source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-6544 | ph, titration
Title: Experimental determination of pH I am trying to determine the experimental pKa for two weak acids that were titrated against 0.20M NaOH.
I have read elsewhere that you can take the point where the graph becomes steep and divide the value of base added by two the corresponding pH value would then be the pKa, but how do i choose which value since it may not be obvious which point the graph becomes steep.
Below I can see that the pka for acetic acid should be close to the theoretical value calculated of 4.76 and the Tris-HCl pka should be approximately 8.3 but there must be a better way than just guessing from a graph.
My textbook doesn't explain how to experimentally find pH just that it's the point where $[A^-]/ [HA]$. I am hoping someone can give me an equation to work with or guide me in the right direction.
Thank you, So I think what you heard is about the right idea. The flat region is your buffering region, and isn't super helpful to deduce the pKa. Adding base consumes the weak acid, and because it is weak, you know you are mostly consuming the [HA] form, and equilibrating back to around the pKa. This is why your pH doesn't change much around the pKa.
As an example, if you had 10 mmol of HA to start, then at the pKa point you would have 5 mmol of HA and 5 mmol of A-. Now, if you keep adding base, at some point you will essentially consume the remaining 5 mmol of HA. Then, there will be negligible amount left and it can't buffer anymore - i.e. your pH will change rapidly because you are adding strong base. Here you will have ~0 mmol of HA, and ~10 mmol of A-. Note that you have twice the amount of A- now. The pKa will have been at the point where you had half of this.
Experimentally, I know two simple ways. Using a pH meter and no indicator, you have to measure the sharp region more carefully (i.e., drop by drop), because you want to be able to find the exact point where the pH changes the fastest. By approximating the derivative, i.e.
The following is multiple choice question (with options) to answer.
Acidity is measured on what kind of scale? | [
"pneumatic scale",
"electromagnetic scale",
"caloric scale",
"ph scale"
] | D | Acidity is measured on a pH scale. Rain that is 5.0 or less on that scale is considered acid rain. |
SciQ | SciQ-6545 | 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.
What is the enclosed, fluid-filled membrane that surrounds and protects the fetus and is attached to the placenta? | [
"amniotic sac",
"epithelial sac",
"umbilical sac",
"womb"
] | A | Attached to the placenta is the amniotic sac , an enclosed membrane that surrounds and protects the fetus. It contains amniotic fluid , which consists of water and dissolved substances. The fluid allows the fetus to move freely until it grows to fill most of the available space. The fluid also cushions the fetus and helps protect it from injury. |
SciQ | SciQ-6546 | pathology
Title: Are all diseases caused by organisms (microorganisms)? Are there other causes? Or is it correct to say that all diseases are in fact caused by organisms (microorganisms)? It is not correct to say that all diseases are caused by foreign organisms. Counterexamples are:
Cancer is caused by random genetic mutations in the cells of our body. The mutations can be caused by many factors such as ionizing radiation, smoking, chemical toxins etc.
Diseases such as stroke or heart attack are caused by blood clots blocking the blood flow to essential organs.
Autoimmune diseases are caused by the immune system falsely recognizing cells of the body as foreign and attacking that tissue leading to a wide variety of symptoms.
Alzheimer's disease is caused by chronic neurodegeneration, meaning that the cells in the brain die. The causes are not quite understood but as Alzheimer's usually appears late in life it is likely related to ageing. Also, it is known that some genetic defects can lead to early-onset Alzheimers.
Prion proteins can cause diseases such as Creutzfeldt–Jakob disease also known as mad-cow disease.
Hereditary diseases such as early-onset Alzheimers or ALS are cause by gene defects inherited from the parents.
Toxins can cause chronic diseases such as lead poisoning.
The list probably goes on...
Please note that the first two on the list are the most common cause of death in developed countries.
The following is multiple choice question (with options) to answer.
Alzheimer’s disease is a disease that occurs mainly in what population? | [
"younger adults",
"female adults",
"white adults",
"older adults"
] | D | Alzheimer’s disease is another disease that occurs mainly in older adults. In Alzheimer’s disease, a person gradually loses most normal mental functions. The patient typically suffers from increasing memory loss, confusion, and mood swings. The cause of Alzheimer’s isn’t known for certain, but it appears to be associated with certain abnormal changes in the brain. There is no known cure for this devastating disease, but medicines may be able to slow its progression. |
SciQ | SciQ-6547 | sociality, olfaction
Sexual Signaling:
In some species, apocrine gland secretions may play a role in sexual attraction and mate selection. The distinct scents emitted by individuals can serve as cues for potential mates to assess each other's fitness and genetic compatibility.
Developmental Timing:
Apocrine glands are not fully functional until puberty in humans. Their activation and development are influenced by hormonal changes during adolescence.
Associated with Hair Follicles:
Apocrine glands are associated with hair follicles, and their ducts open into the hair follicle canal. This is in contrast to eccrine glands, which release sweat directly onto the skin's surface.
Here's a ref from nature stating that human primates may use sweat pheromones to communicate:
https://www.nature.com/articles/npre.2008.2561.1.pdf
Primates, especially those living in social groups, rely heavily on communication to maintain social bonds, establish hierarchies, and coordinate group activities. Scent plays a crucial role in primate communication, and sweat scent could have evolved as a means for individuals to convey information about their identity, reproductive status, and emotional state to other members of their group.
mate selection in primates can be influenced by olfactory cues. Scent signals emitted through sweat may allow potential mates to assess each other's genetic compatibility, overall health, and reproductive fitness.
the scent-marking behavior using secretions from sweat glands may serve as a way to establish territorial boundaries and prevent conflicts with neighboring groups.
The odor produced by sweat may play a role in avoiding predators. For example, certain primate species may produce alarm pheromones through their sweat, signaling danger to other group members.
Sweat scent in primates could be a remnant of their ancestral heritage, where scent communication was crucial for survival and reproduction.
incidentally, horses, dogs, deer, they also have strong pheromones.
The following is multiple choice question (with options) to answer.
What do sudoriferous glands secrete? | [
"tissue",
"water",
"sweat",
"moving"
] | C | Sweat Glands When the body becomes warm, sudoriferous glands produce sweat to cool the body. Sweat glands develop from epidermal projections into the dermis and are classified as merocrine glands; that is, the secretions are excreted by exocytosis through a duct without affecting the cells of the gland. There are two types of sweat glands, each secreting slightly different products. An eccrine sweat gland is type of gland that produces a hypotonic sweat for thermoregulation. These glands are found all over the skin’s surface, but are especially abundant on the palms of the hand, the soles of the feet, and the forehead (Figure 5.14). They are coiled glands lying deep in the dermis, with the duct rising up to a pore on the skin surface, where the sweat is released. This type of sweat, released by exocytosis, is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide. Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis. |
SciQ | SciQ-6548 | periodic-trends, periodic-table
Title: How long the block starting with element 121 will be? I remember from my chemistry classes that (after the initial irregularities) a new block of elements starts every two periods. After the initial s-block and p-block following it shortly, we have d-block starting at period IV, and f-block starting at period VI.
Now that Element 118 has been discovered, we're about to open period VIII and we're two elements short of a new block.
What block will it be? How many groups, what name etc? As you noted, this is a very appropriate question in light of the IUPAC announcement that we have just finished filling Period 7!
The names of the subshells s, p, d, and f are named after the old spectroscopic terms sharp, principal, diffuse, and fundamental. We ran out of fancy names after that, so the subsequent subshells are named in alphabetical order - g, h, and so on - which means that after the 8s block is filled, we would theoretically have a 5g block.
The orbitals in the g subshell would be labelled with the quantum number $l = 4$, so $m_l$ would take integer values between $-4$ and $4$ (inclusive) giving a total of nine g-orbitals. Each g-orbital could hold two electrons with opposite spins, so the g-block would have $18$ electrons.
However, it is worth noting that the electronic configurations may or may not obey the aufbau principle fully. Whether the 5g orbitals will actually be filled or not will certainly not be easy to determine, considering how short the half-lives of those elements are likely to be.
Wikipedia has an article which talks about it.
The following is multiple choice question (with options) to answer.
Group 15 of the periodic table is also called which group? | [
"hydrogen",
"potassium",
"oxygen",
"nitrogen"
] | D | Group 15 of the periodic table is also called the nitrogen group. The first element in the group is the nonmetal nitrogen (N), followed by phosphorus (P), another nonmetal. Arsenic (As) ( Figure below ) and antimony (Sb) are the metalloids in this group, and bismuth (Bi) is a metal. All group 15 elements have five valence electrons, but they vary in their reactivity. Nitrogen, for example, is not very reactive at all, whereas phosphorus is very reactive and found naturally only in combination with other substances. All group 15 elements are solids, except for nitrogen, which is a gas. |
SciQ | SciQ-6549 | physiology, nutrition, organic-chemistry
Title: How is it known that there are only three macronutrients: proteins carbohydrates and lipids? It is stated here that in human nutrition, micronutrients are nutrients required generally in less than 100 mg daily quantities whereas macronutrients are required in gram quantities. It is widely stated that our macronutrients are carbohydrates, lipids, and proteins. How was it shown that these are the human macronutrients and that we don't have other macronutrients?
One answer to this similar question on Quora suggests that ethanol or ketones could be considered macronutrients. Ethanol is mentioned in this article, though ketones are not. Other sources I saw didn't clarify. Summary
The question is based on the misconception that the term “macronutrient” originated as a scientific definition, to which entities satisfying this definition were assigned. In fact it was a default term used as a distinction from compounds falling into the earlier category, “micronutrient”, and was used initially to encompass the three specific classes of food that had been established to be sources of energy through decades of nutritional research. Hence there was no question of whether there “should” be more macronutrients. The term is not a scientific definition, and today is used in different ways so that anyone using the term needs to clarify what it should be taken to mean in that particular context.
Food Energy and the history of Nutrition
Scientific studies of nutrition, dating the late 18th century, were initially concerned with chemical structure, metabolic fate and energy produced by different foods, and this is described in a short readable article by Ned Stafford in Nature (2010) 468, S16–17.
By the end of the 19th century protein, fat and carbohydrate had been established as the chemical fuels that supplied energy from the diet, and the energy values (in terms of the, now obsolete, calorie) had been established by Atwood, using his respiration calorimeter.
Micronutrients
The following is multiple choice question (with options) to answer.
Humans need lipids for many vital functions such as storing energy and forming what? | [
"zygotes",
"ionic bonds",
"cell membranes",
"enzymes"
] | C | Humans need lipids for many vital functions such as storing energy and forming cell membranes. Lipids can also supply cells with energy. In fact, a gram of lipids supplies more than twice as much energy as a gram of carbohydrates or proteins. Lipids are necessary in the diet for most of these functions. Although the human body can manufacture most of the lipids it needs, there are others, called essential fatty acids , that must be consumed in food. Essential fatty acids include omega-3 and omega-6 fatty acids. Both of these fatty acids are needed for important biological processes, not just for energy. |
SciQ | SciQ-6550 | nuclear-physics, protons
Atoms are attracted to atoms through electromagnetism covalent bonds, ionic bondings and electromagnetic residual forces,. The nuclear force is too short range to affect the atoms: size of nucleus order of 10^-15 cm, size of atom order 10^-10 ; and the electron shells do not allow closer contact.
The following is multiple choice question (with options) to answer.
What bond is a force of attraction between ions and atoms? | [
"chemical bond",
"carbon bond",
"Ionic bond",
"radiation bond"
] | A | A chemical bond is a force of attraction between atoms or ions. Bonds form when atoms share or transfer valence electrons. |
SciQ | SciQ-6551 | cell-biology, microbiology
Title: Are there any organisms that are made of more than one (~5-12) cell? Prokaryotes and eukaryotes are unicellular, made of one cell. Great. Eukaryotes are unicellular or multicellular. But the typical examples of multicellular eukaryotes we have are made of, often, trillions of cells, like us humans. Ants must still be made of many millions of cells. Are there known eukaryotes with very few cells that make them up? Like, 5, or something? Or maybe a dozen cells making up the whole organism in its fully developed state? There's Trichoplax adhaerens, a Placozoa, made of a few thousand cells. Then there is Dicyema japonicum, a simple mesozoan, made up of 9 to 41 cells. Arguably, the simplest multicellular organism is the algae Tetrabaena socialis, whose body consists of 4 cells. Then, there's the parasitic Myxozoa which have 7 cells.
The following is multiple choice question (with options) to answer.
What type of cells are the smallest of all human cells? | [
"egg",
"sperm",
"meristematic",
"dna"
] | B | Sperm are tiny cells. In fact, they are the smallest of all human cells. They have a structure that suits them well to perform their function. |
SciQ | SciQ-6552 | metabolism, ecology, photosynthesis
Title: Why isn't phosphorus or nitrogen a limiting nutrient for animals? Nitrogen and Phosphorus are usually the limiting nutrient for plants, especially for algae. Phosphorus is used for DNA, ATP and phospholipids, and Nitrogen is used for pretty much every protein a cell might want to produce. That is, their need for biological processes is not tied specifically to photosynthesis: anything that lives is going to need them, pretty much for anything it might want to do. It would make sense for them to be a limiting nutrient for almost anything that's trying to grow, plant or animal.
Yet for animals the limiting "nutrient" seems to always be energy, ie: food. Why aren't animals limited by lack of nutrients in the same way that plants are? Obviously animals need these nutrients, too. Or to reverse the question, why do plants need so much more phosphorus/nitrogen than animals do?
My best guess is that an animal's digestion of plant material is relatively inefficient energy-wise but relatively efficient nutrient-wise. So for an animal to eat enough food to have sufficient energy to survive, it's probably eaten more than enough Nitrogen and Phosphorus for its needs. But I'm just guessing and I can't find any data that would back up that guess. Phosphorus
Your suggestion that if we are meeting our calorific requirement we will be getting enough is true for phosphorus.
Most foods contain lots of phosphorus. The maximum dietary requirement occurs during adolescent growth, estimated at 1250 mg per day. Assuming a calorie intake of 2500 kcal we can calculate a 2500 kcal equivalent phosphorus content for various foods:
skimmed milk contains 7,400 mg phosphorus per 2500 kcal
roasted chicken breast contains 7,500 mg phosphorus per 2500 kcal
cooked white rice contains 3840 mg per 2500 kcal
(Calculations are based upon values obtained via this site.)
Nitrogen
Our requirement for nitrogen is met by our protein intake: inadequate protein intake manifests as kwashiorkor which is essentially due to a dietary deficiency of essential amino acids. In other words, the only way to achieve a nitrogen-deficient diet is to not eat protein, and this would not be alleviated by any inorganic source of nitrogen, even if we could consume enough of such a N source.
The following is multiple choice question (with options) to answer.
Vertebrates also require relatively large quantities of calcium and phosphorus for building and maintaining what? | [
"brain cells",
"metabolism",
"blood",
"bone"
] | D | |
SciQ | SciQ-6553 | human-biology
Title: Does sweat contain DNA information? I was reading this article : Perspiration
The first question which came to my mind after reading the composition of sweat was whether it contains any information about the DNA or not?
I haven't had much interaction with biology since 12th grade (2010), so kindly answer in layman's terms and detail as well. The Wikipedia page you linked says that sweat is composed of a liquid similar to blood plasma. As all DNA in humans is stored in the nucleus of a cell, it seems unlikely that the sweat itself would contain any DNA.
However, when someone sweats significantly, I can't imagine that no skin cells end up in the sweat. In any case in which this occurs, then the DNA in the cell is in the sweat. Additionally, with small amounts of sweat, I can't imagine how it would be collected without getting any skin cells in it.
This source confirms that sweat contains DNA in some form. Additionally, I think the following quote from here shows that it is stored in cells:
In every case, what is being tested is the DNA contained in cells of human tissue
The following is multiple choice question (with options) to answer.
What contains most of the structures found in skin? | [
"dermis",
"epidermis",
"basal layer",
"subcutaneous layer"
] | A | Structures of the Dermis. The dermis contains most of the structures found in skin. |
SciQ | SciQ-6554 | computability, turing-machines, physics
Title: Can normal physics laws be simulated in Digital physics? Physics is defined as the study of an object {matter or energy} with its interaction with other objects:
Physics is the study of matter, energy, and the interaction between them.
On the other hand, Digital physics is based on computations and information.
Digital physics is a collection of theoretical perspectives based on the premise that the universe is, at heart, describable by information, and is therefore computable.
The following is multiple choice question (with options) to answer.
What is the study of matter and energy referred to as? | [
"biology",
"physical science",
"cosmology",
"geology"
] | B | Physical science is the study of matter and energy. It includes chemistry, which focuses on matter, and physics, which focuses on energy. |
SciQ | SciQ-6555 | electrochemistry, electricity
Title: Open-circuit potential of an electrochemical cell I'm studying electrochemistry without a physics background--never taken it for extenuating reasons--for a research project using Bard's Electrochemical Methods. I'm having trouble understanding the concept of open-circuit potential (OCP): the electric potential measured in a cell when disconnected from a circuit. First off, why can you measure OCP at all? It's a result of thermodynamics--i.e. the sum of the standard potentials of the half reactions at the given electrodes. But wouldn't the lack of a current preclude any measurement of potential? I mean, a voltmeter, with its very high resistance, still allows some current flow. Since you can measure OCP, does that mean the half-reactions are taking place in small quantities?
Second, Wikipedia describes OCP as "the voltage that must be applied to a solar cell or a battery to stop the current." If a given cell has an OCP of 0.5V, that means I apply 0.5V to stop the current once a circuit is completed? But if there exists 0.5V without a current, applying an external 0.5V won't then create a total potential of 1V? In my head I want to apply -0.5V to negate the current flow.
Thank you in advance. The inclusion of mathematical formulae in your answer would be much appreciated! Basically you've have the right ideas.
The open-circuit potential of an electrochemical cell is the theoretical voltage that one would measure as the current flow approaches zero. Think of plotting small current flows against measured voltage and then extrapolating to zero current flow. Pragmatically though common voltmeters will only measure a few significant figures. So a microamp current flow is essentially zero current flow. This isn't math where pi can be calculated to millions of digits.
The following is multiple choice question (with options) to answer.
What do you call the ability of a particular electrochemical cell to generate an electric current? | [
"kinetic energy",
"electromagnetism",
"momentum",
"electrical potential"
] | D | The ability of a particular electrochemical cell to generate an electric current is called its electrical potential. Reduction potentials measure the tendency of a substance to be reduced in a redox reaction. |
SciQ | SciQ-6556 | This is called Weighted Least Squares (WLS), where the observations are weighted by the inverse of p h … first observation, where X has the value of X_1 . heteroscedasticity. The weighted estimates are shown in Figure 24.43. This is the generalization of ordinary least square and linear regression in which the errors co-variance matrix is allowed to be different from an identity matrix. role. coefficients will be wrong and, as a consequence, the t-tests as below: The left picture illustrates homoscedasticity. account the weights which change variance. Heteroscedasticity is a problem because statistical tests of significance assume the modelling errors are uncorrelated and uniform. simple technique to detect heteroscedasticity, which is looking at the to perform WLS. Weighted Least Squares Estimation (WLS) Consider a general case of heteroskedasticity. The WLS regression analysis is shown in Figure 2 using the approach described for Example 1 of WLS Regression Basic Concepts. In general, website owners These weights are calculated on the left side of Figure 7. summary of the dataset is presented below. The psychologist who developed this instrument wants to use regression to determine the relationship between the scores from this instrument and the amount of the stress hormone cortisol in the blood based on the data in columns A, B and C of Figure 12. \frac{Y_i}{\sigma_{\epsilon_i}} = \beta_1\frac{1}{\sigma_{\epsilon_i}}+\beta_2\frac{X_i}{\sigma_{\epsilon_i}} + \frac{\epsilon_i}{\sigma_{\epsilon_i}} Nowadays, having a business implies օwning a website. multiple linear regression model: Visits_i = \beta_0 + \beta_1Budget_i + \beta_2AdType_i + \epsilon_i. vertically (downwards in case of X_1). precision of your regression coefficients. By weights are unknown, we can try different models and choose the best one for all predicted values. w_i=\frac{1}{x_i^2}, w_i=\frac{1}{y_i^2},
The following is multiple choice question (with options) to answer.
What is a controlled scientific study of specific variables called? | [
"experiment",
"variation",
"practicum",
"example"
] | A | An experiment is a controlled scientific study of specific variables. A variable is a factor that can take on different values. |
SciQ | SciQ-6557 | geology, earth-history, paleontology, stratigraphy, mass-extinction
Why did this idea develop only in the 1980s? It was known since the 19th century that extinctions had occurred. Even the stratigraphic time is divided into units constrained by different fauna found in the fossil records. What was it that made the change from a "gradualist" perspective of things to the "catastrophic" point of view? The idea of mass extinction is not that recent actually: Cuvier (1798), Buckland (1823) and d'Orbigny (1851) for instance were already talking about global catastrophes in earth history, linked to extinctions. But during the same period, Brocchi (1814) and Lyell (1832) proposed that extinctions of species occurred individually and were a gradual process (either only linked to an intrinsic taxa longevity for Brocchi, or variations in the environment for Lyell). Darwin, following Lyell, also thought that extinctions were gradual and not catastrophic. He also noted the fact that hiatuses in the fossil record or artificial concentration in some strata could show apparent extinction event.
The issue with mass extinction is that to demonstrate their existence you need to be able to demonstrate extinction synchronicity and quantify the amount of species going extinct (to show that it is more than just background noise).
Demonstrating the synchronicity of one mass extinction is what Alvarez et al. 1980 managed to do thanks to the Iridium layer at the K/Pg boundary. More generally, the possibility of correlating extinctions precisely is something that evolved in par with the evolution of stratigraphic tools, and the 1970-1980s is the period during which high-resolution stratigraphic methods arose (chronostratigraphy, magnetostratigraphy, stable isotope stratigraphy for instance).
Quantifying mass extinction is what Jack Sepkoski did with his compendium of marine invertebrates (see Sepkoski 1978, 1979; Raup & Sepkoski 1982, etc.). Today, the PbDb (PaleoBiology DataBase) is the project which focusses on that specific issue (see for instance Alroy et al. 2001). It still remains today the main hurdle in studying mass extinctions.
Alroy, J. et al., 2001. Effects of sampling standardization on estimates of Phanerozoic marine diversification. PNAS, 98(11): 6261-6266.
The following is multiple choice question (with options) to answer.
What happened to earth's species during the permian period? | [
"division",
"mass extinction",
"evolution",
"duplication"
] | B | The Permian Period ended with Earth’s second mass extinction. During this event, most of Earth’s species went extinct. It was the most massive extinction ever recorded. It’s not clear why it happened. One possible reason is that a very large meteorite struck Earth. Another possibility is the eruption of enormous volcanoes. Either event could create a huge amount of dust. The dust might block out sunlight for months. This would cool the planet and prevent photosynthesis. |
SciQ | SciQ-6558 | 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.
Which organ in the body controls the amount of water loss in urine in response to maintaining homeostasis? | [
"liver",
"spleen",
"kidneys",
"lungs"
] | C | The boy in Figure below is working out on a hot day. He’s losing a lot of water in sweat. To maintain homeostasis, his body can balance the water lost in sweat by excreting less water in urine. The amount of water lost in urine is controlled by the kidneys. The kidneys are organs of excretion. |
SciQ | SciQ-6559 | acid-base, corrosion
Title: Are all corrosives either acids or bases? Are all corrosives either acid or a base? From what I could remember from school, strong acids and bases can be corrosive, but can substances be corrosive from reasons other than that? I tried my best to check for the answer with my limited knowledge.
If it is not just acids and bases what is it then, how can we categorize them, if possible in simple terms? Wikipedia lists many corrosive compounds. While a lot of them function as strong acids or bases, there are also these (not an exhaustive list):
Strong oxidizers including concentrated hydrogen peroxide
Fluorides (they say "fluoride ion", so salts as well as the acid are meant)
Organic compounds that can act as alkylating agents such as methyl sulfate
The moral of the story: Hazards can't be pigeonholed into specific types of chemicals. Best to find and read the safety data sheet with any chemical.
The following is multiple choice question (with options) to answer.
What is corrosive mixture is formulated by the combination of water, air and sulfur? | [
"sulfuric acid",
"sulfuric water",
"nitric acid",
"hydrochloric acid"
] | A | Surface mining exposes minerals that were underground to air and water at the surface. These minerals contain the chemical element sulfur. Sulfur mixes with air and water to make sulfuric acid. This acid is a highly corrosive chemical. Sulfuric acid gets into nearby streams and can kill fish, plants, and animals. Surface mining is safer for the miners. |
SciQ | SciQ-6560 | meteorology, climate-change, gas, pollution
Title: Regarding various types of atmospheric pollution Does all the car pollution (from about 150 million cars at least in the U.S. and a lot more in all of North America and the rest of the world) all the smoke-stack pollution of various factories and all the Airline pollution running day after day have a deleterious and damaging effect on the general atmosphere and, over time, the climate?
Given all the observed pollution that China has caused itself and some of the resulting weird weather events there this certainly seems to be evidence of the damaging effects of car and factory pollution. Has anyone calculated how much exhaust from cars is produced in one day on average in a 'moderate' sized city?
Of course it seems with all the increased oil production in the U.S. and elsewhere we, human beings are going to keep are love-affair with gas-powered cars for the next 200 or 300 years. That is if we don't use up all the oil and gas in the ground before then. As a USA resident, the EPA is the best place to start when wondering about the emissions inventory of atmospheric pollutants or pollutant precursors that affect the National Ambient Air Quality Standards (e.g. Particulate Matter, Carbon Monoxide, Sulfur Dioxide, Lead, Nitrogen Oxides, Volatile Organic Compounds). The EPA compiles a comprehensive emissions inventory of all criteria pollutants at the county level which is available in the National Emissions Inventory (compiled once every 3 years). You can see the summary of your county at http://www.epa.gov/air/emissions/where.htm. As for the effects of atmospheric pollution, it is important to consider the lifetime of said pollutants in the atmosphere in order to put their environmental impacts into perspective. For instance, the air pollutants covered by the National Ambient Air Quality Standards have immediate health effects when high concentrations are breathed in regularly. Both animals and plants are adversely affected by these irritating and sometimes toxic chemicals, but these pollutants are also reactive and do not last long in the atmosphere unless they are constantly being replenished (e.g. daily traffic). Air quality also impacts critical nitrogen loads on ecosystems and possible production of acid rain.
The following is multiple choice question (with options) to answer.
What type of pollutants enter the air directly? | [
"carbon",
"liquid",
"secondary",
"primary"
] | D | Primary pollutants enter the air directly. Some are released by natural processes, like ash from volcanoes. Most are released by human activities. Carbon oxides are released when fossil fuels burn. |
SciQ | SciQ-6561 | thermodynamics
Title: Nature of spontaneous reactions The definition of spontaneous process states that "A spontaneous process is an irreversible process and maybe reversed by some external agency"
So, can we say that all spontaneous reactions are irreversible reactions under the absence of some external force? A spontaneous reaction, as contrasted with a non-spontaneous reaction, is a reaction quantified by a negative free energy change. A reaction is said to be spontaneous if it occurs without being driven by an outside force. So, we can say: In any spontaenous process, the path between the reactants and products is irreversible
The following is multiple choice question (with options) to answer.
What type of reaction is a process in which some substances, called reactants, change into different substances, called products? | [
"toxic reaction",
"physical reaction",
"reversible reaction",
"chemical reaction"
] | D | A chemical reaction is a process in which some substances, called reactants, change into different substances, called products. During the reaction, chemical bonds break in the reactants and new chemical bonds form in the products. |
SciQ | SciQ-6562 | atoms
Title: How many atoms are represented in this equation? $\ce{Pb(NO3)2 + 2KI -> PbI2 + 2KNO3}$
The answer says 26, but shouldn't it be 13? Because actually, the number of atoms involved in the reaction are 13, and once the reaction is completed, again, number of atoms is 13.
Please explain. The referenced atoms on both sides of the arrow are the exact same atoms? I like your thinking!
But, chemical equations do not refer to individual atoms.
The formula $\ce{Pb(NO3)2}$ can be read as "A molecule of this substance consists of six atoms of O, two atoms of N, ...". That is correct.
But the equation $\ce{Pb(NO3)2 + 2KI -> PbI2 + 2KNO3}$, strictly speaking, does not talk about single molecules. The numbers (including the 1's that are nor written) are called "stoichiometric coefficients". The equation means: "Any number of $\ce{Pb(NO3)2}$ molecules react with the double amount of $\ce{KI}$ molecules to yield ...".
Wikipedia supports my view:
In lay terms, the stoichiometric coefficient (or stoichiometric number in the IUPAC nomenclature) of any given component is the number of molecules that participate in the reaction as written.
...
In more technically precise terms, ...
... the stoichiometric coefficient is the number of molecules divided by the progress variable or extent of reaction.
...
The (dimensionless) "units" may be taken to be molecules or moles. Moles are most commonly used, but it is more suggestive to picture incremental chemical reactions in terms of molecules.
The following is multiple choice question (with options) to answer.
What is the number placed in front of a chemical symbol or formula that shows how many atoms or molecules of the substance are involved in the reaction? | [
"coefficient",
"note",
"frequency",
"requirement"
] | A | Coefficients are used to balance chemical equations. A coefficient is a number placed in front of a chemical symbol or formula. It shows how many atoms or molecules of the substance are involved in the reaction. |
SciQ | SciQ-6563 | human-biology
Title: Is urine dirty as soon as it leaves the human body? Human urine is sterile as long as it is in the human body. But is it dirty after leaving the human body? Could you get sick from it, if you drink it or don't wash your hands, for example? It was believed for a long time that urine stored in the urinary bladder is sterile. However, Wolfe et al(1). recently found evidence of bacterial presence in the urine extracted from bladders of healthy women. In an article just published, Hilt et al. found that at least some bacteria found in the bladder of healthy women are viable and can be grown in a laboratory after extraction from the bladder).2 (Paywall). They expect that the same is the case for men.
From the Hilt et al. paper:
Thirty-five different genera and 85 different species were identified
by EQUC. The most prevalent genera isolated were Lactobacillus (15%),
followed by Corynebacterium (14.2%), Streptococcus (11.9%),
Actinomyces (6.9%), and Staphylococcus (6.9%). Other genera commonly
isolated include Aerococcus, Gardnerella, Bifidobacterium, and
Actinobaculum.
Note that these species for the most part (Actinobaculum being one exception, as a possible uropathogen) appear to be part of the normal microbiome (collection of microorganisms) in healthy people in the same way as bacteria inhabit other parts of healthy persons. Additionally, the recovered organisms required special care to achieve growth:
Most of the bacteria isolated required either increased CO2 or
anaerobic conditions for growth, along with prolonged incubation, and
they often were present in numbers below the threshold of detection
used in routine diagnostic urine culture protocols.
The following is multiple choice question (with options) to answer.
Through what does urine enter the bladder? | [
"the ureters",
"the vas deferens",
"the tubules",
"the enterocytes"
] | A | Nephrons filter about ¼ cup of body fluid per minute. In a 24-hour period, nephrons filter 180 liters of fluid, and 1.5 liters of the fluid is released as urine. Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 1½ to 2½ cups of urine but may also hold more if the urine cannot be released immediately. |
SciQ | SciQ-6564 | mammals, sex-chromosome, gender
Title: What processes regulate the sex of offspring? It is known that some species are more likely to born male than female (and some maybe vice versa). I understand that it is due to evolutionary perspective (average number of adult males is close to that of females), I want to know about how it is regulated.
What I thought is that spermatozoa are made by half as Y and half as X chromosome. Then mitosis and meiosis and the probability that one of them will die is equal for both types. So, somewhere I feel lost.
Also, can it be regulated by female body or not? According to this paper claiming that hormone levels in women affect the likelyhood to born son. Possibly it is just because they choose males that are more likely to have more Y spermatozoa than X, but if it is some chemical mechanism to regulate that I'd like to know.
I'm not asking only about humans, mechanisms can be similar in almost all mammals. I'm not asking about other species: I know some are regulated by temperature, etc. This question is only about mammals.
What processes regulate the sex of offspring?
The processes rulating the sex of offspring may occur in both males and females and be direct or indirect.
What I thought is that spermatozoa are made by half as Y and half as X chromosome. Then mitosis and meiosis and the probability that one of them will die is equal for both types. So, somewhere I feel lost.
This may not be entirely true. The phenomenon called "Meiotic drive" may change the ratio from 1:1. Meiotic Drive occurs through selfish genes. See "Selfish-gene theory" for more info.
Also, can it be regulated by female body or not?
if it is some chemical mechanism to regulate that I'd like to know.
Possibly, there is such in mammals. There is a bunch of mechanisms called "Cryptic female choice". Some of them are chemical. Although, the article is about birds, it can be the case similar mechanism is present in mammals.
Given that higher androgen level exposure in mothers affect make their offspring more male-typical in playing behavior we might consider that in general makes offsrpings more masculine. This would be a good reason for female organisms with higher androgen levels to favor sperm with Y chromosome present.
The following is multiple choice question (with options) to answer.
The male and female reproductive system is regulated by follicle-stimulating hormone (fsh) and luteinizing hormone (lh) produced by what gland? | [
"thyroid",
"adrenal",
"pituitary",
"testes"
] | C | 17.8 Gonadal and Placental Hormones The male and female reproductive system is regulated by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) produced by the anterior lobe of the pituitary gland in response to gonadotropin-releasing hormone (GnRH) from the hypothalamus. In males, FSH stimulates sperm maturation, which is inhibited by the hormone inhibin. The steroid hormone testosterone, a type of androgen, is released in response to LH and is responsible for the maturation and maintenance of the male reproductive system, as well as the development of male secondary sex characteristics. In females, FSH promotes egg maturation and LH signals the secretion of the female sex hormones, the estrogens and progesterone. Both of these hormones are important in the development and maintenance of the female reproductive system, as well as maintaining pregnancy. The placenta develops during early pregnancy, and secretes several hormones important for maintaining the pregnancy. |
SciQ | SciQ-6565 | botany, plant-physiology, plant-anatomy
Title: How do plants grow year after year even though they die? How do plants grow, die, and then grow again? For instance, when my plants die during the winter, how do they grow again next year? Does it have something to do with the root system? Or do they even die? It depends on the type of plant, but basically not all of the plant dies. Plants have evolved a number of strategies for winter* dormancy. These are common ones, but probably not an exhaustive list.
Deciduous trees and bushes simply drop their leaves in the fall, and so may look "dead" to the unskilled eye - though with practice, it's usually easy to distinguish between dead and dormant. Then when the weather warms in the spring, new leaves grow.
Other perennial plants may lose some or all of their top growth, even dying back to ground level, but the roots will be alive, and will start growing when the ground warms.
Still other plants have developed specialized underground structures like bulbs & rhizomes - think daffodils, tulips, irises, and similar. The rest of the plant dies, only to grow again from the bulb when conditions are right.
It's worth noting that most, if not all, of these are used for propagation as well, often naturally, and frequently with a bit of human help. Bulbs and rhizomes multiply: the daffodil bulb you planted a few years ago may now be a dozen bulbs, each of which can be moved to grow new ones. Many perennials can be increased by dividing the root mass into pieces, each of which will become a new plant. And cuttings from many trees & bushes can be induced to form new root systems, and become new plants.
Or summer, dry season, &c. For simplicity, I'll just say "winter".
The following is multiple choice question (with options) to answer.
How do plants grow? | [
"through mitosis and cell division",
"through cell growth and sexual reproduction",
"through cell growth and cell division",
"through pollination and cell division"
] | C | Most plants continue to grow throughout their lives. Like other multicellular organisms, plants grow through a combination of cell growth and cell division. Cell growth increases cell size. Cell division increases the number of cells. |
SciQ | SciQ-6566 | neuroscience, neuroanatomy
Title: Why is the anterior pituitary not considered part of the diencephalon? According to the wikipedia page on the diencephalon, the posterior pituitary gland is considered part of the diencephalon, but the anterior is not. Is there a reason that these two lobes of the same gland are considered different enough not to be part of the same brain region? Worth going to the wikipedia page on the pituitary:
In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary, which is an extension of the hypothalamus.
The anterior pituitary arises from an invagination of the oral ectoderm (Rathke's pouch). This contrasts with the posterior pituitary, which originates from neuroectoderm.
The posterior lobe develops as an extension of the hypothalamus, from the floor of the third ventricle.
In other words, the different parts of the pituitary are, developmentally, entirely separate. The posterior lobe is actually part of the hypothalamus. The anterior lobe is not even part of the brain.
Lumping them together with one label happened because the anatomists who originally named the thing didn't know much about it, which is not surprising because anatomical names are quite old and understanding of the functions of any parts of the brain is quite new. Old names stick.
The following is multiple choice question (with options) to answer.
What part of the brain is attached to the brain stem but considered a separate region of the adult brain? | [
"frontal lobe",
"parietal lobe",
"temporal lobe",
"cerebellum"
] | D | Brain Stem The midbrain and hindbrain (composed of the pons and the medulla) are collectively referred to as the brain stem (Figure 13.12). The structure emerges from the ventral surface of the forebrain as a tapering cone that connects the brain to the spinal cord. Attached to the brain stem, but considered a separate region of the adult brain, is the cerebellum. The midbrain coordinates sensory representations of the visual, auditory, and somatosensory perceptual spaces. The pons is the main connection with the cerebellum. The pons and the medulla regulate several crucial functions, including the cardiovascular and respiratory systems and rates. |
SciQ | SciQ-6567 | 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 are described by what term, meaning their cells have a nucleus and membrane-bound organelles? | [
"complex",
"eukaryotic",
"walled",
"prokaryotic"
] | B | Plants are multicellular and eukaryotic, meaning their cells have a nucleus and membrane-bound organelles. |
SciQ | SciQ-6568 | human-biology, digestive-system, circadian-rhythms
Title: Is there a circadian component to hunger? I'm wondering what produces the feeling of hunger in humans. Checking Wikipedia revealed that leptin and ghrelin are two hormones involved. I've also read that the digestive system produces its own melatonin.
Because melatonin is related to circadian rhythm and the biological clock,Is melatonin involved in feeling hungry? Is there a circadian pattern to the levels of leptin and ghrelin in humans? Yes, absolutely. A major focus of understanding obesity, diabetes and other metabolic disorders are targeted to understanding the circadian (and other cyclical nature) systems in neurobiology and endocrinology. I can speak within the study of diabetes, there is an observed diabetic "dawn effect" in which there is an early morning (dawn) spike in blood glucose. The exact mechanism for this spike in blood glucose is not fully known, but the general circadian nature is intriguing and would suggest a dominant hormonal cause.
Some other review articles may be found here. An overall review of homeostatic balance as it relates to the central nervous system and apetite regulation. The second review more closely focuses on the biochemistry and endocrinology of central and peripheral regulation on food intake and physical activity.
Berthoud HR, Morrison C. The brain, appetite, and obesity. Annu Rev Psychol. 2008;59:55-92.
Lenard NR, Berthoud HR. Central and peripheral regulation of food intake and physical activity: pathways and genes. Obesity (Silver Spring). 2008 Dec;16 Suppl 3:S11-22.
The following is multiple choice question (with options) to answer.
What is a primary source of the hormone melatonin? | [
"thyroid gland",
"pineal gland",
"pituitary gland",
"thymus"
] | B | |
SciQ | SciQ-6569 | biochemistry, bacteriology, food, toxicology
The Food and Nutrition Board of the U.S. Institute of Medicine indicates that Tolerable Upper Intake Levels (known as ULs) for iron is 45 mg/day. [Source].
Note: Tolerable upper intake level (UL) is the highest level of daily nutrient consumption that is considered to be safe for, and cause no side effects in, 97.5% of healthy individuals in each life-stage and sex group.
The World Health Organization (2003) suggests:
The average lethal dose of iron is 200–250 mg/kg of body weight, but death has occurred following the ingestion of doses as low as 40 mg/kg of body weight
Of course, one can get iron poisoning due to an acute overload of Fe.
Toxic effects begin to occur at doses above 10–20 mg/kg of elemental iron.
Ingestions of more than 50 mg/kg of elemental iron are associated with severe toxicity
See Abhilash et al. (2013) for an example study examining fatail Fe overdoe in adults.
Note: inhalation of Iron Oxide dusts is complicated but potentially dangerous, but should be of no concern to you.
However, outside of trying to OD on iron supplements, it's not easy to consume that much iron. So even given all tose nasty numbers, I wouldn't be too concerned
According to 2 citations (Greentree & Hall 1995 and Goyer 1996) in The toxicity of iron, an essential element:
Because iron must be ionized to be absorbed, metallic iron and iron oxide (rust) are not generally of concern when they are ingested.
Even when iron is heated (and supposedly ionized) very little becomes available for ingestion:
This source cites a 1986 study that found that cooking in a cast iron skillet added typically 1-4 mg (though as high as 7 mg) of iron into the food (well below dangerous levels)
Besides, iron oxide is already present in most drinking water.
Concentrations of iron in drinking-water are normally less than 0.3 mg/L [source] and is seldom found at concentrations greater than 10 mg/L or 10 ppm [source].
Bacteria connection:
There are bacteria associated with rust:
Iron-oxidizing bacteria are chemotrophic bacteria that derive the energy by oxidizing dissolved ferrous iron
The following is multiple choice question (with options) to answer.
How many more times likely are men to suffer from iron overload? | [
"twenty times",
"ten times",
"eight times",
"two times"
] | B | |
SciQ | SciQ-6570 | organic-chemistry, bond, covalent-compounds
Title: The difference between peptide bonds and the bonds between polypeptides? I was doing some tests for the multiple-choice final we've got ahead. And it was on me to count the peptide bonds in an Insulin hormone with 51 aminoacids arranged in two polypeptides with 30 and 21 aminoacids. (these are not true in reality) the number of bonds were 49, not 50, and that means the bond between two polypeptides doesn't count as a peptide bond. Additionally, I know that polypeptide bonds make the proteins' molecular structure, as it is now. (just look at that shape.) PEPTIDE COVALENT BONDS CAN NEVER cause that kind of 3d orientation in space. So there must be some fundamental difference between those bonds. What is it?
My research couldn't find any results as simple things have jammed the internet. Aside from covalent bonds (amide and disulfide), the sturcture of a protein is determined by hydrogen bonds, salt bridges, and less specific interactions such as hydrophobic and hydrophilic effects. Hydrophobic portions of the protein chain tend toward the interior of the folded protein and hydrophilic regions to the exterior, in aqueous solution.
The following is multiple choice question (with options) to answer.
Misfolding of polypeptides is a serious problem in what? | [
"lipids",
"muscles",
"blood",
"cells"
] | D | |
SciQ | SciQ-6571 | biochemistry, cell-biology, cell-membrane, cellular-respiration, membrane-transport
Title: Membrane Permeability to Pyruvate Pyruvate seems to pass easily through the outer membrane of the mitochondrion but has difficulty entering the inner membrane (and gets in by H+ symport). I have two questions: (1) what property of pyruvate disallows it from passing through the inner membrane? Is it its charge? and (2) what structural differences are there between the outer and inner membranes of the mitochondrion that create their disparate permeabilities to pyruvate? Pyruvate is negatively charged and quite polar, which makes it unfavourable to diffuse directly through any membrane. The outer mitochondrial membrane contains porins, which allow small molecules, like pyruvate, to passively diffuse through. Specifically, pyruvate uses voltage dependent anion channels. The inner mitochondrial membrane lacks such channels and depends on active transport by the long anticipated but only recently discovered mitochondrial pyruvate carrier (Herzig et al. and Bricker et al., 2012).
The following is multiple choice question (with options) to answer.
What does the inner membrane divide into two internal compartments? | [
"golgi apparatus",
"mitochondrion",
"chitin",
"epidermis"
] | B | |
SciQ | SciQ-6572 | homework-and-exercises, kinematics, velocity, calculus, displacement
Also is it just that my understanding of the concept of velocity is wrong? If so please provide with a good definition for explaining the concept of velocity. Thanks! Without getting into calculus, average velocity is total displacement divided by total time of the journey. Average speed is total distance divided by total time. Total displacement is the arrow that points from the start position to the end position, all the little displacement vector arrows added together into one total vector arrow. Total distance can be what an odometer reads. It can be the number of steps taken, all of the little distances added together. It is the length of the path followed, regardless of direction. A person can run around a one-mile track and end up at the starting point. The person traveled a distance of one mile. If this takes ten minutes, the the person's average speed is six miles per hour. Displacement is zero. The run around the track did not result in a total change of position at all. Although velocity during the run was never zero, the average velocity is zero. The eastward effects balance the westward effects. The northward effects balance the southward effects. We use both speed and velocity because each can be important, depending on what we are trying to accomplish.
The following is multiple choice question (with options) to answer.
Defined as total distance traveled divided by elapsed speed, average speed is a scalar quantity that does not include what? | [
"size",
"shift",
"pressure",
"direction"
] | D | • Average speed is the total distance traveled divided by the elapsed time. (Average speed is not the magnitude of the average velocity. ) Speed is a scalar quantity; it has no direction associated with it. |
SciQ | SciQ-6573 | circulatory-system, lymphatic-system, veins
Title: How does most of lymph get back into the blood stream? (I don't mean the lymphatic system) I once read that it was because of osmotic pressure that it returns to the blood stream, by entering the venules. But why? If lymph originated as plasma how come that the solute concentration is higher in the venule? Doesn't plasma contain solutes such as salts, nutrients, oxygen, etc. ? Technically 'lymph' is used to refer to the fluid found within the lymphatic system. If it's not in the lymphatic system, it is not lymph fluid. Thus, your question is really asking about interstitial fluid or the plasma that was filtered out of blood capillaries.
The answer to your question is based on the Starling equation. Normally fluid leaves a capillary due to a net pressure that favors the interstitium. This net pressure is based on the hydrostatic pressure within the capillary being greater than the interstitial pressure of the surrounding tissues, and the oncotic pressure of the capillary (that draws fluid in) being weaker than the hydrostatic pressure of the capillary (that pushes fluid out). At the venule end of this system, the capillary oncotic pressure is stronger than the capillary hydrostatic pressure, drawing fluid back into the circulatory system.
Remember that albumin is the most important component which establishes the oncotic pressure within a vessel, and that this protein is normally NOT released out of a vessel during filtration. Thus, it passes from the capillary into its corresponding venule directly.
The following is multiple choice question (with options) to answer.
Lymph capillaries collect fluid that leaks out of what? | [
"lymph nodes",
"blood capillaries",
"alveoli",
"bladder"
] | B | Lymph capillaries collect fluid that leaks out from blood capillaries. The lymphatic vessels return the fluid to the cardiovascular system. |
SciQ | SciQ-6574 | biochemistry
Now we can go on to explain the action potential in the neuron, which is not something I originally wanted to go into, but since the original question has been edited I feel that I have to address this now. Even though the original question now makes no reference to the action potential, it is describing exactly those events that occur during an action potential.
The inside and the outside of the neuron is separated by a cell membrane, which is selectively permeable to ions such as $\ce{Na+}$, $\ce{K+}$, $\ce{Ca^2+}$, and $\ce{Cl-}$. Of these four, sodium and potassium ions are the most important as they are directly involved in depolarisation and repolarisation when an action potential is generated.
The distribution of ions is not symmetrical across the membrane. When at rest, the extracellular concentration of $\ce{Na+}$ is much higher than the intracellular concentration of $\ce{Na+}$; the converse is true for $\ce{K+}$. Due to the membrane having different permeabilities to $\ce{Na+}$ and $\ce{K+}$ (for details of this, one can consult a neuroscience text), the resting membrane potential is -70 mV. Conventionally, the membrane potential is described as the intracellular potential with respect to the potential of the extracellular potential; this means that the inside of the cell is more negative.
Neurons react to certain stimuli by having $\ce{Na+}$ enter the cell, via various means which are not important to the current discussion. Since positively charged ions are entering the cell, this causes the membrane potential to rise. Once the membrane potential has risen to roughly -55 mV, voltage-gated $\ce{Na+}$ channels open, making the membrane permeable to $\ce{Na+}$.
At this stage, we have to consider the two factors that influence the diffusion of $\ce{Na+}$:
Since the potential difference is still negative, it favours influx of $\ce{Na+}$.
Since the extracellular concentration of $\ce{Na+}$ is larger than the intracellular concentration, the concentration gradient also favours influx of $\ce{Na+}$.
The following is multiple choice question (with options) to answer.
Action potentials occur whenever a depolarization increases the membrane voltage to a particular value called what? | [
"threshold",
"velocity",
"ohms",
"fraction"
] | A | |
SciQ | SciQ-6575 | cell-biology, apoptosis, autophagy
Apoptosis: A Review of Programmed Cell Death
Apoptosis vs. Necrosis
Cell death by necrosis: towards a molecular definition
Review Necrosis: a specific form of programmed cell death?
The following is multiple choice question (with options) to answer.
Programmed cell death is also known as? | [
"apoptosis",
"sepsis",
"suicide",
"necrosis"
] | A | |
SciQ | SciQ-6576 | homework-and-exercises, radiation, radioactivity
So, let`s say if a radioactive substance has decay constant $ k = 0.05s^{-1}$
This means $P(\text{a undecayed nuclei to decay in 1s}) = 0.05$
But by using $ N = N_0 e^{-kt}$ (where $N_0$ is original no. of undecayed nuclei, N is no. of undecayed nuclei after time $t$)
to find the above probability by putting $t = 1s$:
$ N = N_0 e^{-kt}$
$ \frac{N}{N_0}= e^{-kt}$
$ 1 - \frac{N}{N_0}= 1 - e^{-(0.05)(1)}$
$ \frac{N_0 - N}{N_0} = 1 - e^{-(0.05)(1)}$
$ \frac{\text{no. of decayed nuclei}}{\text{original no. of undecayed nuclei}} = 1 - e^{-(0.05)(1)}$
$ P(\text{a undecayed nuclei to decay in 1s})≈ 0.048770575 ≠ 0.05 ≠ k$
Why does this contradiction happen ? Let $$N(t) \equiv N_0 \exp{(-\kappa (t-t_0))} \tag{1}$$
denote the population of a sample at time $t$, where $\kappa >0$ and $N_0 \equiv N(t_0) >0$. The number of decayed particles at time $t$ is then given by $N_\mathrm{D} (t) \equiv N_0 - N(t).$
Taking the derivative of $N(t)$ shows that
$$ \frac{\mathrm{d}N(t)}{\mathrm{d}t} = -\kappa\, N(t) $$ and thus
The following is multiple choice question (with options) to answer.
What happens to the mass number during a nuclear decay process by positron emission? | [
"remains unchanged",
"it increases",
"it rises",
"it decreases"
] | A | During a nuclear decay process that occurs by positron emission, a proton is converted into a neutron and a positron. The neutron remains in the nucleus, and the positron is expelled. Overall, the atomic number of the parent nucleus increases by one, and the mass number is unchanged. For example, carbon-11 emits a positron to become boron-11:. |
SciQ | SciQ-6577 | molecular-genetics, gene-expression, chromosome
Title: Why is aneuploidy usually lethal? So, I was reading about aneuploidy and how a zygote with one extra or less chromosome usually would not survive to full term. I suppose this happens because aneuploidy leads to some kind of protein imbalance. So, in case of monosomy we would have a shortage of proteins, and in case of trisomy we would have an excess of proteins.
On the other hand, a conventional argument for having two copies of each gene is that, if one gene gets corrupted because of some kind of mutation, we still have another copy that produces the correct protein. So, in case of a recessive genetic disorder, the zygote can survive even with half the amount of protein.
My question is then, why can't monosomic aneuploidy be looked at the same way? Moreover, I read that monosomic aneuploidy is almost always fatal, while trisomic aneuploidy is sometimes tolarated. What causes zygotic termination in aneuploidy often isn't an issue with proteins or other gene products i.e. being "too sick" to live. It's that the zygote is basically "self error checking" and if it encounters a serious genetic error (e.g. aneuploidy) it self-terminates, as it would likely not survive anyway. Sometimes this self-termination fails, and the zygote develops. Depending on the specific aneuploidy, it may not make it to term, or perhaps it will, and you will have a child born, albeit the child will usually have a decreased quality of life/life-span.
A similar mechanism works in your somatic (non-reproductive) cells everyday when they replicate and divide - if they detect and error in their DNA that cannot be repaired, the cells SHOULD kill themselves. Sometimes this fails, and can give rise to cancer.
The following is multiple choice question (with options) to answer.
Embryos usually don't survive if they have extra or too few of these genetic units? | [
"genes",
"ribosomes",
"phenotypes",
"chromosomes"
] | D | Outside of chromosome 21 and the sex chromosomes, most embryos with extra chromosomes do not usually survive. Because chromosomes carry many, many genes, a disruption of a chromosome can cause severe problems with the development of a fetus. Individuals with one (or more) fewer chromosome usually don't survive either. Can you explain why?. |
SciQ | SciQ-6578 | planet, jupiter, planetary-atmosphere, saturn
Ammonia ice, like all ice, is very reflective, so the colder bands with ice are lighter. Ammonia gas is transparent, but anyone who has ever flown over the ocean knows that if you have enough of a transparent thing (water), it has a distinct color. While the quote from Wikipedia above says the reason for the darker colors is uncertain, less ice in its uppermost atmosphere means less reflected light and darker color.
Saturn, Neptune and Uranus are far enough away from the Sun where they always have ice in their upper most atmospheres, so they have less variation in color. Earth's clouds are also primarily ice (not water vapor), so that is basically the answer. Jupiter is the right distance from the Sun for its upper atmosphere to transition and have distinct bands, some with ice, some without.
"But why are the bands in straight lines?"
This is due to the Coriolis effect. Viewed from above, the Coriolis effect creates bands that line up with the equator. Jupiter and Saturn both rotate quite quickly (9.5 and 10.8 hours respectively), so both have strong Coriolis effects.
The following is multiple choice question (with options) to answer.
Like the other outer planets, neptune has rings of ice and what? | [
"gas",
"dust",
"glass",
"mercury"
] | B | Like the other outer planets, Neptune has rings of ice and dust. These rings are much thinner and fainter than Saturn's. Neptune's rings may be unstable. They may change or disappear in a relatively short time. |
SciQ | SciQ-6579 | visible-light, waves, electromagnetic-radiation, photons, wave-particle-duality
So, let's answer your questions:
a) The peaks and troughs are the points where the magnitude of the field is maximum in one direction or the other. As such, it doesn't make much sense to distinguish between peaks and troughs, because if you look from the other side they switch places.
b,c,d) A wave doesn't really take up space. There might be fields over a region of space, but the arrows you see in the animations don't have a physical length. They represent the magnitude of the fields, but they don't occupy physical space. Remember that there are two arrows (because of $\mathbf{E}$ and $\mathbf{B}$) at every point in space. As I've said before and has been said in the comments, wavelengths are lengths because they are the distance between two maxima, but amplitudes are not lengths.
The mental picture you describe in your question is, if you forgive me, a mess. You're mixing this description of EM waves with the quantum mechanical point of view, which is almost sure to lead to errors. QM usually deals in terms of particles, so the basic idea is that now light is thought of as a bunch of particles (photons), with a certain probability at each point in space to find a photon. The thing with quantum mechanics is that it's extremely weird and even the very best physicists have trouble forming an intuitive mental image of how it works. So please just forget about photons until you really understand the classical waves I've described in this post.
The following is multiple choice question (with options) to answer.
In an electromagnetic wave, what do the crests and troughs represent? | [
"particles fields",
"vibrating fields",
"ocean waves",
"oscillating fields"
] | D | The black line represents the straight path of the light itself. Along this path, there exists an electric field that will reach a maximum positive charge, slowly collapse to zero charge, and then expand to a maximum negative charge. Similarly, there is an changing magnetic field that oscillates from maximum north pole field to maximum south pole field. Along the path of the electromagnetic wave, these changing fields repeat, oscillating over and over again. However, the oscillating electric and magnetic fields demonstrate a weaving pattern that is not the way light travels. For an electromagnetic wave, the crests and troughs represent the oscillating fields, not the path of the light. |
SciQ | SciQ-6580 | ecology
Title: Statement about Tropical Rainforests I made a statement about tropical rainforests, and I want to know if it's somewhat true or not:
The soil in tropical rainforests is not exceptionally fertile, because it contains few minerals. The reason that a tropical rainforest has a huge amount of vegetation is because of the quick mineralisation. If a dead leaf falls onto the ground, it immediately gets turned into minerals, which the plants immediately use for sustaining theirselves There are many websites which describe this phenomenon. They all seem to confirm the basic premise of the question: in tropical rain forests most of the minerals are held in the biomass and rapid decomposition contributes to the recycling of these nutrients for new growth. One example is here.
Tropical rainforests are noted for the rapid nutrient cycling that occurs on the ground. In the tropics, leaves fall and decompose rapidly. The roots of the trees are on the surface of the soil, and form a thick mat which absorbs the nutrients before they reach the soil (or before the rain can carry them away). The presence of roots on the surface is a common phenomenon in all mature forests; trees that come along later in succession win out in competition for nutrients by placing their roots over top of the competitors, and this pattern is seen in the temperate rainforest as well. What does not occur in the temperate rainforest, however, is a rapid cycling of nutrients. Because of the cold conditions and the acidity released by decomposing coniferous needles on the forest floor, decomposition is much slower. More of the nutrients are found in the soil here than would be the case in a tropical forest, although like the tropical forest most of the nutrients are held in the plants and animals themselves.
I looked for actual evidence of these differences in rates of decomposition and I found this:
Salinas, N. et al. (2011) The sensitivity of tropical leaf litter decomposition to temperature: results from a large-scale leaf translocation experiment along an elevation gradient in Peruvian forests. New Phytologist 189: 967-977
The following is multiple choice question (with options) to answer.
What biome is located between the temperate and tropical biomes? | [
"mountainous",
"subtropical",
"Desert",
"Tropical"
] | B | Latitude means how far a biome is from the equator. Moving from the poles to the equator, you will find (in order) Arctic, boreal, temperate, subtropical, and tropical biomes. |
SciQ | SciQ-6581 | metabolism, human-anatomy, pharmacology, liver
For drugs introduced through an injection, for example, metabolism occurs throughout the circulatory system and in the liver. Remember that it's all the same blood supply, but the first-pass effect just refers to the blood that goes to the liver before entering the systemic circulation (by which it can travel to its target).
The following is multiple choice question (with options) to answer.
Metabolism is the sum of all catabolic and which other reactions in the body? | [
"systic",
"abolic",
"inbolic",
"anabolic"
] | D | CHAPTER REVIEW 24.1 Overview of Metabolic Reactions Metabolism is the sum of all catabolic (break down) and anabolic (synthesis) reactions in the body. The metabolic rate measures the amount of energy used to maintain life. An organism must ingest a sufficient amount of food to maintain its metabolic rate if the organism is to stay alive for very long. Catabolic reactions break down larger molecules, such as carbohydrates, lipids, and proteins from ingested food, into their constituent smaller parts. They also include the breakdown of ATP, which releases the energy needed for metabolic processes in all cells throughout the body. Anabolic reactions, or biosynthetic reactions, synthesize larger molecules from smaller constituent parts, using ATP as the energy source for these reactions. Anabolic reactions build bone, muscle mass, and new proteins, fats, and nucleic acids. Oxidation-reduction reactions transfer electrons across molecules by oxidizing one molecule and reducing another, and collecting the released energy to convert Pi and ADP into ATP. Errors in metabolism alter the processing of carbohydrates, lipids, proteins, and nucleic acids, and can result in a number of disease states. |
SciQ | SciQ-6582 | pathology
Title: Are all diseases caused by organisms (microorganisms)? Are there other causes? Or is it correct to say that all diseases are in fact caused by organisms (microorganisms)? It is not correct to say that all diseases are caused by foreign organisms. Counterexamples are:
Cancer is caused by random genetic mutations in the cells of our body. The mutations can be caused by many factors such as ionizing radiation, smoking, chemical toxins etc.
Diseases such as stroke or heart attack are caused by blood clots blocking the blood flow to essential organs.
Autoimmune diseases are caused by the immune system falsely recognizing cells of the body as foreign and attacking that tissue leading to a wide variety of symptoms.
Alzheimer's disease is caused by chronic neurodegeneration, meaning that the cells in the brain die. The causes are not quite understood but as Alzheimer's usually appears late in life it is likely related to ageing. Also, it is known that some genetic defects can lead to early-onset Alzheimers.
Prion proteins can cause diseases such as Creutzfeldt–Jakob disease also known as mad-cow disease.
Hereditary diseases such as early-onset Alzheimers or ALS are cause by gene defects inherited from the parents.
Toxins can cause chronic diseases such as lead poisoning.
The list probably goes on...
Please note that the first two on the list are the most common cause of death in developed countries.
The following is multiple choice question (with options) to answer.
Diarrhea due to food poisoning is an example of a problem involving what organ system? | [
"skeletal system",
"muscular system",
"digestive system",
"lung system"
] | C | Much of the time, you probably aren’t aware of your digestive system. It works well without causing any problems. But most people have problems with their digestive system at least once in a while. Did you ever eat something that didn’t “agree” with you? Maybe you had a stomachache or felt sick to your stomach. Perhaps you had diarrhea. These can be symptoms of food poisoning. |
SciQ | SciQ-6583 | visible-light, electromagnetic-radiation
Realistically, All wavelengths should differ in shades considering the red hue increases in every colour as wavelength increases. Then how come we say that only Seven colours form White light?
The important thing here is that this spectrum is a $\textbf{continuum}$, which results in no clearly defined limit or frontier between colours because of the smooth color gradient that exists. Looking at this spectrum the first thing that we can tell is that there are seven big categories that result in a range (continuum) of wavelenghts that we can very easily distinguish: purple, blue, cyan, green, yellow, orange and red. Looking for example at 550 nm and 600 nm in the previous figure, we can say that both wavelenghts correspond to the same "bag" of wavelenghts which we name $\textbf{green}$, but if we carefully observe
those colours we note that we can actually tell that they are $\textit{different}$ hues of green because of the shading.
Do all wavelengths between A to B correspond to Yellow light? So, (A+1) nm, (B-1) nm, along with A nm & B nm are all exactly of the same colour ? Is there any difference even in their shades?
The following is multiple choice question (with options) to answer.
White light is a mixture of all wavelengths of what? | [
"visible light",
"gamma radiation",
"x-rays",
"infrared radiation"
] | A | |
SciQ | SciQ-6584 | homework, plant-physiology, plant-anatomy
and 'Vascular Plants = Winning! - Crash Course Biology #37'
https://youtu.be/h9oDTMXM7M8?t=373
[5] Osmosis (water compensating solutes) "In Da Club - Membranes & Transport: Crash Course Biology #5"
https://youtu.be/dPKvHrD1eS4?list=PL3EED4C1D684D3ADF&t=148
Ian (and dad <= all errors and approximations are his :) ).
The following is multiple choice question (with options) to answer.
What prevents solutes that have accumulated in the xylem from leaking back into the soil solution? | [
"the exodermis",
"the endodermis",
"the altostratus",
"the exoskeleton"
] | B | |
SciQ | SciQ-6585 | electronegativity, dipole, hydrogen-bond
Title: Why is HCl not considered to have hydrogen bonding? A molecule that has hydrogen bonding usually follows these two premises.
1.) There is a hydrogen atom involved
2.) Hydrogen must be bonded to a highly electronegative element which are nitrogen ($\ce{N}$), fluorine ($\ce{F}$) and oxygen ($\ce{O}$).
Seeing that both oxygen and chlorine have a small difference in their electronegativity (oxygen being roughly 3.5 and chlorine being roughly 3.0), why does chlorine in a hydrogen chloride molecule ($\ce{HCl}$) have a dipole-dipole interaction, while the oxygen in a water molecule ($\ce{H2O}$) causes the water molecule to have a stronger form of dipole-dipole interaction called hydrogen bonding? I do not understand this since chlorine is just as electronegative as oxygen and nitrogen?
Edit: I should also added that nitrogen and chlorine have the same EN value (3.0) Very, very related. Check it for a more in depth answer.
Well, first-of-all you need to understand that the $\ce{H}$ bonding isn't actually bonding. It is just a covalent attraction. Also since $\ce{Cl}$ is larger than $\ce{N}$, $\ce{F}$ and $\ce{O}$ it does not make a strong $\ce{H}$ bond. The size of the $\ce{Cl}$ makes the dipole-dipole attraction weaker. However $\ce{N}$, $\ce{F}$ and $\ce{O}$ are smaller and thus have an $\ce{H}$ bond.
Although in reality, compared to other covalently bonded structures, $\ce{HCl}$ has a very strong covalent bond.
The following is multiple choice question (with options) to answer.
Hydrogen chloride contains one atom of hydrogen and one atom of what? | [
"chlorine",
"calcium",
"nitrogen",
"magnesium"
] | A | Hydrogen chloride contains one atom of hydrogen and one atom of chlorine. Because the. |
SciQ | SciQ-6586 | organic-chemistry, aromatic-compounds, phenols, organic-oxidation
Thus the migratory aptitude and stability of the carbocation are the two effects which create the differences in the product formation in case of oxidation of Cumene and Toluene.
(Note : For clarification, see the migratory aptitude order here : https://en.wikipedia.org/wiki/Migratory_aptitude )
The following is multiple choice question (with options) to answer.
What property of toluene and xylene makes them important in the chemical industry? | [
"corrosive property",
"solvent property",
"excess property",
"isolate property"
] | B | Toluene and xylene are important solvents and raw materials in the chemical industry. Styrene is used to produce the polymer polystyrene. |
SciQ | SciQ-6587 | 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.
The earliest cells were prokaryotes, surrounded by a cell membrane but lacking which key structure? | [
"nucleus",
"ribosomes",
"lysosomes",
"mitochondria"
] | A | The first organisms were made of only one cell ( Figure below ). The earliest cells were prokaryotes . Prokaryotic cells are surrounded by a cell membrane. They do not have a nucleus. Their organelles are free in the cell. The cells get their nutrients directly from the water they live in. The cells need to use these nutrients to live and grow. |
SciQ | SciQ-6588 | reaction-mechanism, equilibrium, kinetics
\begin{align}
k_1\ce{[A][B]} &\gg k_2\ce{[C][E]} \\
k_{-1}\ce{[C][D]} &\gg k_2\ce{[C][E]} \\
K_1 &= {k_1 \over k_{-1}}
\end{align}
$$
The relative values of the forward and reverse rate constants can vary, with their ratio described by $K_1$, but at all points through the reacting process of interest, both the forward and reverse equilibrium reactions are assumed to be much faster than the final, product-forming reaction. If this assumption doesn't hold, then we can't treat the first reaction as "just" an equilibrium reaction.
The following is multiple choice question (with options) to answer.
When is the rate of the forward reaction equal to the rate of the reverse reaction? | [
"before equilibrium",
"after equilibrium",
"at equilibrium",
"at conduction"
] | C | At equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. |
SciQ | SciQ-6589 | cell-biology, gene-expression, development, embryology
I'm reluctant to go into too much detail on this because you're asking about a complex process that is still under active study and I'm unclear as to how much information you actually want. A book could be written on this subject alone, and many review papers have been published. Here's a recent one:
Development: Do Mouse Embryos Play Dice?
I suggest you read that and then if you have further, more specific questions, we can try and answer them for you.
The following is multiple choice question (with options) to answer.
In which process do signaling molecules from embryonic cells cause transcriptional changes in nearby target cells? | [
"maturation",
"orientation",
"induction",
"replication"
] | C | |
SciQ | SciQ-6590 | evolution, dna, theoretical-biology, genomes, species
Title: Biodiversity is restricted by genome combinatorics? Me and some friends are interested in opinions for the following:
Conjecture
The maximum number of species must be limited by the maximum
combinatorial/permutational space that can be occupied by DNA. Thus if
there is a maximum physical genome size this is what will determine
the maximum number of species that can possibly exist.
Explanation
E.G. say maximum number of DNA base pairs able to fit in a genome was $3$, each base pair can be one of either ${A,G,T,C}$. Then there are $4^3 = 64$ possible combinations of genomes. Extrapolate to genome sizes of $x$ base pairs, then there are $4^x$ combinations.
Questions
Would it be possible to claim that the underlying "blueprint" that codes for living diversity sets the absolute maximum for the total "diversity space"?
**Does it make sense to define the total number of species life can achieve with the simple function:
$S < 4^x$, where X is the maximum genome size measured in DNA base pairs?**
Notable Comments
The following is multiple choice question (with options) to answer.
Every species has a characteristic number of what? | [
"receptors",
"chromosomes",
"ribosomes",
"DNA"
] | B | |
SciQ | SciQ-6591 | dna, virology, human-genetics, human-genome
Title: What is the contribution of viruses to the evolution of mankind? I'm interested in horizontal gene transfer in bacteria, viruses, and organisms such as Bdelloid Rotifers. I've just read in Carl Zimmer's 'A Planet of Viruses' the following passage:
As a host cell manufactures new viruses, it sometimes accidentally adds some of its own genes to them. The new viruses carry the genes of their hosts as they swim through the ocean, and they insert them, along with their own, into the genomes of their new hosts. By one estimate, viruses transfer a trillion trillion genes between host genomes in the ocean every year.
It's interesting to consider the scale of DNA-swapping that has occurred given the frequency by which it happens and the evolutionary timescale.
Are there any examples of genes in the human genome that we know were deposited by viruses that would have given an evolving human a physical/mental advantage? Where did they come from? What benefit did they provide?
I'm interested in genetic additions from non-human-ancestor species, rather than the transfer of genes that occurred as mutations from other humans. The processes that control the germline of metazoans (multicellular animals) are highly regulated compared to single cell bacteria and eukaryotes as well as plants.
At this point there are no clear stories of gene transfer into a complex animal, though there are some for plants:
"animals and fungi seem to be largely unaffected, with a few exceptions, while lateral gene transfer frequently occurs in protists with phagotrophic lifestyles, possibly with rates comparable to prokaryotic organisms."
Bacteria fungi and plants are more permissive and more susceptible to gene transfer and it probably is more important to their evolutionary path.
Its been estimated that as much as eight percent of the human genome has been affected by viral integration. But viral genomes are highly selected against carrying non essential material - other genes rarely come along for the ride it seems. What is probably more influential is that viral insertions could participate in rewiring the regulatory network of animal cells, not adding genes, but modifying the conditions under which they are active.
The following is multiple choice question (with options) to answer.
Ecologists already use the abilities of many prokaryotes to carry out bioremediation of soils and what else? | [
"air",
"gas",
"plasma",
"water"
] | D | |
SciQ | SciQ-6592 | 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.
How is most evidence gathered in science? | [
"field research",
"observation",
"lab experiments",
"hypothesis"
] | C | Lab experiments are the main method of gathering evidence in some branches of science. Why might lab experiments not be the best way to study living things, such as wild animals?. |
SciQ | SciQ-6593 | inorganic-chemistry, acid-base, molecular-structure, lewis-structure, pnictogen
D. E. C. Corbridge, In Studies in Inorganic Chemistry, Volume 20: Phosphorus – An Outline of its Chemistry, Biochemistry and Uses; Elsevier B.V.: New York, NY, 1995, Pages 1-1208 (https://www.sciencedirect.com/bookseries/studies-in-inorganic-chemistry/vol/20).
F.A. Cotton, G. Wilkinson, C.A. Murillo, M. Bochmann, Advanced Inorganic Chemistry, 6th Edn.; Wiley-Interscience: New York, NY, 1999, “Chapter 10: The Group 15 Elements: $\ce{P, As, Sb, Bi}$,” pp. 380-443.
G.A. Haight Jr., M. Rose, J. Preer, “Reactions of chromium(VI) with phosphorus(III) and phosphorus(I). I. Dihydrogen phosphite, phosphorous acid, and hypophosphorous acid,” J. Am. Chem. Soc. 1968, 90(18), 4809-4814 (DOI: 10.1021/ja01020a011).
R.O. Griffith, A. Mckeown, “Kinetics of the reaction of iodine with phosphorous acid and with phosphites,” Trans. Faraday Soc. 1940, 36, 766-779 (DOI: 10.1039/TF9403600766).
J. P. Guthrie, “Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and $\mathrm{p}K_a$ values for ionization of the $\ce{P—H}$ bond in phosphonic acid and phosphonic esters,” Canadian Journal of Chemistry 1979, 57(2), 236-239 (https://doi.org/10.1139/v79-039).
The following is multiple choice question (with options) to answer.
Phosphate groups are found within phospholipids and what else? | [
"hydrocarbon chains",
"nucleotides",
"amino acids",
"carotenoids"
] | B | Phosphate groups are found within phospholipids and nucleotides. |
SciQ | SciQ-6594 | food, biotechnology
Title: How to increase the shelf life of yogurt without refrigeration? When we make yogurt at home and do not refrigerate it, it will become sour because of conversion of lactose into lactic acid by Lactobacillus bacteria, but this does not happen in case of Nestle's yogurt or any other brand until it remains air tight.
I wonder though bacteria is still present in it and continue to convert lactose into lactic acid then why does not packed yogurt becomes sour? How these companies increase the shelf life of yogurt..? This article gives an excellent review on yogurt manufacturing, but to summarize:
-Raw milk goes through centrifugation to remove somatic cells and other solid impurities.
-Thermalization is conducted at "60–69 °C for 20–30 s, aiming at the killing of many vegetative microorganisms and the partial inactivation of some enzymes."
After this point, the milk may be inoculated with lactic acid bacteria or other microfloras.
-Then, standardization occurs which for milk refers to the standardization of fat and solid-non-fat content (SNF). This in short affects the fermentation process ("an increase of SNF increases the duration of the fermentation process").
-The next step is homogenization, which prevents milk fat from rising to the top of the liquid. This has an effect on the stability of the emulsion.
-I think this step is where "sterility" comes into play, "heat treatment of milk reduces the number of pathogenic microorganisms to safe limits for the consumer’s health. Various heat treatments can be applied, which are classified based on the duration and the temperature. The most common are known as thermalization, low and high pasteurization, sterilization and UHT (Ultra Heat Treatment)." The review goes into more detail about each type and what they eliminate or don't eliminate (spores, vegetative bacteria, etc.).
The following is multiple choice question (with options) to answer.
Yogurt is made with milk fermented with what? | [
"disease",
"viruses",
"bacteria",
"pathogens"
] | C | Describe hurricane formation and the damage they cause. |
SciQ | SciQ-6595 | homework-and-exercises
Title: Is geothermal energy ultimately derived from solar energy? The following question is taken from 10th class science NCERT book chapter 14th.
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) geothermal energy (b) wind energy
(c) nuclear energy (d) bio-mass.
The answer is given as (c) nuclear energy.
I understand that the wind moves because of the uneven heating of the earth by the sun. And biomass uses solar energy for photosynthesis.
How is geothermal energy ultimately derived from the sun? It is not a correct statement:
Geothermal energy comes from the heat within the earth. The word "geothermal" comes from the Greek words geo, meaning earth," and therme, meaning "heat." People around the world use geothermal energy to produce electricity, to heat buildings and greenhouses, and for other purposes.
The earth's core lies almost 4,000 miles beneath the earth's surface. The double-layered core is made up of very hot molten iron surrounding a solid iron center. Estimates of the temperature of the core range from 5,000 to 11,000 degrees Fahrenheit (F). Heat is continuously produced within the earth by the slow decay of radioactive particles that is natural in all rock
italics mine.
Geothermal energy comes from the original energy of the matter solidifying into the sun-planetary system, ultimately from the Big Bang, and from continuous nuclear decays and reactions .
The following is multiple choice question (with options) to answer.
What is energy from the sun called? | [
"potential energy",
"thermodynamic energy",
"kinetic energy",
"solar energy"
] | D | |
SciQ | SciQ-6596 | soil, minerals, terminology, soil-science
Title: "Down wash" as a source for mineral particles in the soil In a previous IGCSE examination paper$^1$, the following question was asked and answer provided:
State one source of mineral particles in soil.
Marking Scheme:
Accept any one of:
rock;
down wash;
What's "down wash" and how is it responsible for providing minerals to soil? Googling the term lead me to an aerodynamics definition, which I doubt is the one referred to by the marking scheme.
$^1$ UCLES. Environmental Management, 0680/12, Paper 1. Cambridge International General Certificate of Secondary Education, February/March 2017. Downwash can be part of some erosion environments where minerals are moved down from their host rock environment to another location.
Black Snake Range - Granite Slopes, Victoria, Australia
The crest of the divide rises to almost 400 metres and at this site there are numerous exposed granite slopes and large boulders near the ridge crest. The lower slopes have a cover of granite downwash and the minor valleys have become partly infilled with this granitic sand wash, and hence they are swampy
Southdowns, UK, page 4
Overlying the bedrock geology are drift deposits of alluvium (along the numerous
streams) and ‘head’ (downwash deposits at the base of the Greensand Hills around
Liss and Petersfield).
In the Discussion section of Slope Stability and Slope Formation in the Flysch Zone of the Vienna Forest (Austria)
The downwash of the basal clays and marls, uncovering the solid bedrock, has to be regarded as the main aspect of this phase
The following is multiple choice question (with options) to answer.
What is the term for when gravity pulls soil, mud, and rocks down cliffs and hillsides? | [
"mass momentum",
"mass pressure",
"mass movement",
"avalanche"
] | C | Gravity can pull soil, mud, and rocks down cliffs and hillsides. This is called mass movement. The most destructive types of mass movement are landslides and mudslides. They occur suddenly and without warming. They engulf everything in their path. |
SciQ | SciQ-6597 | physical-chemistry, molecules, conductivity
Title: What attributes cause a substance to be nonconductive or conductive I understand what causes elements to be conductive or nonconductive. But what causes a substance say rubber to be nonconductive at a molecular level? Conductivity requires mobile electrons. Metals tend to have loosely held valence electrons so metals are generally conductive. Metals have loosely held valence electrons for two reasons: metals tend not to be very electronegative (able to stabilize electron density) and metals tend to be somewhat big atoms by nature of many metals having a d-group of electrons. D electrons are further from the nucleus on a time average basis than s electrons or p electrons.
However, conductors do not have to be metals. Consider graphite. Graphite is $\ce{sp^2}$ hybridized. Graphite is made solely of carbon atoms - and carbon isn't a metal! The mobile pi electrons in graphite due to resonance allows graphite to be a good conductor.
I should also note that conductivity does not always imply mobile electrons; solutions can be conductive too and this is due to mobile electrolytes (ions). For example, you will find that deionized water is completely unconductive. However, regular tap water is generally conductive due to the presence of ions (e.g. chloride ions from chlorination). Gatorade is also very conductive because it is especially formulated to contain a lot of electrolytes.
The following is multiple choice question (with options) to answer.
Metals are good conductors of what? | [
"light",
"sound",
"metabolism",
"electricity"
] | D | Metals are elements that are good conductors of electricity. They are the largest of the three classes of elements. In fact, most elements are metals. Look back at the modern periodic table ( Figure above ) in this chapter’s lesson "How Elements Are Organized. " Find the metals in the table. They are all the elements that are color-coded blue. Examples include sodium (Na), silver (Ag), and zinc (Zn). |
SciQ | SciQ-6598 | botany
Title: Do any plants exhibit hormonal changes similar to puberty? Just what the title states.
Are there any plants/trees that exhibit a growth spurt at a definite interval after the shoot appears? In flowering plants (the angiosperms) there are several developmental transitions in the life of the plant. I won't list the plants, because the list includes pretty much all of them (although the magnitude in the change of developmental pace differs widely between taxa and environments).
First there is seed germination, which is controlled hormonally. Absence of germination is usually imposed by abscisic acid, whilst germination is caused at the appropriate time by gibberellic acid and ethylene (among other things; Holdsworth, Bentsink & Soppe, 2008).
Next, in many herbaceous species there is a transition between a spreading growth stage (e.g. rosette growth) and the flowering stage. The 'growth spurt' here is the differentiation and elongation of the flowering stem, and then subsequently the sudden flowering of buds. The transition is also controlled hormonally, by a variety of hormones including auxin (Zhao, 2010), gibberellic acid, ethylene (Schaller, 2012), and the long anticipated, recently confirmed florigen (Choi, 2012). Ethylene and abscisic acid then play important roles in the next developmental transition when seeds and fruits are produced and dehisced.
Small RNAs are also now being revealed to play a large role in controlling the timing of developmental, but they are upstream of the hormonal changes. In particular some key miRNAs are involved in auxin-based regulation of branching, and in embryogenesis (Nodine & Bartel, 2010), and RNA silencing is involved in the switch from rosette growth to flowering growth (reviewed in Poethig, 2009 and Baurle & Dean 2006).
The following is multiple choice question (with options) to answer.
What plant hormone allows plants to curve in a specific direction? | [
"auxin",
"pheremone",
"peptides",
"apoptosis"
] | A | Plants may not be able to move to another location, but they are able to change how they grow in response to their environment. Growth toward or away from a stimulus is known as a tropism ( Table below ). Auxins, a class of plant hormones, allow plants to curve in specific directions as they grow. The auxin moves to one side of the stem, where it starts a chain of events that cause rapid cell growth on just that one side of the stem. With one side of the stem growing faster than the other, the plant begins to bend. |
SciQ | SciQ-6599 | organic-chemistry, inorganic-chemistry
But then, some inorganic compounds do have carbon too, and there may even be some compounds that some call organic, and others call inorganic, like $CO_2$.
As I have felt it, in my learnings so far, it's like inorganic chemistry is the default chemistry and organic chemistry goes a step beyond.
But I don't quite grasp the difference.
What is the real semantics behind the word "organic"?
For example, we humans are made of loads of water, and that's a pretty organic thing to me. But then, water is inorganic.
Diamonds are the carbon top of the cake, and do not transmit the idea of being an "organic" thing.
Another very confusing thing are polymers, chanins of loads of carbons with other elements, in many shapes and textures. To me, a piece of "plastic" is not a very organic thing, but indeed, they are!
That brings the semantics into an even more confusing level.
And of course, there must be historical reasons for those chosen words.
Could someone please point out where this distinction comes from and why it is important?
With all my respect to science and the people who made chemistry a useful thing. This question is not about critics, it's about not knowing the facts, so of course I am the ignorant here.
Related and useful: What is the definition of organic compounds? IUPAC is the International Union of Pure and Applied Chemistry, they make recommendations on the nomenclature. IUPAC mentions that the difference between organic and inorganic is not distinct. To quote "The boundaries between ‘organic’ and ‘inorganic’ compounds are blurred." in Brief Guide to the Nomenclature of Inorganic Chemistry R. M. Hartshorn, K.-H. Hellwich, A. Yerin.
Since the terminology of organic vs. inorganic is all human classification, it is not a binary system 0 or 1. What we can say now is that traditionally, all organic compounds do contain carbon. It can come from natural sources or purely synthetic. There is no such restriction. Plastic is an organic compound because it contains a lot of carbon chains.
Note that this word organic, as used in chemistry, has nothing to with the buzz word used in marketing of organic food, organic fruits, organically grown stuff. The word organic comes from French organique designating the jugular vein, hence related to organs or living beings.
The following is multiple choice question (with options) to answer.
What is the most common type of organic compound? | [
"proteins",
"vitamins",
"carbohydrates",
"fats"
] | C | Carbohydrates are the most common type of organic compound. A carbohydrate is an organic compound such as sugar or starch, and is used to store energy. Like most organic compounds, carbohydrates are built of small, repeating units that form bonds with each other to make a larger molecule. In the case of carbohydrates, the small repeating units are called monosaccharides. Carbohydrates contain only carbon, hydrogen, and oxygen. |
SciQ | SciQ-6600 | ocean, thermodynamics
Your friend is half right, and half wrong. Air has a bit over 1/4th the heat capacity compared to water and it's about 800 times less dense, so he's correct, but it's not that simple.
Sunlight - somewhat counter-intuitively, isn't great at warming oceans because the photons from sunlight are energetic enough to evaporate water molecules into gas molecules. Oceans have low albedo which means they absorb most of the energy from the sunlight, but much of that heat is lost in evaporation by visible light photons. While that has nothing to do with your question, it's worth pointing out that sunlight isn't as good at warming oceans as one might think. (If anyone has one of those solar mirror ovens, I'd be curious to see how well they work on pure water . . . just out of curiosity, evaporation loss vs rate of warming).
The back-radiation from the atmosphere is comparatively much less total solar energy, but oceans are good at absorbing and storing thermal back-radiation reflected back off the greenhouse gas rich atmosphere into the ocean. This is a tiny amount of the total heat Earth gets from sunlight, and the increase of this radiation due to greenhouse gas is a fraction of one percent of solar energy, but it adds up.
One way to explain this is that 85 degree air will warm 80 degree water. That's a thermodynamic law. It just takes a while and because the heat capacity and density of water is much greater, it takes about 4 liters of air to give 1 degree back to warm 1 cc of water 1 degree. But despite the inefficiency, warmer air still transfers heat into colder water. It takes many decades, perhaps centuries, for the oceans to catch up to the warming air, but air, however inefficiently, does warm the oceans.
The following is multiple choice question (with options) to answer.
Dissolved oxygen in seawater is critical for sea creatures, but as the oceans warm, oxygen becomes less what? | [
"saturated",
"insoluble",
"soluble",
"abundant"
] | C | Introduction Coral reefs are home to about 25% of all marine species. They are being threatened by climate change, oceanic acidification, and water pollution, all of which change the composition of the solution we know as seawater. Dissolved oxygen in seawater is critical for sea creatures, but as the oceans warm, oxygen becomes less soluble. As the concentration of carbon dioxide in the atmosphere increases, the concentration of carbon dioxide in the oceans increases, contributing to oceanic acidification. Coral reefs are particularly sensitive to the acidification of the ocean, since the exoskeletons of the coral polyps are soluble in acidic solutions. Humans contribute to the changing of seawater composition by allowing agricultural runoff and other forms of pollution to affect our oceans. Solutions are crucial to the processes that sustain life and to many other processes involving chemical reactions. In this chapter, we will consider the nature of solutions, and examine factors that determine whether a solution will form and what properties it may have. In addition, we will discuss colloids—systems that resemble solutions but consist of dispersions of particles somewhat larger than ordinary molecules or ions. |
SciQ | SciQ-6601 | visible-light, geometric-optics
Coming to the second question. It is useful to think that the color of the light is associated to the frequency, which never changes in refraction, reflection and diffraction processes. Frequency is important because the "sensors" in our eye are sensitive to the photon energy, which depends on the frequency. On the other hand, the speed of light in our eye depends on the material of the eye itself, so there is also a well defined and fixed relation between wave length and frequency!
So said, a beam with a given color, after passing through a glass prism or a lens, will still have the same color. Of course, its wave length will change along its path, but our eye will never know it.
Finally, what does it mean that a beam is the superposition of various wave lengths? This would deserve a separate question, but this can help to understand the principles:
https://demonstrations.wolfram.com/SuperpositionOfWaves/
The following is multiple choice question (with options) to answer.
Light waves differ based on their frequency and what else? | [
"density",
"amplitude",
"weight",
"voltage"
] | B | 36.5 Vision Vision is the only photo responsive sense. Visible light travels in waves and is a very small slice of the electromagnetic radiation spectrum. Light waves differ based on their frequency (wavelength = hue) and amplitude (intensity = brightness). In the vertebrate retina, there are two types of light receptors (photoreceptors): cones and rods. Cones, which are the source of color vision, exist in three forms—L, M, and S—and they are differentially sensitive to different wavelengths. Cones are located in the retina, along with the dim-light, achromatic receptors (rods). Cones are found in the fovea, the central region of the retina, whereas rods are found in the peripheral regions of the retina. Visual signals travel from the eye over the axons of retinal ganglion cells, which make up the optic nerves. Ganglion cells come in several versions. Some ganglion cell axons carry information on form, movement, depth, and brightness, while other axons carry information on color and fine detail. Visual information is sent to the superior colliculi in the midbrain, where coordination of eye movements and integration of auditory information takes place. Visual information is also sent to the suprachiasmatic nucleus (SCN) of the hypothalamus, which plays a role in the circadian cycle. |
SciQ | SciQ-6602 | immunology, parasitology
Title: Why is untreated trypanosomiasis invariably fatal in humans? If left untreated, African trypanosomiasis will invariably kill the patient. The human immune system is unable to clear the infection.
I am aware of a few other infectious diseases with this property and I have a rudimentary understanding of the reason why. For example, I'm told that rabies has evolved to be uniquely good at attacking the brain because that's the only way it can spread to other hosts, and the neuroimmune system, being quite different from the peripheral immune system, is not capable of dealing with a virus that has this property.
I do not understand why the human immune system is ineffective against trypanosomiasis. One explanation I was offered is that the human immune system is just not very good at fighting parasitic infections (compared to viral and bacterial infections). However, this can't be the full answer, because there are other parasitic infections that may go away on their own without treatment. African trypanosomiasis, or sleeping sickness, is caused by the protozoan Trypanosoma brucei, a single-celled eukaryote. Being eukaryotic, it has a cell nucleus and a larger genome than most bacteria; it also has a flagellum with which it can propel itself. Infection with T. brucei occurs via the bite of a blood-sucking fly, one of several species of tsetse fly.
The mammalian immune system has a difficult time with T. brucei because of an effective set of adaptations. The protozoan's surface maintains a dense coat of a particular glycoprotein on its surface which generally hide other necessary surface features such as chemical receptors and ion channels. Since it is this glycoprotein that the adaptive immune system will encounter, that molecule is the one which it will develop antibodies to recognize.
The following is multiple choice question (with options) to answer.
What kind of diseases can be difficult to treat because they live inside the host's cells, making it hard to destroy them without killing host cells? | [
"nucleus diseases",
"cancerous diseases",
"viral diseases",
"superfluous diseases"
] | C | Viral diseases can be difficult to treat. They live inside the cells of their host, so it is hard to destroy them without killing host cells. Antibiotics also have no effect on viruses. Antiviral drugs are available, but only for a limited number of viruses. |
SciQ | SciQ-6603 | respiration
Here is what happens at the molecular level.
The $\rm CN^-$ ions diffuse into the mitochondria. They have high affinity to the ferrous ion of the mitochondrial enzyme cytochrome c oxidase involved in the electron transport chain (ETC), one of the phases of cellular respiration where $\rm ATP$ is generated from $\rm NADH$ and $\rm FADH_2$. And it is this process that actually requires oxygen. The inhibited cytochrome c oxidase is of no good in transporting electrons, thus no $\rm ATP$ molecules are generated. The oxygen molecules waiting for those electrons remain empty handed resulting in the increase in the concentration of molecular oxygen. Remember, ETC occurs in almost all living cells except a few like RBC which get their major share of ATP from the highly inefficient anaerobic glycolysis. Also, $\rm ATP$ is the energy currency of our body and is required in a wide variety of bodily processes like osmotic balance, nerve impulse transmission, muscle contraction etc. With no $\rm ATP$ your heart and respiratory muscles can't contract, your medulla can't regulate breathing, your kidneys can't concentrate urine and the list goes on. Death is imminent if a high concentration of cyanide gets into your blood.
The symptoms of panic like tachypnea and tachycardia (that result due to low oxygen in blood) are not usually seen unless the victim himself knows he is poisoned. The end effects like cardiac and respiratory arrest, seizures and coma, however, are similar to those of suffocation.
For further read:
The Mechanism of Cyanide Intoxication and its Antagonism
The following is multiple choice question (with options) to answer.
What type of cellular respiration occurs in the presence of oxygen? | [
"hyperbaric",
"extracellular",
"anaerobic",
"aerobic"
] | D | There are two types of cellular respiration (see Cellular Respiration concept): aerobic and anaerobic. One occurs in the presence of oxygen ( aerobic ), and one occurs in the absence of oxygen ( anaerobic ). Both begin with glycolysis - the splitting of glucose. |
SciQ | SciQ-6604 | biochemistry, botany, plant-physiology, photosynthesis
What are typical characteristics of different plants in this regard? I.e., how do common species of plants manage their C consumption before (and after) the development of leaves? There are quite a few questions and thoughts in there, I'll try to cover them all:
First, to correct your initial word equation: During photosynthesis, a plant translates CO2 and water into O2 and carbon compounds using energy from light (photons).
You are correct to assume the C is further used for the growing process; it is used to make sugars which store energy in their bonds. That energy is then released when required to power other reactions, which is how a plant lives and grows. C is also incorporated into all the organic molecules in the plant.
Plants require several things to live: CO2, light, water and minerals. If any of those things is missing for a sustained period, growth will suffer. Most molecules in a plant require some carbon, which comes originally from CO2, and also an assortment of other elements which come from the mineral nutrients in the soil. So the plant is completely reliant on minerals.
Most plants, before a leaf is established or roots develop, grow using energy and nutrients stored in the endosperm and cotyledons of the seed. I whipped up a rough diagram below. Cotyledons are primitive leaves inside the seed. The endosperm is a starchy tissue used only for storage of nutrients and energy. The radicle is the juvenile root. The embryo is the baby plant.
The following is multiple choice question (with options) to answer.
Stomata must control the transpiration of water vapor and the exchange of carbon dioxide and oxygen that take place during what process? | [
"glycolysis",
"photosynthesis",
"fertilization",
"spermatogenesis"
] | B | For photosynthesis, stomata must control the transpiration of water vapor and the exchange of carbon dioxide and oxygen. Stomata are flanked by guard cells that swell or shrink by taking in or losing water through osmosis. When they do, they open or close the stomata. |
SciQ | SciQ-6605 | embryology
Title: What is a zygote? During fertilization, the nuclear membrane of the pro-nucleus of the ovum and sperm degenerate. Is the cell is stage called a zygote?
After the dissolution, mitosis occurs and two cells are formed.Or is the cell is stage called a zygote?
I'm confused as i knew a zygote was single-celled. Conventionally, a zygote is considered to be formed the moment that a spermatozoum, penetrates the cell membrane of the ovum and yields its genetic material into the ovum. Effectually, however, there is a lag between the instant of fertilization and the fusion of the male and female pronuclei. In mammals, the duration of this lag period is ~12 hours. There are also additional actions that must be completed before the first mitosis as in most mammals, including humans, the ovum is actually in the second metaphase of meiosis at the time of fertilization.
The following is multiple choice question (with options) to answer.
If pollination and fertilization occur, a diploid zygote forms within an ovule, located where | [
"uterus",
"bladder",
"ovary",
"testicle"
] | C | If pollination and fertilization occur, a diploid zygote forms within an ovule in the ovary. The zygote develops into an embryo inside a seed, which forms from the ovule and also contains food to nourish the embryo. The ovary surrounding the seed may develop into a fruit. Fruits attract animals that may disperse the seeds they contain. If a seed germinates, it may grow into a mature sporophyte plant and repeat the cycle. |
SciQ | SciQ-6606 | atmosphere, geography
Title: How much atmoshphere is there compared to land and water We know our earth has 71% water and 29% land, but compared to that land and water, how much air do we have in our atmosphere?
I mean:
How big is our atmosphere
Is there any increase or decrease in the amount of atmosphere over time
Is there any change in percentage of oxygen over time 71% of Earth's surface is covered with water and 29% land.
Thinking in that regard, that's saying that on 29% of Earth's "surface" locations you have land below your feet, and in 71% of the locations, you have water. So to continue in such terms, you'd then ask... ok, what percentage of Earth's surface locations would have air above them!?! Well that's all of them. So to if you're comparing it with those percentages, I guess you'd have to say it's another 100%. Or, if we put them together into a full 3-dimensional surroundings at the surface, well it'd basically be 50% air, 36% water, 14% land.
But to compare how much of each there REALLY is, you need to include depth, getting some sort of 3 dimensional understanding of it. But the picture that reveals is certainly not the picture we are used to from daily experience. From the values I was able to find:
In terms of the room each takes up, the volume:
Surface water (oceans+lakes+rivers, glaciers, etc) is 1.4 billion km³
The inside of the Earth is about 1 trillion = 1000 billion km³
For the atmosphere, as mentioned in comments, it's a little more difficult, as the gases only gradually give way to space. You find less and less gas as you go up, but there's no set spot where there is none, as some tiny amount is always floating off into space. So where do you draw the line? A commonly used boundary between the atmosphere and space is the Karman line. This would lead to a volume of 53 billion km³ (using Earth's radius = 6371 km). Note that only about half of that is in the troposphere and stratosphere, which are perhaps the familiar zones of the atmosphere where weather and the ozone layer (and 95% of air molecules) reside.
The following is multiple choice question (with options) to answer.
What makes up 99 percent of air? | [
"dioxide and nitrogen",
"oxygen and dioxide",
"nitrogen and oxygen",
"phosphorus and oxygen"
] | C | Figure below shows the main gases in air. Nitrogen and oxygen make up 99 percent of air. Argon and carbon dioxide make up much of the rest. These percentages are the same just about everywhere in the atmosphere. |
SciQ | SciQ-6607 | electricity
Title: Electricity production Are there alternate means to produce electricity than magnetic induction?
I observe that all places this method is used .Do other methods exist even if this being the most profitable way. Magnetic induction is by far the most efficient way to generate electricity, but there are other methods. The obvious common method is photoelectricity, as used in solar panels. This is around 10% - 20% efficient.
There are plenty of other ways of generating small amount of electricy that have found specialist niches. For example the Voyager spacecraft use the Seebeck effect to generate electricity from heat. This type of electricity generation is generically known as thermoelectricity. Voyager uses a radioactive source to generate the heat, but any source of heat will work.
Alternatively mechanical forces can generate electricity using piezoelectricity. This is used to generate electric sparks in gas lighters.
Or another method is triboelectricity, of which the most famous example is that schoolchild's favourite the Van de Graaff generator.
And I'm sure there are many others I haven't thought of but commenters will add :-)
The following is multiple choice question (with options) to answer.
What is the process in which producers get their energy from sources other than the sun? | [
"chemosynthesis",
"electrolysis",
"biosynthesis",
"phototropism"
] | A | There are also bacteria that use chemical processes to produce food. They get their energy from sources other than the sun, but they are still called producers. This process is known as chemosynthesis , and is common in ecosystems without sunlight, such as certain marine ecosystems. |
SciQ | SciQ-6608 | botany, plant-physiology, ecology, virology, host-pathogen-interaction
Note about symbiosis - comes in reaction to @Gerhard's comment
Different authors use the word symbiosis differently. From wikipedia:
The definition of symbiosis is controversial among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any type of persistent biological interaction (i.e. mutualistic, commensalistic, or parasitic).4 After 130+ years of debate,5 current biology and ecology textbooks now use the latter "de Bary" definition or an even broader definition (i.e. symbiosis = all species interactions), with the restrictive definition no longer used (i.e. symbiosis = mutualism)
The following is multiple choice question (with options) to answer.
Parasitism, mutualism, and commensalism are instances of what type of interaction? | [
"semantic",
"enzymatic",
"symbiotic",
"antibiotic"
] | C | |
SciQ | SciQ-6609 | biochemistry
Another important difference with respect to resulting polymers formed from these bonds - polysaccharides, in contrast to proteins and nucleic acids, form branched as well as linear polymers
α-Amylose is a linear polymer of several thousand glucose residues linked by α(1 >4) bonds. Note that although α-amylose is an isomer of cellulose, it has very different structural properties. This is because cellulose’s β-glycosidic linkages cause each successive glucose residue to flip 180° with respect to the preceding residue, so that the polymer assumes an easily packed, fully extended conformation.
Peptide bond
The resulting linkage formed when α-amino acids polymerize, through the elimination of a water molecule is known as a peptide bond (sometimes called an amide bond):
Peptide bond (shown in red)
Glycosidic bonds between monosaccharide units are the basis for the formation of oligosaccharides and polysaccharides.
The glycosidic bond is therefore the carbohydrate analog of the peptide bond in proteins. (The bond in a nucleoside linking its ribose residue to its base is also a glycosidic bond)
The following is multiple choice question (with options) to answer.
The cell wall of plants is made up of a complex carbohydrate that is a polymer of what sugar? | [
"insulin",
"sucrose",
"fructose",
"glucose"
] | D | complex carbohydrate that is a polymer of glucose and that makes up the cell wall of plants. |
SciQ | SciQ-6610 | material-science, metals
Title: Why is chromium more brittle than iron at room temperature? Why is chromium more brittle than iron? I understand that both of them are BCC at room temperature. Is it to do with the grain size? Why is it different between the two metals? The brittleness is caused primarily by interstitial impurities. That's the case of chromium as well as all Group VI A metals. For chromium, the nitrogen atoms are the main impurities.
The following is multiple choice question (with options) to answer.
Which metal is not a solid even at room temperature? | [
"iron",
"mercury",
"copper",
"aluminum"
] | B | A metal is an element that is a good conductor of heat and electricity. Metals are also malleable, which means that they can be hammered into very thin sheets without breaking, and ductile, which means that they can be drawn into wires. When a fresh surface of any metal is exposed, it will be very shiny, because it reflects light well. This property is referred to as luster. All metals are solid at room temperature except mercury (Hg), which is a liquid. The melting points of different metals vary widely. Mercury has the lowest melting point of all pure metals (−39°C), and tungsten (W) has the highest (3422°C). On the periodic table in Figure above , the metals are shaded blue and are located to the left of the bold stair-step line. About 80 percent of the elements are metals (see examples in Figure below ). |
SciQ | SciQ-6611 | energy, combustion, explosives
Title: What really happens atomically in an explosion? Let's say a room is filled with butane, I then throw a cigarette into the room. What happens to the atoms/molecules of the butane when they are in contact with the heat from the cigarette? The combustion of alkanes like butane is fearsomely complicated involving dozens of transient compounds and hundreds of different reaction. If you have a few spare hours there is a dissertation that presents a nice summary of the process here (this is a 1MB PDF).
A butane molecule is pretty stable and doesn't react with oxygen on contact so you need some way to get the reaction going. Typically the reaction is started by the generation of free radicals. These will react with stable molecules to split them up and generate more free radicals so in effect we have a chain reaction.
So the ignition process is basically the generation of free radicals, and that's what the lit cigarette does. The heat of the burning tobacco generates free radicals that then start the butane oxygen reaction. You can also generate free radicals in lots of other ways e.g. using shock, from an electric spark, or by using a suitable catalyst such as the catalytic convertor on your car exhaust.
The following is multiple choice question (with options) to answer.
How do molecules react when a gas is heated? | [
"they disintegrate",
"they explode",
"they move faster",
"they move slower"
] | C | Gases are compressible, meaning that when put under high pressure, the particles are forced closer to one another. This decreases the amount of empty space and reduces the volume of the gas. Gas volume is also affected by temperature. When a gas is heated, its molecules move faster and the gas expands. Because of the variation in gas volume due to pressure and temperature changes, the comparison of gas volumes must be done at one standard temperature and pressure. Standard temperature and pressure (STP) is defined as 0°C (273.15 K) and 1 atm pressure. The molar volume of a gas is the volume of one mole of a gas at STP. At STP, one mole (6.02 × 10 23 representative particles) of any gas occupies a volume of 22.4 L ( Figure below ). |
SciQ | SciQ-6612 | earthquakes, soil-science, bedrock
Title: Question regarding underground man-made facilities Why is it that underground facilities (or underground military bases) are almost always built into hollowed out mountains? Examples of (publicly known ones anyway) are Cheyenne Mountain Complex and Mount Weather government/ military facilities. Is having a highland/mountain a prerequisite for construction of military/government facilities? Is is not possible to construct facilities beneath lower ground, plains, dessert or under cities, besides subway stations and tunnels? Say if we wanted to build NORAD bunker somewhere deep beneath San Jose population centers, is this possible discounting the fault lines and permits for now? This question is not about earth science. If anything, it has more to do with engineering.
Strategic or critical defense or government infrastructure needs to be protected against explosive attacks, particularly nuclear attacks. A mountain offers a sizeable protective cap/roof to an underground installation. Similar levels of protection can be provided in flat ground, but the underground installation would need to be significantly deeper.
Critical parts of the installation would not be established within the mountain above the level of the ground surrounding the mountain; it would be established below.
Additionally, many mountains are composed on igneous rock: rock that solidified from a molten mass. Such rock, such as basalt or dolerite (diabase), is typically stronger than sedimentary rock and can thus offer better blast protection than sedimentary rock.
Also, if the installation is established igneous rock, the same strength parameters can also mean reduced geotechnical and subsequent ground support measures would be required for the underground voids that if they were established in sedimentary rock.
Cheyanne Mountain is composed of granite, and igneous rock that solidified while still underground. The NORAD installation within Cheyanne Mountain "was designed to ride out a nuclear attack". Having been completed in 1966, when tunnel boring machines were not a consideration, it was established using drill and blast methods and consumed 500 tons of explosives.
The following is multiple choice question (with options) to answer.
Mountain building and earthquakes are some of the responses of rocks when subected to what? | [
"weather",
"erosion",
"time",
"stress"
] | D | When plates are pushed or pulled, the rock is subjected to stress. Stress can cause a rock to change shape or to break. When a rock bends without breaking, it folds. When the rock breaks, it fractures. Mountain building and earthquakes are some of the responses rocks have to stress. |
SciQ | SciQ-6613 | quantum-mechanics, thermodynamics, energy, energy-conservation
Altogether, for all practical purposes, we can regard $U=\langle H\rangle$ as "the" total internal energy of the system as long as $\Delta U$ is sufficiently small. Measurement is not required for this to make sense, and equation (1) implies that this $U$ is indeed constant in time.
The following is multiple choice question (with options) to answer.
What is defined as maintaining a stable internal environment? | [
"ketosis",
"homeostasis",
"peristalsis",
"consciousness"
] | B | Lenses are made of transparent material such as glass or plastic with an index of refraction greater than that of air. At least one of the faces is a part of a sphere; a convex lens is thicker at the center than the edges, and a concave lens is thicker at the edges than the center. Convex lenses are called converging lenses, because they refract parallel light rays so that they meet. They are one of the most useful and important parts of all optical devices, and are found in eyeglasses, telescopes, microscopes, magnifying glasses, cameras and many other objects. |
SciQ | SciQ-6614 | metallurgy, nuclear-chemistry, geochemistry
Title: Why are rare earth metals and platinum group metals are often found clustered together in ores Rare earth and platinum group metals are often found clustered together in the earth's crust. Mining for platinum, for instance, also yields Rhodium and Ruthenium belonging to the same group. Likewise, rare earth elements such as Neodymium, Europium and Samarium also cooccur in the same ore, so much so, that they are difficult to chemically separate.
It could be reasoned that it's the result of nucleogenesis where elements are formed consecutively based on their atomic number. While it might explain the first row and the second row of each group, where each metal is only one atomic number apart, it doesn't explain why metals from both rows are found together which are much further apart.
Alternatively, the similar chemistry of each group could explain the clustering. The two groups are the only group with this property. It fails to explain, however, how these metals found each other in a molten soup of heterogeneous elements. There may be some geological factors in the clustering, but it's unclear.
Why are the two groups of elements found clustered together? The factors that generate mineral concentrations are complex and often only partly known
Introduction: geology is complicated
The one thing we can be very certain about is is that the distribution of minerals in the earth's crust has very little to do with the primordial origins of the component elements (that is where they came from in the early solar system and how they were originally generated). Most "heavy" elements are originally formed in the cores of supernovae and not in either the big bang or in normal stars.
The distribution of elements in the earth is mostly unrelated to the cosmic origins of elements because the earth's crust is not static but is frequently churned up by a variety of processes on a geological timescale. If we go back far enough in the history of the planet, everything was molten and this allowed some of the denser components to separate out before the surface cooled enough to be solid. The led to the core being mostly metallic (and consisting of mostly iron and nickel). Higher layers contain less dense minerals containing a lot of silicate minerals. At the top there is a thin layer, the crust, which is where we find useful minerals and it is even more concentrated in silicate minerals and even less dense.
The following is multiple choice question (with options) to answer.
What element chemically weathers rock by combining with a metal? | [
"nitrogen",
"oxygen",
"carbon",
"hydrogen"
] | B | Oxygen chemically weathers rock by combining with a metal. |
SciQ | SciQ-6615 | taxonomy
Title: Why are sponges sometimes not considered multicellular? I read somewhere (I can't find where) that there is no scientific consensus whether sponges should be considered multicellular organisms.
It seems I don't understand where is the line between unicellular and multicellular life.
I am not able to find a more elaborate explanation of that doubt. What are the reasons for it? Sponges are generally considered as colonial organisms because there is little cell specialization and little separation of function/role. All cells do pretty much the same thing; it looks more like a pile of individual cells than an actual multicellular organism. In reality it is a little bit in between.
In any case, what one wants to call multicellular or unicellular is a matter of definition and preferences. You cannot find the line between unicellular and multicellular because there is no such line that would not be very arbitrary and filled with special cases.
You can study a little more the physiology of sponges and then decide for yourself if it looks sufficiently like a multicellular organism or more like a colony of cells (a colonial organism).
The following is multiple choice question (with options) to answer.
Porifera are parazoans that exhibit simple organization and lack true what? | [
"tissues",
"molecules",
"nuclei",
"cell membranes"
] | A | 15.2 Sponges and Cnidarians Animals included in phylum Porifera are parazoans and do not possess true tissues. These organisms show a simple organization. Sponges have multiple cell types that are geared toward executing various metabolic functions. Cnidarians have outer and inner tissue layers sandwiching a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion. The cnidocyte is a specialized cell for delivering toxins to prey and predators. Cnidarians have separate sexes. They have a life cycle that involves morphologically distinct forms—medusoid and polypoid—at various stages in their life cycle. |
SciQ | SciQ-6616 | mechanical-engineering, mechanical-failure, product-testing, failure-analysis
This leaves us with 3 "factors" that we now want to evaluate (and which also seem reasonable):
Temperature of the Water
Amount of salt added
Time spent boiling.
Once a DOE is set up, we would define a number of different experiments where we boiled an egg while varying those parameters in known amounts. Eventually we'd end up with some data that we could statistically analyze to help us understand what input factors we want to control. We'd end up finding that the temperature of the water is somewhat influenced by the amount of salt added. We'd also learn that the amount of time we needed to boil was correlated with the temperature. Eventually, through our analysis, we'd likely come to the conclusion that while temperature is important, the amount we raise it by adding an acceptable amount of salt, doesn't impact the way our egg end up nearly as much as does the time we actually spend boiling it! Not long enough and we end up with raw egg. Too long and we turn it to dried rubber. Our DOE has helped us identify that, when we now go to boil eggs, controlling the time we boil is the best way to guarantee us an egg made exactly the way we want it!
Now, while this may seem a super trivial example, hopefully you can envision how the concept of a DOE as a "tool" could be extremely useful. And just as there were multiple different tools for performing RCA, the same exits for design analysis!
Hope this helps to better understand how these tools relate.
The following is multiple choice question (with options) to answer.
The values of which factors are controlled by the experimenter over the course of an experiment? | [
"independent approaches",
"independent variables",
"independent elements",
"other variables"
] | B | A variable is a factor that can change over the course of an experiment. Independent variables are factors whose values are controlled by the experimenter to determine its relationship to an observed phenomenon (the dependent variable). Dependent variables change in response to the independent variable. |
SciQ | SciQ-6617 | neuroscience, brain, pain
Let's take stabbing as another cause of pain. One stab in a less dangerous place missing all important structures may be not that harmful but may be painful. However multiple small stabs into important structures like arteries or spinal cord could be horribly destructive.
Then let's look at headaches or nerve pain. Here it is only the pain and usually there isn't any destructive or harmful process. Most individuals would take one really, really bad headache followed by never having a headache then chronic daily "tension" headaches.
Psychologically though usually the chronic daily pain is the worst. Particularly as without adequate pain management from the start, it is less responsive to painkillers (analgesia). It frequently adds to depression if it does not cause it itself and can lead to suicide. Also painkillers themselves may cause chronic pain which does not help.
In summary, acute severe pain suggests something is seriously wrong and needs to be dealt with immediately biologically as there is likely a damaging process underlying it. However if this event is survived, it may be linked with high disability from any biological process that underpinned the pain. Chronic daily pain suggests a long continuing process. The cause of this may be life threatening, such as cancers, but is usually less dangerous at least compared to acute severe pain biologically. However the psychological aspects of this pain are seriously important as they can be particularly detrimental.
The following is multiple choice question (with options) to answer.
What are the most common causes of brain injuries? | [
"lightning strikes",
"alcohol poisoning",
"falls",
"excessive shaking"
] | C | Brain injuries can range from mild to extremely severe, but even mild injuries need medical attention. Brain injuries can result from falls, car accidents, violence, sports injuries, and war and combat. Falls are the most common cause of brain injuries, particularly in older adults and young children. |
SciQ | SciQ-6618 | physical-chemistry, atoms
Title: Why don't electrons simply stick to the nucleus on account of being *oppositely* charged, instead of moving around it? Why don't electrons stick to the nucleus on account of being oppositely charged charged (the nucleus being positively charged)? But contrary to my intuition, electrons seem to follow a whole bunch of wacky paths (orbitals) around the nucleus (as demarcated by orbital wave-functions). Why is this?
Do note:
I'm not asking "What keeps the electron in orbit". All I want to know, is why electrons don't simply find themselves attached to the nucleus, and why do they even bother moving around the nucleus (in orbitals) at all? My textbooks, unfortunately, make no reference to this issue...they wholeheartedly adopt the "current" QM model of the (hydrogen) atom. Richard Feynman alludes to this exact problem in the first volume of the Feynman Lectures on Physics. I'll present his argument here (based on the Uncertainty Principle), albeit, in my own words ;)
The German physicist [since he dealt with atomic chemistry/physics...by all means, go ahead and call him a "chemist" ;) ], Werner Karl Heisenberg came up with what we now know as "The Heisenberg Uncertainty Principle"... a revolutionary idea that points to an "inherent fuzziness", that exists within quantum systems (which is a fancy word that refers to any region of space that is sufficiently "small" enough to introduce wave-particle duality), and becomes apparent when we try to "measure" the various parameters that constitute them.
Basically, what (one version of) the Uncertainty Principle states is that:
The product of the uncertainty in measurement of velocity and the uncertainty in measurement of the position of a particle can never be less than a certain constant; i.e- ħ/2
Rephrasing this
If we were to know a particle's position to a very high precision (i.e- small uncertainty in measurement of position) then the corresponding uncertainty in the measurement of the particle's velocity (or momentum, if you know its mass) increases greatly. The same holds true vice versa.
In other words,
You cannot know both a particle's position and momentum in a quantum system to a great precision simultaneously.
The following is multiple choice question (with options) to answer.
Electrons are located at fixed distances from the nucleus, what are they called? | [
"energy concentrations",
"Positive levels",
"Energy layers",
"energy levels"
] | D | Electrons are located at fixed distances from the nucleus, called energy levels. You can see the first three energy levels in the Figure below . The diagram also shows the maximum possible number of electrons at each energy level. |
SciQ | SciQ-6619 | climate-change, climate
In this case, as it is an area that it is almost constantly cloudy with high humidity, temperature is varying just a little bit, and except the first day of the period, it seems that there is no relationship. In fact, on the second day there was a storm (I am living now at Singapore) and it is reflected in a quick change in temperature (both) and solar radiation.
Conclusion: It is not as simple as it seems.
Hope it helps!
The following is multiple choice question (with options) to answer.
Which factor has a big impact on coastal climates? | [
"large ocean currents",
"tide",
"tsunami",
"ocean waves"
] | A | Large ocean currents can have a big impact on the climate of nearby coasts. The Gulf Stream, for example, carries warm water from near the equator up the eastern coast of North America. Look at the map in Figure below . It shows how the Gulf Stream warms both the water and land along the coast. |
SciQ | SciQ-6620 | general-relativity, electromagnetic-radiation, spacetime, refraction, aether
Title: Bending light due to gravity My question is can you consider the fabric of spacetime to be a medium? And if so, can one explain the bending light due to gravity, that warps spacetime, as analogous to light changing between the medium of air and glass in Snell's law.
Let me clarify further:
Imagine a cartesian coordinate system with a mass located at the origin with mass $M$.
a beam of light is shot parallel to the plane $x=1$.
at the point <1,0,0> gravity is warping the space time medium between the the beam of light and the mass much more than the the space time on the opposite side of the plane x=1. Therefore the discrepancies in the density(this maybe the wrong terminology do not murder me on this) of the medium on both sides light is propagating through has created an effect that is exactly the same as the the case we experience on earth and teach in class room when light is shot a block of glass and refracts.
So to summarize, can the bending of light due to gravity simply be thought of as refraction. First we need to clarify:
According to GR, it is spacetime itself that bends, due to stress-energy (not mass).
Even particles with no rest mass, like a photon, have energy, so they bend spacetime.
When there is a large mass, like the sun, it bends spacetime around it, so when light passes next to it, light's path will be bent, because it goes through a bent spacetime.
We do not know what it is exactly or how it bends, GR only talks about the extent to what spacetime bends.
The photon passing next to the sun will bend spacetime too, and the sun will bend it too, so they both have gravitational effects on each other.
It is not like with the case of glass.
When spacetime is bent because of the sun's gravity, and light passes next to it, it is not going in any medium, it is going in vacuum.
In the case of glass, whenever light interacts with an atom, three things can happen:
elastic scattering, the photon keeps its energy, but changes angle.
inelastic scattering, the photon gives part of its energy to the atom, and changes angle.
absorption, the photon gives all its energy to the atom.
The following is multiple choice question (with options) to answer.
What occurs when light bends as it passes from one type of matter to another? | [
"reflection",
"refraction",
"vibration",
"resonance"
] | B | Light may be refracted by matter. The light is bent when it passes from one type of matter to another. Refraction of light is similar to refraction of sound waves. You can also read more about refraction of light in the lesson “Optics. ”. |
SciQ | SciQ-6621 | organic-chemistry, reaction-mechanism, polymers, regioselectivity
Title: Chain transfer in polystyrene synthesis while I was studying the many side reactions of radical polymerization, I stumbled across this source which illustrates the chain transfer side reaction in polystyrene synthesis:
Of course, there is a typo in this picture, it shouldn’t be -CH2-H- but -CH-H-, but you get the idea. A monomer radical can abstract a hydrogen atom from an already existing chain in the first step, so that it’s radical function is forwarded to the chain.
The chain then, in a second step attacks another styrene molecule from the back side of the double bond so that the more stable, secondary radical forms, so the molecule can also form branches.
Everything alright with me, but I don’t get the regiochemistry here. In the first step,a secondary carbon atom is attacked, which also forms a secondary radical intermediate; but wouldn’t an attack on the tertiary -CH group be more favorable thermodynamically as it is a tertiary radical intermediate which is also stabilized by the phenyl group? Or is it a kinetically controlled process, where more hydrogens can be subtracted on the bridging carbon atoms, so that after the chain transfer, the bridging carbons are tertiary as a result?
Any tips would really be appreciated! The image shown in the question can be found with some context at https://www.open.edu/openlearn/science-maths-technology/science/chemistry/introduction-polymers/content-section-4.3.3
In that document, they say of chain transfer:
A similar mechanism accounts for the side branches in LDPE where it is a more important mode of termination than in polystyrene
This indicates that chain transfer is a rare event in a typical synthesis of polystyrene.
[...] but wouldn’t an attack on the tertiary -CH group be more favorable thermodynamically as it is a tertiary radical intermediate which is also stabilized by the phenyl group?
As this is a rare event, you don't expect any of the intermediates to be the most favorable ones.
Or is it a kinetically controlled process [...]
The following is multiple choice question (with options) to answer.
What is a polymer formed by chain addition reactions between monomers that contain a double bond called? | [
"an addition monolayer",
"a branched polymer",
"an addition polymer",
"a linear polymer"
] | C | An addition polymer is a polymer formed by chain addition reactions between monomers that contain a double bond. Molecules of ethene can polymerize with each other under the right conditions to form the polymer called polyethylene. |
SciQ | SciQ-6622 | algorithm
Title: Which algorithm to use to solve this optimization problem?
I have items called 'Resources' from 1 to 7.
I have to use them in different actions identified from 1 to 10.
I can do a maximum of 4 actions each time. This is called 'Operation'.
The use of a resource has a cost of 1 per each 'Operation' even if it is used 4 times.
The following table indicates the resources needed to do the related actions:
| | Resources |
|--------|----------------------------------|
| Action | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|--------|----------------------------------|
| 1 | 1 | 0 | 1 | 1 | 0 | 0 | 0 |
| 2 | 1 | 1 | 0 | 0 | 1 | 0 | 0 |
| 3 | 1 | 0 | 1 | 0 | 0 | 1 | 0 |
| 4 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| 5 | 1 | 0 | 1 | 1 | 0 | 1 | 0 |
| 6 | 1 | 1 | 1 | 0 | 0 | 0 | 0 |
| 7 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| 8 | 1 | 0 | 1 | 0 | 1 | 0 | 0 |
| 9 | 0 | 1 | 0 | 1 | 0 | 0 | 0 |
| 10 | 1 | 1 | 1 | 0 | 0 | 0 | 1 |
The following is multiple choice question (with options) to answer.
What do you call resources that can be replaced at the rate they are being used? | [
"renewable",
"viable",
"abundant",
"innovative"
] | A | Renewable resources can be replaced at the rate they are being used. |
SciQ | SciQ-6623 | biochemistry, cell-biology, neurotransmitter, membrane-transport, synapses
Title: Exocytosis of synaptic vesicles I'm reading the following paper:
http://jcs.biologists.org/content/123/6/819
The part I am really confused about is when they say:
Exocytosis appears to use two alternative pathways: clathrin-mediated endocytosis (CME), which is well established by numerous lines of evidence, and the more controversial ‘kiss-and-run’ pathway, which involves direct retrieval of a vesicle at the site of fusion
My question is .. How can exocytosis (contents inside of cell are transported to outside of cell) use clathrin mediated endocytosis?
I thought endocytosis is the opposite of exocytosis, so why do synaptic vesicles use clathrin mediated endocytosis as a method of exocytosis? That sentence is located in a paragraph titled "Stages 5-7: Endocytosis and recycling": it's talking about recycling exocytosed membrane which is necessary for making vesicles for further exocytosis.
The sentences before the part you quoted are:
Synapses possess highly efficient mechanisms for retrieving SVs from the plasma membrane of the presynaptic terminal after exocytosis. Fast regeneration of functional SVs is a prerequisite for synapses to function during prolonged activity.
I think the passage is just somewhat confusingly worded, in that "exocytosis" is used as the subject of the sentence which is strange in this context. You could rewrite that sentence:
There appear to be two alternative pathways to recycle membrane for exocytosis: clathrin-mediated...
The following is multiple choice question (with options) to answer.
The type of vesicle transport that moves a substance out of the cell is called? | [
"exocytosis",
"endocytosis",
"morphogenesis",
"metabolism"
] | A | Exocytosis is the type of vesicle transport that moves a substance out of the cell. A vesicle containing the substance moves through the cytoplasm to the cell membrane. Then, the vesicle membrane fuses with the cell membrane, and the substance is released outside the cell. You can watch an animation of exocytosis at the link below. |
SciQ | SciQ-6624 | evolution, ornithology, palaeontology
One thing those many, many bird and proto-bird fossils also made clear is that the traits of modern birds (feathers, wings, toothless beaks, etc) didn't evolve in a simple line from non-bird to bird. Many of those traits evolved convergently in several lineages, were lost in some, maybe regained in others, and feathers in particular turn out to be a widespread dinosaur feature that cannot be considered a uniquely bird trait anymore (unless we want to call T-rexes "birds"). Still, saying "beaks evolved several times" or "feathers evolved several times" doesn't mean that birds, let alone modern birds, evolved from several different ancestors. It can mean that the common ancestor of birds had lots of variously bird-like more-or-less distant cousins living around the same time.
The following is multiple choice question (with options) to answer.
What characteristic of birds is related to the food they eat? | [
"beak",
"feet",
"feathers",
"tail"
] | A | The size and shape of the beak is related to the food the bird eats and can vary greatly among different birds. Parrots have down-curved, hooked bills, which are well-adapted for cracking seeds and nuts ( Figure below ). Hummingbirds, on the other hand, have long, thin, pointed bills, which are adapted for getting the nectar out of flowers ( Figure below ). Hawks, eagles, falcons and owls have a sharp, hooked beak. |
SciQ | SciQ-6625 | human-biology
Title: Is urine dirty as soon as it leaves the human body? Human urine is sterile as long as it is in the human body. But is it dirty after leaving the human body? Could you get sick from it, if you drink it or don't wash your hands, for example? It was believed for a long time that urine stored in the urinary bladder is sterile. However, Wolfe et al(1). recently found evidence of bacterial presence in the urine extracted from bladders of healthy women. In an article just published, Hilt et al. found that at least some bacteria found in the bladder of healthy women are viable and can be grown in a laboratory after extraction from the bladder).2 (Paywall). They expect that the same is the case for men.
From the Hilt et al. paper:
Thirty-five different genera and 85 different species were identified
by EQUC. The most prevalent genera isolated were Lactobacillus (15%),
followed by Corynebacterium (14.2%), Streptococcus (11.9%),
Actinomyces (6.9%), and Staphylococcus (6.9%). Other genera commonly
isolated include Aerococcus, Gardnerella, Bifidobacterium, and
Actinobaculum.
Note that these species for the most part (Actinobaculum being one exception, as a possible uropathogen) appear to be part of the normal microbiome (collection of microorganisms) in healthy people in the same way as bacteria inhabit other parts of healthy persons. Additionally, the recovered organisms required special care to achieve growth:
Most of the bacteria isolated required either increased CO2 or
anaerobic conditions for growth, along with prolonged incubation, and
they often were present in numbers below the threshold of detection
used in routine diagnostic urine culture protocols.
The following is multiple choice question (with options) to answer.
What tube carries urine out of the body? | [
"uterus",
"urethra",
"kidney",
"fallopian tube"
] | B | The penis is a cylinder-shaped organ. It contains the urethra. The urethra is a tube that carries urine out of the body. The urethra also carries sperm out of the body. |
SciQ | SciQ-6626 | species-identification, botany, ecology, trees
Title: Identifying a shrub with unusual "many shoots" growth behavior While recently hiking in the southern mountains of New Hampshire, we came across a plant, and some of them were exhibiting what we interpreted to be a disease, or least unusual growth. On some of the nodes, there were a large number of extra stalks:
On each plant, the number and locations of these things varied, and not all of them had it. And we first assumed it was some ivy, or parasite, or separate plant, but it seemed pretty clear to us that it was coming right from the same branch.
We soon saw there were dead versions of this plant, and all of them had this "extra shoot" variation:
So we reasoned that no matter what this thing was -- natural variation or some kind of disease -- it was killing the plants.
Google image search was no help. It possibly identified the plant as a "viburnum", but was unable to help with the growth.
Anyone know what plant this is, or what this growth behavior is the result of? Possibly an example of a "Witch's Broom."
Witch's Broom is a deformity in plants (typically woody species) which typically causes dense patches of stems/shoots to grow from a single point on the plant. The name comes from the broom-like appearance of the stems.1
Witch's broom may be caused by many different types of organisms, including fungi, oomycetes, insects, mistletoe, dwarf mistletoes, mites, nematodes, phytoplasmas, or viruses.2
Sources:
1. Wikipedia
2. Book of the British Countryside. Pub. London : Drive Publications, (1973). p. 519
Image1. Gardeningknowhow.com
Image2. Iowa state University
The following is multiple choice question (with options) to answer.
What plant products may be classified as simple, aggregate, multiple, or accessory, depending on their origin? | [
"leaves",
"pods",
"flowers",
"fruits"
] | D | Fruits may be classified as simple, aggregate, multiple, or accessory, depending on their origin (Figure 32.22). If the fruit develops from a single carpel or fused carpels of a single ovary, it is known as a simple fruit, as seen in nuts and beans. An aggregate fruit is one that develops from more than one carpel, but all are in the same flower: the mature carpels fuse together to form the entire fruit, as seen in the raspberry. Multiple fruit develops from an inflorescence or a cluster of flowers. An example is the pineapple, where the flowers fuse together to form the fruit. Accessory fruits (sometimes called false fruits) are not derived from the ovary, but from another part of the flower, such as the receptacle (strawberry) or the hypanthium (apples and pears). |
SciQ | SciQ-6627 | terminology, metrology
¹ Be aware of references in which it is not clear whether what is being referred to is, e.g., 2 m, length or the length of this table. Now that I have a better understanding of what you're asking, I think a good candidate would be "quantity value", also known as the "value of a quantity", from p. 28 of the International Vocabulary of Metrology, Basic and General Concepts and Associated Terms (VIM) by the Joint Committee for Guides in Metrology, online in pdf form here. I found this linked in the "physical quantity" wiki article, and although that term is also close to what you're asking, it appears to include vectors. "Quantity" is defined on p. 18 of the pdf file as:
property of a phenomenon, body, or substance, where the property has a
magnitude that can be expressed as a number and a reference
Note 2 explains that by "reference" they mean a reference to a physical unit, measurement procedure, or "reference material" (not sure if that refers to a type of physical material or to 'reference material' in the literary sense of texts that people can refer to for more information):
NOTE 2 A reference can be a measurement unit, a measurement procedure,
a reference material, or a combination of such.
And on p. 19 they add the following (somewhat confusing) note to this definition, which seems to say that vectors can be included in this term:
NOTE 5 A quantity as defined here is a scalar. However, a vector or a
tensor, the components of which are quantities, is also considered to
be a quantity.
The term "quantity value" on p. 28 (with two synonyms listed below it, "value of a quantity" and "value") is defined more narrowly to be a magnitude rather than a vector, though (it can be the magnitude of a vector, but not the vector itself):
quantity value
value of a quantity
value
number and reference together expressing magnitude of a quantity
So combined with the earlier definition of quantity as something that "can be expressed as a number and a reference", this seems to fit the the bill. I think the synonyms "value of a quantity" and just "value" sound a bit more natural, I believe I've read physicists using them in the past, but I can't remember reading anyone talk about a "quantity value" before.
The following is multiple choice question (with options) to answer.
What term describes the amount of material present in an object? | [
"volume",
"mass",
"weight",
"density"
] | B | |
SciQ | SciQ-6628 | taxonomy, mammals, cladistics
Title: Why aren't mammals and reptiles considered amphibians? We've all heard it: birds descend from dinosaurs, so they're dinosaurs too. But this got me thinking: doesn't this mean that, for instance, all terrestrial vertebrates – including humans – are technically fish? A recent video by MinuteEarth and the Wikipedia article for "Fish" confirmed my shower thought hypothesis.
Interesting. But... all amniotes, i.e. reptiles (and, by extension, birds) and mammals, descend from amphibians, right? If so, then why aren't they considered amphibians too? Mammals and reptiles aren't considered amphibians, because amniotes are not hypothesized to descend from Amphibia. That is to say that Amphibia did not evolve into Amniota. They are sister clades (actually Reptiliomorpha in the Tree of Life tree below).
The following is multiple choice question (with options) to answer.
What class of animals includes the subgroups rodents, carnivores, insectivores, bats, and primates? | [
"amphibians",
"mammals",
"insects",
"reptiles"
] | B | Subgroups of the mammals include rodents, carnivores, insectivores, bats, and primates. |
SciQ | SciQ-6629 | thermodynamics, electricity, dissipation, thermoelectricity
Title: Can a Peltier/Seebeck cell transfer energy from a "thermally insulated" system converting (a part of) thermal energy into electrical energy? Suppose you have a closed system, as per the schema attached below, which walls are thermally insulated.
Suppose you want to reduce the temperature of the fluid inside the closed system, without dissipating 100% of the fluid thermal energy into the environment.
Can a Seebeck cell convert (a part of) the thermal energy of the fluid into electrical energy?
Is the Seebeck cell able to convert a part of the thermal energy into electrical energy (with a given efficiency), or the generation of electrical energy is only a cause of the temperature gradient and this thermal energy will eventually entirely return to the environment thorugh the cell (which, differently from the walls of the system, is clearly not insulated)?
Say, we have a stick of some fitting material. It has some temperature, so all electrons in the material bounce around wildly. Some randomly bounce leftwards; others randomly bounce rightwards. There is no net flow of electrons in any direction. There is no current.
Now, heat up one end. Those now hotter electrons will now bounce around even more wildly. This will make them "fill more space" (more wild random motion means much more pushing on the surrounding particles).
When the electrons "fill more" in one end, there is less "space" there. They start drifting towards the other and still more "spacious" end.
Drifting electrons is a current; electrical energy. This is the essence of the thermoelectric Seebeck effect.
The energy that caused them to move more wildly is directly the thermal energy absorbed at the hot end. They still carry this thermal energy, now in the form of a higher amount of kinetic energy at the micro-scale. So, yes, the Seebeck effect converts thermal energy into electric energy so that there is less thermal energy present - although we are talking about tiny, tiny amounts depending on your situation.
The following is multiple choice question (with options) to answer.
What is the transfer of thermal energy by waves that can travel through empty space called? | [
"convection",
"radiation",
"vibration",
"induction"
] | B | Radiation is the transfer of thermal energy by waves that can travel through empty space. When the waves reach objects, they transfer thermal energy to the objects. This is how the sun’s energy reaches and warms Earth. |
SciQ | SciQ-6630 | thermodynamics, visible-light, temperature, thermal-radiation, biology
Title: Why are people dark skinned in hotter areas despite dark colour absorbing the most heat? I’m not sure if the reason is in the field of biology or more towards physics but as my reasoning is based on the physics part being that perfectly black bodies are perfect absorbers of heat and light while white is a perfect reflector but we have darker skinned humans near equator and lighter skinned people (as well as animals like polar bears) near the poles, I’ve posted it on physics stackexchange. Also, if the answer is based on the biology of animals and this should belong to biology stack exchange, feel free to let me know. This is a bio question.
The biggest threat to fitness is not lack of cooling, but damage from UV rays. A pigment in black (actually all skin to differing degrees) absorbs the UV so that skin cells don't.
Fair skinned people, from higher latitudes, have another risk to their fitness which is a lack of vitamin D which is produced by the skin when exposed to UV.
As a result of this, fair skinned people in the tropics get more skin cancer than otherwise, and dark people are more likely to have a vitamin D deficiency if far from the tropics.
The following is multiple choice question (with options) to answer.
The lighter photic zone and darker aphotic zone are determined by what? | [
"water reflection",
"water shape",
"water depth",
"water density"
] | C | Two main zones based on depth of water are the photic zone and aphotic zone. The photic zone is the top 200 meters of water. The aphotic zone is water deeper than 200 meters. The deeper you go, the darker the water gets. That’s because sunlight cannot penetrate very far under water. Sunlight is needed for photosynthesis. So the depth of water determines whether photosynthesis is possible. There is enough sunlight for photosynthesis only in the photic zone. |
SciQ | SciQ-6631 | botany
Title: Do any plants exhibit hormonal changes similar to puberty? Just what the title states.
Are there any plants/trees that exhibit a growth spurt at a definite interval after the shoot appears? In flowering plants (the angiosperms) there are several developmental transitions in the life of the plant. I won't list the plants, because the list includes pretty much all of them (although the magnitude in the change of developmental pace differs widely between taxa and environments).
First there is seed germination, which is controlled hormonally. Absence of germination is usually imposed by abscisic acid, whilst germination is caused at the appropriate time by gibberellic acid and ethylene (among other things; Holdsworth, Bentsink & Soppe, 2008).
Next, in many herbaceous species there is a transition between a spreading growth stage (e.g. rosette growth) and the flowering stage. The 'growth spurt' here is the differentiation and elongation of the flowering stem, and then subsequently the sudden flowering of buds. The transition is also controlled hormonally, by a variety of hormones including auxin (Zhao, 2010), gibberellic acid, ethylene (Schaller, 2012), and the long anticipated, recently confirmed florigen (Choi, 2012). Ethylene and abscisic acid then play important roles in the next developmental transition when seeds and fruits are produced and dehisced.
Small RNAs are also now being revealed to play a large role in controlling the timing of developmental, but they are upstream of the hormonal changes. In particular some key miRNAs are involved in auxin-based regulation of branching, and in embryogenesis (Nodine & Bartel, 2010), and RNA silencing is involved in the switch from rosette growth to flowering growth (reviewed in Poethig, 2009 and Baurle & Dean 2006).
The following is multiple choice question (with options) to answer.
Plant cuttings are an example of what type of reproduction? | [
"heterosexual",
"autosexual",
"homosexual",
"asexual"
] | D | |
SciQ | SciQ-6632 | electromagnetic-radiation, radio
Title: How do radiowaves have constructive/destructive interference? When you have radios you often find interference happening. As far as I am personally aware radio waves are the only waves that I am sure can interfere. If all EM apply do put it in that perspective in your answer. The thing that I can't wrap my head around is the fact that although the photons have no size and are just points, how can they overlap to interfere with another. It's like two entities in a game with no hitboxes colliding with each other. EM waves travel in the EM field which is a theoretical field that fills all space. Like waves in a pond they can overlap or superimpose or interfere or convolute or add together etc etc. its all the same terminology. Particles smash into one another and waves just pass each other by, example : 2 waves adding in collision will make a bigger wave only temporarily but then the waves will continue on travelling in each their own direction.
The following is multiple choice question (with options) to answer.
Destructive interference in waves occurs when what things overlap? | [
"two troughs",
"three troughs",
"three waves",
"two waves"
] | A | Destructive interference in waves occurs when two troughs overlap. |
SciQ | SciQ-6633 | geophysics, plate-tectonics, earth-history, continent
Title: Why Do Supercontinents Form? It would seem, on the face of it, improbable that the continental land-masses would accumulate into a single composite, yet it has happened numerous times, and is expected to again in the future.
There must likely then be some aspect of plate tectonics which favors these arrangements.
Can anyone provide an explanation?
EDIT: This is not, as I see it, a duplicate of the 'What are the causes of the supercontinent cycle?' question. This question goes to what process drives the formation of any & all supercontinent formations, which I assert should be improbable, made more improbable by their recurrence, not so much the cycle itself. The other question did not address this more fundamental aspect, or in any case receive a pertinent account of its resolution. If anyone wants to engage on this, or doesn't see the distinction, please do so in the comments or a chat. I think the mechanisms that you're looking for are subduction, paired with the "stickiness" of continental crust.
The subduction of oceanic crust under continental crust inevitably creates a net movement of crustal material toward a continental plate. Any oceanic plate that is carrying continental material will therefore always drag that continent toward the continental plate that it is subducting underneath, always resulting in eventual collision.
If an oceanic plate has subduction occurring on both sides, the ocean will inevitably narrow until it closes, thereby causing the continental plates on either side to collide.
In every case, subduction inevitably pulls continents together.
Furthermore, once continental plates collide, they have a tendency to stick together for long periods of time, increasing the likelihood that all continental material will eventually accumulate there.
The following is multiple choice question (with options) to answer.
When two plates of continental crust collide, the material pushes upward and forms what? | [
"valleys",
"fault lines",
"low mountain range",
"high mountain range"
] | D | When two plates of continental crust collide, the material pushes upward. This forms a high mountain range. The remnants of subducted oceanic crust remain beneath the continental convergence zone. |
SciQ | SciQ-6634 | fusion
Title: Where does the energy produced by fusion come from? Fission, in layman's (or "initiate's") terms, is easy enough to understand; a large atom with a lot of protons and neutrons requires a large amount of force provided by the strong interaction to overcome electromagnetism and keep the nucleus together. The necessary energies were imparted to the atom during its formation, which we can replicate to some degree within a nuclear reactor; a combination of heat and fast-moving free protons/neutrons recaptured by the atoms of the fuel turns uranium into plutonium, even as the actual atom-splitting produces much lighter krypton and barium isotopes (or a host of other possibilities, some more likely than others, as with many other types of reactions). That atom-splitting, by the way, reduces the size of the resulting nuclei, and therefore reduces the amount of strong interaction force required to contain them; the leftover energy is released as a high-frequency gamma photon.
Fusion, however, is an odder beast. A fusion reaction requires a large amount of starting energy; enough to strip the electrons off of the deuterium/tritium nuclei and form plasma. That heat is also enough to accelerate the particles fast enough that when they collide, the initial electromagnetic repulsion is overcome and the strong interaction binds them together.
Now, that's a lot of energy required; the Sun's inner core where most of the fusion occurs is estimated to be about 15 million Kelvin. The reaction, however, doesn't seem to release any energy, based at least on this simplistic explanation. Now, obviously that's wrong; pretty much all the energy we have available to us right now is, however indirectly, a result of the Sun bathing us in the energy from nuclear fusion. The rest of it, such as from nuclear fission, is also star-based, via creation of superheavy elements in stellar nucleogenesis.
The following is multiple choice question (with options) to answer.
What is split to produce nuclear energy? | [
"molecules",
"atoms",
"chemicals",
"protons"
] | B | Nuclear energy is produced by splitting atoms. It also produces radioactive wastes that are very dangerous for many years. |
SciQ | SciQ-6635 | mass, measurements
Title: How precise can current technologies measure the mass of an object? Masses of various objects are listed on this wikipedia page: Orders of magnitude (mass). For example, mass of an HIV-1 virus is on the order of 1 femtogram.
Are these data actually measured (which I really doubt), or calculated?
What is the most precise measurement technique we have to measure the mass of an object? The most precise measurement of the mass of an electron was reported by Sturm et al in Nature 506, 467–470 (27 February 2014), quoting a relative precision of $3\times 10^{-11}$, meaning they determined the mass to better than $3\times 10^{-41}~\rm{kg}$.
If that is not the best, at least it gives you an upper bound...
Note that if you could weigh such a small mass directly with scales on earth, the force would be equivalent to the gravitational pull of a mosquito (mass 2.5 mg) on a grain of sand (0.7 mg) at a distance of about 6 million kilometers - about 17 times the distance to the moon...
Astonishing.
Acknowledgement: CuriousOne's comment got me thinking about the measurement of the mass of the electron, and led me to the above analysis.
The following is multiple choice question (with options) to answer.
What measures the amount of matter in an object? | [
"concentrations",
"weight",
"mass",
"amounts"
] | C | The inheritance of traits is not always as simple as Mendel's rules. Each characteristic Mendel investigated was controlled by one gene that had only two possible alleles, one of which was completely dominant over the other. We now know that inheritance is often more complicated than this. In blood types, for example, there are actually three alleles instead of two. And some traits even have more than three alleles. |
SciQ | SciQ-6636 | steel, metallurgy, material-science
Title: Effect of multiple alloying elements on steel's eutectoid properties Mechanical engineering student here (the professor is not being helpful). When a single alloying element is added to a normal iron-carbon steel, the resulting changes in eutectoid temperature and composition are relatively easy to determine using graphs such as the following:
How would you predict the changes if multiple alloying elements were added instead of just one? I understand that some elements tend to stabilize ferrite versus austenite (you can tell by the relative slopes of the upper graph), but this only provides a qualitative answer. Is there any way to calculate exactly what the changes would be? Thanks.
Image source: https://www.tf.uni-kiel.de/matwis/amat/iss/kap_9/illustr/s9_2_1.html The effect of multiple alloy elements is not as simple as single elements. The addition of one element changes how the material interacts with another and each element combination has a different effect. Additions of Mn, for example, will change how much Ni or C the matrix can solubilize, and that should change the behavior of your upper plot.
You could qualitatively approach this problem, for example, by using Carbon Equivalent, Chromium Equivalent or Nickel Equivalent Formulae to understand different phase diagrams, like the Schaeffler Diagram, shown below.
[
The method most used nowadays in alloy design and research is that of CALPHAD, or CALculation of PHAse Diagrams. Experimental data is modeled and chemical activity models calculate phase stability criteria, yielding exactly what your question tries to understand. Via a CALPHAD software (like Thermocalc), one could generate plots or tables to understand the effect of many different variables, including alloying elements.
The following is multiple choice question (with options) to answer.
What is the primary component of steel alloys? | [
"carbon",
"titanium",
"iron",
"alluminum"
] | C | Steels are a very important class of alloys. The many types of steels are primarily composed of iron, with various amounts of the elements carbon, chromium, manganese, nickel, molybdenum, and boron. Steels are widely used in building construction because of their strength, hardness, and resistance to corrosion. Most large modern structures like skyscrapers and stadiums are supported by a steel skeleton (see Figure below ). |
SciQ | SciQ-6637 | light, radio-astronomy, photons, electromagnetic-spectrum
Title: Does a photon need to have EXACTLY the right energy to be absorbed by a gas molecule? From an answer to this question, https://physics.stackexchange.com/questions/281660/how-does-an-electron-absorb-or-emit-light,
Absorption of a photon will occur only when the quantum energy of the photon precisely matches the energy gap between the initial and
final states of the system. (the atom or a molecule as a whole)
i.e., by the absorption of a photon, the system could access to some
higher permissible quantum mechanical energy state. If there is no
pair of energy states such that the photon energy can elevate the
system from the lower to the upper energy state, then the matter will
be transparent to that radiation.
The following is multiple choice question (with options) to answer.
Light energy is absorbed by which kind of molecule? | [
"parasite",
"chlorophyll",
"nutrient",
"inorganic"
] | B | Figure 5.12 Light energy is absorbed by a chlorophyll molecule and is passed along a pathway to other chlorophyll molecules. The energy culminates in a molecule of chlorophyll found in the reaction center. The energy “excites” one of its electrons enough to leave the molecule and be transferred to a nearby primary electron acceptor. A molecule of water splits to release an electron, which is needed to replace the one donated. Oxygen and hydrogen ions are also formed from the splitting of water. |
SciQ | SciQ-6638 | species-identification, marine-biology
Title: help identify this fish
I came across this washed up fish in Panama City, Florida in November 2015. I'm guessing it's a puffer fish but I can't find anything like it online.
Thanks. This is a kind of trunkfish. (They have different names, this could be a smooth or spotted trunkfish.). It's really a lovely and comical little fish when observed alive in coral reefs. It has the ability to change its coloration depending on whether it's excited or calm, or to minimize its contrast to the background. It is related to puffer fish.
It has a boxy, triangular body shape, and propels itself with relatively tiny, delicate fins. Like pufferfish, they are toxin producers.
In death, the body shape and coloration are different, of course. Never saw a dead one before; sad. The juveniles are adorable:
Members of this family occur in a variety of different colors, and are notable for the hexagonal or "honeycomb" patterns on their skin. - Wikipedia
The following is multiple choice question (with options) to answer.
What is the second class of fish after ray-finned fish? | [
"star-finned fish",
"pine - finned fish",
"spar - finned fish",
"lobe-finned fish"
] | D | There are about 27,000 species of bony fish ( Figure below ), which are divided into two classes: ray-finned fish and lobe-finned fish. Most bony fish are ray-finned. These thin fins consist of webs of skin over flexible spines. Lobe-finned fish, on the other hand, have fins that resemble stump-like appendages. |
SciQ | SciQ-6639 | 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.
Regulation of endocrine depends on the hypothalmus and what other gland? | [
"salivary",
"thyroid",
"adrenal",
"pituitary"
] | D | 45.3 The hypothalamus and pituitary are central to endocrine regulation. |
SciQ | SciQ-6640 | zoology, ethology, behaviour, psychology, death
Title: Do animals suffer from "Human" mental disorders? It is tragic, but apparently Killer whales and Dolphins can commit suicide too (e.g. here)...
This suggests they can become depressed. I wondered whether they were "clinically" depressed like many people are, and what other mental illnesses have been observed in animals in general.
Questions
Which mental disorders have been observed in animals? Which animals?
What is the prevalence of these mental disorders in those animals?
Are the causes and treatments of these disorders similar to Humans?
The following is multiple choice question (with options) to answer.
What according to scientists is the major cause of depression? | [
"high fat diets",
"high serotonin levels",
"low thyroid levels",
"low serotonin levels"
] | D | Some people have low levels of the neurotransmitter called serotonin in their brain. Scientists think that this is one cause of depression. Medications called antidepressants help bring serotonin levels back to normal. For many people with depression, antidepressants control the symptoms of their depression and help them lead happy, productive lives. |
SciQ | SciQ-6641 | materials, plastics
Title: Which material to use for athletic accessories? I'm looking for some guidance in selecting the right material for dance shoes heels and women's self-defense accessories.
I'm looking for a material that 1) has a superb strength-to-weight ratio, can withstand punishing and frequent impact, and very light (like plastic).
The part for the shoe will be very, very slender (stiletto heel), but will have to be able to endure hours of jumping, sliding, stomping, spinning, and skidding dancers… is compression strength the right term?
2) The material must also be safe to use as jewelry, so nothing toxic. Also, I am looking for something that tends to snap, rather than shatter, when it fails under pressure.
3) Lastly, it would be great if this material can be 3D printed, although that is not a must.
An inexpensive material would be ideal, of course, but I am open to learning about a fuller range of materials, including the more expensive ones. I am willing to consider a higher priced material if it will offer substantial value to the accessories in terms of strength, quality, and safety. For plastics, my first instinct for the first two properties would be a polycarbonate plastic. Polycarbonates are known to be very strong plastics (tensile strength up to ~70 MPa) and deform without breaking under many conditions, which is why they're commonly used in things like safety glasses and bullet-resistant glass. It also looks very interesting as it's quite optically clear. PC is 3D printable, I've seen a few people using it in hobby printers (http://www.protoparadigm.com/blog/2011/12/printing-polycarbonate/) and in very high end StrataSys printers, but it's not a super common material so it might take some experimenting.
Another option is a nylon. There are a number of different types available and many have similar properties to polycarbonates (minus the optical clarity). Nylons seem to be a bit more popular for 3D printing and I've heard good things about the Taulman filaments.
The following is multiple choice question (with options) to answer.
What is a soft, malleable, and corrosion resistant material called? | [
"gold",
"lead",
"tin",
"copper"
] | B | Lead is a soft, malleable, and corrosion resistant material. The ancient Romans used lead to make water pipes, some of which are still in use today. |
SciQ | SciQ-6642 | Momentum is a derived quantity, calculated by multiplying the mass, m (a scalar quantity), times velocity, v (a vector quantity). @J.Murray If we consider the mythical classical point mass, it has a 4-momentum determined by its mass and its world-line. To me, the most natural definition of momentum is via the Lagrangian formalism, which yields the one-form $p_\mu = \frac{\partial L}{\partial \dot x^\mu}$. Momentum is a vector: it has size AND direction. Calculate its acceleration. Since force is also the time derivative of momentum, it seems reasonable to consider momentum to be a 1-form. It is made of mass (scalar) multiplied by velocity (vector). A car accelerates in 12s from 10m/s to 50m/s. Momenta met in traditional problems often feel just like numbers on a number-line, because only one dimension is considered in order to simplify the problem. A covector maps vector to a scalar. (velocity).-- Velocity is a vector. Momentum being the product of a scalar quantity and a vector quantity, it is also a vector quantity. Momentum is naturally dual to velocity since it usually makes sense to perform the matrix multiplication between momentum (as row vector) and velocity (as column vector) and gets a scalar with units of energy. But I don't have an ontological argument to consider that to be an inherent property of momentum. Asking for help, clarification, or responding to other answers. I could ask the same thing about the electromagnetic field tensor, but momentum seems to be a good place to start. Example During this elastic collision the momentum of small … Either that, or we have … This video describes momentum in terms of its vector properties. Mass is an example of a scalar quantity (mass doesn't point in any direction!) By using our site, you acknowledge that you have read and understand our Cookie Policy, Privacy Policy, and our Terms of Service. Momentum is a vector quantity. Is a password-protected stolen laptop safe? Generator of translations in classical mechanics. The above problem is a one dimensional problem, so the object is moving along a straight line. Angular momentum is a vector quantity (more precisely, a pseudovector) that represents the product of a body's rotational inertia and rotational
The following is multiple choice question (with options) to answer.
Momentum is a vector quantity that has the same direction as what? | [
"object ' s velocity",
"object energy",
"initial speed",
"inertia"
] | A | Momentum is a vector quantity that has the same direction as the velocity of the object. |
SciQ | SciQ-6643 | 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.
What type of role does cartilage play in the human skeleton? | [
"important",
"insignificant",
"life saving",
"variable"
] | B |
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