source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-6244 | human-biology, evolution, immunology
Title: In which order did the cells of the immune system evolve? Thinking about how complex the interactions between different types of immune system cells (T-helpers, T-Killers, Phagocytes, B-Cells etc.) are, it's fascinating how they all combine to get the desired effect.
However, I assume that they didn't all evolve simultaneously! Is there any way to tell which immune cell developed first or any theories to that effect? Perhaps that question is too specific, in which case was it humoral or cell mediated immunity that developed first?
You may find this paper helpful - unfortunately I'm still months off a campus so can't access it. As I'm lucky enough to have access to that article, I'm going to extract whatever I can find to answer your question.
To begin with, innate immunity must have evolved first - we can see it at almost all stages of evolution. According to Cooper & Herrin, ever since aerobic respiration gave rise to multicellular organisms which in turn needed protection from invasion by single-cell organisms.
They state that around 500 million years ago, the first adaptive immune systems evolved in vertebrates, but do not explain how although they attempt to. Instead, they explain why we are not able to discern at the moment how this evolution came about. The main reason given is that it is unknown when some key cells evolved (namely natural killer cells and dendritic cells) Additionally, mice and humans evolved two different kinds of natural killer cell receptors relatively recently while sharing a common ancestor only quite a long time ago.
Apparently jawed and jawless vertebrates have also evolved two different kinds of adaptive immune systems. They both seem to rely on the same mechanisms but on a different molecular and genetic basis. Cooper & Herrin conclude that at the current level of research, we are not able to determine the evolution of our immune system.
Source: How did our complex immune system evolve?
The following is multiple choice question (with options) to answer.
The earliest cells were called what? | [
"carbohydrates",
"eukaryotes",
"microcytes",
"prokaryotes"
] | D | The first organisms were made of only one cell ( Figure below ). The earliest cells were prokaryotes . Prokaryotic cells are surrounded by a cell membrane, but they do not have a nucleus. The cells got their nutrients directly from the water. The cells needed to use these nutrients to live and grow. |
SciQ | SciQ-6245 | 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.
Protists are the simplest of what? | [
"eukaryotes",
"prokaryotes",
"plants",
"fungi"
] | A | Protists are the simplest eukaryotes. They are easiest to define by what they are not. Protists are not animals, plants, or fungi. |
SciQ | SciQ-6246 | quantum-mechanics, measurements, electrons, measurement-problem
Title: Measuring the magnitude of the magnetic field of a single electron due to its spin Is it possible to measure the magnitude of the magnetic field of a single electron due to its spin? The electron's intrinsic magnetic field is not dependent upon the amount of energy it has does it? Does this require a SQUID, a Superconducting Quantum Interference Device? What published papers or experiments have been done to answer this question? The following publication measures single electrons:
Researchers at the Delft University of Technology's Kavli Institute of Nanoscience and the Foundation for Fundamental Research on Matter (FOM) have succeeded in controlling the spin of a single electron merely by using electric fields. This clears the way for a much simpler realization of the building blocks of a (future) super-fast quantum computer.
I suppose they have taken as given the value of the electron magnetic field, but the apparatus could be used to measure it, I am sure.
The following is multiple choice question (with options) to answer.
The measure of magnetic fields is named after a serbian physicist. what is his name? | [
"nikola tesla",
"Albert Einstein",
"Carl Sagan",
"Niels Bohr"
] | A | For static electric charges, the electromagnetic force is manifested by the Coulomb electric force alone. If charges are moving, an additional force emerges, called magnetism. The century realization that electricity and magnetism are dual aspects of the same force completely changed our understanding of the world we live in. Insights due to Ampere, Gauss, and Maxwell led to the understanding that moving charges – electric currents – create magnetic fields. Varying magnetic fields create electric fields. Thus a loop of wire in a changing magnetic field will have current induced in it. This is called electromagnetic induction. Magnetic fields are usually denoted by the letter and are measured in Teslas, in honor of the Serbian physicist Nikola Tesla. |
SciQ | SciQ-6247 | physical-chemistry, geochemistry
it is present in all rocks and soil
if a rock is broken or if soil is disturbed, radon will be released
it is gaseous and air currents / thermal gradients will carry it up to the earth's surface producing a detectable plume
it is radioactive, this makes detecting small amounts or small changes in radon concentration relatively routine due to well-developed and very sensitive methods for detecting and accurately measuring radioactivity.
radon has a very short radioactive half-life, a bit under 4 days. Being a gas and having a short half-life is very useful in terms of measuring radon emissions. If a radon emission spike occurs, the gas will dissipate quickly and after about 10 half-lives (40 days) normal background levels of radioactivity will return.
The following is multiple choice question (with options) to answer.
Radon (rn) is a radioactive gas formed by the decay of naturally occurring uranium in rocks such as granite. it tends to collect in the basements of houses and poses a significant health risk if present in indoor air. many states now require that houses be tested for radon before they are what? | [
"sold",
"modified",
"seen",
"built"
] | A | M = dRTP Exercise Radon (Rn) is a radioactive gas formed by the decay of naturally occurring uranium in rocks such as granite. It tends to collect in the basements of houses and poses a significant health risk if present in indoor air. Many states now require that houses be tested for radon before they are sold. Calculate the density of radon at 1.00 atm pressure and 20°C and compare it with the density of nitrogen gas, which constitutes 80% of the atmosphere, under the same conditions to see why radon is found in basements rather than in attics. Answer: radon, 9.23 g/L; N2, 1.17 g/L A common use of Equation 10.23 is to determine the molar mass of an unknown gas by measuring its density at a known temperature and pressure. This method is particularly useful in identifying a gas that has been produced in a reaction, and it is not difficult to carry out. A flask or glass bulb of known volume is carefully dried, evacuated, sealed, and weighed empty. It is then filled with a sample of a gas at a known temperature and pressure and reweighed. The difference in mass between the two readings is the mass of the gas. The volume of the flask is usually determined by weighing the flask when empty and when filled with a liquid of known density such as water. The use of density measurements to calculate molar masses is illustrated in Example 10. |
SciQ | SciQ-6248 | physical-chemistry, thermodynamics, gas-laws, equation-of-state
I am confused by this argument-- what exactly is the definition of 'volume' here? They seem to be saying that it is the empty space around the gas molecules, but it seems to me that volume should be defined as the space 'taken up' by the gas. Why should the space taken up by the particles themselves be subtracted? This isn't done for solids or liquids as far as I know.
These thoughts have also made me realize that I'm not quite sure what it means for a gas to 'take up' space. Does anyone have a rigorous definition of gas volume?
EDIT: The exchange with Chris in comments has raised further questions. It now seems to me that the $V-nb$ correction actually accounts for repulsions rather than attractions. I think I was incorrect in thinking that the $V-nb$ correction dominated at intermediate volumes and $a(n/V)^2$ at low volumes. If $V-nb$ is for repulsions, then it should dominate at low volumes, but I can't tell from the equation which correction will actually be dominant. Also I am now wondering whether it even makes sense to connect one correction with repulsions and one with attractions.
EDIT: Follow-up questions for F'x:
- I thought that 'density' meant mass/volume. Is the use of it to represent the inverse of molar volume (as you have used it) common?
- Where is the phase-transition in the red van der Waals curve?
- I am still a little unclear on gas volume. Are the 'volume available to the gas' and 'volume of the gas' the same? You say it's the same as the shape of the container, but aren't we subtracting the volume of the actual gas particles from that? The $V$ term represents the volume of the gas, correct? And $V-nb$ represents the 'volume available to the gas'. The van der Waals equation can't be derived from first principles. It is an ad-hoc formula. There is a "derivation" in statistical mechanics from a partition function that is engineered to give the right answer. It also cannot be derived from first principles.
The following is multiple choice question (with options) to answer.
What state of matter takes neither the shape nor the volume of its container? | [
"hot",
"liquid",
"solid",
"gas"
] | C | All three containers contain a substance with the same mass, but the substances are in different states. In the left-hand container, the substance is a gas, which has spread to fill its container. It takes both the shape and volume of the container. In the middle container, the substance is a liquid, which has spread to take the shape of its container but not the volume. In the right-hand container, the substance is a solid, which takes neither the shape nor the volume of its container. |
SciQ | SciQ-6249 | newtonian-mechanics, forces, work, time
Title: Calculate work from Force and time Everywhere it states, that time does not matter when calculating work, but can't you do this:
$$F=ma$$
so $a=F/m$
taking the second integral (dt): $$s=\frac{1}{2}\frac{F}{m}t^2$$ since Force is constant.
now plugging that into $W=Fs$:
$$W=\frac{1}{2}\frac{F^2}{m}t^2$$
Now you can put the m, F and t into the equation and get W.
Did I do a mistake or is it possible to do this? Your answer is correct - assuming no other force act.
The general statement:
$$W=F\cdot s$$
holds for the work done by the force $F$ but also permits other forces to be present.
The above formula is indeed independent of $t$, however if $F$ is the only force then greater $t$ means greater $s$ so greater $W$.
A better statement would be that:
time does not matter when calculating work provided that the distance covered remains the same.
In your calculation the distance covered changes.
The following is multiple choice question (with options) to answer.
Force times distance is the equation for what? | [
"work",
"gravity",
"power",
"speed"
] | A | Work is directly related to both the force applied to an object and the distance the object moves. It can be represented by the equation: Work = Force × Distance. |
SciQ | SciQ-6250 | molecular-biology, molecular-genetics, development, sex
Quote from a Review (Yao 2005):
We have just begun to glimpse into the mechanisms underlying ovarian development. Convincing evidence challenges us to reconsider the existing paradigm that describes ovarian development as a default system. The default concept was first proposed in the early 1950s when Jost performed the groundbreaking experiments to demonstrate mechanisms of sex differentiation of reproductive tracts (Jost, 1947, 1953, 1970). The term “default” was not originally intended to describe the developmental status of the ovary. Instead, it is referred to the female reproductive tract or the Mullerian duct based on the fact that the female reproductive tract forms in both XX and XY individuals in the absence of gonads. Indeed, now it has become evident that early ovarian development is an active process involving intrinsic cell fate decisions and complex crosstalks between germ cells and somatic cells. Most intriguingly, the appearance of testicular structures in XX individuals where Sry and its downstream components are absent further raises the improbable question: Could the testicular development be default after all?
The following is multiple choice question (with options) to answer.
What is the name for a series of changes in the reproductive system of mature females that repeats every month on average? | [
"puberty",
"menstrual cycle",
"urinary cycle",
"periodic table"
] | B | Egg production in the ovary is part of the menstrual cycle. The menstrual cycle is a series of changes in the reproductive system of mature females that repeats every month on average. These changes include the development of an egg and follicle in the ovary. |
SciQ | SciQ-6251 | human-biology, biochemistry, hematology, red-blood-cell, human-physiology
Title: Besides hemoglobin, what proteins are present in red blood cells? I knew that mature red blood cells (RBCs) lacked nuclei, but I wasn't aware until just now that they also lacked ribosomes and mitochondria. Most cells in the human body all contain a common laundry list of housekeeping proteins and RNAs (including mitochondrial proteins and ribosomal RNAs), but I guess RBCs lack a number of them. Do they still have all of the other organelles? Obviously hemoglobin (and to a lesser extent carbonic anhydrase) makes up a large portion of the dry weight of RBCs, but are other proteins still present? If so, what are their relative abundances?
For example, do red blood cells have any of the normal metabolic (i.e. ATP producing) proteins? Obviously they don't have any of the TCA cycle proteins, but do they still have the glycolysis ones? Reticulocyte stage is when the ribosomes are still present and after that no new protein synthesis occurs. However RBCs have a lot of proteins and major proteins other than haemoglobin are cytoskeletal proteins and ion channels/pumps (In fact, cytoskeletal proteins are more abundant than haemoglobin). It is the Na+-K+-ATPase that consumes most ATP. As you correctly identified the RBCs produce ATP via glycolysis and glycolytic enzymes are also present. Note that deficiency of pyruvate kinase leads to haemolytic anaemia.
For a detail on the proteins present in human RBSs, see this paper. They have studied the RBC proteome by ion-trap MS. The top 5 proteins (from Table-1) are:
No. Protein description Molecular mass (Da) Gi Number Sequence No. of identified
coverage(%) peptides
1 Spectrin α chain, erythrocyte 279,916.5 1174412 48.0 77*
2 Spectrin β chain, erythrocyte 246,468.1 17476989 48.0 76*
3 Ankyrin 1, splice form 2 206,067.9 105337 45.0 55
The following is multiple choice question (with options) to answer.
What is the name of the iron-containing oxygen-transport protein in the red blood cells of all vertebrates? | [
"platelet",
"hemoglobin",
"ferric acid",
"plasma"
] | B | Hemoglobin is the iron-containing oxygen-transport protein in the red blood cells of all vertebrates. The hemoglobin molecule is an assembly of four globular protein subunits, each tightly associated with a non-protein heme group. The heme group binds to the iron ion. The most common hemoglobin is hemoglobin A, a tetramer consisting of two alpha and two beta subunits, denoted as α2β2. |
SciQ | SciQ-6252 | aqueous-solution
Can anyone poke holes in our thinking? Or refine it? Or suggest ways to make it easier for the lay-person locked-in without access to other surface sanitizers?
Thank you in advance! Yes, do use household dilute H2O2 but, in general, do not use commercial percarbonates powders as they can contain an additive to convert the friendly percarbonate into more powerful Peracetic acid (PAA). The latter allows the otherwise weak bleaching power of the H2O2 to compete with chlorine-based bleaching. However, this comes at a price (safety). Hence, the dire warning labels, usually in at least two languages, on Oxi-Bleach and generic related products.
I quote myself on this subject:
The following is multiple choice question (with options) to answer.
What is the active ingredient in household bleach? | [
"iodine",
"oxygen",
"magnesium",
"chlorine"
] | D | Chlorine is the active ingredient in household bleach. It removes stains from clothes. It can also be used to disinfect countertops and other surfaces. |
SciQ | SciQ-6253 | bacteriology
Saier, MH. & Bogdanov, V. (2013) Membranous Organelles in Bacteria. JOURNAL OF MOLECULAR MICROBIOLOGY AND BIOTECHNOLOGY 23: 5-12 DOI: 10.1159/000346496
Free full text here.
The language used in this review seems to support the existence of mesosomes as some sort of intermediate in the formation of intracellular membranes in prokaryotes. This review is a polemic in favour of the idea that prokaryotes do indeed contain intracellular membrane-bounded compartments. It has no abstract, but the first paragraph gives a flavour of its stance:
The traditional view of life on Earth divides the living world into two major groups, prokaryotes and eukaryotes. These two groups were originally suggested to differ in very basic respects. While eukaryotes had complex cell structures including a cytoskeleton and intracellular membrane-bounded organelles, prokaryotes were believed to lack them. In fact, numerous textbooks and current sources still note this distinction and hold it to be true. For example, in Campbell’s Biology [Campbell, 1993, p. 515] it is stated without equivocation: ‘Prokaryotic cells lack membrane-enclosed organelles.’ In ‘Functional Anatomy of Prokaryotic and Eukaryotic Cells’ [Tortora et al., 2009, chapt. 4] it is similarly claimed that ‘Prokaryotes lack membrane-enclosed organelles, specialized structures that carry on various activities’. In the current Wikipedia, under ‘Prokaryote’ the following statement can be found: ‘The prokaryotes are a group of organisms whose cells lack a cell nucleus (karyon) or any other membrane-bounded organelles’. In the same online compendium under ‘Organelle’, one can read: ‘whilst prokaryotes do not possess organelles per se, some do contain protein-based microcompartments’. Proteinceous microcompartments will be the subject of a forthcoming Journal of Molecular Microbiology and Biotechnology written symposium, but this one will show that these generalizations, suggesting a lack of subcellular compartmentalization in prokaryotes, are blatantly in error [Murat et al., 2010a].
The following is multiple choice question (with options) to answer.
What are the membrane-bound organelles that are usually larger than vesicles and can have secretory, excretory, and storage functions? | [
"nucleolus",
"ribosomes",
"vacuoles",
"tubules"
] | C | Vacuoles are membrane-bound organelles that can have secretory, excretory, and storage functions. They are usually larger than vesicles. |
SciQ | SciQ-6254 | ichthyology, homeostasis, osmoregulation
Pillans, R.D. and C.E. Franklin, 2004. Plasma osmolyte concentrations and rectal gland mass of bull sharks Carcharhinus leucas, captured along a salinity gradient. Comparative Biochemistry and Physiology, Part A 138: 363-371.
The following is multiple choice question (with options) to answer.
What broad category of animals is primarily ectothermic and covered with scales that facilitate swimming? | [
"turtles",
"armadillo",
"fish",
"deer"
] | C | Fish show great diversity in body size. They range in length from about 8 millimeters (0.3 inches) to 16 meters (about 53 feet). Most are ectothermic and covered with scales. Scales protect fish from predators and parasites and reduce friction with the water. Multiple, overlapping scales provide a flexible covering that allows fish to move easily while swimming. |
SciQ | SciQ-6255 | biochemistry, dna, rna
Title: Can a dNTP be built into a RNA strand? DNA consists of deoxyribonucleotides, RNA consists of ribonucleotides. They differ mainly (apart from the uracil / thymine difference) in the sugar part, the deoxyribose and the ribose. Those two molecules differ in the hydroxy group in the ribose which is only a single proton in the deoxyribose. This part of the sugar molecule is not directly involved in binding reactions, nevertheless it causes the whole difference in RNA and DNA.
I wonder: could a dNTP be used in an RNA strand (or vice versa)? Is it chemically possible that we have a RNA molecule that contains a dNTP next to its NTPs? This is rather easy to do if you synthesize oligonucleotides chemically and not enzymatically. This is typically done using phosphoramidite chemistry, and it allows for the synthesis of chimeric RNA/DNA oligos. You can even incorporate modified nucleosides like 2'-O-Me or LNA.
This is typically done if you want to change the properties of an oligo, e.g. if you want to make it resistant to degradation by enzymes.
The following is multiple choice question (with options) to answer.
What has two chains of nucleotides, one more than rna? | [
"dna",
"mna",
"gna",
"fna"
] | A | RNA consists of just one chain of nucleotides. DNA consists of two chains. Nitrogen bases on the two chains of DNA form hydrogen bonds with each other. Hydrogen bonds are relatively weak bonds that form between a positively charged hydrogen atom in one molecule and a negatively charged atom in another molecule. Hydrogen bonds form only between adenine and thymine, and between guanine and cytosine. These bonds hold the two chains together and give DNA is characteristic double helix, or spiral, shape. |
SciQ | SciQ-6256 | neuroscience, neurophysiology, biophysics, muscles, electrophysiology
Title: What is the point in the Neuromuscular Junction? Surely a direct connection (i.e. an electrical synapse) between motor neurone and the sarcolemma would allow for much faster neuromuscular transmission? It is my understanding that chemical synapses are only useful in facilitating spatial summation of action potentials from multiple presynaptic terminals... muscles have no need for this as they are innervated by a single motor neurone only? After much searching on the internet I've found an answer to this question: the neuromuscular junction facilitates amplification of the motor neurone potential to generate a large enough current to depolarise a muscle fibre as muscle fibres have a much larger area of membrane (ie a larger capacitance) than neurons.
Source: Encyclopedia of Neuroscience: Volume One
The reason is the tremendous amplification of the neuromuscular junction. The amplification occurs since a small current is generated in a nerve can rekease large amounts of molecules of the transmitter acetyl-choline ($\require{mhchem} \ce{ACh}$), each of which can open channels in the much larger muscle membrane and can create much larger currents. In addition, a motor nerve fiber often branches profusely to innervate hundreds of muscle fibers, thus providing further amplification.
Finally, the capacitance of the muscular membrane has long been known to be much greater than the capacitance of the nerve membrane, because of the additional membranous systems, such as the transverse tubules in muscular fibers. Thus the capacity of the muscle to store charge is much greater than that of a nerve membrane and much more current must be supplied to depolarize muscle cells directly.
The following is multiple choice question (with options) to answer.
The axon terminates on muscle fibers at the neuromuscular junction. acetylcholine is released at this specialized synapse, which causes the muscle action potential to begin, following a large potential known as an end plate potential. when the lower motor neuron excites the muscle fiber, it contracts. all of this occurs in a fraction of a second, but this story is the basis of how this functions? | [
"respiratory system",
"cardiovascular system",
"muscular system",
"nervous system"
] | D | described in the chapter on muscle tissue, an action potential travels along the motor neuron axon into the periphery. The axon terminates on muscle fibers at the neuromuscular junction. Acetylcholine is released at this specialized synapse, which causes the muscle action potential to begin, following a large potential known as an end plate potential. When the lower motor neuron excites the muscle fiber, it contracts. All of this occurs in a fraction of a second, but this story is the basis of how the nervous system functions. |
SciQ | SciQ-6257 | evolution
Title: Is there any biological evidence that is not suggestive of or seems to disprove evolution? Often, in science, when we have evidence that doesn't fit our paradigm, we bend it until the paradigm collapses.
Although there is plenty of decent evidence for evolution, is there anything that does not fit the evolutionary paradigm? Is there any biological evidence that is not suggestive of or seems to disprove evolution? Or is everything merely hunky-dorey? Evolution is a broad field of knowledge. There are definitely a few elements of our current theory of evolution that does not perfectly match observations. However, those concern small details and might not of much interest to you. Here are a few examples
We don't know the relative importance of background selection and selective sweep at explaining genome-wide variation in genetic diversity.
We don't really have much of an idea what fraction of speciation happen in sympatry.
We don't understand well how recombination rate evolves to differ in different genders.
We don't really understand what are the limits and/or costs of phenotypic plasticity that makes phenotypic plasticity less frequent that we would otherwise expect.
We don't really understand the patterns of genetic diversity on sexual chromosomes at the intersection with the pseudo-autosomal region (PAR).
We don't fully understand how much expansion load (a type of mutation load caused by the sampling of individuals at the expansion edge of a population) there is in human population.
We don't really know whether the mitochondrion (and other double membranes organelles) was first a endo-parasite or a endo-symbiont.
If you are asking whether there are evidences suggesting that evolution is not happening or that humans and chimpanzee do not actually share a common ancestor but were created independently, then no, there is no such evidence.
You should have a look at the related post Is Evolution a fact?
The following is multiple choice question (with options) to answer.
Misconceptions about what theory contribute to the controversy that still surrounds this fundamental principle of biology? | [
"darwin on evolution",
"cycle of evolution",
"theory of evolution",
"brain of evolution"
] | C | Today, evolution is still questioned by some people. Often, people who disagree with the theory of evolution do not really understand it. For example, some people think that the theory of evolution explains how life on Earth first began. In fact, the theory explains only how life changed after it first appeared. Some people think the theory of evolution means that humans evolved from modern apes. In fact, the theory suggests humans and modern apes have a common ancestor that lived several million years ago. These and other misconceptions about evolution contribute to the controversy that still surrounds this fundamental principle of biology. |
SciQ | SciQ-6258 | circuits, battery
Title: Looking for a device that breaks the circuit if the voltage gets too low I'm looking for a device that breaks a circuit once the voltage of my battery gets too low. This to protect the battery.
Example: I have a 12V battery, once it reaches ~11V the huge voltage drop begins, but the device that is connected to the battery still runs and draws current. I need another device that can detect the voltage goes below 11V and then automatically breaks the circuit, preventing the circuit to draw more current from the battery. Basically, it shuts down the whole circuit.
Since English is not my native language and I'm not aware of any kinds of systems in my own language, I'm having a hard time finding something like this. Thanks in advance.
EDIT: or can I make my own? The simple answer is that you can get off the shelf modules which does exactly what you want.
They are often called 'split charge modules' and are designed for installations like boats and motor-homes which have batteries charged off an engine alternator but prevent the starter battery form being fully discharged.
This is one example http://www.12voltplanet.co.uk/voltage-sensitive-relay-12v-140a.html
They are not expensive and are easy to fit with basic knowledge of electronic systems.
There are also more sophisticated systems which allow for conditioning and management of auxiliary batteries
I have used this brand before :
I can't remember the exact specification but they would certainly be in the 1A sort of range for a 12V system. I suggest this one in particular as it is easy to disassemble so you could discard the case and screw terminals to make it a lot more compact to package with the rest of your circuit.
The following is multiple choice question (with options) to answer.
What device is used to stop a current in a circuit? | [
"a switch",
"a signal",
"a mirror",
"a valve"
] | A | Understand current as it passes through a series circuit. |
SciQ | SciQ-6259 | organic-chemistry, everyday-chemistry, aqueous-solution
(source: ekshiksha.org.in)
Because the non-polar parts of the surfactants come together, the center of the micelle is also non-polar and can hold small droplets and pieces of other non-polar substances like the sebum that builds up on your hair naturally over time.
Almost all shampoos use a nearly identical set of surfactants. Common examples are sulfates (ammonium lauryl sulfate, Sodium laureth sulfate, sodium pareth sulfate, sodium lauryl sulfate) and/or polysorbates (PEG20 and PEG80).
There are also additives that thicken it up, keep it from going bad and make that rich wonderful lather that we've all come to know and love.
What you are paying for aside from the above is mainly botanical or synthetic additives meant to soothe or beautify. The best way is to look up these ingredients on a case by case basis and decide if they would benefit you. I would say "be wary"; a large number of ingredients provide virtually zero added benefit for your money. Some work extremely well for certain people; you never know until you try.
Always read your labels! If you don't know what something is, google it!
The following is multiple choice question (with options) to answer.
What oily substance prevents the hair and skin of living things from drying out? | [
"pancreatic enzymes",
"sebum",
"progesterone",
"pus"
] | B | Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out. |
SciQ | SciQ-6260 | ornithology
Title: How do birds learn their tunes in isolation from their own species? I wonder what a bird would sing if it didn't have its parents around (or any other birds for that matter) to learn its chirping sounds from.
I'm interested in how a bird would sing...
in complete isolation from creatures communicating through sound;
in isolation from its own species, but with other birds;
in isolation from all birds (other animals and creatures are there for it)
For example,
Would a bird even feel the need to speak up if there wasn't any other vocalizing creature around?
Would a bird learn other species' signals? Would it only learn from one species, the one which it would think of a fitting mate?
Would a bird try to mimic a non-flying creature's signals?
These are similar questions, but if you think they should be separated, let me know in the comments. Birds have to learn their song patterns.
They are able to chirp, but the songs with "meaning" are learned from their parents or whatever they learned to be their "parent".
Here is a paper that related bird song learning to human learning (of speech, for example).
Birds brought up by parents from another species learned to sing their songs.
There are many birds that learn to imitate other animals or sounds, so in isolation from all birds they will probably do this.
I can't recall where, but I read a paper once, where little finches brought up by humans developed a song resembling the "Hello there, now there's food", their caretaker always greeted them with. (Not the speech, but the overall sound pattern.) They might not understand the signals, but they try to communicate nevertheless. Some birds use sound from other species to mock others, scare them off or lure them into thinking they might be more powerful than they are.
Birds brought up in total isolation do sing, but not the typical songs you know from their species. Deaf birds who can't hear themselves, though, do not (always) sing.
The following is multiple choice question (with options) to answer.
What two types of communication do both humans and birds use primarily? | [
"visual and auditory",
"material and auditory",
"interaction and auditory",
"sensual and auditory"
] | A | |
SciQ | SciQ-6261 | genetics, cell-biology, embryology, meiosis, gamete
Title: Fertilization of the human egg- where does our centrosome come from? Is there a centrosome in a human egg cell? Is the reason why the egg cell remains paused before meiosis 2 because there isn't a centrosome, and it only divides when the sperm fertilizes it thus it can have a centrosome? If this is so, then how did oogenesis happen? ? To answer the first part of your question. The sperm actually introduces two centrosomes. The centrosome then nucleates the new microtubule assembly to form the sperm aster — a step essential for successful fertilization. You can visit these sites Simerly, et al as well as Paweltz, et al
The following is multiple choice question (with options) to answer.
Eggs are produced in what organs and, upon fertilization, develop in what other organ? | [
"ovaries, uterus",
"fallopian tubes, ovaries",
"uterus, vagina",
"cervix, ovaries"
] | A | |
SciQ | SciQ-6262 | quantum-mechanics, molecules
Title: Explanation of rotational barrier in molecular physics I remember that in my molecular physics lecture, I learned that rotating molecules have to pass a rotational barrier before they can dissociate, in contrast to only vibrating ones.
Could someone give an intuitive argument as to why this barrier exists for rotations? Thanks! Consider a diatomic, non-rotating molecule. In this case the potential energy $U(R)$ depends on the distance $R$ between the two atoms; this could be described for example by a Morse potential. For distances $R$ that are larger than the equilibrium bond length this potential is typically attractive.
If the molecule is rotating then the effect of the rotation can be absorbed into an effective potential
$$
U_{\mathrm{eff}} (R) = U(R) + L^2 / (2 \mu R^2)
$$
where $L$ is the angular momentum and $\mu$ is the reduced mass. This new term is purely repulsive (unless the angular momentum is zero, i.e., this molecule is not rotating). Intuitively, this term gives rise to the centrifugal force that stretches the bond. The competition between the attractive $U(R)$ and the repulsive centrifugal potential can give rise in a barrier in $U_{\mathrm{eff}} (R)$.
Here is a link where you can read more about this effect.
The following is multiple choice question (with options) to answer.
The first line of defense includes mechanical, chemical, and which other barrier? | [
"independent",
"surgical",
"physical",
"biological"
] | D | The first line of defense includes mechanical, chemical, and biological barriers. |
SciQ | SciQ-6263 | optics, visible-light, everyday-life, diffraction
Addendum 2: Before the comments below were cleaned out, there was some discussion there about the usefulness of this phenomenon as a quick self-diagnostic test for myopia (nearsightedness).
While I Am Not An Opthalmologist, it does appear that, if you experience this effect with your naked eye, while trying to keep the background in focus, then you may have some degree of myopia or some other visual defect, and may want to get an eye exam.
(Of course, even if you don't, getting one every few years or so isn't a bad idea, anyway. Mild myopia, up to the point where it becomes severe enough to substantially interfere with your daily life, can be surprisingly hard to self-diagnose otherwise, since it typically appears slowly and, with nothing to compare your vision to, you just get used to distant objects looking a bit blurry. After all, to some extent that's true for everyone; only the distance varies.)
In fact, with my mild (about −1 dpt) myopia, I can personally confirm that, without my glasses, I can easily see both the bending effect and the sharpening of background features when I move my finger in front of my eye. I can even see a hint of astigmatism (which I know I have; my glasses have some cylindrical correction to fix it) in the fact that, in some orientations, I can see the background features bending not just away from my finger, but also slightly sideways. With my glasses on, these effects almost but not quite disappear, suggesting that my current prescription may be just a little bit off.
The following is multiple choice question (with options) to answer.
What is another term for nearsightedness? | [
"astigmatism",
"hypoxia",
"myopia",
"anemia"
] | C | Nearsightedness, or myopia, is the condition in which nearby objects are seen clearly, but distant objects appear blurry. The Figure below shows how it occurs. The eyeball is longer (from front to back) than normal. This causes images to be focused in front of the retina instead of on the retina. Myopia can be corrected with concave lenses. The lenses focus images farther back in the eye, so they fall on the retina instead of in front of it. |
SciQ | SciQ-6264 | 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.
Because all animals require an external source of what, they are called heterotrophic? | [
"water",
"energy",
"fuel",
"food"
] | D | 27.1 | Features of the Animal Kingdom By the end of this section, you will be able to: • List the features that distinguish the kingdom Animalia from other kingdoms • Explain the processes of animal reproduction and embryonic development • Describe the roles that Hox genes play in development Even though members of the animal kingdom are incredibly diverse, most animals share certain features that distinguish them from organisms in other kingdoms. All animals are eukaryotic, multicellular organisms, and almost all animals have a complex tissue structure with differentiated and specialized tissues. Most animals are motile, at least during certain life stages. All animals require a source of food and are therefore heterotrophic, ingesting other living or dead organisms; this feature distinguishes them from autotrophic organisms, such as most plants, which synthesize their own nutrients through photosynthesis. As heterotrophs, animals may be carnivores, herbivores, omnivores, or parasites (Figure 27.2ab). Most animals reproduce sexually, and the offspring pass through a series of developmental stages that establish a determined and fixed body plan. The body plan refers to the morphology of an animal, determined by developmental cues. |
SciQ | SciQ-6265 | acid-base, reaction-mechanism
Title: Litmus paper - turning red, blue and even bleached I have blue litmus paper, and if I put it in an acid it turns red. I also have red litmus paper, and if I put it in a base, it turns blue.
I know the question about litmus was asked and answered and I like the answer:
How does the litmus pH indicator work?
However, damp litmus paper also becomes bleached in presence of chlorine gas. I believe it has nothing to do with the mechanism described in aforementioned question. I wonder what the mechanism is. Wikipedia actually suggests:
For instance, chlorine gas turns blue litmus paper white – the litmus dye is bleached, because of presence of hypochlorite ions. This reaction is irreversible, so the litmus is not acting as an indicator in this situation.
I also found an equation which describes formation of hypochloric acid (source):
$$\ce{Cl2 (g) + H2O (l) -> HClO (aq) + HCl (aq)}$$
The problem that I have now is as follows: We know that litmus paper gets discolored because of contact with hypochloric acid. But what is actually the chemical reaction for that? I can supply some details now, and hopefully this ought to qualify as an answer.
As I mentioned earlier litmus is a mixture of 10-12 dyes (CAS number: 1393-92-6).
The acid-base indicator properties of litmus are primarily due to 7-hydroxyphenoxazone chromophore (pictured below)
The answer you linked to discusses the acid-base indication mechanism in some detail, so I shall skip over that.
Anyway, what this serves to establishing that it is indeed a extended $\pi$-conjugated system that we are dealing with in the chromophore.
Now, $\ce{HOCl}$ would bring about halohydrination (basically an electrophilic addition) across the $\pi$ bonds, thus disrupting the conjugated system.
Halohydrins are compounds that contain an $\ce{-OH}$ and $\ce{-X}$ groups on adjacent carbons.
This image describes the general mechanistic scheme in a simpler case:
The following is multiple choice question (with options) to answer.
What causes blue litmus to turn red? | [
"carbon",
"base",
"acid",
"oxygen"
] | C | Acids change the color of certain acid-base indicators. Two common indicators are litmus and phenolphthalein. Blue litmus turns red in the presence of an acid, while phenolphthalein turns colorless. |
SciQ | SciQ-6266 | thermodynamics, physical-chemistry, chemical-potential, combustion
Title: How to thermodynamically understand process of burning a piece of coal? Let's imagine that I have a match in hand and nugget of coal on my desk. Then I light up the match and place it for few seconds near the coal so a tiny piece of nugget catches fire.
Then another piece catches fire, then another and soon all the nugget is burnt down.
How did it happen? I gave the nugget just enough heat to burn the first piece. Where does come energy to burn the rest of nugget from? It is called combustion, and it happens in materials which have a lower energy content when their component molecules join with the oxygen in the atmosphere, than when in a solid/liquid structure. When energy is given to start the fire the piece of coal burns and releases energy with excess enough to sustain the reaction and leave heat energy for use.
Combustion is a high-temperature exothermic chemical reaction between a fuel and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke.
The following is multiple choice question (with options) to answer.
When fossil fuel is burned the chemical energy is converted into what? | [
"atmospheric energy",
"kinetic energy",
"thermal energy",
"natural energy"
] | C | Watching movies, eating hot popcorn, and many other activities depend on electrical energy. Most electrical energy comes from the burning of fossil fuels, which contain stored chemical energy. When fossil fuels are burned, the chemical energy changes to thermal energy and the thermal energy is then used to generate electrical energy. These are all examples of energy conversion. Energy conversion is the process in which one kind of energy changes into another kind. When energy changes in this way, the energy isn’t used up or lost. The same amount of energy exists after the conversion as before. Energy conversion obeys the law of conservation of energy, which states that energy cannot be created or destroyed. |
SciQ | SciQ-6267 | python, python-2.x, genetic-algorithm, traveling-salesman
newPopulation.append(Citizen())
newPopulation[-1].route = citizen1.route[:middle] + citizen2.route[middle:]
self.population = newPopulation[:]
break
elif(i == (10*len(fitPopulation))-1):
newPopulation.append(Citizen())
newPopulation[-1].route = citizen1.route
self.population = newPopulation[:]
The following is multiple choice question (with options) to answer.
What two activities are especially important when a number of local populations are linked, forming a metapopulation? | [
"immigration and emigration",
"flow and emigration",
"family reunions and emigration",
"immigration and family reunions"
] | A | |
SciQ | SciQ-6268 | evolution
Firstly, it is a little bit weirdly phrased. By "superior" I suppose you would refer to a species that could outcompete all the other. This sounds very impossible to me firstly for simple ecological reasons. However, it would be a long answer to fully address this point and I don't feel like addressing (I might not be very much able to) in addition to the other questions.
Evolution vs Natural Selection
Just for a start. Evolution is way more than just Natural selection. There are plenty of other absolutely essential processes such as mutation and drift that are important to understand.
What is Natural Selection?
Natural selection is the process by which most fit individuals end up being at higher frequency in the population as a result of reproducing more and surviving better. Natural selection does not necessarily diminish the probability of a species to get extinct. It will not necessarily increase the ability of a species to compete another. It will not necessarily increase the rate of increase in the number of individuals in the species.
local vs global optima
Reading you post you seem to understand the concept of local vs global optimum (from algorithmic maybe). If selection alone was acting in the population and if mutations were feeding genetic variation to this population at a low enough rate, then population will ultimately reach a local optimum and will get stuck there forever. They would never reach a potential higher local optimum somewhere else. Drift may allow for such switch though, it is refer to "shifting balance theory".
Envrionmental change
The environment changes much faster at a local scale that you seem to think. When talking about environmental change for a lineage, we are not only talking about important ice age or current days global warming but we are talking about more subtle and more frequent changes. Imagine a species of unicellular living in a 50 cubic centimeter puddle. For them environmental change are drastic and frequent. So do population really have time to achieve any equilibrium. It is here a general question that comes in many field of evolutionary biology and also outside biology. Are the system that we study expected to be at equilibrium (in regards at some variables at least) in nature or are they never given the time to reach any equilibrium?
Mutations and drift
The following is multiple choice question (with options) to answer.
What is the physical environment in which a species lives and to which it has adapted? | [
"land mass",
"habitat",
"farmland",
"ecosystem"
] | B | Another important aspect of a species’ niche is its habitat. Habitat is the physical environment in which a species lives and to which it has adapted. Features of a habitat depend mainly on abiotic factors, such as temperature and rainfall. These factors influence the traits of the organisms that live there. |
SciQ | SciQ-6269 | human-biology, endocrinology, organs
Title: Is there a blood panel lab test that measures all the hormone-producing glands? I understand that there are gland-specific hormone tests, such as:
Secretin: for the pancreas; and
Prolactin/ACTH: for the pituitary; and
PTH: for the payathyroid, etc.
However, are there any "composite" blood panels that test the "entire gamut/spectrum" of organs/glands, similar to what composite metabolic panels do for your cell counts? There are no composite tests that measure all the clinically important hormone producing glands. There are too many hormones produced by too many hormone producing cells/tissues in the body to test for all of them all at once (i.e. in a panel).
For illustrative purposes only... if you go to wikipedia they have a list of all hormones in the human body which is definitely far from complete! But it gives you an indication of just "how many" hormones there are and why testing for all of them is impossible in a panel.
Even with regard only to pancreatic hormones, there are several hormones produced (e.g. insulin, glucagon, somatostatin) that aren't necessarily a marker of the glands overall function (because they are not necessarily involved in the same function). Each of these hormones has different functions even though they are produced by the same gland.
Regardless, from a medical perspective you would never have a reason to test for all of them anyway. If you tested enough of them you'd find at least one of them that would - by chance - be abnormal.
Additionally, if you asked a handful of scientists to name fifty hormones there would be a lot of different hormones on each of their lists. The definition of hormone is vague, and we are learning more about new hormones every day. In the last decade we have learned that bile acids - chemicals predominately produced by the liver that are involved in dietary fat absorption - also act as hormones. There aren't clinical reasons to study all of these molecules just yet, but this demonstrates that it would be impossible to measure all of them all at the same time in one particular "panel".
The following is multiple choice question (with options) to answer.
What kind of tests may detect substances associated with particular disorders? | [
"electrical",
"biochemical",
"hormonal",
"genetic"
] | B | |
SciQ | SciQ-6270 | solar-system, comets
Title: How does a comet form? As the title explains,
How does a comet form?
What are the elements, what is a comet composed of?
Why didn't they become part of planets, moons or asteroids?
Comets are some of the material left over from the formation of the planets. Our entire solar system, including comets, was created by the collapse of a giant, diffuse cloud of gas and dust about 4.6 billion years ago. Much of the matter merged into planets, but some remained to form small lumps of frozen gas and dust in the outer region of the solar system, where temperatures were cold enough to produce ice.
A comet is generally considered to consist of a small nucleus embedded in a nebulous disk called the coma. the nucleus, containing practically all the mass of the comet, is a “dirty snowball” conglomerate of ices and dust.For one, of the observed gases and meteoric particles that are ejected to provide the coma and tails of comets, most of the gases are fragmentary molecules, or radicals, of the most common elements in space: hydrogen, carbon, nitrogen, and oxygen. The radicals, for example, of CH, NH, and OH may be broken away from the stable molecules CH4 (methane), NH3 (ammonia), and H2O (water), which may exist as ices or more complex, very cold compounds in the nucleus.
3.Many astronomers believe that these small objects never became planets or other large objects because of the gravity of the large planets. For example, the pull of Jupiter's kept 'stirring the pot' of the asteroid belt, so that the gravitational pull of the asteroids on each other was constantly being disturbed.
For the Kuiper belt and Oort cloud, there is a popular theory called 'planetary migration.' The main idea behind this theory is that the large outer planets of our Solar System started out much closer to the Sun when the Solar System was formed. As they migrated outward through the cloud of small objects still there, the gravity of these large planets pulled a lot of the small objectsout of their orbits. Some were pulled into the planets, and some were flung far into the outer reaches of the Solar System.
The objects that were flung very far out by Jupiter became the Oort cloud. The object that were not flung out quite as far by the movement of Neptune became the Kuiper belt.
Source
The following is multiple choice question (with options) to answer.
Scientists think the solar system formed from a big cloud of gas and dust called what? | [
"Oort cloud",
"supernova",
"nebula",
"comet"
] | C | Scientists think the solar system formed from a big cloud of gas and dust, called a nebula . This is the solar nebula hypothesis. The nebula was made mostly of hydrogen and helium. There were heavier elements too. Gravity caused the nebula to contract ( Figure below ). |
SciQ | SciQ-6271 | evolution, zoology, anatomy, species
Title: Examples of animals with 12-28 legs? Many commonly known animals' limbs usually number between 0 and 10. For example, a non-exhaustive list:
snakes have 0
Members of Bipedidae have 2 legs. Birds and humans have 2 legs (but 4 limbs)
Most mammals, reptiles, amphibians have 4 legs
Echinoderms (e.g., sea stars) typically have 5 legs.
Insects typically have 6 legs
Octopi and arachnids have 8 legs
decapods (e.g., crabs) have 10 legs
....But I can't really think of many examples of animals containing more legs until you reach 30+ legs in centipedes and millipedes. Some millipedes even have as many as 750 legs! The lone example I am aware of, the sunflower sea star, typically has 16-24 (though up to 40) limbs.
So my question is: what are some examples of animals with 12-28 legs? As a couple of counterexamples, species in the classes Symphyla (Pseudocentipedes) and Pauropoda within Myriapoda have 8-11 and 12 leg pairs respectively, so between 16 to 24 legs (sometimes with one or two leg pair stronlgy reduced in size).
(species in Symphyla, from wikipedia)
Another common and species-rich group with 14 walking legs (7 leg pairs) is Isopoda.
(Isopod, picture from wikipedia)
You also need to define 'legs' for the discussion to be meaningful. As you say, decapods have 10 legs on their thoracic segments (thoracic appendages), but they can also have appendages on their abdomens (Pleopods/swimming legs), which will place many decapods in the 10-20 leg range.
(Decapod abdominal appendages/legs in yellow, from wikipedia)
So overall, in Arthropoda, having 12-28 legs doesn't seem all that uncommon. There are probably other Arthropod groups besides those mentioned here that also have leg counts in this range.
However, for a general account, the most likely answer (if there is indeed a relative lack of 12-28 legged animals) is probably evolutionary contingencies and strongly conservative body plans within organism groups.
The following is multiple choice question (with options) to answer.
What are the largest phylum of the animal kingdom? | [
"Chelicerata",
"arthropods",
"Crustacea",
"Pycnogonida"
] | B | Two chemical species combine to produce a new compound. The general expression for this reaction is A + B → C. |
SciQ | SciQ-6272 | thermodynamics, energy, terminology
You are absolutely correct. Heat is not a form of energy. It is a mechanism by which energy is transferred from one substance, object, etc., to another due solely to temperature difference.
When I was learning about thermodynamics I found a particular description that, at least for me, help differentiate between the energy of something and the transfer of energy (by work or heat) from one thing to another. In this case the transfer of energy by heat. I'd like to share it with you in case it might be helpful. For simplicity, the description is for heat conduction.
Consider two solid objects, one having a higher temperature than the other. Which means the molecules of the higher temperature object 1 have a higher average translational kinetic energy than the molecules of the lower temperature object 2.
The objects are placed in contact with each other. At the interface between the objects the molecules of the higher temperature object collide with the molecules of the lower temperature object. On average, this results in the transfer of kinetic energy from the molecules of the higher temperature object to molecules of the lower temperature object causing the temperature of the higher temperature object to decrease, and the temperature of the lower temperature object to increase.
This transfer of kinetic energy from the molecules of the higher temperature object to the molecules of the lower temperature object is what we mean by heat. But the increase in the average kinetic energy of the molecules of the lower temperature object and decrease in the average kinetic energy of the molecules of the higher temperature object is what we mean by a change in the internal (kinetic) energy of the two objects. Thus the difference between the transfer of energy and the energy itself.
Hope this helps.
The following is multiple choice question (with options) to answer.
What is the name for a material that prevents the transfer of heat energy? | [
"thermal insulator",
"physical insulator",
"thermal condenser",
"structure insulator"
] | A | Another example of a thermal insulator is pictured in the Figure below . The picture shows fluffy pink insulation inside the attic of a home. Like the down filling in a snowsuit, the insulation traps a lot of air. The insulation helps to prevent the transfer of thermal energy into the house on hot days and out of the house on cold days. Other materials that are thermal insulators include plastic and wood. That’s why pot handles and cooking utensils are often made of these materials. Notice that the outside of the toaster pictured in the opening image is made of plastic. The plastic casing helps prevent the transfer of thermal energy from the heating element inside to the outer surface of the toaster where it could cause burns. You can learn more about thermal insulators at this URL: http://www. school-for-champions. com/science/thermal_insulation. htm . |
SciQ | SciQ-6273 | geology, mineralogy, minerals, metamorphism
Title: Is there any mineral that survives hard degree metamorphism? When a protolith enters in metamorphism, the minerals transform in other new stable minerals while the pressure and/or temperature increase.
Is there any mineral that would not be affected by a high degree metamorphism processes and would remain the same without experiencing any change? Zircon is one mineral which survives metamorphism.
Zircons can survive processes like erosion, transport and metamorphism, so they preserve a record of past geological processes.
From Wikipedia,
Zircon is common in the crust of Earth. It occurs as a common accessory mineral in igneous rocks (as primary crystallization products), in metamorphic rocks and as detrital grains in sedimentary rocks.
This makes zircon very useful in determining the age of rocks.
The following is multiple choice question (with options) to answer.
What is a rock exposed to if it's undergoing metamorphism? | [
"time and energy",
"heat and pressure",
"humidity and pressure",
"gravity and precipitation"
] | B | Metamorphism. This long word means “to change form. “ A rock undergoes metamorphism if it is exposed to extreme heat and pressure within the crust. With metamorphism, the rock does not melt all the way. The rock changes due to heat and pressure. A metamorphic rock may have a new mineral composition and/or texture. |
SciQ | SciQ-6274 | hydrology, mountains, rivers
Title: Why do rivers have 'wells' in mountains? Why/how can rivers have sources in places high above the sea level? The presence of water underground has nothing to do with sea level in mountainous country.
When rain fails on a mountain, or snow falls on a mountain and the snow eventually melts, the water from the rain or snow melt mostly travels downhill via rivers to the sea.
In getting to a river some of the water will fall on the ground. In places where the ground is covered by soil, water can travel through the soil via the pore spaces between the grains of soil. Similarly if porous rock, such as sandstone lies beneath the soil water can travel through the pores in the rock.
If a layer of impervious rock lies under the porous rock or soil, the water cannot move downwards, due to gravity, any further. This can lead to water accumulating in the soil or porous rock and saturating the soil or rock. In such situations an aquifer can form. The top of the saturated zone in an aquifer is called a water table.
The ground beneath a river is saturated and the surface of the river shows the water table exposed to atmosphere. Thus in mountainous regions the ground beneath rivers will be saturated and capable of supporting a well developed from the bank of a river.
The following is multiple choice question (with options) to answer.
Water infiltrates the ground because soil and rock may have air spaces between the grains. these pores, or tiny holes, result in the rock's what? | [
"shine",
"sheen",
"energy",
"porosity"
] | D | Identify features caused by groundwater erosion and deposition. |
SciQ | SciQ-6275 | forces, classical-mechanics, energy
Title: What's the work done in an object to change its direction? Say, for example an object is moving 2m/s right and some force makes it travel 2m/s left. What would be the work done on this object? It starts and ends with the same kinetic energy, but clearly something had to be done to it to make it start moving left. Let's assume the force acting to the left is constant.
For it to change the velocity from 2 m/s to the right to 2 m/s to the left the force must first decelerate the object to 0 m/s. That means the force did negative work on the object because the direction of the force is opposite to the movement of the object while it slows down. Net negative work decreases the kinetic energy of the object.
But since the force remains, it now accelerates the object from 0 m/s to 2 m/s to the left. Now the force is doing positive work since its direction is the same as the motion of the object. Net positive work increases the kinetic energy of the object.
The amount of negative work done by the force to decelerate the object to 0 m/s equals the amount of positive work done by the force to accelerate the object to 2 m/s, for a net work of zero. Per the work energy theorem the net work done on an object equals its change in kinetic energy. Since the net work is zero, the change in kinetic energy is zero.
Hope this helps.
The following is multiple choice question (with options) to answer.
Work is done only if a force is exerted in the direction of what? | [
"north",
"gravity",
"motion",
"wind"
] | C | Work is done only if a force is exerted in the direction of motion. If the motion is perpendicular to the force, no work has been done. If the force is at an angle to the motion, then the component of the force in the direction of the motion is used to determine the work done. |
SciQ | SciQ-6276 | life, replication
Title: What is the name of the smallest self-replicating thing? Some time last year, I found an article on Wikipedia about the smallest something to be able to reproduce.
I don't remember exactly what it was, but I am fairly certain that after the initial discovery another of the previous organism (this one slightly smaller) was discovered.
I think that the smallest something might have been the smallest self-replicating protein, or smallest self-replicating molecule, or something like that.
It was not mentioned in this thread: Which organism has the smallest genome length?
It had a strange, stand-out name and I believe it was discovered in the 90s. You're probably thinking of the Spiegelman Monster. It was actually discovered in 1965, but it was discovered that it became shorter over time in 1997.
It also wasn't included in that thread, and it has a strange name.
http://en.wikipedia.org/wiki/Spiegelman_Monster
The following is multiple choice question (with options) to answer.
What is the smallest independently functioning unit of a living organism? | [
"molecule",
"atom",
"cell",
"proteins"
] | C | A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells. A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based cellular fluid together with a variety of tiny functioning units called organelles. In humans, as in all organisms, cells perform all functions of life. A tissue is a group of many similar cells (though sometimes composed of a few related types) that work together to perform a specific function. An organ is an anatomically distinct structure of the body composed of two or more tissue types. Each organ performs one or more specific physiological functions. An organ system is a group of organs that work together to perform major functions or meet physiological needs of the body. This book covers eleven distinct organ systems in the human body (Figure 1.4 and Figure 1.5). Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system. |
SciQ | SciQ-6277 | 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.
All animals have specialized types of what basic structures, which can then do different jobs? | [
"atoms",
"muscles",
"cells",
"proteins"
] | C | Animals are multicellular eukaryotes in the Animal Kingdom. All animals are heterotrophs. They eat other living things because they can’t make their own food. All animals also have specialized cells that can do different jobs. Most animals have higher levels of organization as well. They may have specialized tissues, organs, and even organ systems. Having higher levels of organization allows animals to perform many complex functions. For a visual introduction to what makes a living thing an animal, watch this short video: https://www. youtube. com/watch?v=DXPhJUHooP8 . |
SciQ | SciQ-6278 | statistical-mechanics, entropy, phase-space
The volume of phase space can be seen as the number of microstates a system can occupy (given some constraints, like energy in your case).
Say I have two systems; one can take 2 microstates and the other 3. Then, a combination of these two systems will allow for $2 \times 3$ microstates and not $2 + 3$.
The following is multiple choice question (with options) to answer.
What term describes the number of items in a given area or volume? | [
"alkalinity",
"fraction",
"concentration",
"density"
] | C | In its most general form, concentration describes the number of items in a given area or volume. The units generally depend on the types of items being counted. For example, if we were to calculate the concentration of people that live in a city, we would divide the total number of people by the area. If we measured the area in square miles, the units of concentration for this measurement would be people per square mile. Or, we could determine the concentration of fish in a lake by dividing the total number of fish by the volume of the lake. If we measure the volume in cubic meters, the concentration would have units of fish per cubic meter. |
SciQ | SciQ-6279 | zoology, ornithology, ethology, behaviour
Title: Crow branch pecking behaviour I was walking through a small park when two crows started cawing at me, and followed me, flying from tree-to-tree as I walked. I speculate that this is a territorial or protective behaviour, but what I found different was the crows were violently pecking the branches nearby them. I have no memories coming to mind of seeing this behaviour beforehand. I speculate that this behaviour could be threat displays, but a quick search on Google did not reveal to me any authoritative studies on this phenomenon. I'd appreciate more information and sources.
This question has been added as a casual observation on iNaturalist. This is a good question. This type of behavior -- pecking at a branch, wiping the side of the beak on a branch, pulling off twigs and dropping them, or knocking off pieces of bark -- is quite common among many corvid species, particularly when they are interrupted by something or someone that they might consider a threat. This includes not only potential predators but also potentially hostile conspecifics.
It is typically considered to be a form of displacement behavior. The concept of displacement behavior, from classical ethology, posits that when an animal experiences two conflicting drives to do two different things, it doesn't know which to do and does a third thing instead to dissipate the drive or anxiety. For branch-pecking in crows, see E.g Kilham and Waltermire 1990 Ch. 12.
Referece: Kilham, L., & Waltermire, J. (1990). The American crow and the common raven. Texas A&M University Press.
The following is multiple choice question (with options) to answer.
Birds are known for flying south in the winter to avoid what? | [
"rain",
"solar radiation",
"cold weather",
"hurricanes"
] | C | |
SciQ | SciQ-6280 | evolution
Title: In this representation of the tree of life, what are the lateral connections?
I found this simple representation of the tree of life in a wikipedia article, and I was curious what these horizontal connections shown here are supposed to be, like the ones between plants and protists, or bacteria and protists going to plants. Do they represent things like lateral gene transfer or potential endosymbiotic origin relationships? (like the theory that eucaryotes came from a merging of a bacteria with an archae). Yes, pretty much! Lateral branches here indicate endosymbiotic events and major horizontal gene transfers.
I'd warn though that the diagram is not very accurate, and additions I'd make would complicate it further as a bush (rather than a tree). Each branch root itself is an instance of cladogenesis, and for this reason the diagram is not very accurate (e.g. fungi and metazoans seem to arise within the same "branch"), and also misses a few lateral branches that otherwise exist. My favorite example of atypical horizontal gene transfer is that of prokaryote-insect transfers which occur frequently. This has been known for some time; many insects contain genes of Wolbachia origin and some (not all) are definitively functional, and are understood to facilitate obligate (fully-dependent) mutualisms.
The following is multiple choice question (with options) to answer.
The root system is usually anchored by one main root developed from what? | [
"nuclei radicle",
"organisms radicle",
"embryonic radicle",
"sperm radicle"
] | C | Eudicots Eudicots, or true dicots, are characterized by the presence of two cotyledons. Veins form a network in leaves. Flower parts come in four, five, or many whorls. Vascular tissue forms a ring in the stem. (In monocots, vascular tissue is scattered in the stem. ) Eudicots can be herbaceous (like dandelions or violets), or produce woody tissues. Most eudicots produce pollen that is trisulcate or triporate, with three furrows or pores. The root system is usually anchored by one main root developed from the embryonic radicle. Eudicots comprise two-thirds of all flowering plants. Many species seem to exhibit characteristics that belong to either group; therefore, the classification of a plant as a monocot or a eudicot is not always clearly evident (Table 14.1). |
SciQ | SciQ-6281 | machine-learning
Title: What was going on before PAC learning I am investigating PAC learning (computational learning theory) as a beginner with no previous knowledge of machine learning / AI. I am investigating the model mainly from a historical point of view.
For this, the most important things are of course the results based on the model. There are enough papers out there that document these results. But I also want to write something about what was going on before PAC learning, as to sketch the historical context up to where Valiant came with the notion of the PAC model.
No papers/surveys I've found so far document this, and as someone with no real knowledge of machine learning, it is hard to find this out. I am therefore asking this soft question here, because I believe there are enough experts that can help me with this. References are highly appreciated.
When I can research and study what was going on before PAC, I might get a better appreciation as to why the academic world is so enthusiastic about the PAC model, which is also something interest to document in my historical work!
References are highly appreciated.
An author is expected to address the question of the context and relevance of his results at the begin of his publication. I just skimmed over the introduction of "L. Valiant. A theory of the learnable. Communications of the ACM, 27, 1984." again, and found out that Valiant indeed well covered your question.
The original paper by Valiant is both freely available and not too difficult to read. (Except section 7, which only proves that the author can also tackle challenging mathematical problems, but doesn't contribute much to the real content of the paper.) Reading at least its introduction will be more rewarding than reading my overly long answer to this question, so I suggest to really try it.
The rest of this answer tries to cite some passages from the introduction which should indicate whether reading this introduction might answer the question about the historical context. Note however that an author has the natural prerogative to be biased with respect to such questions.
... such a system would, at least, be a very good start. First, when one examines the most famous examples of systems that embody preprogrammed knowledge, namely, expert systems such as DENDRAL and MYCIN, essentially no logical notation beyond the propositional calculus is used.
The following is multiple choice question (with options) to answer.
What type of learning is done from past experiences and reasoning? | [
"rational learning",
"consequence learning",
"transformation learning",
"insight learning"
] | D | Insight learning is learning from past experiences and reasoning. It usually involves coming up with new ways to solve problems. Insight learning generally happens quickly. An animal has a sudden flash of insight. Insight learning requires relatively great intelligence. Human beings use insight learning more than any other species. They have used their intelligence to solve problems ranging from inventing the wheel to flying rockets into space. |
SciQ | SciQ-6282 | 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.
Where is the pituitary gland? | [
"thyroid",
"lung",
"heart",
"brain"
] | D | The regulation of Leydig cell production of testosterone begins outside of the testes. The hypothalamus and the pituitary gland in the brain integrate external and internal signals to control testosterone synthesis and secretion. The regulation begins in the hypothalamus. Pulsatile release of a hormone called gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the endocrine release of hormones from the pituitary gland. Binding of GnRH to its receptors on the anterior pituitary gland stimulates release of the two gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These two hormones are critical for reproductive function in both men and women. In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis. FSH also stimulates the Sertoli cells to produce hormones called inhibins, which function to inhibit FSH release from the pituitary, thus reducing testosterone secretion. These polypeptide hormones correlate directly with Sertoli cell function and sperm number; inhibin B can be used as a marker of spermatogenic activity. In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone. A negative feedback loop predominantly controls the synthesis and secretion of both FSH and LH. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream. In the testis, LH binds to LH receptors on Leydig cells and stimulates the release of testosterone. When concentrations of testosterone in the blood reach a critical threshold, testosterone itself will bind to androgen receptors on both the hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH and LH, respectively. When the blood concentrations of testosterone once again decline, testosterone no longer interacts with the receptors to the same degree and GnRH and LH are once again secreted, stimulating more testosterone production. This same process occurs with FSH and inhibin to control spermatogenesis. |
SciQ | SciQ-6283 | evolution, mycology
Title: Why are some fungi poisonous? There are many poisonous fungi in nature. For example Amanita Phalloides.
What reasons could a fungus need poison for? Some species, like venomous snakes, use poison to kill other species as prey. But what about fungi? I can't think of any purpose for poison in fungi. If poison has no real function in fungi shouldn't evolution get rid of it? The same reason some plants are poisonous: to stop animals from eating them.
The visible part of the fungus is called, rather misleadingly, the fruiting body. It exists to produce and spread spores and thus produce the next fungal generation. Getting eaten, rather obviously, inhibits its ability to do this. Being poisonous discourages animals from eating the fruiting body and thus permits it to complete its life cycle.
The following is multiple choice question (with options) to answer.
Which fungi eaten by people all over the world? | [
"mushrooms",
"legumes",
"algae",
"fruits"
] | A | Mushrooms are fungi that are eaten by people all over the globe. |
SciQ | SciQ-6284 | species-identification, botany
Weakley (2015) "Flora of the Southern and Mid-Atlantic States"
1 Leaflets 3, toothed, lobed, or entire; shrub or vine.
2 Fruits pubescent or papillose; leaflets entire, coarsely toothed, undulate, or round-lobed; lower surfaces of leaflets either velvety puberulent, sometimes becoming glabrate in age (T. pubescens) or glabrous (glabrescent or rarely pilose beneath) but with prominent tufts of tannish hairs present in the vein axils (T. radicans var. radicans).
3 Leaves sparsely pubescent (rarely pilose beneath), the apex and the lobes (if present) generally acute to acuminate; drupes papillose, scabrous or puberulent; plant a high-climbing vine or stoloniferous shrub; [of mesic, swampy, or dry habitats].......... T. radicans var. radicans
3 Leaves velvety puberulent (sometimes becoming glabrate in age), the apex and the lobes (if present) generally obtuse to broadly acute; drupes pubescent (becoming glabrate); plant a stoloniferous shrub; [of dry habitats, especially sandhills] ............. T. pubescens
2 Fruits glabrous (or very sparsely pubescent); leaflets coarsely toothed or notched (rarely entire); lower surfaces of leaflets glabrous to pubescent, but without tufts of tannish hairs in the vein axils.
The following is multiple choice question (with options) to answer.
The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. botanists call the upper side the adaxial surface (or adaxis) and the lower side this? | [
"posterior surface",
"abaxial surface (or abaxis)",
"anterior surface",
"dorsal surface"
] | B | Leaf Structure and Function The outermost layer of the leaf is the epidermis; it is present on both sides of the leaf and is called the upper and lower epidermis, respectively. Botanists call the upper side the adaxial surface (or adaxis) and the lower side the abaxial surface (or abaxis). The epidermis helps in the regulation of gas exchange. It contains stomata (Figure 30.24): openings through which the exchange of gases takes place. Two guard cells surround each stoma, regulating its opening and closing. |
SciQ | SciQ-6285 | seismology, earthquakes, seismic-hazards, drilling
Title: Why aren't seismic stations installed very deep underground so as to pre-warn from earthquakes? The velocity of p-waves emanating from earthquakes is in the range of 5-8 km/s (link)--let's assume it is 5 km/s. The earthquake depth is up to hundreds of kms deep underground (link)--let's assume it is 100 km.
That said, if a seismic station is installed at a depth of 50 km, and there are many of them in any given metropolitan area, then we can have a warning that is tens of seconds before the earthquake reaches the surface.
While I realize that drilling down to 50 kn is no easy task, I would have imagined that saving human life is well worth the efforts. Why hasn't this been done so far? Is it that such a short notice (10s of seconds) isn't worth it? The simple answer is that you can't drill to 50 km depth.
The deepest holes ever drilled were to a little more than 12 km, one is named the Kola Superdeep Borehole in Russia, which was a scientific drilling project. The very few others were oil exploration boreholes.
Drilling that deep is extremely expensive and hard. If you go and ask anyone who ever worked on a drill rig, drilling the second 100 metres is always harder than the first 100 metres. And we're talking about kilometres here! There are several problems with drilling that deep. It's extremely hot down there, and the drilling equipment just breaks and stops working. You also need to pump cooling water in and pump out the stuff you're drilling and it gets harder with depth.
This is simply not feasible. Now let's say that you did somehow manage to drill a hole to that depth. How would you put monitoring equipment inside? That equipment has to sustain heat and pressure and still keep working, while being able to transmit whatever it's reading back to the surface. This is not going to happen, not at 50 or 10 km depth.
Another problem is that not all earthquakes are that deep. Some earthquakes originate near the surface, or just several km deep. Having a monitoring station down there isn't going to help. The 2011 Tohoku earthquake (the one that triggered the tsunami at Fukushima) was only 30 km deep. Same thing for the 2004 Indian Ocean earthquake.
The following is multiple choice question (with options) to answer.
A small quake preceding a large quake is called what? | [
"foreshock",
"warning shock",
"preshock",
"aftershock"
] | A | There are sometimes signs that a large earthquake is coming. There may be small quakes, called foreshocks . These can occur a few seconds to a few weeks before a major quake. Unfortunately, foreshocks are not very useful for predicting large earthquakes. Many quakes do not have foreshocks. Also, small earthquakes are not necessarily followed by a large earthquake. |
SciQ | SciQ-6286 | meteorology, tornado, coriolis
And then conversely, Australia doesn't have a lot of land Poleward yet is still a reasonably busy tornado spot.
Mountain ranges Poleward also generally aren't a big deal... even pretty large ones; one of the biggest tornado areas is Bangladesh\India, despite the disruption the Himalayas presents. Because enough cold air can filter into the region in spite of the blockage.
The only thing that would be a real large scale geographic issue to the needed cold air would be a warm sea Poleward that modifies the incoming cold air significantly.
But that's pretty tough to have geographically. Perhaps more possible in the Autumn... maybe the Great Lakes serves as a slight dampener on fall season tornadoes in parts of the US? Though their effect is still mostly pretty small overall. Bring too near any large body of water, in any direction, is really a downer on supercellular tornadoes, as it modifies temperature gradients and instability.
To your direct question... there actually is a very good example of what Tornado Alley would look like in the Southern Hemisphere already: the Pampas Lowlands of Argentina.
It has that big mountain range to the west, in the midlatitudes, and does have fairly warm water a ways northward.
But it doesn't have quite as large of a region east of the mountains to have the tornadoes in, the cold air (and storm system strength) is probably modified due to the closed nature of the Antarctic vortex and the widespread oceans of the SH modifying air masses, and the source water isn't probably as well located being so far north (and is it warm?).
But even still, Pampas area might be the second most consistent tornado region on Earth. Such that some US storm chasers have traveled down there in our winter.
In the end, local effects play a huge role too, creating mesoscale ingredients (seabreezes\temperature boundaries, upsloping, local vortex flow, etc) to add plenty of rotation to the ledger (see Florida, one of highest tornadoes per square mile in US, in large part due to seabreeze water spouts and hurricanes). But all things equal, being east of mountains in the midlatitudes is a jackpot ingredient to climatological tornado formation (regardless of hemisphere).
The following is multiple choice question (with options) to answer.
What do winter storms develop from at higher latitudes? | [
"humidity",
"cyclones",
"temperatures",
"clouds"
] | B | Winter storms develop from cyclones at higher latitudes. They include blizzards and lake-effect snow storms. |
SciQ | SciQ-6287 | thermodynamics, material-science, phase-transition, states-of-matter
Title: Why does matter exist in 3 states (liquids, solid, gas)? Why does matter on the earth exist in three states? Why cannot all matter exist in only one state (i.e. solid/liquid/gas)? The premise is wrong. Not all materials exist in exactly three different states; this is just the simplest schema and is applicable for some simple molecular or ionic substances.
Let's picture what happens to a substance if you start at low temperature, and add ever more heat.
Solid
At very low temperatures, there is virtually no thermal motion that prevents the molecules sticking together. And they stick together because of various forces (the simplest: opposite-charged ions attract each other electrostatically). If you picture this with something like lots of small magnets, it's evident enough that you get a solid phase, i.e. a rigid structure where nothing moves.
Actually though:
Helium won't freeze at any temperature: its ground state in the low-temperature limit at atmospheric pressure is a superfluid. The reason is that microscopically, matter does not behave like discrete magnets or something, but according to quantum mechanics.
There is generally not just one solid state. In the magnet analogy, you can build completely different structures from the same components. Likewise, what we just call “ice” is actually just one possible crystal structure for solid water, more precisely called Ice Ih. There are quite a lot of other solid phases.
Liquid
Now, if you increase temperature, that's like thoroughly vibrating your magnet sculpture. Because these bonds aren't infinitely strong, some of them will release every once in a while, allowing the whole to deform without actually falling apart. This is something like a liquid state.
Actually though:
The following is multiple choice question (with options) to answer.
What is the only substance on earth that is present in all three states of matter? | [
"air",
"water",
"carbon",
"mercury"
] | B | Water is the only substance on Earth that is present in all three states of matter. This means that water is present as a solid, liquid, and gas. Earth is the only planet where water is present in all three states. All three phases may be present in a single location or in a region. The three phases are solid (ice or snow), liquid (water), and gas ( water vapor ). See ice, water, and clouds pictured below ( Figure below ). |
SciQ | SciQ-6288 | gene-expression, transcription, gene-regulation
Title: Transcription of Genes: Are Specific Transcription Factors + Enhancers Necessary? I learned about transcription in my AP Biology class and we discussed how transcription occurs, but I was wondering whether transcription always requires the enhancers, activators (specific transcription factors), DNA-bending proteins, etc. to be present, or if this is only used for higher-level production of RNA transcripts?
Can transcription occur if only the RNA Polymerase (I, II, or III) and the General Transcription Factors are present?
Thanks! enhancers, activators, silencers, repressors are necessary in controlling of the transcriptional process. Utilization of enhancers/silencers plays a part in differentiation of developmental processes (i.e. maturation, growth)
https://en.wikipedia.org/wiki/Enhancer_(genetics)
The following is multiple choice question (with options) to answer.
What is essential for forming new genes? | [
"large mutations",
"chromosome deversity",
"enough mutations",
"enough chromosomes"
] | A | It is believed that large mutations form new genes. Mutations that duplicate large sections of DNA are a major source of genetic material for new genes. It is thought that tens to hundreds of genes are duplicated in animal genomes every million years. Most genes belong to larger families of genes of shared ancestry. These gene families have domains within the protein with a particular and independent function. These domains have corresponding conserved regions within their genes. It is through duplication mutations that such gene families formed. Genetic recombination after duplication of different domains forms new combinations of domains with new functions. For example, the human eye uses four genes to make structures that sense light: three for color vision and one for night vision; all four arose from a single ancestral gene. |
SciQ | SciQ-6289 | fluid-dynamics, friction, drag, flow, viscosity
Title: Friction in a fluid when an object is moving in a fluid(air for example), the air will resist the object's movement: molecules of the air will collide with the surface of the object (no slip condition) and then we will have many layers of fluid "above" the surface of the object due to viscosity of the fluid. My question is: are the layers responsible for the friction between the air and the solid or it is just to the molecules that collide at the surface of the object or both? Tried to comment on question, need 50 rep. (why??)
I believe what you are referring to is viscosity in laminar flow. If I recall correctly, non-laminar flow is a precondition for turbulence, but I believe you can have viscosity which is not turbulent.
Is this the direction you had in mind?
EDIT:
Fluid molecules far away from the object will feel nothing.
Fluid molecules in the object's path will be pushed aside (and exert an equal and opposite force on the object).
As fluid molecules are pushed aside, they come into interaction with fluid close to the object path, and secondary interactions ensue.
So I think the answer to your question is: Both. Particles not in the object's path affect it indirectly, by causing those molecules directly in its path to escape less quickly. Imagine how the fluid density and molecular mass will affect the situation.
The following is multiple choice question (with options) to answer.
What is fluid friction with air called? | [
"wind resistance",
"air resistance",
"gravity",
"buoyancy"
] | B | Types of friction include static friction, sliding friction, rolling friction, and fluid friction. Fluid friction with air is called air resistance. |
SciQ | SciQ-6290 | photosynthesis, cellular-respiration, energy, sugar
Basically, points 4-7 convey that Calvin-Benson cycle not only produces sugar but what it actually does is fix inorganic carbon (as CO2) to organic form (in the form of sugar). So, most (practically all) of the carbon that a photosynthetic plant has, comes from this carbon fixation process and that's how plants are photoautotrophic.
The following is multiple choice question (with options) to answer.
Plants produce their own sugars and other food molecules through what process? | [
"photosynthesis",
"spermatogenesis",
"glycolysis",
"hydrogenesis"
] | A | |
SciQ | SciQ-6291 | nuclear-physics, nuclear-engineering
Title: Water-cooled fast neutron reactors Can anyone explain why fast neutron reactor designs use sodium/lead/salt cooling, instead of water (heavy/light)?
Is that because neutron absorption by water would not allow to break even in fuel cycle?
Will heavy water help here?
Or water slows neutrons so efficienly so that even if we reduce amount of water inside the reactor (by increasing flow speed) - it still will significantly lower neutron energy, while sodium does not slowdown neutrons at all? First question: Na for fast reactors
Sodium is better for faster reactors because it has a lower total cross section than water. Fast reactors still has some moderation and obviously all types have some neutron loss due to absorption from the moderator in addition to whatever other materials may be in the core. For numbers, I'm going to reference NIST:
H http://www.ncnr.nist.gov/resources/n-lengths/elements/h.html
Na http://www.ncnr.nist.gov/resources/n-lengths/elements/na.html
Sum up all of the cross sections for all types of reactions, which is the total scattering + absorption from that link. You find $82 \text{b}$ for Hydrogen and $3.8 \text{b}$ for Sodium. For water you add Oxygen. Combine that with density and atomic weight information to get the macroscopic cross sections. For water, we have $3.45 cm^{-1}$ and for Na we have $0.115 cm^{-1}$. These numbers are from my reference.
A fast reactor primarily wants the moderator to do nothing. Indeed, without a coolant or moderator the reaction works just fine... aside from getting cooled. Even if a moderator wouldn't absorb any neutrons, it would muck with your intent, which is to get the fuel atoms (U, Th, Pu) to absorb fast neutrons from fission. The reason you want fast neutrons to hit the fuel atoms includes:
to breed new fuel, for which the isotope chain is only neurotically favorable with fast neutrons
some isotopes are only fissile at fast energies, and at lower energies will have small fraction fission, meaning you couldn't sustain the chain reaction ($k<1$) with a thermal spectrum
The following is multiple choice question (with options) to answer.
What do fission reactors use to slow down the neutrons? | [
"brake",
"moderator",
"inertia",
"control"
] | B | U-235 nuclei can capture neutrons and disintegrate more efficiently if the neutrons are moving slower than the speed at which they are released. Fission reactors use a moderator surrounding the fuel rods to slow down the neutrons. Water is not only a good coolant but also a good moderator, so a common type of fission reactor has the fuel core submerged in a huge pool of water. This type of reactor is called a light water reactor or LWR. All public electricity generating fission reactors in the United States are LWRs. |
SciQ | SciQ-6292 | audio, filter-design, noise, denoising
I did a quick dirty hack on that and found it sounded already a lot better (although certainly not clean either). Below is a picture that shows the first pulse before and after.
That's work in progress and there are certainly ways to refine this further.
The following is multiple choice question (with options) to answer.
What term is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood? | [
"garble",
"whisper",
"music",
"murmur"
] | D | The term murmur is used to describe an unusual sound coming from the heart that is caused by the turbulent flow of blood. Murmurs are graded on a scale of 1 to 6, with 1 being the most common, the most difficult sound to detect, and the least serious. The most severe is a 6. Phonocardiograms or auscultograms can be used to record both normal and abnormal sounds using specialized electronic stethoscopes. During auscultation, it is common practice for the clinician to ask the patient to breathe deeply. This procedure not only allows for listening to airflow, but it may also amplify heart murmurs. Inhalation increases blood flow into the right side of the heart and may increase the amplitude of right-sided heart murmurs. Expiration partially restricts blood flow into the left side of the heart and may amplify left-sided heart murmurs. Figure 19.30 indicates proper placement of the bell of the stethoscope to facilitate auscultation. |
SciQ | SciQ-6293 | organic-chemistry, carbonyl-compounds
Title: Counting number of acidic-H in a molecule In a recent exam, following question was asked:
Number of acidic hydrogen present in X are:
I've found 8 of them as shown:
7 of them (marked with numerals) were correct according to solution, but 8th one (pointing with red arrow) was not. Is it because of the fact that the carbon was bridge-headed or something else? An aldehyde or a ketone with an alpha hydrogen forms a carbanion that resonates to enolate form. This leads to two canonical structures that are in resonance. The example below is a polyphenol compound extracted from turmeric, called curcumin.
source: Biomaterials. 2010 May;31(14):4179-85. doi: 10.1016/j.biomaterials.2010.01.142. Epub 2010 Feb 23. (https://www.ncbi.nlm.nih.gov/pubmed/20181392)
The hydrogens between two keto groups are most acidic. This is due to formation of two equivalent enol structures stabilized by hydrogen bonding. The structural requirement would be planarity of atoms involved in hydrogen bonding.
Below are 3-D structures of the given compound in the question above.
Structure without hydrogens
Bridgehead carbon is 4. Keto groups are at 2 , 5 and 8 (shaded in grey). Keto groups on 5 and 8 are not in the same plane . Hence Hydrogen on 4 , 22 (see figure with hydrogens) does not form stable hydrogen bonded enol structures as discussed in the above example.
Therefore, hydrogen at 8th one (pointing with red arrow) may not be acidic.
Note: 3-D structures have been drawn on Chem3Dpro
Structure with hydrogens
Structure with hydrogens (2nd view)
The following is multiple choice question (with options) to answer.
Carbon atoms are bonded to as many hydrogen atoms as possible in what type of fatty acids? | [
"super",
"oily",
"saturated",
"unsaturated"
] | C | Saturated fatty acids have only single bonds between carbon atoms. As a result, the carbon atoms are bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogens. Saturated fatty acids are found in fats. |
SciQ | SciQ-6294 | entomology
Title: What is the name of this tiny creature? It looks like a tiny piece of moving cotton? By chance, I saw this tiny insect on my bag a few days ago in Sydney. Am I the first person who has pinpointed this animal?! If not can you please let me know its name? From your image, it looks like it might be a woolly aphid. I just did a bit of cursory research, and it looks like they're often described as floating pieces of fluff, that seem to wander instead of directly heading somewhere. The fluff on their back is actually wax produced as a defense mechanism from predators and the like. I hope this is what you were looking for!
The following is multiple choice question (with options) to answer.
What kind of mouthparts do aphids have? | [
"siphoning mouthparts",
"sponging mouthparts",
"chewing mouthparts",
"piercing-sucking mouthparts"
] | D | Some insects, such as aphids, have piercing-sucking mouthparts. Other insects, like grasshoppers, have chewing mouthparts. |
SciQ | SciQ-6295 | zoology, sensation
Title: Can animals that rely heavily on sonar sense colour? Apparently there're species around as rely heavily on sonar to sense the world around them.
E.g. Bat, Dolphin, Whale ...
The humans, and other terrestrial beings in a lighted world are capable of distinguishing colour in varying degrees of acuity. Is this ability to sense colour in our environment applicable to species (terrestrial, avian, and marine) that rely heavily on sonar? Any animal using sound cannot sense color though sonar directly, though these animals are not entirely blind and can probably see colors in the infrared we can't.
Even on the darkest night there is some light around and all bats use this. Old World fruit bats have colour vision, which is useful to them as they are often quite active in daytime, roosting on trees in exposed positions, rather than tucked away in dark crevices like most microbats, which can see only in black-and-white.
Dolphins have additional senses in addition to seeing they can sense electrical fields. So if an animal has its eyes covered, they will seem to be able to do things you would not expect. Its not the same as seeing the color though.
Such animals using sonar can additionally sense density and hardness as well as other material attributes which would cause the acoustic properties of the material as well as movement.
A hard-bodied insect produces a different quality of echo from one with a soft body, so bats can distinguish between some different groups of insects in this way. They can also determine the size of the object.
What's really interesting is that even human beings can experience this unusual sense. Blind people have learned to echolocate by making clicks with their mouth, and there is a movement to teach this skill.
Anyone can try it. In just an hour or two I was able to tell how close I was to a wall, whether the wall was concrete. I couldn't play video games (2:20 on the link) or see colors though.
The following is multiple choice question (with options) to answer.
Sounds, chemicals, and visual cues are examples of what between animals? | [
"circulation",
"migration",
"procreation",
"communication"
] | D | For individuals to cooperate, they need to communicate . Animals can communicate with sounds, chemicals, or visual cues. For example, to communicate with sounds, birds sing and frogs croak. Both may be communicating that they are good mates. Ants communicate with chemicals called pheromones . For example, they use the chemicals to mark trails to food sources so other ants can find them. Male dogs use pheromones in urine to mark their territory. They are “telling” other dogs to stay out of their yard. You can see several examples of visual communication in Figure below . |
SciQ | SciQ-6296 | gas-laws, kinetic-theory-of-gases
The size of the force will be proportional to the product of the number of molecules /unit area and the size of the inward force. Both of these will be be proportional to the density ($Nm/V$) or equivalently molar concentration. The reduction in pressure can thus be written as $-a(n/V)^2$ where $a$ is a positive constant that depends on the gas and is determined only by experiment.
The following is multiple choice question (with options) to answer.
What is pressure times area equal to? | [
"mass",
"force",
"volume",
"density"
] | B | There is a pressure difference when the channel narrows. This pressure difference results in a net force on the fluid: recall that pressure times area equals force. The net work done increases the fluid’s kinetic energy. As a result, the pressure will drop in a rapidly-moving fluid, whether or not the fluid is confined to a tube. There are a number of common examples of pressure dropping in rapidly-moving fluids. Shower curtains have a disagreeable habit of bulging into the shower stall when the shower is on. The high-velocity stream of water and air creates a region of lower pressure inside the shower, and standard atmospheric pressure on the other side. The pressure difference results in a net force inward pushing the curtain in. You may also have noticed that when passing a truck on the highway, your car tends to veer toward it. The reason is the same—the high velocity of the air between the car and the truck creates a region of lower pressure, and the vehicles are pushed together by greater pressure on the outside. (See Figure 12.4. ) This effect was observed as far back as the mid-1800s, when it was found that trains passing in opposite directions tipped precariously toward one another. |
SciQ | SciQ-6297 | zoology, ecology
Giraffes' this is an energy saving feature. Giraffes don't need to use muscles to hold their neck. They just use when flexing their necks down, when drinking water etc.
According to Wikipedia, for an alternative hypothesis Ouranosaurus have a hump. (Other hypothesis is display sail or termoregulation sail of course. Also spinosaurus have this kind of alternative hypotesis but this hypothesis not accepted much as sail. and spinosaurus' spine different from bisons. Bison spines concentrating at shoulder but spinosaurs' not at the shoulder. You can find spinosaurus info from this page.)
The following is multiple choice question (with options) to answer.
What part of the kangaroo helps it balance when it leaps as well as when it sits? | [
"the pouch",
"large feet",
"the spine",
"the tail"
] | D | |
SciQ | SciQ-6298 | sequence-alignment, phylogenetics, genome, phylogeny
Title: What is the most appropriate way to find the most recent common ancestor between two distantly related species I want to specifically find the common ancestor between a lobster and a humans. I suspect it was an aquatic worm of some description. But I want to know about the nervous system of this common ancestor. Because I've now posted several comments, I'll just roll them all up.
For background on the approaches used to identify most recent common ancestors and a high-level look at how animal taxonomy has been inferred, I suggest Lynch 1999.
I think that there are 2 interpretations of this question. If you are interested in just looking up a single MRCA of well-defined clades, such as lobster and human, here are some approaches:
Easy way:
Look at a tree diagram, e.g. this:
Find the tips that correspond to your species of interest (arthropods for lobster, chordata for humans).
Find where they join together in the diagram (the branch labeled "true coelom").
You have your answer, the MRCA is the group of organisms with a true coelom, coelomates.
A more involved way using a database
Go to this website.
Find the group of species 1 (arthropods, protostomes, etc. for lobster, chordata, deuterostomes etc. for human)
navigate around until you see the group containing the two groups (in this case listed as "bilateria"). In this case you are looking for the bilaterian common ancestor.
another database
Go to this website.
Point and click your way to a view where you see your 2 clades of interest (arthropods, chordates in this case). See figure.
Find where they join (in this case, it is less certain about the existence of a coelomate common ancestor, so it just says "bilaterians").
The following is multiple choice question (with options) to answer.
What is the evolutionary history of a group of related organisms called? | [
"phylogeny",
"lineage",
"superfamily",
"ancestry"
] | A | Linnaeus classified organisms based on obvious physical traits. Basically, organisms were grouped together if they looked alike. After Darwin published his theory of evolution in the 1800s, scientists looked for a way to classify organisms that showed phylogeny. Phylogeny is the evolutionary history of a group of related organisms. It is represented by a phylogenetic tree , like the one in Figure below . |
SciQ | SciQ-6299 | eeg, terminology
Now, the brain is a lump of neurons. Different types of neurons that are there for different types of tasks. Some of them respond to electrical activity (from the nervous system) by propagating or inhibiting electrical activity. We can see this in the lab, by observing how does one single neuron behaves but to date it has been impossible to observe what EACH neuron is doing in-vivo in a functioning brain. This is the "promise" of Neuroimaging.
So, when it comes to electroencephalography, an electrical activity (of the brain) is sensed by an instrument (the EEG aparratus). Actually, in this case, a ridiculously small number of electrodes (a few tenths) is used to sense the combined functioning of a ridiculously large number of neurons (a few billions).
Because of this "imbalance" we see patterns in the electroencephalography measurements that, macroscopically, correspond to brain function. We don't really know what is happening at the neuron level, but we can observe waves of electrical activity spreading throughout the surface of the brain and we hypothesize that this is probably because of the brain's properties of segregation and specialisation (and this, go through the introduction, at least once).
In other words, certain parts of the brain are devoted to certain functions and they "connect" together to exchange information as the brain functions.
Because of this, certain "states" of cognition can be cross referenced with certain electrical patterns.
For example:
The following is multiple choice question (with options) to answer.
What are specialized cells in the brain that monitor the concentration of solutes in the blood called? | [
"osmoreceptors",
"sporozoans",
"staurikosaurus",
"ionconcentrate"
] | A | Many marine invertebrates have internal salt levels matched to their environments, making them isotonic with the water in which they live. Fish, however, must spend approximately five percent of their metabolic energy maintaining osmotic homeostasis. Freshwater fish live in an environment that is hypotonic to their cells. These fish actively take in salt through their gills and excrete diluted urine to rid themselves of excess water. Saltwater fish live in the reverse environment, which is hypertonic to their cells, and they secrete salt through their gills and excrete highly concentrated urine. In vertebrates, the kidneys regulate the amount of water in the body. Osmoreceptors are specialized cells in the brain that monitor the concentration of solutes in the blood. If the levels of solutes increase beyond a certain range, a hormone is released that retards water loss through the kidney and dilutes the blood to safer levels. Animals also have high concentrations of albumin, which is produced by the liver, in their blood. This protein is too large to pass easily through plasma membranes and is a major factor in controlling the osmotic pressures applied to tissues. |
SciQ | SciQ-6300 | 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.
Bones consist of four types of tissue, compact bone, spongy bone, bone marrow, and what? | [
"epithelium",
"collagen",
"plasma",
"periosteum"
] | D | Bones consist of four different types of tissue: periosteum, compact bone, spongy bone, and bone marrow. Ossification gradually changes the cartilage skeleton of the fetus to the bony skeleton of the adult. |
SciQ | SciQ-6301 | physiology
So, now the question is shifted: why do kisspeptin neurons show up only at puberty? We don't know for sure, but it looks like increased levels of E2 could be important for this.
Again, we get into a self-sustaining cycle. Growth of the body generates an increase in E2 production (possibly due to increased volume of the gonads?), which, when over a certain level permits the development of kisspeptin neurons, which will then stimulate the GnRH neurons, resulting in increased LH and E2. We then have more E2 and this makes kisspeptin neuron grow even more etc etc.
The following is multiple choice question (with options) to answer.
During adolescence, what causes most of the changes associated with puberty? | [
"methane",
"estrogen",
"testosterone",
"nicotine"
] | C | During adolescence, testosterone causes most of the changes associated with puberty. It causes the reproductive organs to mature. It also causes other adult male traits to develop. For example, it causes the voice to deepen and facial hair to start growing. |
SciQ | SciQ-6302 | evolution, biochemistry, mitochondria
Title: Is there any advantage of having mitochondria for aerobic respiration? If we consider the pathway of breakdown of glucose which includes glycolysis, the citric acid cycle and the electron transport chain, all these processes takes place in some prokaryotes and eukaryotes. In prokaryotes all these processes take place in cytoplasm while in eukaryotes the last two processes take place in mitochondria.
So is there any advantage of performing the last two processes in the mitochondria? Does it yield more energy? If there is no advantage, what is the point of having a mitochondria (at least for this process)? From the evolutionary point of view, the eukaryotes acquired these metabolisms (except glycolysis) from their prokaryotic endosymbionts. Not all prokaryotes have the ETC. The free living ancestor of mitohondria is supposed to be the alpha-proteobacterium.
Now, glycolysis is a common pathway in lot of lifeforms perhaps because of abundance of glucose. TCA cycle is coupled with ETC at certain steps which makes it essentially a part of aerobic metabolism.
The reason for having a dedicated organelle for respiration
ATP synthesis is a membrane process. Imagine a large prokaryotic cell- as big as an animal cell. Such a cell cannot take care of its energetic demands which primarily consists of protein synthesis with the given area of membrane i.e it needs much more ATP-synthases than it can have to cope up with the energy demands of maintaining such a huge cell (this index is approximated based on surface to volume ratio). Therefore it is wise to harbor multiple efficient organelles i.e. mitochondria which themselves have just a small essential genome and proteome to maintain.
For a better understanding, please read this article. I just loved it.
There is also a book by the same author about mitochondria called Power, Sex, Suicide.
The following is multiple choice question (with options) to answer.
What is essential for cellular respiration for all aerobic organisms? | [
"water",
"carbon",
"oxygen",
"nitrogen"
] | C | An online guide from the University of Illinois about air masses and fronts is found here: http://ww2010. atmos. uiuc. edu/%28Gh%29/guides/mtr/af/home. rxml . |
SciQ | SciQ-6303 | sexual-reproduction
So when it's not maintained -- when there's no selection pressure on two populations -- inevitably there will be genetic drift that will randomly disrupt this fine-tuned system. If a population of, say, voles is isolated on an island, they will continue to have pressure to be able to interbreed with other voles on the island, but if they can't interbreed with those on the mainland there won't be any consequences, and so over long enough time they'll drift and lose that ability -- just as many apes, not suffering any consequences from not synthesizing vitamin C, gradually lost that ability from random drift.
There's another side to it. Two populations in the same location may be positively selected to not be able to interbreed. Think about two groups of finches, one with small fine beaks that eat tiny seeds deep inside pine cones, and one with heavy beaks that crush and eat thick-shelled nuts. They each do fine, but they can interbreed and produce offspring that have intermediate beaks -- too thick to reach the fine seeds that one parent eats, but too delicate to crush the nuts that the other parent eats. Those intermediate offspring will die off, and both parents will have wasted their resources raising them. Both parents would be better off not breeding with each other, but only breeding with their own kind to produce specialized and efficient offspring. There is now selection pressure on the birds to recognize their own kind (perhaps through songs or mating displays) and ultimately to be inter-sterile, so they never waste resources on the un-fit offspring. There's a gradation of separation over time, in which the different populations become more and more distinct. Eventually, at some arbitrary point, humans start calling them "species", but that's just us, not biology.
"Species" is an important concept, but it's not special in evolution; speciation is just one aspect of natural selection, there's nothing magical about it.
The following is multiple choice question (with options) to answer.
Breeding in birds occurs through an internal type of what process? | [
"segmentation",
"fertilization",
"sedimentation",
"stimulation"
] | B | Breeding in birds is through internal fertilization, where the egg is fertilized inside the female. |
SciQ | SciQ-6304 | terminology, metabolism, energy-metabolism
As Wikipedia puts it (emphasis mine):
An endotherm is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions instead of relying almost purely on ambient heat.
That really does seem to better match the "exo-" prefix.
Is there a real inconsistency here, or do I just understand this incorrectly? The prefix "endo" comes from the Greek "endon" meaning "inner". "Therm" comes likewise from the Greek "therme" meaning heat.
Thus Endo = inner, Therm = heat, heat from inside!
The confusion applies in chemistry, not in that someone has it wrong, but that molecular reactions sometimes release heat - this is obviously to the outside so it must be "exo". The Greek opposite of exo is endo, so the converse reaction (absorbing heat) must be endothermic.
Note also that in the case of an endothermic reaction, the heat supplied for the reaction to work comes from within the materials of the reaction, it's just that in the process of the reaction occurring the heat is "used up" so the reaction vessel feels cold. Because the heat is coming from inside the reaction "endo" makes sense here too.
I did my basic chemistry too long ago for me to remember for endothermic reactions if environmental heat is needed for the reaction to proceed, but I suspect that at any temp above 0 K, the answer is generally no; the heat comes from breaking of intra-molecular bonds.
The following is multiple choice question (with options) to answer.
In an endothermic reaction, what is absorbed by the reaction? | [
"energy",
"fuel",
"food",
"atoms"
] | A | Because energy is a product, energy is given off by the reaction. Therefore, this reaction is exothermic. Because energy is a reactant, energy is absorbed by the reaction. Therefore, this reaction is endothermic. |
SciQ | SciQ-6305 | genetics
Title: Can there be medium height(neither tall nor short) pea plants in Mendel's experiment? Can there be medium height(neither tall nor short) pea plants in Mendel's experiment?
All textbooks I have read seem to imply that pea plants have to be either tall or short, nothing in between. Medium height (like in people) and other traits that seem like a mixture of two extremes are often a result of incomplete dominance. For example, a red and white flower are bred to produce an offspring with pink petals.
Mendelian genetics does not include incomplete dominance (which is classified as, surprisingly, non-Mendelian genetics).
Basically, Mendel got very lucky with his choice of plant. Pea plant height is strictly dominant, meaning one dominant allele results in tall plants, regardless of the identity of the second inherited allele. This is a consequence of the genetic makeup of pea plants. Had he tried a similar experiment with snapdragon flower color, he would be very confused.
(See https://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel2.htm for snapdragon incomplete dominance example.)
The following is multiple choice question (with options) to answer.
What scientist and monk is best known for his experiments with pea plants? | [
"steiner mendel",
"charles darwin",
"aristotle",
"gregor mendel"
] | D | Gregor Mendel was born in 1822 and grew up on his parents’ farm in Austria. He did well in school and became a monk. He also went to the University of Vienna, where he studied science and math. His professors encouraged him to learn science through experimentation and to use math to make sense of his results. Mendel is best known for his experiments with the pea plant Pisum sativum (see Figure below ). You can watch a video about Mendel and his research at the following link: http://www. metacafe. com/watch/hl-19246625/milestones_in_science_engineering_gregor_mendel_and_classical_genetics/ . |
SciQ | SciQ-6306 | rain, natural-disasters, flooding
Edit 2 August 2020
Concerning successful flood control measures, two quickly come to mind, the Thames Barrier in London, England and the Aswan Dam in Egypt, particularly the Aswan High Dam.
The Thames Barrier is a movable barrier system that is designed to prevent the floodplain of most of Greater London from being flooded by exceptionally high tides and storm surges moving up from the North Sea. It has been operational since 1982. When needed, it is closed (raised) during high tide; at low tide, it can be opened to restore the river's flow towards the sea.
Based on the success of the Low Dam, then at its maximum utilization, construction of the High Dam became a key objective of the government following the Egyptian Revolution of 1952; with its ability to better control flooding, provide increased water storage for irrigation and generate hydroelectricity the dam was seen as pivotal to Egypt's planned industrialization. Like the earlier implementation, the High Dam has had a significant effect on the economy and culture of Egypt.
The following is multiple choice question (with options) to answer.
What are structures that protect the coast like barrier islands called? | [
"dunes",
"domes",
"fortresses",
"breakwaters"
] | D | Breakwaters are structures that protect the coast like barrier islands. Groins are structures that help prevent longshore drift from eroding a beach. |
SciQ | SciQ-6307 | genetics
Title: How does chromosome cross-over occur? I have heard that during meiosis, homologous chromosomes from each parent "cross-over", which enables the off-spring to inherit some alleles from the mother and some alleles from the father. The picture below illustrates this "cross-over", but of course this must occur at multiple sites, rather than just the one shown in the picture.
Now my question is what causes the chromosomes to align perfectly during cross-over so that the loci of a particular gene will substitute for the corresponding loci on the homologous chromosome, as opposed to being substituted with a completely random locus? Does each gene have a unique non coding sequence before it specifying what gene it is to enable this process to occur? Quite simply, because chromosome pairing is sequence specific. Holliday Junctions, which are the functional structures of a cross-over, occur through a process called "strand invasion," during which a region of one chromosome physically base-pairs with that of another. Thus one locus cannot pair with a random locus, as there is generally insufficient sequence complimentarity between two random regions to form a functional Holliday Junction. One interesting consequence of this mechanism is gene duplication and deletion in repetitious regions of the chromosome. For example, genes with large repeated regions, such as the gene responsible for Huntington's disease, can expand and contract during homologous recombination due to strand invasion occurring at non-equivalent, but still homologous, sites. Wikipedia does a nice job going over homologous recombination. I also recommend looking over the relevant sections in Molecular Biology of the Cell, available on the PubMed Bookshelf.
The following is multiple choice question (with options) to answer.
What leads to multiple copies of a chromosomal region? | [
"subtractions",
"duplications (or amplifications )",
"gene modification",
"minimilizations"
] | B | Duplications (or amplifications ) lead to multiple copies of a chromosomal region, increasing the number of the genes located within that region. Some genes may be duplicated in their entirety. |
SciQ | SciQ-6308 | plant-physiology, photosynthesis, botany
Having a larger total leaf area (La Rocca et al. and also see this question)
Only developing large white areas if there's plenty of light as they grow (Garland et al.)
Increasing the mitochondrial activity in its white areas, which could lead to other energy efficiencies (Toshoji et al.)
Using Homo sapiens to help it reproduce and provide plenty of light for it. Many of these extreme variegation patterns are found in horticulturally bred varieties!
Just using its green areas for photosynthesis, and "accepting" the fact that the white areas are not producing energy. In natural populations, you often don't find varieties as completely white as in that picture: they usually show white spots and plenty of green. This is true of Caladium species in the wild, which may use the variegation to mimic and to prevent herbivory: potential pests think the leaves are already infested, and avoid them (Soltau et al.). In other words, even if the white patches represent decreased photosynthesis efficiency, it could be a trade-off in order to achieve less herbivory.
The following is multiple choice question (with options) to answer.
The larger surface area of leaves allows them to capture more what? | [
"pollen",
"chlorophyll",
"molecules",
"sunlight"
] | D | Roots: Support for the Plant Roots are not well preserved in the fossil record; nevertheless, it seems that they did appear later in evolution than vascular tissue. The development of an extensive network of roots represented a significant new feature of vascular plants. Thin rhizoids attached the bryophytes to the substrate. Their rather flimsy filaments did not provide a strong anchor for the plant; neither did they absorb water and nutrients. In contrast, roots, with their prominent vascular tissue system, transfer water and minerals from the soil to the rest of the plant. The extensive network of roots that penetrates deep in the ground to reach sources of water also stabilizes trees by acting as ballast and an anchor. The majority of roots establish a symbiotic relationship with fungi, forming mycorrhizae. In the mycorrhizae, fungal hyphae grow around the root and within the root around the cells, and in some instances within the cells. This benefits the plant by greatly increasing the surface area for absorption. Leaves, Sporophylls, and Strobili A third adaptation marks seedless vascular plants. Accompanying the prominence of the sporophyte and the development of vascular tissue, the appearance of true leaves improved photosynthetic efficiency. Leaves capture more sunlight with their increased surface area. In addition to photosynthesis, leaves play another role in the life of the plants. Pinecones, mature fronds of ferns, and flowers are all sporophylls—leaves that were modified structurally to bear sporangia. Strobili are structures that contain the sporangia. They are prominent in conifers and are known commonly as cones: for example, the pine cones of pine trees. |
SciQ | SciQ-6309 | botany, plant-physiology, plant-anatomy
Title: Sporophyte and gametophyte
My textbook says that in both groups of seedless plants (vascular plants, non-vascular plants) the gametophyte is a free-living plant, independent of the sporophyte.
I don't understand this statement and am now wondering if the sporophyte and gametophyte are stages in a plant's lifecycle, or are they individual parts of the plant, or are the sporophyte and the gametophyte different plants altogether? Secondly, does this differ depending on the organism?
Different plants or different structures that make up the same organism? The sporophtye is the diploid stage in the life cycle. In comparison, with humans, you and I would be sporophytes.
The Gametophyte is the haploid stage in the life cycle. In comparison, with humans, spermatozoids and ovules are gametophytes.
The following is multiple choice question (with options) to answer.
What is connected to, and dependent on, the gametophyte? | [
"the zygote",
"the sperm",
"the sporophyte",
"the chromosomes"
] | C | Following fertilization, the sporophyte forms. The sporophyte is connected to, and dependent on, the gametophyte. |
SciQ | SciQ-6310 | metabolism, human-anatomy, pharmacology, liver
Title: Circulation through the liver in light of drug metabolism I have a lingering question which stems from an answer that I gave to What hydrolyses aspirin within the digestive tract and blood stream?
When a drug or any other substance is absorbed into the bloodstream in the stomach or small intestine, it ultimately passes through the hepatic portal vein and into the liver sinusoids, where it is processed by hepatocytes and introduced into the general circulation via the vena cava. In terms of metabolism, this is what causes a "first-pass" effect for drugs that are ingested.
For drugs that are delivered either by intravenous, intramuscular, or sub-lingually (as in the other Biology.SE question), this first-pass effect is avoided, and the drug is introduced into the general circulation without being metabolized by the liver first.
Even though the first pass is avoided, the blood in the body still makes its way back through the liver eventually via the hepatic artery, which is a branch off of the celiac artery.
The issue I still have is, does the incoming blood from the hepatic artery merge with the blood from the hepatic portal vein? If not, does the blood from the hepatic artery still interact with the hepatocytes in some way? (it makes sense that it does, and I have also read that one of the main functions of the hepatic artery was to deliver blood supply for the liver's metabolic needs) If this is not the case, where in the body would these drugs that were introduced via IV, etc., be metabolized? Yes, the blood from the hepatic artery (proper) and the portal vein mix in the sinusoids of the liver. The hepatic vein supplies about 75% of the blood to the liver, and the hepatic artery the remaining 25%. Because the portal vein provides such a large part of the blood supply to the liver, then any disease that causes the blood to build up can cause portal hypertension.
The hepatic artery carries oxygen-rich blood from the heart. The portal vein is part of the portal system and connects the capillary beds of the gastrointestinal tract to those of the liver. Because of the larger volume through the portal vein, I think that each vessel carries about half the oxygen supply to the liver.
The following is multiple choice question (with options) to answer.
After passing through capillaries and being filtered, clean blood leaves what organ through a vein? | [
"kidney",
"liver",
"pancreas",
"heart"
] | A | Blood with wastes enters each kidney through an artery, which branches into many capillaries. After passing through capillaries and being filtered, the clean blood leaves the kidney through a vein. |
SciQ | SciQ-6311 | genetics, covid
Title: Searching for a vaccine vs searching for poor genes in the covid-19 pandemic I have only basic knowledge about biology. I have some propositions (may be wrong) and a question about the covid-19 pandemic.
In 1918, the world had a similar pandemic, the Spanish Flu. Millions of people died because of natural selection. Poor genes on flu were eliminated and strong genes survived. Nowadays flu is just an ordinary disease for people because we are the generation of strong genes and our genes are also strong for flu.
Similarly, for the Covid-19 pandemic, poor genes are getting eliminated unfortunately. (I think Covid-19 disease will be just as ordinary as flu in 5-10 years.) For almost 2 years, people have worked for vaccines and we learned that the mortality ratio of Covid-19 is nearly %3 by statistical data.
My question is, instead of quarantining all people for almost 2 years, trying to find a vaccine for almost 2 years and trying to vaccinate all people (only %3 of people are under a death risk), couldn't we just had searched for a pattern for poor genes? So that we might have to quarantine only those with poor genes and might have searched for a cure or vaccine for them?
Is anyone working on something like this, or am I thinking too simply for such a complex problem? Unfortunately your assumptions are almost completely incorrect.
The reasons some get sick and die and others don't are multi(multi)factorial. There will be some genetic component, but also things like prior exposure to similar disease(s),socio-economic status, health status, age (this is a big one for COVID-19), all play into it.
The 1918 H1N1 influenza outbreak had a large number of confounding factors - it was in the middle of a global war, with large numbers of people (especially troops) crowding together (e.g. transport boats, barracks), often in terrible conditions (trenches), large portions of the world (esp. western Europe, China, Korea, parts of Africa) being refugees with poor nutrition, stress etc.
The following is multiple choice question (with options) to answer.
What kind of medical intervention seeks to eradicate diseases like polio and measles? | [
"vaccination",
"malnutrition",
"surgical intervention",
"nutrition"
] | A | |
SciQ | SciQ-6312 | zoology, ornithology
Bancroft, G. T., & Woolfenden, G. E. (1982). The molt of scrub jays and blue jays in Florida. Ornithological Monographs, (29), iii-51.
Conant, S. (1972). Visual and acoustic communication in the blue jay, Cyanocitta cristata (Aves, Corvidae). The University of Oklahoma.
Dwight, J. (1900). The sequence of plumages and moults of the passerine birds of New York. New York Academy of Sciences.
The following is multiple choice question (with options) to answer.
The ostrich, kiwi, rhea, cassowary, and moa are examples of what kind of birds? | [
"flightless",
"raptors",
"predators",
"prehistoric"
] | A | Some birds have lost the ability to fly during the course of their evolution. Several flightless birds are shown in Figure below . They include the ostrich, kiwi, rhea, cassowary, and moa. All of these birds have long legs and are adapted for running. The penguins shown in the figure are also flightless birds, but they have a very different body shape. That’s because they are adapted for swimming rather than running. |
SciQ | SciQ-6313 | sexual-reproduction
So when it's not maintained -- when there's no selection pressure on two populations -- inevitably there will be genetic drift that will randomly disrupt this fine-tuned system. If a population of, say, voles is isolated on an island, they will continue to have pressure to be able to interbreed with other voles on the island, but if they can't interbreed with those on the mainland there won't be any consequences, and so over long enough time they'll drift and lose that ability -- just as many apes, not suffering any consequences from not synthesizing vitamin C, gradually lost that ability from random drift.
There's another side to it. Two populations in the same location may be positively selected to not be able to interbreed. Think about two groups of finches, one with small fine beaks that eat tiny seeds deep inside pine cones, and one with heavy beaks that crush and eat thick-shelled nuts. They each do fine, but they can interbreed and produce offspring that have intermediate beaks -- too thick to reach the fine seeds that one parent eats, but too delicate to crush the nuts that the other parent eats. Those intermediate offspring will die off, and both parents will have wasted their resources raising them. Both parents would be better off not breeding with each other, but only breeding with their own kind to produce specialized and efficient offspring. There is now selection pressure on the birds to recognize their own kind (perhaps through songs or mating displays) and ultimately to be inter-sterile, so they never waste resources on the un-fit offspring. There's a gradation of separation over time, in which the different populations become more and more distinct. Eventually, at some arbitrary point, humans start calling them "species", but that's just us, not biology.
"Species" is an important concept, but it's not special in evolution; speciation is just one aspect of natural selection, there's nothing magical about it.
The following is multiple choice question (with options) to answer.
What occurs when individuals of different species strive for a limited resource in the same area? | [
"asexual competition",
"vegetal competition",
"interspecific competition",
"intraspecific competition"
] | C | Interspecific competition happens when individuals of different species strive for a limited resource in the same area. Since any two species have different traits, one species will be able to out-compete the other. One species will be better adapted to its environment, and essentially "win" the competition. The other species will have lower reproductive success and lower population growth, resulting in a lower survival rate. For example, cheetahs and lions feed on similar prey. If prey is limited, then lions may catch more prey than cheetahs. This will force the cheetahs to either leave the area or suffer a decrease in population. |
SciQ | SciQ-6314 | mycology
Title: How do fairy rings propagate? It was somewhat new to me that mushrooms usually aren't individual organisms, but are merely the visible bodies of a bunch of fungi living in the soil. I know that mushrooms emit spores to reproduce, but what has been bizarre to me is how fairy rings form. Why do the fruiting bodies arrange themselves in a more or less circular shape, as opposed to the random scattering one would expect from wind-borne spores? When a fungal spore germinates in a suitable location, the growing mycelium will spread underground in all directions. In the ideal situation, the result is that the mycelium will become circular. Over time, the center of the mycelium will die out whereas the newly formed mycelium (underground) will develop the familiar mushrooms above ground and this will result in a fairy ring.
The following is multiple choice question (with options) to answer.
Most fungi reproduce asexually by producing what? | [
"seeds",
"ions",
"spores",
"toxins"
] | C | Almost all fungi reproduce asexually by producing spores. A fungi spore is a haploid cell produced by mitosis from a haploid parent cell. It is genetically identical to the parent cell. Fungi spores can develop into new haploid individuals without being fertilized. |
SciQ | SciQ-6315 | history-of-chemistry, salt
I can provide the references he uses if requested.
The problem was introducing a systematic nomenclature for describing substances because there was an ever-increasing number of them being discovered.
The general historical evolution starts with the fields of botany and chemistry at the beginning of the 18th century, where Linnaeus' botanical binomial nomenclature was used by Bergman toward the end of the century. Guyton de Morveau extended and refined Bergman's scheme and collaborated with Lavoisier to establish what we work with today.
In the 16th century, Paracelsus referred to potassium bisulphate (which is more soluble than potassium sulphate) as ${\it sal\ enixum}$ in the alchemical literature. Paracelsus was famous (in part) for putting forth the theory that metals are composed of "Mercury, Sulphur and Salt," arising in alchemy.
Later, in 1664, the French chemist Le Fubure published work in which he differentiated salts of nitre by crystal habit. Duhamel, in 1736, showed that the salts of potassium and sodium were distinguishable by their bases.
In any case, there was a pressing need to formalize a nomenclature. Torbern Bergman (1735-84) is credited with taking on the task of reform in the first orderly manner. He introduced (via publication) his ideas towards a binomial system for naming, which was limited although a good start.
Guyton de Morveau expanded on Bergman's ideas and was able to systematically name 500 salts from 18 acids and 24 bases (earths, alkalis, and metals).
The big arrival was ${\it Méthode\ de\ nomenclature\ chimique}$ in 1787 and was authored by Guyton de Morveau, Lavoisier, Berthollet, and Fourcroy. It is at the point that the system for naming chemicals was in place. From here, the contributions of British, German, and other chemists was incorporated.
By the early 19th century, additions and revisions to the above were made and the systems of naming was largely in place. The evolution of naming things from the earth as 'salts' to naming things in a certain class as 'salts' largely took place during the last quarter of the 18th century.
The following is multiple choice question (with options) to answer.
Alchemists, as early as the eighth century, knew nitric acid as aqua fortis, which means? | [
"strong water",
"applied water",
"isolated water",
"clean water"
] | A | Nitrogen Oxyacids and Salts Nitrogen pentaoxide, N2O5, and NO2 react with water to form nitric acid, HNO3. Alchemists, as early as the eighth century, knew nitric acid (shown in Figure 18.50) as aqua fortis (meaning "strong water"). The acid was useful in the separation of gold from silver because it dissolves silver but not gold. Traces of nitric acid occur in the atmosphere after thunderstorms, and its salts are widely distributed in nature. There are tremendous deposits of Chile saltpeter,. |
SciQ | SciQ-6316 | inorganic-chemistry, solubility, analytical-chemistry
Title: Solubility and wetting of substances in water We have seen that, when we pour salt in water then it gets dissolved, that means it is soluble in water. But when we pour sand into water then it doesn't dissolve in water, that means it is insoluble, but still sand gets wet. But there are certain substances which doesn't get wet by water for example, sulfur particles don't get wet by water but wet in oil, as I was studying about froth floatation method.
My question is that:
What is the difference between solubility and wetting in water ?
What is the reason that the sulfur particle doesn't get wet by water? Polar/hydrophilic soluble substances get dissolved, like table salt or sugar.
Polar/hydrophilic insoluble substances get wet, as they attract water, like sand, or limestone.
Nonpolar/hydrophobic insoluble substances do not get wet, as they repulse water, like wax, teflon or silanized glass.
The following is multiple choice question (with options) to answer.
Particles of sand and what other substance are carried by longshore drift? | [
"rock",
"bone",
"magma",
"soil"
] | A | Longshore drift carries particles of sand and rock down a coastline. |
SciQ | SciQ-6317 | homework, embryology
Title: Why are Birds and Reptiles with abundant yolk sac polyspermic? I was given an explanation that birds and reptiles are polyspermic because they have an abundant yolk sac. But how does it explain the thing?
Chicken as an adult is not using in my opinion yolk as an energy source.
Yolk is used during embryogenesis as the primary energy source with blastula and gastrula -stages and during organogenesis, since the embryo needs proteins and energy somewhere.
How does abundant yolk sac make birds and reptiles polyspermic? My professor says that
The yolk sac is not connected to the mechanism of polyspermy or
monospermy. [Amount of yolk inside the oocyte is then again.] The
oocytes of reptiles and birds are yolk rich - polylecithal for instance.
where
lecithal = yolk containing and some pieces of information about here.
The following is multiple choice question (with options) to answer.
Most reptiles reproduce sexually and have what type of fertilization? | [
"additional",
"external",
"internal",
"mechanical"
] | C | Most reptiles reproduce sexually and have internal fertilization. |
SciQ | SciQ-6318 | physical-chemistry, aqueous-solution, gas-laws, vapor-pressure
An example of this situation playing out in the environment can be seen in the growth of water and ice particles in clouds. The vapor pressure of one particle can differ from that of another due to solute concentration, particle size (small droplets have a greater vapor pressure than larger droplets) and phase (supercooled water droplets have a greater vapor pressure than ice particles at the same temperature). Regardless of the cause of the vapor pressure difference, whether it's solute concentration or one of the other factors, the situation is the same as depicted in your question. And the result is the same; the particles having greater vapor pressure will end up evaporating and then condensing onto the particles having lower vapor pressure (of course we're talking about vapor pressure of water/ice only, not any solute). This is generally referred to as the Wegener–Bergeron–Findeisen process, although this technically only refers to water-to-ice vapor transfer.
The following is multiple choice question (with options) to answer.
What is type of substance is formed when water vapor condenses or when ice melts? | [
"gaseous water",
"chemical water",
"toxic water",
"liquid water"
] | D | Liquid water is formed when water vapor condenses (i. e. , H 2 O(g) → H 2 O(l) or when ice melts (i. e. , H 2 O(s) → H 2 O(l)). Because water is a molecular substance, it is a poor conductor of electricity in its pure form. However, as we will see later, its conductivity can be improved by the addition of certain substances. Water molecules are polar, and this overall polarity gives rise to many of the properties of water. For example, an interesting effect is seen when water is placed in a static electric field, as shown in the Figure below and the video below. This phenomenon can be explained in terms of the polarity of water molecules. |
SciQ | SciQ-6319 | exoplanet
It's probably possible to have volcanic eruptions even though dozens or maybe even hundreds of miles of exotic ice because the heat has to go somewhere, eventually, assing it's likely to build up over time, so either by circulation of eruption, the heat has push through at some point. This even happens on so called "dead" planets like Mars or even the Moon. Mars still has the occasional volcanic eruption, just not very often.
But water worlds certainly can have plate tectonics. There's nothing in the water that would prevent it from happening. Plate Tectonics is, as I understand it, primarily a factor of the size of the planet. Gas planets - different story, but planets with a hard surface, Earth sized, a tiny bit smaller to a fair bit but not much bigger are good candidates for plate tectonics (I think). There's some debate on how large, I think, still going on. But I remember reading that ocean/water worlds might even be more likely to have plate tectonics. Plate tectonics is definitely something we'd look for if we ever get a close enough look at other planets in different solar-systems (exoplanets).
Just my thoughts on this. Not meant to be complete or definitive.
The following is multiple choice question (with options) to answer.
What occur because solid lithosphere travels on a round planet? | [
"intraplate earthquakes",
"volcanos",
"aeration earthquakes",
"ejecta earthquakes"
] | A | Intraplate earthquakes occur because solid lithosphere travels on a round planet. |
SciQ | SciQ-6320 | evolution, genetics, molecular-genetics, theoretical-biology, molecular-evolution
Title: Smallest unit on which selection can act Traditionally, the individual was considered to be the smallest unit on which Natural Selection (NS) acts. Today, we usually consider the gene as being the unit of NS. Of course, we should also consider all sequences that affect the fitness even though they are not genes (even though the do not code for polypeptide). And theoretically, any sequence of DNA does have an effect on fitness because it influences the time and energy for DNA replication (although it might be negligible). The decision of considering the gene as the smallest unit of NS seems rather arbitrary to me. We might as well consider a group of genes or a given exon of even a smaller sequence.
Here are my questions:
What factors influence the minimal size of a sequence to be considered as a unit on which NS acts? Mutation rate, generation time, selection differential for this sequence, recombination rate, ...?
Could we consider a nucleotide as a unit of NS? Why?
How does the quasispecies model fit into the question of what is the smallest unit of NS? (for those interested, you will also find a very good explanation of this model in Martin Nowak's book called Evolutionnary Dynamic: exploring the equations of life)
Is it worth talking about that? Is this question biologically relevant? Or is it rather a question based on a choice of definition such as "Is a virus alive?"
As I asked several questions, let me know if I should split my post into several. Otherwise, please do not hesitate to answer only very partially to this post!
UPDATE
Terdon's answer makes sense to me. I should be a bit more accurate in the reas of my question. I read The extended Phenotype from Richard Dawkins quite a long time ago and if I'm not mistaken, Dawkins says the following things
A unit on which selection acts has to be:
active
germ-line
replicator
A replicator has the 3 following properties:
fecundity
longevity
fidelity while being copied
The following is multiple choice question (with options) to answer.
What is the unit of evolution? | [
"population",
"biome",
"species",
"community"
] | A | Remember that individuals do not evolve. Their genes do not change over time. The unit of evolution is the population. A population consists of organisms of the same species that live in the same area. In terms of evolution, the population is assumed to be a relatively closed group. This means that most mating takes place within the population. The science that focuses on evolution within populations is population genetics . It is a combination of evolutionary theory and Mendelian genetics. |
SciQ | SciQ-6321 | intermolecular-forces, boiling-point, dipole
Title: Why are the dispersion forces in CS2 stronger than the dipole-dipole forces in COS? London dispersion forces supposedly have the least strength out of all the intermolecular forces. But $\ce{CS2}$, which has only dispersion forces, has a higher boiling point (and thus stronger intermolecular forces) than $\ce{COS}$, which has dipole-dipole attraction in addition to dispersion forces. Why is this?
I suppose that it has something to do with $\ce{CS2}$ having a thicker/more inducible electron shell, but then a new question arises: how would you know if the dispersion forces in one molecule are stronger that the dipole-dipole forces in another?
(Theoretically, without using boiling points or other experimental data. Also, this is based on question 4a from the 2018 AP chemistry free response.) Although individual dispersion forces are weak, they are cumulative, and increase with molar mass. As a general rule, boiling point increases with molar mass.
Polar molecules will have higher boiling points when compared to molecules with similar molar masses. For example, ethanol($\ce{CH3CH2OH}$) has a higher boiling point than dimethyl ether ($\ce{CH3OCH3}$).
$\ce{CS2}$ is ~16 g/mol heavier than COS.
The following is multiple choice question (with options) to answer.
The boiling points of liquid also correlate to the strength of which forces? | [
"intermolecular",
"gravitational",
"supramolecular",
"centrifugal"
] | A | The boiling points of liquid also correlate to the strength of the intermolecular forces. Recall that diethyl ether has weak dispersion forces, which meant that the liquid has a high vapor pressure. The weak forces also mean that it does not require a large an input of energy to make diethyl ether boil and so it has a relatively low normal boiling point of 34.6°C. Water, with its much stronger hydrogen bonding, has a low vapor pressure and a higher normal boiling point of 100°C. |
SciQ | SciQ-6322 | everyday-chemistry, biochemistry, food-chemistry, terminology
Vitamin D is not strictly a vitamin, rather it is the precursor of one
of the hormones involved in the maintenance of calcium homeostasis and
the regulation of cell proliferation and differentiation, where it has
both endocrine and paracrine actions.
The name vitamin D1 was originally given to the crude product of irradiation of ergosterol,
which contained a mixture of ergocalciferol with inactive lumisterol (an isomer of ergosterol) and suprasterols. When ergocalciferol was identified
as the active compound, it was called vitamin D2. Later, when cholecalciferol was identified as the compound formed in the skin and found in foods, it was
called vitaminD3.
Remarks
The "Vitamin B" naming of these compounds must have been through discovery, and no clear experiments had accurately produced identity of these compounds, there were named as they were discovered but since they have been identified they they now have systematic names
abeit vitamin B still being used today and are formulated as "vitamin B complexes" in pharmaceutical products (perhaps to avoid confusion) hence systematic names are used (folic acid, pantonthenic acid, biotin, thiamin, niacin, cobalamin etc) I have never come across complexes of other Vitamins. Remember for a compound to be named a vitamin it must fit the description above, but I am not disputing the fact that other compounds with similar biological activities exist as "K" group.
References
Nutritional Biochemistry of Vitamins (Bender)
Nutritional biochemistry (Brody)
Modern Nutrition in Health and Disease (Rosset al)
The following is multiple choice question (with options) to answer.
Vitamin d is made in the skin when it is exposed to what? | [
"water",
"darkness",
"dirt",
"sunlight"
] | D | Vitamins are organic compounds that the body needs in small amounts to function properly. Humans need 16 different vitamins. Six of them are listed in Table below . Vitamin D is made in the skin when it is exposed to sunlight. Bacteria that normally live in the gut make vitamins B12 and K. All other vitamins must come from food. The table shows good food sources of the vitamins. |
SciQ | SciQ-6323 | radiation, material-science, radioactivity
Title: Working out the penetration of radioactive decay products From my understanding of the products of radioactive decay (alpha particles, beta particles, and gamma are all I know of), the particles (or energy I guess?) are stopped by a medium according to it's density, and the atomic size of the atoms that make it up (I could quite easily be wrong). Without conducting an experiment, how would you calculate how far the three types of radioactive decay can travel through a certain material, knowing only the material's density (or any other documentable property)? We take into account the inelastic interactions that take place between the respective type of particle and the material, i.e. interaction that can consume part of the energy of the radiation particle, and calculate the mean-free path of the respective type of particle in the material. In this calculus we also consider the density and the structure of the material. In general, for particles with rest-mass, the higher is the velocity, the lower is the cross section of interaction with the material, and longer the free path in it. But the charge of the particle and mass are also relevant. For instance, $\alpha$ particles although very energetic, have low velocities, are highly ionizing and can travel only a few centimeters in air.
The opposite example are $\gamma$ rays. The higher is their energy the harder is to stop them. Before being finally being absorbed by some photoelectric event or pair production (for energy > 1.02Mev), they can interact a lot on the way by Compton scattering. Thick walls of concrete are needed to stop them, or isolation by lead layers. $\beta$ radiation has intermediate properties.
The following is multiple choice question (with options) to answer.
Of the three basic types of radioactive emissions, what particle is the most penetrating? | [
"alpha",
"gamma",
"neutron",
"beta"
] | B | The various emissions will differ considerably in their ability to go through matter, known as their penetrating ability . The α-particle has the least penetrating power since it is the largest and slowest emission. It can be blocked by a sheet of paper or a human hand. Beta particles are more penetrating than alpha particles, but can be stopped by a thin sheet of aluminum. Of the three basic types of emissions, gamma particle are the most penetrating. A thick lead shield is required to stop gamma emissions. Positrons represent a special case in that they annihilate when they come in contact with electrons. The collision of a positron and an electron results in the formation of two gamma emissions that go 180 degrees away from each other. |
SciQ | SciQ-6324 | ocean, oceanography, sea-level, tides
However, I'm really curious as which are the most important amongst them? Or is it even possible to guess the tide height if I know the Lunar phase and I have a good globe with sea depth? I don't know about the size of land masses, but their distribution and the shape of ocean basins definitely play a big role.
When considering the ideal case of an all-ocean globe, i.e. one with no land masses (equilibrium tidal theory), the combined effect of sun and moon give a theoretical tidal range of less than 1 m(1). As tidal ranges can be much larger than this, there are other effects that has a greater influence.
The Bay of Fundy for example, is one of the places with the largest difference between low tide and high tide, at about 16 m. The large difference in this location has to do with the shape of the bay. The bay has a natural frequency for waves that is about the same as the frequency of the tide itself, giving an amplification of the tidal amplitude. In addition there is a funnelling effect in the inner part of the bay, giving an additional contribution.(2)
Another example of large tidal differences is the English channel, particularly the French side. In this case the tides are large at least partly because the tide moves as a coastal trapped Kelvin wave. These are waves that propagate along land, with the land to the right when looking in the direction of propagation (on the Northern hemisphere, land to the right on SH). The amplitude of the wave is highest near the coast, decaying exponentially away from the coast. As the tide in the English channel moves northward, the largest tidal range is on the French side.
With regard to guessing the tidal range, this is not entirely straight forward.
First, when discussing tides, we generally split the tidal potential into a series of oscillations having different frequencies, mainly either diurnal (period of ~24 h) or semi-diurnal (period of ~12 h).
These given frequencies are obtained through trigonometric considerations, and depend on the latitude of the point, the declination of the moon or sun relative to the equator, and the hour angle.
(The hour angle is basically the longitudinal difference between the sub-lunar point and the point we consider.)
Each of these components can vary in time and space.
The following is multiple choice question (with options) to answer.
Which ocean zone is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide? | [
"deep zone",
"calcareous zone",
"miniscule zone",
"intertidal zone"
] | D | One of the most familiar ocean zones is the intertidal zone. This is the narrow strip along a coastline that is covered by water at high tide and exposed to air at low tide. You can see an example of an intertidal zone in Figure below . There are plenty of nutrients and sunlight in the intertidal zone. Producers here include phytoplankton and algae. Other organisms include barnacles, snails, crabs, and mussels. They must have adaptations for the constantly changing conditions in this zone. |
SciQ | SciQ-6325 | genetics, biochemistry, proteins, rna
Title: Where do amino acids get attached to tRNA and where is it synthesized? Some very basic parts of transcription/translation seem to be left out in various literature. I can't find the answer to this anywhere:
How exactly is tRNA synthesized? I realize that mRNA is synthesized through transcription and I know a lot about that. However tRNA is supposedly synthesized the same way but every time you read about transcription they just talk about how the mRNA then gets this and that...?
Where do the amino acids get attached? Is it in the nucleus or outside the nucleus?
Thanks. A pre-tRNA is transcribed from tRNA genes in DNA by RNA polymerase III. Processing occurs in the nucleus, where a 5' sequence is cleaved by RNase P, the 3's CCA motif is added, and ~10% of the nucleotides are substituted. The tRNA are transported out via the pore complexes. Aminoacyl-tRNA synthetase enzymes attach amino acids in the cytoplasm in a 2-step reaction that requires ATP. You'll find there's a unique splicing mechanism in tRNA that additionally splices out an anticodon intron which is abesnt in mature tRNA's:
The wikipedia article notes RNA Pol III generally recognizes internal control elements rather than upstream control elements as in a normal gene.
Source: Qiagen
Source: Molecular Cell Biology. 4th edition.
Addendum: I said in my post that tRNA is charged in the cytoplasm, this is somewhat true. In mammalian cells, we also see that tRNA are charged in the nucleus as well, and it might aid in the export of some of these charged tRNAs. (Source)
The following is multiple choice question (with options) to answer.
Elongation is the addition of what to the mrna strand? | [
"codons",
"glycine",
"nucleotides",
"filaments"
] | C | Elongation is the addition of nucleotides to the mRNA strand. |
SciQ | SciQ-6326 | coordinate, positional-astronomy
Title: What is the connection between declination and latitude? The celestial equator is a projection of the terrestrial equator on the celestial sphere. So doesn't that mean the geographical latitude and the declination will be "exactly" equal, as they are measured from the same reference point (Celestial Equator = Geographical Equator)?
$$\lambda = \delta \pm (90° - \rm{Altitude})$$
latitude = the star's declination ± its zenith distance
= the star's declination ± (90° - the star's altitude)
Source : https://cseligman.com/laboratory/navcalc.htm
So what is the meaning of this formula as Latitude = Declination?
Also I'm unable to understand that plus-or-minus sign (north of zenith and south of zenith). It may be easier to visualize the formula by calculating the altitude based on the observer's latitude (lat) and the object's declination ($\delta$), and then re-arranging the equation to find the observer's latitude. First, the equation is only true when the object is on the meridian. Here is a diagram through the meridian (for an observer at a northern latitude):
The following is multiple choice question (with options) to answer.
What is the distance north or south of the equator called? | [
"latitude",
"Prime Meridian",
"longitude",
"inclination"
] | A | Latitude is the distance north or south of the equator. It’s measured in degrees, from 0° to 90°. Several climate factors vary with latitude. |
SciQ | SciQ-6327 | newtonian-mechanics, forces, classical-mechanics, conservation-laws
Title: Questions about isolated systems and conservative vs non-conservative forces Is it correct to say that mechanical energy will always be conserved in any conservative system (a system with no non-conservative forces), no matter if it's isolated or not? Are there any examples of isolated systems that have non-conservative forces, and if so, can the friction force be one of them? Or is a system with friction force always non-isolated?
I also don't fully understand this example I read about a non-isolated system:
"Hans Full is doing the annual vacuuming. Hans is pushing the Hoover vacuum cleaner across the living room carpet."
The explanation is that it's a non-isolated system because "the friction between the cleaner and the floor and the applied force exerted by Hans are both external forces. These forces contribute to a change in total momentum of the system."
I'm confused because we were never told which elements are part of the system and which are not. If we consider the system to be the floor/carpet and the cleaner, then why is the friction force between them external? I would have thought the friction force is coming from the floor, which is part of the system, therefore it's internal. What if we considered Hans to be part of the system too? Would it then become an isolated system (supposing that the friction force is also considered internal)? All the examples I read about non-isolated systems are systems in which there is friction force. But I don't understand why that force HAS to be external. Is it always so, or is it just that I'm reading too many similar examples?
Is it correct to say that mechanical energy will always be conserved
in any conservative system (a system with no non-conservative forces)
The following is multiple choice question (with options) to answer.
The force exerted by a diving board is conservative, provided the internal friction is this? | [
"negligible",
"significant",
"intrinsic",
"static"
] | A | 7.4 Conservative Forces and Potential Energy 9. What is a conservative force? 10. The force exerted by a diving board is conservative, provided the internal friction is negligible. Assuming friction is negligible, describe changes in the potential energy of a diving board as a swimmer dives from it, starting just before the swimmer steps on the board until just after his feet leave it. Define mechanical energy. What is the relationship of mechanical energy to nonconservative forces? What happens to mechanical energy if only conservative forces act? 12. What is the relationship of potential energy to conservative force?. |
SciQ | SciQ-6328 | 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.
Along with other elements, most ores are made of what? | [
"sodium",
"coal",
"crystals",
"metal"
] | D | When the ore leaves the mine, it is not yet a useful material ( Figure below ). Most ores are a combination of metal and other elements. The rocks are full of valuable minerals. They also contain rock that isn't valuable, which is called waste rock. The valuable minerals must be separated from the waste rock. |
SciQ | SciQ-6329 | fluid-dynamics
Title: Are waves affected by an under-water barrier? Given a wave propagating at the surface of still water towards a barrier that is below the surface, but at a distance that is of the order of the dimensions of the wave (such as depicted in the scheme below).
How will the course of the wave be affected ?
Will it be blind to it and pursue its course unaffected ?
Will it only partially pursue and a part of it will bounce back ?
Something else ?
<
wave
/~~~
/~~~~\ ->
~~~~/~~~~~~`~~~~~~~~~~~~~~~~~~~~~~~~ water surface
____
| |
| |
____________________| |__________
barrier Ocean surface waves that are said to 'feel' bottom are known as shallow water waves which are categorically differentiated from deep water waves according to wavelength and depth, and which are not as affected by the depth of the sea floor.
Ocean surface waves are a movement of energy, not a bulk forward motion of water but do result in local circular orbits of the water particles. With depth the circular orbits flatten into elliptical orbits and eventually vanish, and it's at this depth obstacles will no longer influence surface wave motion. For obstacles that do intrude into this space, the circular or elliptical motions are disturbed and energy is dissipated towards the upper water layers, building up wave height. IN very shallow water the build up can get high enough that the wave can no longer sustain its shape and you have a breaking wave.
The property that actually leads to the loss of energy from obstacles is the viscosity of the water, the ability for layers of water to flow over one another.
The following is multiple choice question (with options) to answer.
The bottoms—but not the tops—of the wave slow down because of what? | [
"vibration",
"temperature",
"friction",
"size"
] | C | In shallow water close to shore, waves start to drag on the bottom of the water. The bottoms—but not the tops—of the wave slow down because of friction. This causes the waves to steepen until they break and fall over, carrying water onto the shore as surf. |
SciQ | SciQ-6330 | molecular-structure, molecules
Title: How to draw the 2D representation of ammonia molecule In the 2D representation of the ammonia molecule, we see one solid line, one solid triangle and one dashed triangle
A plane can be made to pass through any three given points. In other words, we can always find a plane which will pass through any three given points in space. So the central N atom and two H atoms will lie in a plane. Only one H will be out of plane. So I think, in the 2D representation, we need to show two solid lines and one solid triangle. Please give your opinion about this. Thanks According to the rules, yes, Ammonia can be drawn with three of it's atoms in one plane and the other outside the plane. Here's an example, along with a 3D projection:
However, what do you comprehend from this structure? This structure does not convey the trigonal pyramidal geometry of the molecule very convincingly. It might be mistaken for trigonal planar at a glance, and this defeats the purpose of using the wedge/dash notation. Ammonia (and several other tetrahedral molecules) are represented in that manner since it is easiest to interpret their 3d structure from a 2d image.
The following is multiple choice question (with options) to answer.
Molecular geometry is the three-dimensional arrangement of atoms in a what? | [
"molecule",
"genes",
"DNA",
"nucleus"
] | A | Molecular geometry is the three-dimensional arrangement of atoms in a molecule. The molecular geometry, or shape, of a molecule is an important factor that affects the physical and chemical properties of a compound. Those properties include melting and boiling points, solubility, density, and the types of chemical reactions that a compound undergoes. In this lesson, you will learn a technique to predict molecular geometry based on a molecule’s Lewis electron dot structure. |
SciQ | SciQ-6331 | inorganic-chemistry, crystal-structure, geochemistry, glass, minerals
You are correct. The main difference is that sand is crystalline and glass is not—it is amorphous.
The main component (> 95%) of common yellow sand is quartz (the mineral whose composition is SiO2). Note that not all sand is quartz. There are white sands containing calcite (CaCO3) and black sand (containing various heavy minerals). But the most common sand is indeed quartz sand: SiO2.
Glass, the type you see in your everyday life, on the other hand, is not composed of pure SiO2. It has a bunch of other additives such as Na, K, B, and others. This is done to modify the properties of the glass and make it more suitable for human use. It doesn't matter much though for our discussion.
So if they are made of the same thing, why the difference? The answer is cooling rate. If you cool molten SiO2 slow enough, the atoms have enough time to organize themselves into a crystalline structure. In the case of pure SiO2, this is a network of SiO4 tetrahedra: One silicon atom surrounded by four oxygens. If it cools too fast, then the crystalline structure does not form. It may be completely amorphous, or form into a sub-microscopic array of SiO2 crystals in various structures (CT-opal for example).
What determines the cooling rate? Well, in the case of glass it is a matter of minutes. You've seen glass making: The glass is molten and very quickly it solidifies to a solid. In contrast, most of the quartz sand you're seeing is actually broken fragments of rocks called granite. This type of rock has abundant quartz in it, and it forms deep underground (as in 10s of kilometers) at very slow cooling rates. While a glass maker can take his glass and let it cool in the atmosphere or in water, molten silicate magma ("glass") deep in the Earth is surrounded by rocks that are in the hundreds of degrees. This slow cooling facilitates crystallization of the SiO2 into quartz rather than glass. How slow is this? At least tens of years, more commonly hundreds or even thousands of years. This is much slower than the seconds and minutes in glass making.
The following is multiple choice question (with options) to answer.
What mineral is used to produce glass? | [
"pyrite",
"feldspar",
"lead",
"quartz"
] | D | Silver is used to make sterling silver jewelry. Table salt is the mineral halite. Glass is produced from the mineral quartz. |
SciQ | SciQ-6332 | solutions, electrons, metal, optical-properties, solvated-electrons
Title: What is happening in this video of solvated electrons donated from sodium in ammonia? I just saw the Periodic Video Liquid Electrons - Periodic Table of Videos where sodium is added to liquid ammonia. The demonstration shows that even if electrons are solvated, if you have a high enough electron density, the substance will turn shiny and reflective and metallic. Sodium is dissolved in liquid ammonia and donates the electrons to the solution.
There are a number of things happening in the demonstration that I don't understand.
There is supposed to be a separation - once a high enough electron density is reached, the solution is supposed to separate into a high electron density and low electron density layer. Why the separation instead of a uniform concentration? And why would the high electron concentration layer float on top?
Also, at concentrations below the metallic appearance, the sodium in ammonia solution starts out very strongly blue colored. Why? What is it about adding sodium to liquid ammonia that instantly produces such a deep blue, almost black color?
It seems that the demonstration did not go quite as planned, so isopropyl alcohol was added, producing sodium isopropoxide. Why? I'll try an answer to this question because I watched this video a while back and did a bit of reading on it at the time and I think I understand the big picture. The problem is that these solvated electrons are very complicated things, and do not lend themselves to the traditional ways that chemists would like to think about things. For that reason, there is quite a lot of literature coming from physicists which is very complicated but nonetheless valuable. Additionally, solvated electrons show up in more than just this rather unusual metal-liquid ammonia solution. For instance, a recent paper in Nature chemistry by Sieferman et. al. [1] showed that there are transient solvated electrons at the surface of water which can have major implications for natural electron transfer reactions. So, understanding these systems is truly quite important.
The Blue Color:
In order to get at the deep blue color which is seen in this sodium-ammonia solution, we must understand what it is that is absorbing (reddish) visible light and hence leading to the transmission of a lot of blue light.
The following is multiple choice question (with options) to answer.
What is caused by atoms or ions when they share or transfer valance electrons? | [
"force of repulsion",
"gain of charge",
"force of attraction",
"loss of charge"
] | C | No, not all birds can fly. And not all birds have wings. This penguin is a good example. Their wings have evolved into flippers, adapted for swimming instead of flying. The kiwi of New Zealand is another bird without wings. |
SciQ | SciQ-6333 | cosmology, space-expansion, universe, faster-than-light, galaxies
Title: Why are the most distant galaxies "only" around 13 billion light years away? According to Wikipedia's List of the most distant astronomical objects, the most distant galaxy (GN-z11) is estimated to be around 13.39 billion light years away from earth.
However, the observable universe has a diameter of 92 billion light years. I understand that galaxies needed some time to form, however I'm a bit confused by the fact that all of the objects are within the radius of 13.8 billion light years (which is the age of the universe). To me, it would make more sense if some objects would be also 20 or 30 billion light years away.
Are our telescopes simply not good enough to receive light from such far away galaxies or is there any "rule" that prevents galaxies to be farther away than the age of the univere in light years?
Also, if the second is true, how can astronomers know the universe is actually 92 billion ligt years across? It seems that there are two distance measures
1) Light Travel Distance
Basically the light travel distance $(D)$ is equal to the light travel time ($t_o - t_e)$ times the speed of light ($c$).
$$D = c \times (t_o-t_e)$$
2) The Proper distance
In this case we are using the distance measured by,
$d_p = a(t_0)r$ where $r = c \int_0^a \frac{dt}{a(t)}$ and $a(t_0)=1$
In the wikipedia page that you shared the distance is given in terms of the light travel distance.
For this case, the light travel distance means that the object formed around $13.39$ billion years ago. It does not say that the object is $13.39$ billion light years away (which I admit using this convention is pretty confusing)
The object is actually around $32$ billion light year away which you can see this information when you look at the wikipedia page of that galaxy GN-z11.
The following is multiple choice question (with options) to answer.
Due to the time it takes for light to reach us, galaxies at the edge of the universe are distant in terms of space and what else? | [
"time",
"gravity",
"energy",
"temperature"
] | A | The galaxies at the edge of the Universe are a great distance away. But they are something else that is distant. Because it takes so long for light from so far away to reach us, they are also very far back in time ( Figure below ). |
SciQ | SciQ-6334 | cell-biology, proteins, cell-membrane, membrane-transport
Title: Why can't H3O+ ions pass through aquaporins? Aquaporins are proteins that facilitate the movement of water (and related molecules) through cell membranes. (Also, these transport proteins are very specific about what they transport.) Interestingly, aquaporins can facilitate the passage of glycerol but not H3O+ ions. This is difficult to comprehend as the structure of glycerol is quite dissimilar to H2O while H3O+ is quite similar to H2O.
What is the reason behind this? This question has been directly addressed by the paper The Mechanism of Proton Exclusion in the Aquaporin-1 Water Channel. I think it's a pretty good one too! I paste the abstract below:
Aquaporins are efficient, yet strictly selective water channels.
Remarkably, proton permeation is fully blocked, in contrast to most
other water-filled pores which are known to conduct protons well.
Blocking of protons by aquaporins is essential to maintain the
electrochemical gradient across cellular and subcellular membranes. We
studied the mechanism of proton exclusion in aquaporin-1 by multiple
non-equilibrium molecular dynamics simulations that also allow proton
transfer reactions. From the simulations, an effective free energy
profile for the proton motion along the channel was determined with a
maximum-likelihood approach. The results indicate that the main
barrier is not, as had previously been speculated, caused by the
interruption of the hydrogen-bonded water chain, but rather by an
electrostatic field centered around the fingerprint Asn-Pro-Ala (NPA)
motif. Hydrogen bond interruption only forms a secondary barrier
located at the ar/R constriction region. The calculated main barrier
height of 25-30 kJ mol(-1) matches the barrier height for the passage
of protons across pure lipid bilayers and, therefore, suffices to
prevent major leakage of protons through aquaporins. Conventional
molecular dynamics simulations additionally showed that negatively
charged hydroxide ions are prevented from being trapped within the NPA
region by two adjacent electrostatic barriers of opposite polarity.
The following is multiple choice question (with options) to answer.
Some membrane proteins that actively transport ions contribute to what? | [
"organism potential",
"cellular potential",
"protein potential",
"membrane potential"
] | D | |
SciQ | SciQ-6335 | human-anatomy
Title: Why is a penis an organ? According to Wikipedia an "An organ is a group of tissues with similar functions". I don't know anything about anatomy but it doesn't seem to me that a penis can be delimited somewhere to form a "group". Therefore I do not understand why a penis is considered an organ.
Can you explain it to me ? Frankly, that's a terrible definition by Wikipedia.
Merriam-Webster defines an organ as:
a differentiated structure (such as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism
or
bodily parts performing a function or cooperating in an activity
The important defining feature of an organ is not that the tissues have similar functions but that, together, the tissues comprise a functional whole that achieves some end goal.
For the penis, it consists of multiple tissues with different functions:
(from https://www.ncbi.nlm.nih.gov/books/NBK525966/figure/article-20668.image.f1/ - original from Gray's Anatomy)
The different tissues pictured here: the fibrous envelope, the corpora cavernosa, the septum pectiniforme, the urethra and blood vessels, the nervous tissue in the skin: all of these tissues have different individual functions: structural, erectile, carrying urine or semen, etc.
The key that unifies them into an organ is that the functions of the penis at the organism level (principally sexual function) are not served by any of these tissues alone, but rather by their combination in a full structure: an organ.
Ultimately, organ definitions are somewhat opinion-based: people are lumpers and splitters, so you might find conflicting definitions for which groupings of tissues reflect distinct organs, but I think by most standards you would find the penis to be considered a distinct organ, affiliated with but distinct from the primary sex organs and associated glands.
The following is multiple choice question (with options) to answer.
In which human organ do the juveniles develop into sexually mature adults? | [
"tissues",
"intestines",
"liver",
"muscles"
] | B | |
SciQ | SciQ-6336 | zoology, experimental
Title: Fish "coming back to life" after being frozen I've encountered a clip on Youtube showing a goldfish thrown in liquid nitrogen and immediately after to normal water and swimming normally. In the explanation to the clip it says:
For everyone that is worried about the goldfish, it survived and was perfectly fine until we fed him and a few of his friends to our turtles. (Which is what they were bought for in the first place!)
I am wondering now as to several issues.
If the goldfish wasn't fed to the turtles and was allowed to live out its life, would it suffer any long term damages from the act?
Is time an issue here, if the fish was kept frozen for a longer time, would it suffer more damage and would it be able to be revived?
Is the size and nature of the fish's body a factor? Would a larger animal or an animal with better resistance to frost that would take more time to completely freeze have damage due to gradual freezing of body and systems?
Does the fact that fish have cold blood affect the result of the experiment? I have no idea what's the real reason for the survival of the poor fish, but I would guess this is all in the timing. I know for certain ;-) that one can submerge a hand in liquid nitrogen for a short time or in general one can pour liquid nitrogen on the skin with no harm done whatsoever.
The reason is that the difference in temperature that interface (-180 deg C or so for liquid nitrogen and 20-30 for the skin surface) is so large that nitrogen vaporizes instantly and does not penetrate/affect the tissue. The demonstrator could have pulled the fish with bare hands.
I think that for the goldfish the time was too short and while it was cooled/shocked a bit, it might have been too short to do any serious damage. But -
As a scientist, I can't help but notice that we don't really know the condition of the fish before or after the liquid nitrogen 'treatment'. We only see it flapping for a few seconds when back in water. I wonder what happened to the eyes and the mouth, both quite sensitive tissues for such a shock. Also, the water the fish was in was a factor probably, providing additional buffer between the fish and the liquid nitrogen.
Last but not least, the ethical committee quite certainly did not approve that demonstration.
The following is multiple choice question (with options) to answer.
Both sexes of sockeye salmon turn red with green heads just prior to what? | [
"dying",
"feeding",
"spawning",
"migrating"
] | C | Wild male and female Sockeye salmon before spawning. Sockeye salmon are blue tinged with silver in color while living in the ocean. Just prior to spawning, both sexes turn red with green heads. Sockeye spawn mostly in streams having lakes in their watershed. The young fish spend up to three years in the freshwater lake before migrating to the ocean. Migratory fish spend from one to four years in salt water, and thus are four to six years old when they return to spawn. Navigation to the home river is thought to be done using the characteristic smell of the stream, and possibly the sun. |
SciQ | SciQ-6337 | optics
Title: Maximum resolution per lens size This question is more practical than theoretical, but I am interested in the theoretical considerations as well.
My wife just bought a Samsung S3 phone with a 8 MP image sensor hiding behind a tiny lens. In daylight the pictures come out fine, but it suffers horribly in low-light conditions. Is there a theoretical limit as to how fine an image sensor can be behind a lens of a specific aperture, given a reasonable amount of ambient light and a reasonable shutter speed? Will increasing the sensor resolution beyond this limit decrease the actual resolution (the ability to resolve two points as individual points) of the final image?
Thanks. The resolution is controlled by diffraction at the smallest part of the lens system. The Wikipedia article on angular resolution goes into this in some detail. To quote the headline from this article, for a camera the spatial resolution at the detector (or film) is given by:
$$ \Delta \ell = 1.22 \frac{f\lambda}{D} $$
where $f$ is the distance from the plane of the lens to the detector, $\lambda$ is the wavelength of the light and $D$ is the camera aperture. Making the pixel size smaller than $ \Delta \ell$ won't do any harm, but it won't make the pictures any sharper.
I don't know if smartphone cameras contain a variable aperture. With conventional cameras larger apertures produce less diffraction so the picture quality should actually improve in low light. However larger apertures expose a larger area of lens and optical aberration dominates the quality. The end result is that there is an optimum aperture below which diffraction dominates and above which optical aberration dominates.
Incidentally, the poor performance at low light probably isn't due to diffraction. I'd guess it's just that the signal to noise ratio of the detected light falls so far the pictures get very noisy.
The following is multiple choice question (with options) to answer.
While the numerical aperture can be used to compare resolutions of various objectives, it does not indicate how far the lens could be from the what? | [
"diameter",
"specimen",
"focal point",
"microscope"
] | B | While the numerical aperture can be used to compare resolutions of various objectives, it does not indicate how far the lens could be from the specimen. This is specified by the “working distance,” which is the distance (in mm usually) from the front lens element of the objective to the specimen, or cover glass. The higher the NA the closer the lens will be to the specimen and the more chances there are of breaking the cover slip and damaging both the specimen and the lens. The focal length of an objective lens is different than the working distance. This is because objective lenses are made of a combination of lenses and the focal length is measured from inside the barrel. The working distance is a parameter that microscopists can use more readily as it is measured from the outermost lens. The working distance decreases as the NA and magnification both increase. |
SciQ | SciQ-6338 | radiation, sun, blackbody
Title: Calculating the Sun's emitted power in a wavelength range? Is there an equation that describes the Sun's emitted power on the surface [in $\frac{W}{m^2}$] over a selected wavelength range (from $\lambda_1$ to $\lambda_2$) ?
I am guessing this can be calculated using Planck's law, but I just can't find the right equation to integrate it and get the result.
EDIT:
http://www.wikiwand.com/en/Stefan%E2%80%93Boltzmann_law#/Derivation_from_Planck.27s_law
Could I integrate this equation from $\nu_1$ to $\nu_2$ intead of 0 to $\infty$:
$\frac{P}{A} = \frac{2 \pi h}{c^2} \int_0^\infty \frac{\nu^3}{ e^{\frac{h\nu}{kT}}-1} d\nu$
Like this:
$\frac{P}{A} = \frac{2 \pi h}{c^2} \int_{\nu_1}^{\nu_2} \frac{\nu^3}{ e^{\frac{h\nu}{kT}}-1} d\nu$
Where $\nu_1$ and $\nu_2$ are the frequencies of the light.
And then I would use Simpsons rule to numerically integrate and get the result?
And just a quick question, how inaccurate is Planck's law for the Sun at UV spectrum? The Planck function is tricky to integrate. I found the following
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19680008986.pdf
might help. In particular, Appendix C contains numerical tables of integrals for the Planck function between some frequency $\nu$ and infinity. Obviously, by subtracting one of these results using $\nu_1$ and another using $\nu_2$ will give the integral between $\nu_1$ and $\nu_2$.
The following is multiple choice question (with options) to answer.
Energy from the sun has a wide range of wavelengths.what is the total range of energy called? | [
"heat spectrum",
"electromagnetic spectrum",
"light spectrum",
"thermal spectrum"
] | B | Energy from the Sun has a wide range of wavelengths. The total range of energy is called the electromagnetic spectrum . You can see it in Figure below . |
SciQ | SciQ-6339 | inorganic-chemistry
Title: Why do metals tend to lose electrons, as opposed to maintaining electric neutrality? Metals tend to lose electrons to obtain the stable noble gas configuration of 8 valence electrons.
Why do they want to obtain this configuration, and how does the strength of their "desire" to obtain this configuration compare with the "desire" to maintain neutral charge. If the answer depends on the chemical, I'm happy for you to provide some examples.
Thanks. Firstly, atoms "want" to achieve the noble gas configuration of 8 valence electrons because it is the most stable form. All that means is that it doesn't tend to react under normal conditions that we experience on Earth, therefore it will stay in that configuration for quite a while and are less likely to react. There is a more complex quantum physical answer for that but you'll have to go elsewhere for than.
The main force that keeps electrons in atoms is the electrical attraction between the electrons and the protons in the nucleus and so, if it is more energetically favourable to lose that electron in order to form a bond, then that is what will happen.
Focusing on the Alkali metals as an example, as you move down the group, they get more and more reactive. This is because of two main reasons that are a result of the electrons being further away from the nucleus:
Because they're further away, the attraction between the protons and the outer most electron is less
Secondly, taking Rubidium as an example, it has 37 electrons and 37 protons. From the perspective of the outer-most electron, there are 36 electrons repelling it, and 37 protons attracting it, therefore acting as a net charge of 1. However, if you take into account the first point, the repulsion of the closer electrons is stronger than the attraction of the protons so it could even be less than one
The following is multiple choice question (with options) to answer.
When something loses electrons, it must also? | [
"gain protons",
"gain electrons",
"reduce protons",
"slow down"
] | B | Solution The charges, as well as the atoms, must balance in reactions. The silver atom is being oxidized from the 0 oxidation state to the 1+ state. Whenever something loses electrons, something must also gain electrons (be reduced) to balance the equation. Oxygen is a good oxidizing agent for these reactions because it can gain electrons to go from the 0 oxidation state to the 2− state. |
SciQ | SciQ-6340 | evolution, biochemistry, life-history
Title: Was iron important for the first life on Earth? Some ions or compounds are thought not to have become involved or important in the metabolism of living organisms until some time after certain mutations took place. For instance, early life is thought to selectively allow calcium ions through its membrane, but eventually also evolved the ability to selectively allow sodium ions, specifically through a mutation that lead to a change in the composition of a channel protein from glutamine to lysine.
Currently, iron is involved in oxidations involving molecular oxygen, such as in cytochromes and clearly holds a key role in modern life, despite that free iron or even ferric compounds are rarely accessible. From my understanding, iron most likely became incorporated into the metabolism of microbes after during/after aerobic organisms had developed, but this does not rule out the possibility that iron was involved earlier on. So, I am wondering if iron was involved in early life, and details on how would be appreciated. Cyanobacteria require iron for photosynthesis and can be found as fossil stromatolites dating back to 3.5 billion years ago. Stromatolites are layered structures made up of cyanobacteria and sediment.
Source: https://en.wikipedia.org/wiki/Stromatolite
Modern stromatolites can be found at Shark Bay in Australia, Chetumal Bay in Belize, and Laguna Bacalar in the Yucatan Peninsula.
Cyanobacteria are also believed to have evolved into the first microbes to produce oxygen by photosynthesis, which was a catalyst for the Great Oxygenation Event which occurred around 2.45 billion years ago.
The following is multiple choice question (with options) to answer.
Water and chemical elements that organisms need keep recycling through biogeochemical what? | [
"mutations",
"effects",
"levels",
"cycles"
] | D | Water and chemical elements that organisms need keep recycling through biogeochemical cycles. These cycles include biotic and abiotic components of ecosystems. |
SciQ | SciQ-6341 | 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.
What is the most abundant biochemical compound, making up the cell walls of plants? | [
"cellulose",
"magnesium",
"cytoplasm",
"mitochondria"
] | A | Cellulose is the most abundant biochemical compound. It makes up the cell walls of plants and gives support to trunks and stems. Cellulose also provides needed fiber in the human diet. We can’t digest cellulose, but it helps keep food wastes moving through the digestive tract. |
SciQ | SciQ-6342 | zoology, ichthyology, marine-biology
Switek goes on to to talk about exceptions in some marine mammals:
At this point some of you might raise the point that living pinnipeds like seals and sea lions move in a side-to-side motion underwater. That may be true on a superficial level, but pinnipeds primarily use their modified limbs (hindlimbs in seals and forelimbs in sea lions) to move through the water; they aren’t relying on propulsion from a large fluke or caudal fin providing most of the propulsion with the front fins/limbs providing lift and allowing for change in direction. This diversity of strategies in living marine mammals suggests differing situations encountered by differing ancestors with their own suites of characteristics, but in the case of whales it seems that their ancestors were best fitted to move by undulating their spinal column and using their limbs to provide some extra propulsion/direction.
The following is multiple choice question (with options) to answer.
What organisms use cilia, pseudopods, or flagella to move? | [
"prokaryotes",
"bacteria",
"protists",
"arthropods"
] | C | Protists use cilia, pseudopods, or flagella to move. |
SciQ | SciQ-6343 | genetics, cell-biology, chromosome, meiosis, mitosis
https://www.khanacademy.org/science/biology/cellular-molecular-biology/meiosis/a/phases-of-meiosis
So, during metaphase I, homologue pairs—not individual
chromosomes—line up at the metaphase plate for separation.
The following is multiple choice question (with options) to answer.
During which phase do sister chromatids separate and the centromeres divide? | [
"cell phase",
"gap cycle",
"anaphase",
"passivation"
] | C | During anaphase , sister chromatids separate and the centromeres divide. The sister chromatids are pulled apart by the shortening of the spindle fibers. This is like reeling in a fish by shortening the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes. |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.