; see for example this review. Cell growth is a separate phenomenon from cell division: cells can grow without dividing (fat cells, muscle fibers and neuron do this, for example), or divide without growing (as mentioned above). So with this definition, growth factor and mitogen are two completely unrelated concepts. Now, it is certainly true that many proteins can act both as growth factors and mitogens; Matej Pribis gives some nice examples in the other answer. But that is an empirical fact, not a question of definitions.
The following is multiple choice question (with options) to answer.
With what does cytokinins act in concert to stimulate cell division and influence the pathway of differentiation? | [
"auxin",
"dna",
"ribosomes",
"hormone"
] | A |
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