source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-4244 | 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 explains why two different species cannot occupy the same niche in the same place for very long? | [
"evolution",
"natural selection",
"competive exclusion princple",
"survival exclusion princple"
] | C | A given habitat may contain many different species, but each species must have a different niche. Two different species cannot occupy the same niche in the same place for very long. This is known as the competitive exclusion principle . If two species were to occupy the same niche, what do you think would happen? They would compete with one another for the same food and other resources in the environment. Eventually, one species would be likely to outcompete and replace the other. |
SciQ | SciQ-4245 | osmosis, prokaryotes
Title: Does osmosis take place in prokaryotic cells? As far as I know, osmosis occurs in Eukaryotic cells, and I'm wondering if it could take place in prokaryotic cells too. Osmosis works across every cell membrane along a concentration gradient as its a physico-chemical principle. Water can cross the membrane (or cell wall), while the substance dissolved in it (for example salts) can not. Because eukaryotic cells only have a cell membrane, they will burst eventually, while bacteria (and also plant cells) have a more rigid cell wall, which will mostly prevent bursting. However the influx (or outflux) of water creates a pressure which is called turgor pressure. How this works is shown below (figure from here), bacterial cells and plant cells work pretty much the same way:
The following is multiple choice question (with options) to answer.
The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes. therefore, the osmotic pressure within the cell is what? | [
"relatively low",
"relatively normal",
"relative",
"relatively high"
] | D | The Cell Wall The cytoplasm of prokaryotic cells has a high concentration of dissolved solutes. Therefore, the osmotic pressure within the cell is relatively high. The cell wall is a protective layer that surrounds some cells and gives them shape and rigidity. It is located outside the cell membrane and prevents osmotic lysis (bursting due to increasing volume). The chemical composition of the cell walls varies between archaea and bacteria, and also varies between bacterial species. Bacterial cell walls contain peptidoglycan, composed of polysaccharide chains that are cross-linked by unusual peptides containing both L- and D-amino acids including D-glutamic acid and D-alanine. Proteins normally have only L-amino acids; as a consequence, many of our antibiotics work by mimicking D-amino acids and therefore have specific effects on bacterial cell wall development. There are more than 100 different forms of peptidoglycan. S-layer (surface layer) proteins are also present on the outside of cell walls of both archaea and bacteria. Bacteria are divided into two major groups: Gram positive and Gram negative, based on their reaction to Gram staining. Note that all Gram-positive bacteria belong to one phylum; bacteria in the other phyla (Proteobacteria, Chlamydias, Spirochetes, Cyanobacteria, and others) are Gram-negative. The Gram staining method is named after its inventor, Danish scientist Hans Christian Gram (1853–1938). The different bacterial responses to the staining procedure are ultimately due to cell wall structure. Gram-positive organisms typically lack the outer membrane found in Gram-negative organisms (Figure 22.15). Up to 90 percent of the cell wall in Gram-positive bacteria is composed of peptidoglycan, and most of the rest is composed of acidic substances called teichoic acids. Teichoic acids may be covalently linked to lipids in the plasma membrane to form lipoteichoic acids. Lipoteichoic acids anchor the cell wall to the cell membrane. Gram-negative bacteria have a relatively thin cell wall composed of a few layers of peptidoglycan (only 10 percent of the total cell wall), surrounded by an outer envelope containing lipopolysaccharides (LPS) and lipoproteins. This outer envelope is sometimes referred to as a second lipid bilayer. The chemistry of this outer envelope is very different, however, from that of the typical lipid bilayer that forms plasma membranes. |
SciQ | SciQ-4246 | gwas, quality-control, genotyping
Allopatry caused by genetic isolation and genetic drift is your null hypothesis. However Darwinian positive selection is the alternative hypothesis.
I would be wary against suggesting contamination unless you've a clear suspicion this is occuring. I do accept that in human genetics its often difficult to avoid, particularly in ancient DNA type work. In this case you would need to try and control for it. The argument I would put against contamination is that 'genetic relatedness' is localised within the genome, whereas contamination would be a genome-wide phenomena.
Convergence is common within for example HLA genotypes (T-cell) loci between global populations.
You could perform formal tests for postive selection either within pop gen (the locus will associate with significant homozygosity) or phylogeny (point mutation).
The following is multiple choice question (with options) to answer.
What are the ultimate source of genetic variation? | [
"parasites",
"proteins",
"gravity",
"mutations"
] | D | Mutations and evolution There are often multiple alleles of a particular gene in the population and they all may be equally normal, that is have similar effects on reproductive success andin terms of the phenotypes they produce. If there is no significant selective advantage between them, their relative frequencies within a population will drift. At the same time, the phenotype associated with a particular allelecan be influenced by which alleles are present at other genetic loci, known as the genetic background. Since most traits are the results of hundreds or thousands of genes functioning together, and different combinations of alleles can produce different effects, the universe of variation is large. This can make identifying the genetic basis of a disease difficult, particularly when variation at any one locus may make only a minor contribution to the disease phenotype. On top of that, environmental and developmental differences can outweigh genetic influence on phenotype. Such genetic background effects can lead to a particular allele producing a disease in one person and not another.270 Mutations are the ultimate source of genetic variation – without them evolution would not occur. Mutations can lead to a number of effects, in particular, they can create new activities. At the same time these changes may reduce the original (and necessary) activity of an important gene. Left unresolved such molecular level conflicts would greatly limit the flexibility of evolutionary mechanisms. For example, it is common to think of a gene (or rather the particular gene product it encodes) as having one and only one function or activity, but in fact, when examined closely many catalytic gene products (typically proteins) can catalyze “off-target” reactions or carry out, even if rather inefficiently, other activities - they interact with other molecules within the cell and the organism. Assume for the moment that a gene encodes a gene product with an essential function as well as potentially useful (from a reproductive success perspective) activities. Mutations that enhance these “ancillary functions” will survive (that is be passed on to subsequent generations) only to the extent that they do not (overly) negatively influence the gene’s primary and essential function. The evolution of ancillary functions may be severely constrained or blocked altogether. This problem can be circumvented based on the fact that the genome is not static (→). There are molecular level processes through 270. |
SciQ | SciQ-4247 | experimental-physics, material-science, microscopy
Title: What are the theoretical prerequisites for experimental work with SEM and TEM? What level of knowledge and in what areas would be required to perform experimental work with an SEM (Scanning Electron Microscope) and a TEM (Transmission Electron Microscope) respectively? E.g. would a strong background in quantum mechanics be necessary for EELS (Electron Energy Loss Spectroscopy) using a TEM?
Assume that both the SEM and TEM machines are modern (made within the last 3 years).
Samples to be observed in the microscope would be metal alloys for materials science research.
Imaging methods of particular interest are EBSD and Surface Imaging for the SEM, and BSE, EELS, and Electron Diffraction for the TEM. No theoretical prerequisites to using a SEM or TEM, you'll need training to use the instrument. I've used three different SEMs and basically learned how to use each in an afternoon. TEM is more difficult, students may be required to take a training course.
Many times a researcher merely needs to image a specific sample, in which case you might be able to work with a technician. If you are interested in becoming a technician yourself then inquire about what's required.
The following is multiple choice question (with options) to answer.
The electron beam scans the surface of the sample, usually coated with a thin film of which metal? | [
"gold",
"copper",
"platinum",
"silver"
] | A | |
SciQ | SciQ-4248 | waves, acoustics, ultrasound
Title: Longitudinal wave propagation in 3D When a longitudinal wave is sent through a body, there is a strain in the emitted direction (x). What about the three-dimensional body with the strains in the direction perpendicular to the emitting direction (y, z). This strains must inevitably occur due to the "pressure wave". how can these be calculated? We can write the displacement vector as
$$\mathbf{u} = A \cos(kx)\cos(\omega t)(1, 0, 0)\, .$$
Thus, the strain tensor that is defined as
$$\epsilon = \frac{1}{2}[\nabla \mathbf{u} + (\nabla\mathbf{u})^T]\, ,$$
is
$$\epsilon = -Ak\sin(kx)\cos(\omega t)
\begin{bmatrix}
1 &0&0\\
0 &0 &0\\
0 &0 &0\end{bmatrix}\, .$$
Furthermore, the stress tensor, that for a linear elastic material isotropic is defined as
$$\sigma = \lambda \mathrm{tr}(\epsilon) + 2\mu\epsilon\, ,$$
looks like
$$\sigma = -Ak\sin(kx)\cos(\omega t)\left[\begin{matrix}\lambda + 2 \mu & 0 & 0\\0 & \lambda & 0\\0 & 0 & \lambda\end{matrix}\right]\, .$$
The following is multiple choice question (with options) to answer.
In a longitudinal wave, what term is a measure of how compressed particles of the medium become when the wave passes through? | [
"magnitude",
"voltage",
"amplitude",
"frequency"
] | C | In a longitudinal wave, amplitude is a measure of how compressed particles of the medium become when the wave passes through. The closer together the particles are, the greater the amplitude. |
SciQ | SciQ-4249 | cell-biology, terminology
Title: What is the difference between cytosol and cytoplasm? I've generally seen cytosol defined as the solution inside cells minus the organelles, cytoskeleton, etc and cytoplasm as the cytosol plus the organelles, cytoskeleton, etc. This naturally leads to the impression that cytosol is the cytoplasm minus all the solids. The problem here is that there are all sorts of other large molecules in the cells which could be thought of as solid. Are they also part of the cytosol or are they suspended in it? (I.e. are they part of the cytosol or are they non-cytosol components of the cytoplasm?)
Basically, I'm asking if the precise definition of cytosol is just anything in the cell that's not behind an endomembrane (save the exoskeleton) or if the dividing line is something else.
Subquestion: things can get even more terminologically confused because the cytosol is sometimes called the matrix. What the heck is the preferred terminology with this stuff? IMO, the definitive answer to this question is given in a paper by J. S Clegg. He traced the origin of the term cytosol to a book chapter by H. A. Lardy, and confirmed by email that Lardy had indeed coined the term. Their definition of cytosol is as follows:
... that portion of the cell which is found in the supernatant fraction after centrifuging the homogenate at 105 000 x g for 1 hour.
The following is multiple choice question (with options) to answer.
All cells have certain parts in common. these parts include the cell membrane, cytoplasm, dna, and what? | [
"lipids",
"crystals",
"chromosomes",
"ribosomes"
] | D | All cells have certain parts in common. These parts include the cell membrane, cytoplasm, DNA, and ribosomes. |
SciQ | SciQ-4250 | zoology, ecology, diet, predation
Cheetahs have been reported to suffer from intraguild competition by lions Panthera leo, spotted hyenas Crocuta crocuta and occasionally leopards Panthera pardus. These larger predators represent a threat to the smaller-bodied cheetahs as they can affect their food intake by limiting access to high resource areas or kleptoparasitism (e.g. 10–12% of kills are kleptoparasitized in Serengeti National Park (SNP)), and reduce population sizes via increased cub mortality (e.g. 73% of cub mortality was due to predation in the SNP). In response, cheetahs often demonstrate avoidance behavior to minimize interactions with dominant carnivores , with spatial and temporal partitioning regarded as the principal behavioral mechanisms by which this is achieved. Accordingly, cheetahs have been described as a refugial species that seeks competition refuges within the landscape with low densities of lions and spotted hyenas.
Rostro-García S, Kamler JF, Hunter LT. To kill, stay or flee: the effects of lions and landscape factors on habitat and kill site selection of cheetahs in South Africa. PLoS One. 2015;10(2):e0117743. Published 2015 Feb 18. doi:10.1371/journal.pone.0117743
(removed the citations)
The definition of the terms used in the above citation:
Intraguild predation, or IGP, is the killing and sometimes eating of a potential competitor of a different species. This interaction represents a combination of predation and competition, because both species rely on the same prey resources and also benefit from preying upon one another. - Wikipedia
Kleptoparasitism, literally meaning parasitism by theft, is a form of resource acquisition where one animal takes resources from another. Although kleptoparasitism of food (i.e., kleptoparasitic foraging) is the best known example, the stolen resources may be food or another resource such as nesting materials. - Sciencedirect.com
The following is multiple choice question (with options) to answer.
Competition within a species is called what? | [
"internal competition",
"species competion",
"reproducible competition",
"intraspecific competition"
] | D | Competition within a species is called intraspecific competition. It leads to natural selection within the species, so the species becomes better adapted to its environment. |
SciQ | SciQ-4251 | hydrology, water, rainfall, groundwater
Title: How much time does water takes to reach to the ground? I want to understand the phenomena where water droplets after precipitation reaches to the ground.
How much time does it take to become ground water or in other words how much time is taken by water to recharge the ground after rain.
I am assuming the water droplets falls in the plain having no concrete human constructions. It depends upon the hydraulic conductivity, the degree of saturation, and the depth to water table. Generally, water seeping down in the unsaturated zone moves very slowly. Assuming a typical depth to water table of 10 to 20 metres, the seepage time could be a matter of minutes in the case of coarse boulders, to months or even years if there is a lot of clay in fine sediment. Under saturated conditions, the water might move a lot faster. Other factors include the configuration of the wetting front, the unsaturated storage, temperature, and the hydraulic gradient. So basically, there is no simple answer - it's all a matter of the local hydrogeology.
There is no substitute for local measurement - water levels in an observation bore, in the case of water table conditions, or tensiometry in the case of the unsaturated zone.
The following is multiple choice question (with options) to answer.
What occurs when rain falls more quickly than water can be absorbed into the ground or carried away by rivers or streams? | [
"greenhouse effect",
"landslides",
"floods",
"typhoons"
] | C | Floods may occur when deep snow melts quickly in the spring. More often, floods are due to heavy rainfall. Floods happen when rain falls more quickly than water can be absorbed into the ground or carried away by rivers or streams. |
SciQ | SciQ-4252 | dna, terminology
Title: Is a DNA molecule a single strand of polynucleotide or two of them linked together? Our molecular biology teacher told us that a double helix of DNA was composed of two DNA molecules linked together by hydrogen bonds. The thing is, until now, I always thought a DNA molecule was composed of two strands, those being polynucleotides, both of them being linked together. I can't find a link which is saying the same as my teacher, even if it seems technically correct to call a double helix a dimer of two DNA molecules.
I was curious to know what was the exact terminology. As you pointed out, though this may be basic biology, seeking clarification when receiving conflicting information is a good thing. Don't feel embarrassed for asking. :)
.. our molecular biology teacher told us that a double helix of DNA was composed of two DNA molecules linked together by hydrogen bonds.
Respectfully, your teacher is incorrect. A single, double-stranded DNA molecule is comprised of two helical shaped polynucleotides, and are connected together via hydrogen bonding.
Highlight of each polynucleotide
Highlight of hydrogen bonding
And just for further validation, according to Molecular Biology of the Cell, 4th ed., by Alberts B, Johnson A, Lewis J, et al.:
A DNA molecule consists of two long polynucleotide chains composed of four types of nucleotide subunits. Each of these chains is known as a DNA chain, or a DNA strand. Hydrogen bonds between the base portions of the nucleotides hold the two chains together.
So, it would seem that your teacher is referring to each polynucleotide, a.k.a. DNA strand, as a DNA molecule. Instead, she should use the verbiage: a single DNA molecule is composed of two DNA strands, which are helical-shaped polynucleotides.
The following is multiple choice question (with options) to answer.
What are the building blocks of dna? | [
"nucleotides",
"prokaryotes",
"peptides",
"genes"
] | A | The building blocks of DNA are nucleotides. The important components of the nucleotide are a nitrogenous base, deoxyribose (5-carbon sugar), and a phosphate group (Figure 14.5). The nucleotide is named depending on the nitrogenous base. The nitrogenous base can be a purine such as adenine (A) and guanine (G), or a pyrimidine such as cytosine (C) and thymine (T). |
SciQ | SciQ-4253 | Here we used the following logical rewriting step:
\begin{align} & \langle \forall z :: P \rangle \;\not\equiv\; \langle \forall z : Q : P \rangle \\ \equiv & \;\;\;\;\;\text{"split range of left quantification -- to bring out the structural similarity"} \\ & \langle \forall z : Q : P \rangle \land \langle \forall z : \lnot Q : P \rangle \;\not\equiv\; \langle \forall z : Q : P \rangle \\ \equiv & \;\;\;\;\;\text{"bring $\;\lnot\;$ to outside"} \\ & \lnot \left( \langle \forall z : Q : P \rangle \land \langle \forall z : \lnot Q : P \rangle \;\equiv\; \langle \forall z : Q : P \rangle \right) \\ \equiv & \;\;\;\;\;\text{"$\;p \equiv p \land q\;$ is one way to write $\;p \Rightarrow q\;$"} \\ & \lnot \left( \langle \forall z : Q : P \rangle \;\Rightarrow\; \langle \forall z : \lnot Q : P \rangle \right) \\ \equiv & \;\;\;\;\;\text{"$\;\lnot p \lor q\;$ is another way to write $\;\Rightarrow\;$; DeMorgan"} \\ & \langle \forall z : Q : P \rangle \;\land\; \lnot \langle \forall z : \lnot Q : P \rangle \\ \end{align}
And similarly for the second set, we have for all $\;x\;$,
The following is multiple choice question (with options) to answer.
Each line in a structural formula represents a pair of shared what? | [
"ions",
"atoms",
"electrons",
"waves"
] | C | |
SciQ | SciQ-4254 | ichthyology, vertebrates
Title: If an organism is supported only by cartilage, does it have an endoskeleton? Lamprey and sharks lack bones, but does this mean they are not classified as having an endoskelton? Does an organism need bone to be considered as having an endoskeleton? From wikipedia
An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue.
Cartilage is a mineralized tissue so it counts as a skeleton from this definition. A bit further in the wikipedia article it says
The vertebrate endoskeleton is basically made up of two types of tissues (bone and cartilage)
The following is multiple choice question (with options) to answer.
What do vertebrate chordates possess that invertebrate chordates do not? | [
"Milk production",
"backbone",
"parasite",
"Thumb"
] | B | Chordates include vertebrates and invertebrates that have a notochord. Chordates also have a post-anal tail, dorsal hollow nerve cord, and pharyngeal slits. Vertebrate chordates have a backbone, while invertebrate chordates do not. Invertebrate chordates include tunicates and lancelets; both are primitive marine organisms. |
SciQ | SciQ-4255 | tissue
Title: Tissues in plants and animals
What is the equivalent connective tissue in plants?
Connective tissue in animals are mostly made up of collagen.
What about in plants?
Connective tissue in animals are mostly made up of collagen
Tissue is not like a simple chemical mixture ; rather tissue means a group or assemblage of cells, obeying certain defining-characteristics.
Animal connective tissues contain collagen mostly in the extracellular matrix. There are also other cell-constituents like phospholipid(membranes), DNA, RNA, etc. Blood is a liquid connective tissue which do not contain collagen in its matrix (plasma)
What is the equivalent connective tissue in plants?
Connective tissue is defined as all the tissues originated from the mesoderm layer of the animal embryo.
Now plants have a different mode of development than animals (plausibly due to evolution in separate route). So no part of a plant-body is homologous with a part of animal-body. It is impossible to bring a compare.
However; plants too; have their extracellular matrix; which is more popular as plant's cell wall (that contain cellulose, hemicellulose, etc.) as well there are intercellular spaces.
Still, if you forcefully want to bring a comparison; then the ground-tissue system of plant maybe called as a rough analogy with connective tissues in animals ( Similarly epidermal tissue of plant maybe a rough analogy with epithelial tissue of animals)
The following is multiple choice question (with options) to answer.
In vascular plants, what two basic structures are made of dermal, vascular, and ground tissues? | [
"roots and stems",
"stems and flowers",
"roots and seed",
"fruits and nuts"
] | A | Like roots, the stems of vascular plants are made of dermal, vascular, and ground tissues. |
SciQ | SciQ-4256 | evolution, dna, natural-selection
It seems plausible to me that we (advanced life) could have a biological mechanism to "write" needed alterations into either our own DNA or our reproductive DNA over time, triggering the very specific evolutionary developments necessary to our survival without relying on random mutation.
My question:
Is this possible? Does any similar mechanism exist that we know of? If not, how can so many specific (advanced) evolutionary leaps be otherwise explained? This entire answer will be long, so read the short part first, then read the rest if you (or anyone else) is curious. Citations are included in the long section. I can include additional citations in the short section if needed.
Long Story Short
Your question touches on some common misconceptions about how the evolutionary process. Organisms don't "want" to evolve traits. Traits evolve through the biological processes of random mutation and natural selection.
Organisms do not "want" to evolve traits. (Well, OK, I'd love to evolve an extra pair of hands but that is not possible.) Natural selection works by modifying existing traits. Your turtle can stare all she wants at food out of reach but she will not evolve a longer neck. Instead, natural variation exists among neck lengths of the turtles because of variation of the genes that determine features related to overall boxy size. Those individuals with longer necks may be able to get a bit more food, live a little longer, and reproduce a little more. They will pass along their genes to their offspring, so perhaps more of their offspring will also have longer necks. Over many generations, the turtles may have somewhat longer necks.
A common misconception is that the traits of organisms are precisely adapted for a specific need. They are not, for a few reasons. First, natural selection occurs relative to the current environment. Adaptations that work well in one environment may not be so useful in another environment. Environments are rarely stable over evolutionary time so traits are subject to constant change.
Next, as mentioned above, natural selection can only work on what traits are present. While an extra set of arms would be handy, I am a tetrapod. My four appendages, along with the appendages of all other tetrapods, trace back to our common ancestor. The appendages of all tetrapods are modifications of that ancestral trait.
The following is multiple choice question (with options) to answer.
What is the process resulting in living things with beneficial traits producing more offspring? | [
"natural change",
"fluid selection",
"natural selection",
"Natural choice."
] | C | The other idea is that evolution occurs by natural selection . Natural selection is the process that results in living things with beneficial traits producing more offspring than others. This results in changes in the traits of living things over time. |
SciQ | SciQ-4257 | energy, electricity, heat
Title: Electricity directly from heating a material I am looking for some more information about how to obtain electricity from heat directly. This e.g. involves the Seebeck effect, as I have found it is called, where a material produces a voltage across when heated in one end and having the other end slightly cooler. This should be the princip in measuring instruments etc., since just a small voltage is created.
This Wikipedia link explains what the phenomenon is about. But it is not well explained in an understandable language (for me at least). And it doesn't dive deep enough into the reason.
Are there someone who can in a down-to-earth way explain how and why a voltage can be measured between the ends of a bar of a certain material, when it is heated in one end? My question regards what happens on the atomic scale - can heat push electrons or what?
Thanks. The electrons in a metal are whizzing around due to thermal energy. Lattice vibrations excite the electrons, the electrons travel some distance then scatter off the lattice again and transfer energy back to the lattice. Just like a gas, the electrons have some average mean free path, and this depends on the temperature. You would think the mean free path would increase with temperature, because the lattice transfers more energy to the electrons, but the rate of scattering off the lattice also increases with temperature. How the mean free path behaves with temperature depends on the trade-off between these two effects, and the varation with temperature can be positive or negative.
Anyhow, if you heat one end of a metal rod and cool the other then the mean free path will be different at the two ends, and the electrons at the end with the higher mean free path will tend to diffuse into the end with the lower mean free path. The result is a net charge movement, and this creates the potential difference.
The following is multiple choice question (with options) to answer.
Solar cells create voltages directly from light, while thermoelectric devices create voltage from differences in what? | [
"oxygen",
"wire width",
"temperature",
"wattage"
] | C | Electromotive Force You can think of many different types of voltage sources. Batteries themselves come in many varieties. There are many types of mechanical/electrical generators, driven by many different energy sources, ranging from nuclear to wind. Solar cells create voltages directly from light, while thermoelectric devices create voltage from temperature differences. |
SciQ | SciQ-4258 | black-hole, galaxy, astrophysics, space-time, velocity
$^\dagger$Of course you can always define a frame that moves with almost the speed of light, such that all object acquire that speed "artificially", but then the Universe isn't isotropic anymore.
The following is multiple choice question (with options) to answer.
What theory goes beyond classical mechanics to describe the behavior of near-light-speed objects? | [
"special relativity",
"normal relativity",
"simple relativity",
"spacial relativity"
] | A | A great many experiments have been performed to test the predictions of special relativity. No contradictions have been found. Scientists have therefore accepted special relativity as an accurate description of nature. When the relative velocities of objects are considerably less than the speed of light, the formulas for relativistic time, length, and mass all reduce to the classical formulas. It is required that the two theories correspond where they overlap at speeds much less than . Special relativity does not contradict classical mechanics. Rather, it is a more general theory needed for object speeds approaching the speed of light. |
SciQ | SciQ-4259 | human-physiology, digestion, stomach
The stomach accomplishes much of its function by mechanically breaking down the swallowed food particles and mixing them with acid and enzymes into a sort of slurry. To do this, there are three major layers of muscle surround the stomach - from the outside, the longitudinal layer, the circular layer, and the oblique layer. The stomach also has two holes in it - the gastroesophageal opening, coming from the esophagus with the swallowed food/saliva mix, and the pylorus, where the food/acid/enzyme slurry exits into the duodenum, which is the beginning of the small intestine.
Due to the three layers of (rather strong) muscle, the stomach doesn't have a lot of expansion capability once it is filled completely to capacity. Fortunately, this almost never occurs (despite how we may feel after a large meal) because material is always leaving the stomach on its way to enzymatic digestion in the intestines. Additionally, once the stomach is filled to a certain extent, hormones such as leptin are secreted that give you the feeling of being sated, or full, triggering the brain to make you stop eating.
Of course, as we can see with the current epidemic of obesity around the world, the stomach can change its size over time. However, this is a rather slow process (weeks to months to years) of adapting to continuously consuming large meals.
But what would happen if you completely ignored these internal warnings, or were being force-fed, or whatever? Instead of rupturing (the biological equivalent of "exploding"), food would most likely be expelled either into the small intestine or back into the esophagus and back up the way it came down, i.e. causing vomiting.
The following is multiple choice question (with options) to answer.
What type of structure between the esophagus and the stomach normally opens only when a bolus arrives? | [
"gland",
"intestine",
"larynx",
"sphincter"
] | D | |
SciQ | SciQ-4260 | botany, virus
Title: What virus transforms full grown plants? I read an article by a gardener describing how a virus had transmitted a negative trait to his plants. It rather shocked me, because I hadn't realized that a virus could transform an adult plant. I was aware of dipping arabadopsis flowers in agrobacterium tumefaciens, but the concept of non-reproductive structures being transformed seems fascinating. What kind of virus is capable of that? These are just a couple of short examples, but Witch's broom structures in trees can sometimes be caused by viruses - see Wikipedia: Witch's broom (fungi is maybe the most common cause though). In rose species you also have the similar Rose rosette disease (also called witches’-broom of rose), which is caused by a virus. The same webpage from Missouri Botanical Garden also includes a list of other plant viruses that you might find interesting.
Plant viruses that infect non-reproductive structures are common though - a overview can be found here: The American Phytopathological Society: Introduction to Plant Viruses, the Invisible Foe. More indepth information can be found in Plant Pathology (Agrios, 2012) (see ch. 12: "Plant diseases caused by viruses").
The following is multiple choice question (with options) to answer.
Viroids are plant pathogens much simpler than what, but like them can reproduce only within a host cell? | [
"viruses",
"pests",
"bacteria",
"parasites"
] | A | Viroids Viroids are plant pathogens: small, single-stranded, circular RNA particles that are much simpler than a virus. They do not have a capsid or outer envelope, but like viruses can reproduce only within a host cell. Viroids do not, however, manufacture any proteins, and they only produce a single, specific RNA molecule. Human diseases caused by viroids have yet to be identified. Viroids are known to infect plants (Figure 21.18) and are responsible for crop failures and the loss of millions of dollars in agricultural revenue each year. Some of the plants they infect include potatoes, cucumbers, tomatoes, chrysanthemums, avocados, and coconut palms. |
SciQ | SciQ-4261 | 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.
"crossing over" occurs during what phase of mitosis? | [
"prophase i",
"Prophase ii",
"prophase iii",
"prophase VI"
] | A | |
SciQ | SciQ-4262 | zoology
Capybara, rabbits, hamsters and other related species do not have a complex ruminant digestive system. Instead they extract more nutrition from grass by giving their food a second pass through the gut. Soft fecal pellets of partially digested food are excreted and generally consumed immediately. Consuming these cecotropes is important for adequate nutritional intake of Vitamin B12. They also produce normal droppings, which are not eaten.
Young elephants, pandas, koalas, and hippos eat the feces of their mother to obtain the bacteria required to properly digest vegetation found on the savanna and in the jungle. When they are born, their intestines do not contain these bacteria (they are completely sterile). Without them, they would be unable to obtain any nutritional value from plants.
Eating garbage and human feces is thought to be one function of dogs during their early domestication, some 12,000 to 15,000 years ago. They served as our first waste management workers, helping to keep the areas around human settlements clean. A study of village dogs in Zimbabwe revealed that feces made up about 25% of the dogs’ overall diet, with human feces making up a large part of that percentage.
Coprophagia
Daily rhythms of food intake and feces reingestion in the degu, an herbivorous Chilean rodent: optimizing digestion through coprophagy
Coprophagia as seen in Thoroughbred Foals
The following is multiple choice question (with options) to answer.
What is the preferred food for almost all primates except for humans? | [
"grass",
"corn",
"wheat",
"fruit"
] | D | Fruit is the preferred food for almost all primates except humans. However, most primate species are omnivorous and consume a variety of plant and animal foods. For example, they may eat leaves, seeds, bird eggs, insects, and other small animals. Chimpanzees may band together and hunt for animals to kill and eat. They may even sharpen sticks and use them as spears when they hunt. Watch this video to see the incredible teamwork of a group of chimpanzees hunting a monkey: https://www. youtube. com/watch?v=A1WBs74W4ik . |
SciQ | SciQ-4263 | forces, rotational-dynamics, rotational-kinematics
It is due to the viscoelastic behavior of the contacting materials.
For purely elastic materials the relationship between stress and strain is linear so that the loading and unloading (compressing and uncompressing) forces are equal. See the diagram at the left below.
Viscoelastic materials behave like elastic materials in that both eventually recover from deformation when the load is removed. See diagram to the right below. However, the viscous behavior of a viscoelastic material is such that the stress (force) during unloading is less than that during loading for the same amount of deformation giving the material a strain rate dependent on time. The area in red between the loading and unloading curves represents the hysteresis heat loss. In contrast with ideal elastic behavior, the deformation when the material is viscoelastic does not recover right after the load is removed. In other words, there is a time delay for the material strain to fully recover, which is not shown in the diagram to the right.
In terms of say a tire rolling, the above means the forces acting on the leading portion of the tire (in the direction of motion) in contact with the road under compression (loading) are greater than the forces acting on the trailing portion of the tire in contact with the road under decompression (unloading). The overall result is the difference between the compression and decompression forces results in a net torque counter to the rotation of the tire.
Hope this helps.
The following is multiple choice question (with options) to answer.
What property means that something can return to its original shape after being stretched or compressed? | [
"friction",
"elasticity",
"homeostasis",
"viscosity"
] | B | Something that is elastic can return to its original shape after being stretched or compressed. This property is called elasticity . As you stretch or compress an elastic material like a bungee cord, it resists the change in shape. It exerts a counter force in the opposite direction. This force is called elastic force . The farther the material is stretched or compressed, the greater the elastic force becomes. As soon as the stretching or compressing force is released, elastic force causes the material to spring back to its original shape. You can watch a demonstration of elastic force at this URL:. |
SciQ | SciQ-4264 | geology, volcanology, mineralogy, minerals
Title: Where can obsidian be found? Where is obsidian found?
Is it typically found on the surface or underground?
If underground, how far under (meters or feet would be perfect)?
Also, is it found everywhere on Earth, or just in areas where volcanic activity is (or was recently) high? Obsidian is formed when a rhyolitic (or felsic) lava flows cool rapidly. This must mean that it's mostly available on the surface (and I think if you go near volcanos you can find pieces of Obsidian on the ground) because molten rock cools much faster above ground than it does below, allowing the melt to cool with small crystals (as opposed to intrusive rocks which have larger crystals). This means that Obsidian is an extrusive igneous rock.
I am betting that Obsidian is very common around most active volcanos around the world!
The following is multiple choice question (with options) to answer.
Where does all igneous rock come from? | [
"oceans",
"stratosphere",
"the moon",
"magma or lava"
] | D | Great volcanic explosions and glowing red rivers of lava are fascinating. All igneous rock comes from magma or lava. Remember that magma is molten rock that is below Earth's surface. Lava is molten rock at Earth's surface. |
SciQ | SciQ-4265 | waves, electromagnetic-radiation, wavefunction, acoustics, elementary-particles
If you want to learn more about waves, the feynmann lectures are a great start :)
Hope this helps!
The following is multiple choice question (with options) to answer.
Three ways that waves may interact with matter are reflection, refraction, and what? | [
"distortion",
"diffraction",
"dispose",
"absorption"
] | B | Three ways that waves may interact with matter are reflection, refraction, and diffraction. |
SciQ | SciQ-4266 | organic-chemistry, biochemistry, chemical-biology, carbohydrates
Glucose predominantly occurs in nature in the form of the D‐enantiomer, which is generally believed to exist in three crystalline forms: $\alpha$‐D‐glucose monohydrate (Figure 1A)(Ref.2), anhydrous $\alpha$‐D‐glucose (Figure 1B)(Ref.2), and anhydrous $\beta$‐D‐glucose (Figure 1C)(Ref.1,3). Both anhydrous $\alpha$‐D‐ and $\beta$‐D‐glucose crystals are orthorhombic while $\alpha$‐D‐glucose monohydrate crystals are monoclinic (see Fig. 1A-C). However, a fourth form, which is metastable in solution phase at $\pu{38\!-\! 50 ^{\circ}C}$ and thought to be a hydrated form of $\beta$‐D‐glucose, has been reported as well (Ref.1,4).
The crystal structure of $\beta$-D-glucose published in 1960 (Ref.5) clearly showed the exsistence of pyranose ring system. As in the inserted box in Figure 1 state that, in aqueous solutions, 99% of D‐glucose exists as a mixture of the $\alpha$- and $\beta$-forms (approximately 62% $\beta$ and 38% $\alpha$ when equilibrated at $\pu{31 ^{\circ}C}$ (Ref.1). Recent NMR study using fully $\ce{^13C}$ labelled glucose (Ref.6) clearly showed $\alpha/\beta$ ratio of $37/63$, which is almost identical to this literature value (Figure 2):
References:
The following is multiple choice question (with options) to answer.
Sucrose consists of one molecule of glucose and one molecule of what else? | [
"protein",
"alcohol",
"lactose",
"fructose"
] | D | You can see the structural formula of glucose and two other sugars in Figure below . The other sugars in the figure are fructose and sucrose. Fructose is an isomer of glucose. It is found in fruits. It has the same atoms as glucose, but they are arranged differently. Sucrose is table sugar. It consists of one molecule of glucose and one molecule of fructose. |
SciQ | SciQ-4267 | climate-change, co2, greenhouse-gases, geoengineering, methane
Title: What potential geoengineering technologies could help a country "achieve its Paris (agreement) targets"? CNN's China to expand weather modification program to cover area larger than India ends with the following sentence:
"While China has not yet shown signs of 'unilaterally' deploying geoengineering projects on the ground, the scale of its weather modification and other massive engineering projects, including mega-dam projects (such as the Three Gorges), suggests China is willing to deploy large-scale geoengineering schemes to tackle the impacts of climate change and achieve its Paris targets."
and the scope of my question is limited to the Earth Science aspects of geoengineering projects that could "..tackle the impacts of climate change and achieve... Paris (agreement) targets".
To my knowledge the Paris Agreement primarily focuses on the reduction of greenhouse gas emission itself, so I would think that geoengineering solutions might involve removing gases already emitted in the form of new biomass or as gas in geological sequestration sites, or by producing energy with a technology having a lower greenhouse emission rate.
Is that so? If so, what are specific examples?
Since the same article discusses both cloud seeding for precipitation induction and the dispersal of reflective particles to reduce global warming earlier, could there be some atmospheric dispersal technology that could help a country "...achieve its Paris targets"? I think the third paragraph of the article hints at what might be the thinking.
In the next five years, the total area covered by artificial rain or snowfall will reach 5.5 million sq km, while over 580,000 sq km (224,000 sq miles) will be covered by hail suppression technologies. The statement added that the program will help with disaster relief, agricultural production, emergency responses to forest and grassland fires, and dealing with unusually high temperatures or droughts.
The following is multiple choice question (with options) to answer.
Many countries have attempted to reduce the human impact on climate change by reducing their emission of what greenhouse gas? | [
"methane",
"carbon dioxide",
"nitrous oxide",
"acid dioxide"
] | B | Efforts to control population growth led to the one-child policy in China, which used to include more severe consequences, but now imposes fines on urban couples who have more than one child. Due to the fact that some couples wish to have a male heir, many Chinese couples continue to have more than one child. The policy itself, its social impacts, and the effectiveness of limiting overall population growth are controversial. In spite of population control policies, the human population continues to grow. At some point the food supply may run out because of the subsequent need to produce more and more food to feed our population. The United Nations estimates that future world population growth may vary from 6 billion (a decrease) to 16 billion people by the year 2100. There is no way to know whether human population growth will moderate to the point where the crisis described by Dr. Ehrlich will be averted. Another result of population growth is the endangerment of the natural environment. Many countries have attempted to reduce the human impact on climate change by reducing their emission of the greenhouse gas carbon dioxide. However, these treaties have not been ratified by every country, and many underdeveloped countries trying to improve their economic condition may be less likely to agree with such provisions if it means slower economic development. Furthermore, the role of human activity in causing climate change has become a hotly debated socio-political issue in some developed countries, including the United States. Thus, we enter the future with considerable uncertainty about our ability to curb human population growth and protect our environment. |
SciQ | SciQ-4268 | human-anatomy, human-physiology, blood-circulation, physiology
Title: Common site for atherosclerosis My book( textbook of anatomy abdomen and lower limb 2nd edition - by vishram Singh pg.no:286) says:
Acute arterial occlusion: It is mostly caused by embolism or thrombosis. It usually occurs in the femoral artery where it gives off the profunda femoris artery.
The following is multiple choice question (with options) to answer.
What occurs when arterioles lose their normal muscular tone and dilate dramatically? | [
"vascular shock",
"cardio shock",
"respiration shock",
"congenital shock"
] | A | • Vascular shock occurs when arterioles lose their normal muscular tone and dilate dramatically. It may arise from a variety of causes, and treatments almost always involve fluid replacement and medications, called inotropic or pressor agents, which restore tone to the muscles of the vessels. In addition, eliminating or at least alleviating the underlying cause of the condition is required. This might include antibiotics and antihistamines, or select steroids, which may aid in the repair of nerve damage. A common cause is sepsis (or septicemia), also called “blood poisoning,” which is a widespread bacterial infection that results in an organismal-level inflammatory response known as septic shock. Neurogenic shock is a form of vascular shock that occurs with cranial or spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region. Anaphylactic shock is a severe allergic response that causes the widespread release of histamines, triggering vasodilation throughout the body. • Obstructive shock, as the name would suggest, occurs when a significant portion of the vascular system is blocked. It is not always recognized as a distinct condition and may be grouped with cardiogenic shock, including pulmonary embolism and cardiac tamponade. Treatments depend upon the underlying cause and, in addition to administering fluids intravenously, often include the administration of anticoagulants, removal of fluid from the pericardial cavity, or air from the thoracic cavity, and surgery as required. The most common cause is a pulmonary embolism, a clot that lodges in the pulmonary vessels and interrupts blood flow. Other causes include stenosis of the aortic valve; cardiac tamponade, in which excess fluid in the pericardial cavity interferes with the ability of the heart to fully relax and fill with blood (resulting in decreased preload); and a pneumothorax, in which an excessive amount of air is present in the thoracic cavity, outside of the lungs, which interferes with venous return, pulmonary function, and delivery of oxygen to the tissues. |
SciQ | SciQ-4269 | . In normalized notation the exponent b is negative for a number with absolute value between 0 and 1 (e.g., negative one half is written as {{val|-5|e=-1}}). The 10 and exponent are usually omitted when the exponent is 0. Note that 0 itself cannot be written in normalised scientific notation since the mantissa would have to be zero and the exponent undefined.
Normalized scientific form is the typical form of expression of large numbers for many fields, except during intermediate calculations or when an unnormalised form, such as engineering notation
Engineering notation
Engineering notation is a version of scientific notation in which the powers of ten must be multiples of three...
, is desired. (Normalized) scientific notation is often called exponential
Exponentiation
Exponentiation is a mathematical operation, written as an, involving two numbers, the base a and the exponent n...
notation
—although the latter term is more general and also applies when a is not restricted to the range 1 to 10 (as in engineering notation for instance) and to bases other than 10 (as in {{gaps|315|base= 2|e=20}}).
## E notation
Most calculators
Calculator
An electronic calculator is a small, portable, usually inexpensive electronic device used to perform the basic operations of arithmetic. Modern calculators are more portable than most computers, though most PDAs are comparable in size to handheld calculators.The first solid-state electronic...
and many computer programs
Computer program
A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
present very large and very small results in scientific notation. Because superscripted
Subscript and superscript
A subscript or superscript is a number, figure, symbol, or indicator that appears smaller than the normal line of type and is set slightly below or above it – subscripts appear at or below the baseline, while superscripts are above...
The following is multiple choice question (with options) to answer.
Large or small numbers are expressed in scientific notation, which use powers of this? | [
"4",
"10",
"16",
"2"
] | B | Large or small numbers are expressed in scientific notation, which use powers of 10. |
SciQ | SciQ-4270 | taxonomy
Title: Why are sponges sometimes not considered multicellular? I read somewhere (I can't find where) that there is no scientific consensus whether sponges should be considered multicellular organisms.
It seems I don't understand where is the line between unicellular and multicellular life.
I am not able to find a more elaborate explanation of that doubt. What are the reasons for it? Sponges are generally considered as colonial organisms because there is little cell specialization and little separation of function/role. All cells do pretty much the same thing; it looks more like a pile of individual cells than an actual multicellular organism. In reality it is a little bit in between.
In any case, what one wants to call multicellular or unicellular is a matter of definition and preferences. You cannot find the line between unicellular and multicellular because there is no such line that would not be very arbitrary and filled with special cases.
You can study a little more the physiology of sponges and then decide for yourself if it looks sufficiently like a multicellular organism or more like a colony of cells (a colonial organism).
The following is multiple choice question (with options) to answer.
Budding in sponges is a form of what type of reproduction? | [
"sexual",
"reasonable",
"asexual",
"competitive"
] | C | Sponges reproduce both asexually and sexually. Asexual reproduction occurs by budding. Sexual reproduction occurs by the production of eggs and sperm. Males release sperm into the water through the osculum. Sperm may enter a female sponge through a pore and fertilize her eggs. The resulting zygotes develop into larvae. |
SciQ | SciQ-4271 | behaviour, language, genetic-code
Title: How does DNA encode high level features like animal behaviour and language? We know there are complex features which animals supposed to develop based on their genes as opposed to learning from the environment and the collective, also sometimes being very specific to certain species:
Concepts how to build homes
Animal languages including social insect interactions responsible for information transmission (or do they have to learn them through an acquisition process, let's exclude languages of ape tribes where "term" creation has been demonstrated?)
Valid answer: if already known, one or to examples to corresponding research.
Constraint: we are not talking about genes responsible for some sort of tendencies in behaviour but situations where there seems to be a more or less complex "blue print". I suppose we are yet very far from understanding these things. Relation of genotype to phenotype is teh subject of much contemporary research, but it is mainly limited to simple phenotypic features, explainable by action of a few genes, such as the colors of zebra fish mutants: see, e.g., this paper and the related publications by Nüsseln-Vollhardt group. Perhaps closer to your question is circadian rythms, which also have genetic determinants.
The complex behaviors are likely a result of the complex interactions of many genes, which are a very interesting, but also a very difficult problem to solve.
The following is multiple choice question (with options) to answer.
Behaviors that are closely controlled by genes and have little to no environmental influence are called what kinds of behaviors? | [
"innate behaviors",
"generalized behaviors",
"diverse behaviors",
"learned behaviors"
] | A | Behaviors that are closely controlled by genes with little or no environmental influence are called innate behaviors . These are behaviors that occur naturally in all members of a species whenever they are exposed to a certain stimulus . Innate behaviors do not have to be learned or practiced. They are also called instinctive behaviors. An instinct is the ability of an animal to perform a behavior the first time it is exposed to the proper stimulus. For example, a dog will drool the first time—and every time—it is exposed to food. |
SciQ | SciQ-4272 | evolution, genetics, natural-selection
Genetic Adaptation During Lifetime of a multicellular organism
For a beginner in evolutionary biology, saying that a multicellular individual's genome does not change during its lifetime might be considered satisfying. In reality it is slightly more complicated. Two elements that are mostly influent very early in the lifetime of an individual have to be considered.
While most mutations occurs during reproduction, some mutations does also occurs during body growth or stated differently during cell reproduction (Mitosis). In consequence, some pairs of your cells share exactly the same genome while other pairs of cells have a sligthly different genome.
Moreover, once some mutations had occurred within the development of an individual, these mutations might influence the fitness of the cells and therefore some alleles (variant of a gene) might raise in frequency while others decrease in frequency (Natural selection). It is important to understand that this process of natural selection select for cells that have a higher fitness and therefore do not necessarily select for the cells that allows the individual to increase its own fitness.
I don't fully understand what you mean when saying: "But does evolution work by some primitive genetics-engineering too?" Could you try to rephrase this question?
Please, let me know if I answered your question!
Note:
Here is a good way to understand the difference between "gene" and "allele". A gene might be a called the "eyes color" gene for example, while the three alleles of the "eyes color" gene might be callsed "blue eyes", "brown eyes" and "green eyes". In this sense, the alleles are the different variants of a gene. Mutations increase the number of alleles and natural selection reduces the number of alleles by selecting for the allele that cause its holder to have the greatest fitness. If you understood that, it is already good!
Note: Natural selection does not necessarily reduce the number of alleles, several alleles might be kept (polymorphism) in certain "types" of natural selection (frequency dependent selection and overdominance (heterozygote advantage), fitness varies in space and/or time, selection acts on different levels). The "type" of Natural selection that reduces the number of alleles after some time is called directional selection.
The following is multiple choice question (with options) to answer.
Mutations which benefit the organism in which they occur are known as? | [
"beneficial mutations",
"extraordinary mutations",
"helpful mutations",
"healthy mutations"
] | A | Some mutations have a positive effect on the organism in which they occur. They are called beneficial mutations . They lead to new versions of proteins that help organisms adapt to changes in their environment. Beneficial mutations are essential for evolution to occur. They increase an organism’s changes of surviving or reproducing, so they are likely to become more common over time. There are several well-known examples of beneficial mutations. Here are just two:. |
SciQ | SciQ-4273 | simulations, ideal-gas
Title: Oblique collisions in classical gas I am trying to simulate the collisions in classical gas. So the particles are point like and have identical mass. It is easy to find who collides with whom but the what happens to the particles after they collide is bit tricky.
Since if the collision were to be only head-on the energy distribution of particles will not change, only their momentum and energy will get exchanged.
Certainly I need to include the oblique collisions in order to change the distribution. So my question is how to accomplish the oblique collisions for the point particles? The only way to achieve that is to recognize that they are not really point particles. Once you treat them as (small) spheres, you can compute the momentum exchange as a function of lateral offset between them. Some details of the calculation are given in this earlier answer
The math is the same regardless of the size of the spheres - that is, the ratio of probabilities of an almost-head-on vs a slightly-oblique vs a very-oblique collision will be the same; this means that once you normalize to the "total probability of a collision", the actual size of the particles becomes irrelevant.
The following is multiple choice question (with options) to answer.
When gas particles collide, what kinds of collisions are these considered? | [
"inelastic",
"conservative",
"elastic",
"perfect"
] | C | Collisions of gas particles are elastic, so no energy is lost. |
SciQ | SciQ-4274 | evolution, zoology, adaptation
One answer that came to mind is domestic animals - the horse and dog in prehistory, the cat in ancient Egypt, etc. That seems too obvious on one hand, and on the other hand may not really be an answer, as there seems to be no indication that pre-domestic animals were endangered by humans in any meaningful way. Are there animals that have significantly adapted themselves to surviving as wild animals in human-influenced environments? Note: This is an answer to the last line of your question.
A classical example of animals adapting to the influence of humans on their environment is the adaption of the Peppered Moth.
Here is a brief summary:
The peppered moth was originally a mostly unpigmented animal (<1800). During the industrial revolution in the southern parts of the UK a lot of coal was burned. This led to soot blackening the countryside. Soon afterwards, a fully pigmented variety was first observed. Only a hundred years later, in 1895, this pigmented variety almost completely displaced the unpigmented variety.
It has been shown that the pigmentation is under strong selective pressure as birds hunt these moths. Since birds rely on their visual system to detect their prey, the variety that blends in with its environment (=camouflage) has a selective advantage over the variety that stands out.
As pointed out by Tim in the comments, since the 1970s there has been a rapid reversal with unpigmented animals being more abundant. As far as I understand, it is accepted that this reversal is due to a decrease in human induced air pollution leading to less sooty barks on trees which makes the unpigmented variety harder to prey upon.
Addendum: genetic basis of adaption
In a beautiful recent study, the causal mutation for the pigmented, or melanic, variety was identified: A ~9kb transposon insertion in the first intron of the gene cortex. The authors calculate that this mutation happened in the year 1819, a few years after the industrial revolution was in full swing. The interpretation is that due to sooty tree bark this mutation, causing pigmented moth, was under strong selection.
The following is multiple choice question (with options) to answer.
Around 1200 species of what broad animal group are currently at risk of extinction due to human activity? | [
"mammals",
"reptiles",
"birds",
"amphibians"
] | C | Today, some 1,200 species of birds are threatened with extinction by human actions. Humans need to take steps to protect this precious and important natural resource. What can you do to help?. |
SciQ | SciQ-4275 | earthquakes, plate-tectonics, volcanoes, tectonics
Title: What tectonic mechanisms cause the North and South Islands of New Zealand to be so geologically different? New Zealand is a very active seismic and volcanic region of the Pacific Ring of Fire, on the boundary of the Australian and Pacific Plates; however, there is a difference between the 2 islands: volcanoes and earthquakes on the North Island and earthquakes only on the South Island (see maps below):
Location of New Zealand volcanoes
(Image source)
New Zealand Earthquake Map
(Image Source)
What are the tectonic features that account for the difference between the North and South Islands?
Additionally, how will this boundary develop in the future (geologically speaking)? New Zealand sits along an oblique convergent plate boundary, where the Pacific and Australia Plates meet. The boundary between the two plates is shown in your second figure as the grey line, with the Pacific Plate to the east and the Australia Plate to the west of it. In terms of relative movement, we can think of the Australia Plate as being stationary and the Pacific Plate having a west to south-west direction of movement. The angle at which the Pacific Plate moves into the Australia plate changes along the length of New Zealand - this is what causes the differences in tectonic style and thus differences in volcanism and earthquake occurance (and motion) between North and South Islands. The angle changes from north to south due to:
a clockwise rotation of the Pacific Plate, and
Pacific and Australia plates meeting at varying angles.
The following is multiple choice question (with options) to answer.
The galápagos islands are a group of 16 volcanic islands 600 miles off the west coast of what continent? | [
"europe",
"north america",
"asia",
"south america"
] | D | The Galápagos Islands are a group of 16 volcanic islands 600 miles off the west coast of South America. The islands are famous for their many species found nowhere else. It was on these islands where Darwin began to develop his theory of evolution. |
SciQ | SciQ-4276 | cell-biology, nutrition, blood-circulation, liver
Title: How do nutrients get to the cells they need to get to? I understand the basics of digestion. I know that nutrients get absorbed by the microvilli, enter the bloodstream and travel to the liver but after all that, what is the biological mechanism that guides these nutrients to the proper receiving location? Broadly speaking, nutrients that enter the blood from the gut, and those that are released into the blood by the liver, are available to any cells that require them. So there is no "guiding to the correct location" in the sense that you suggest.
Lipids for example are present in the various lipoproteins and can be acquired from these by all cells. Iron is bound to transferrin, and any cell with transferrin receptors can internalise the transferrin and take the iron. Glucose is available in solution in the plasma, and free fatty acids are bound to serum albumin in the blood. During starvation the liver produces ketones ("ketone bodies") which are taken up by many different tissues/cell types.
The following is multiple choice question (with options) to answer.
What structures on the gastrodermal cells keep the contents of the gastrovascular cavity agitated and help distribute nutrients? | [
"flagella",
"sporangia",
"nucleus",
"telomeres"
] | A | |
SciQ | SciQ-4277 | physical-chemistry, equilibrium, aqueous-solution, solubility, ionic-compounds
Title: Seeing solubility in various cases
Match the following:
$\begin{array}{|c|c|c|c|} \hline &\textrm{Column-I}&&\textrm{Column-II} \\\hline \textrm{(A)}&\ce{AgBr}&\mathrm{(p)}&\mathrm{(Solubility~in~water~is~more~than~expectation)} \\ \hline \textrm{(B)}&\ce{AgCN}&\mathrm{(q)}&\mathrm{(Solubility~in~acidic~solution~is more~than~in~pure~water~\\(consider~no~common~ion~effect~from~anion~of~acid)}\\ \hline \textrm{(C)}&\ce{Fe(OH)3}&\mathrm{(r)}&\mathrm{(Solubility~in~strongly~basic~solution~is~more~than~in ~pure~water)}\\ \hline \textrm{(D)}&\ce{Zn(OH)2}&\mathrm{(s)}&\mathrm{(Solubility~decreases~in~presence~of~common~anion)}\\ \hline \end{array}$
The following is multiple choice question (with options) to answer.
What is the factor that affects the solubility of solutes in all three states? | [
"oxygen",
"color",
"heat",
"temperature"
] | D | Temperature affects the solubility of solutes in all three states. Pressure also affects the solubility of gases. |
SciQ | SciQ-4278 | organic-chemistry, acid-base
Title: What are the predominant acids in sphagnum peat moss? I'm trying to figure out what the predominant acidic substances in peat moss are. Peat moss is said to have a pH of approximately 4.0. So, I'm curious what is making it acidic.
I know not all acids bind to various elements in the same ways. So, I'm trying to find out which acids (and/or acidic salts) are present in peat moss in order to aid me in my research to discover approximately how long it might take to acidify soils with it compared with the traditional methods of adding various forms of sulfur to soil. You don't need to tell me how long it takes, by any means. I can do more research after I find out which acids or acidic salts are in peat moss, in what levels.
I'm not familiar with this particular SE site's customs. So, if this is the wrong place to ask, or if I used the wrong tag(s), feel free to let me know. I figured people might be more likely to know here than on Gardening and Landscaping, though. This 1992 article by Gagnon and Glime suggests that the ability of Sphagnum to lower pH depends on the presence of cations in the surrounding environment and is not (contrary to prevalent belief) due to organic acids in the plant itself. Here is a more recent article from New Phytologist amplifying that cation exchange is responsible for lowering of pH.
If you want to acidify soil using sphagnum/peat--assuming the authors are right--it's more important what cations you put into the soil. The sphagnum will then exchange them for $H^+,$ lowering the pH of the soil.
This does not mean there aren't organic acids in moss. You would have to look in specialized journals to determine what acids are found in the plant, but they are not necessarily very acidic and are, according to both articles, not the cause of acidity of the soil associated with the plants.
The following is multiple choice question (with options) to answer.
What kind of ph would you find in water from bogs? | [
"lower ph",
"regular ph",
"higher ph",
"normal ph"
] | A | 44.4 Aquatic Biomes Aquatic ecosystems include both saltwater and freshwater biomes. The abiotic factors important for the structuring of aquatic ecosystems can be different than those seen in terrestrial systems. Sunlight is a driving force behind the structure of forests and also is an important factor in bodies of water, especially those that are very deep, because of the role of photosynthesis in sustaining certain organisms. Density and temperature shape the structure of aquatic systems. Oceans may be thought of as consisting of different zones based on water depth and distance from the shoreline and light penetrance. Different kinds of organisms are adapted to the conditions found in each zone. Coral reefs are unique marine ecosystems that are home to a wide variety of species. Estuaries are found where rivers meet the ocean; their shallow waters provide nourishment and shelter for young crustaceans, mollusks, fishes, and many other species. Freshwater biomes include lakes, ponds, rivers, streams, and wetlands. Bogs are an interesting type of wetland characterized by standing water, lower pH, and a lack of nitrogen. |
SciQ | SciQ-4279 | human-physiology, digestion, stomach
The stomach accomplishes much of its function by mechanically breaking down the swallowed food particles and mixing them with acid and enzymes into a sort of slurry. To do this, there are three major layers of muscle surround the stomach - from the outside, the longitudinal layer, the circular layer, and the oblique layer. The stomach also has two holes in it - the gastroesophageal opening, coming from the esophagus with the swallowed food/saliva mix, and the pylorus, where the food/acid/enzyme slurry exits into the duodenum, which is the beginning of the small intestine.
Due to the three layers of (rather strong) muscle, the stomach doesn't have a lot of expansion capability once it is filled completely to capacity. Fortunately, this almost never occurs (despite how we may feel after a large meal) because material is always leaving the stomach on its way to enzymatic digestion in the intestines. Additionally, once the stomach is filled to a certain extent, hormones such as leptin are secreted that give you the feeling of being sated, or full, triggering the brain to make you stop eating.
Of course, as we can see with the current epidemic of obesity around the world, the stomach can change its size over time. However, this is a rather slow process (weeks to months to years) of adapting to continuously consuming large meals.
But what would happen if you completely ignored these internal warnings, or were being force-fed, or whatever? Instead of rupturing (the biological equivalent of "exploding"), food would most likely be expelled either into the small intestine or back into the esophagus and back up the way it came down, i.e. causing vomiting.
The following is multiple choice question (with options) to answer.
Where do most of the digestion reactions occur? | [
"liver",
"large intestine",
"mouth",
"small intestine"
] | D | Most of the digestion reactions occur in the small intestine. |
SciQ | SciQ-4280 | thermodynamics, visible-light
Title: Is heat always associated with Light? I have found that light always produces heat. The only cases I think heat is absent with light is Fluorescence and Phosphorescence (maybe because they emit low energy but maybe the heat is still present?). So my question is: Is heat energy always present when light is emitted, specially for bright light(more energy)?
If some example or any links can be provided, then it will be very helpful. Thermal radiation is emitted by any surface having a temperature higher than absolute zero. So the short answer to your question is yes. Light (electromagnetic radiation) of any frequency will heat surfaces that absorb it. In case of Fluorescence, the emitted light has a longer wavelength (lower frequency), and therefore lower energy, so that's why you feel the heat is absent.
The following is multiple choice question (with options) to answer.
What is the name of the process where light is produced without heat? | [
"fluorescence",
"effervescence",
"radiation",
"luminescence"
] | D | Some objects produce light without becoming very hot. They generate light through chemical reactions or other processes. Producing light without heat is called luminescence . Luminescence, in turn, can occur in several different ways:. |
SciQ | SciQ-4281 | 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.
Meats and dairy products link to photosynthesis because the animals were fed what? | [
"carnivorous diets",
"plant-based foods",
"biofuel",
"chloroplasts"
] | B | Major grocery stores in the United States are organized into departments, such as dairy, meats, produce, bread, cereals, and so forth. Each aisle contains hundreds, if not thousands, of different products for customers to buy and consume (Figure 5.4). Although there is a large variety, each item links back to photosynthesis. Meats and dairy products link to photosynthesis because the animals were fed plant-based foods. The breads, cereals, and pastas come largely from grains, which are the seeds of photosynthetic plants. What about desserts and drinks? All of these products contain sugar—the basic carbohydrate molecule produced directly from photosynthesis. The photosynthesis connection applies to every meal and every food a person consumes. |
SciQ | SciQ-4282 | quantum-mechanics, bells-inequality
A variant of this would be a deterministic universe where the initial conditions are chosen very carefully to ensure the above sort of correlation between the hidden fruits sent out on each trial and which boxes the experimenters choose to scratch on each trial. The assumption that there is no "conspiracy" in the initial conditions of the universe which predetermines a strong correlation between the hidden variables associated with particles on each trial (or hidden fruits on each pair of cards in my analogy) and what variables the experimenters will choose to measure on each trial (or what boxes they will choose to scratch) is often called the "no conspiracy" assumption, see the paper on the detailed assumptions of Bell's theorem here which discusses it in section D on page 6. Models with violations of no-conspiracy that depend on fine-tuning of initial conditions are sometimes grouped under the label "superdeterminism", see here and here for example.
Another subtle variation on this is the idea that the entity doesn't actually cause the experimenters to make particular choices but merely has a sort of "precognition" about what choices they will in fact make (implying some backwards-in-time causality), and determines what fruits will be under the two boxes that it knows will be scratched in the future using the same type of rule as above. The philosopher of science Huw Price discusses such an idea in his book Time's Arrow and Archimedes' Point.
(As I mentioned in a comment above, advocates of the many-world interpretation also make the point that one can preserve locality if one drops the assumption that each measurement gives a single unique result, as elaborated in this paper by David Deutsch. If you want a simple conceptual toy model of how this could work, see this post I wrote up on physicsforums.com a while ago).
The following is multiple choice question (with options) to answer.
What the scientific concept stating that when looking at two competing theories, the one with fewer assumptions should be chosen? | [
"law of thermodynamics",
"law of averages",
"law of simplicity",
"law of parsimony"
] | D | The formation of scientific theories is generally guided by the law of parsimony. The word parsimony means “thriftiness. ” The law of parsimony states that, when choosing between competing theories, you should select the theory that makes the fewest assumptions. In other words, the simpler theory is more likely to be correct. For example, you probably know that Earth and the other planets of our solar system orbit around the sun. But several centuries ago, it was believed that Earth is at the center of the solar system and the other planets orbit around Earth. While it is possible to explain the movement of planets according to this theory, the explanation is unnecessarily complex. |
SciQ | SciQ-4283 | meteorology, climate-models, era
Concerning the difference between temperature and precipitation: temperature is much easier to correctly simulate than precipitation (e.g. because of the dry/wet-day transition). As such, on a monthly scale, precipitation biases might be already quite large. For more information on precipitation biases, this paper might be relevant: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010jd014532 (Stephens et al. (2010): The dreary state of precipitation in global models)
In essence, the dataset you want to use should depend on your needs. If spatial/temporal coverage and historical data is the most important, the reanalysis is probably your best choice. If you want to know more about this dataset and its biases, this article is a good starting point: https://hess.copernicus.org/articles/24/2527/2020/ (Tarek et al. (2020): Evaluation of the ERA5 reanalysis as a potential reference dataset for hydrological modelling over North America). Or, if your goal is impact assessment, you might immediately check this one: https://essd.copernicus.org/articles/12/2097/2020/ (Cucchi et al. (2020): WFDE5: bias-adjusted ERA5 reanalysis data for impact studies)
The following is multiple choice question (with options) to answer.
What type of map would show average temperatures and rainfall? | [
"rainfall map",
"landscape map",
"carbon map",
"climate map"
] | D | Climate maps show average temperatures and rainfall. |
SciQ | SciQ-4284 | 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.
What is the name of the sugar that plants produce to be used as food? | [
"insulin",
"chlorophyll",
"glucose",
"glucosamine"
] | C | |
SciQ | SciQ-4285 | zoology
Title: What is right below skin? I was skinning a gopher so my cat can eat it (it was a pest and we didn't want to waste it). I thought its organs would fall out and make a mess, but that didn't happen. There was this sticky, transparent substance that surrounded its insides. What is this casing called? My dad said it was mucus but that isn't specific enough since there is mucus inside the stomach so I don't think they are the same.
I think this casing is found in all multicellular animals but I couldn't be sure. Based on your reference to organs falling out and the overall description, I presume you're thinking of the abdominal cavity primarily, so there you'd be looking at the peritoneum or possibly the serous membranes of other organs (e.g., pleura, pericardium). These are membranous (in the general sense, not as a cell membrane) connective tissues covering the organs found in the abdomen and chest.
Other things you'll find underneath skin would include layers of fat, other connective tissues, muscle.
Here's a labeled image of a mouse dissection from Friedrich, L., Schuster, M., de Celis, M. F. R., Berger, I., Bornstein, S. R., & Steenblock, C. (2021). Isolation and in vitro cultivation of adrenal cells from mice. STAR protocols, 2(4), 100999.:
You might also look for dissections of fetal pigs or cats, which are commonly used in laboratory demonstrations for students (more often cats longer ago, more often fetal pigs these days).
The following is multiple choice question (with options) to answer.
Just under their skin, marine mammals have a very thick layer of insulating fat called what? | [
"tissue",
"blubber",
"lipisomes",
"cellulose"
] | B | |
SciQ | SciQ-4286 | biochemistry, gas-laws
Title: What is the state of aggregation (gas, liquid) of oxygen in blood? Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.
When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test
Also, how does the lungs convert the gas into something that is compatible to be in blood?
References:
Amount of Oxygen in the Blood Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.
Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See Wikipedia on this.
Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.
The following is multiple choice question (with options) to answer.
While in the lungs, blood gives up carbon dioxide and picks up what element before returning to the heart? | [
"methane",
"hydrogen",
"oxygen",
"nitrogen"
] | C | Pulmonary circulation is the part of the circulatory system that carries blood between the heart and lungs (the term pulmonary means “of the lungs”). It is illustrated in Figure below . Deoxygenated blood leaves the right ventricle through pulmonary arteries, which transport it to the lungs. In the lungs, the blood gives up carbon dioxide and picks up oxygen. The oxygenated blood then returns to the left atrium of the heart through pulmonary veins. |
SciQ | SciQ-4287 | blood-circulation, immune-system
Title: Are there macrophages in the blood vessels and within the blood stream? Monocytes are phagocytes that "evolve" or "differentiate" into macrophages. I read that there are monocytes in the blood stream and vessels and that macrophages are found mainly in other tissues and in the lymphatic system.
My question: are there macrophages (and not merely monocytes) in the blood vessels and within the blood stream? And if there are, are they numerous there or sparse? Usually, monocytes and neutrophils are present(there are other cells like Lymphocytes and other leukocytes), the only time a macrophage will be present is when inflammation occurs, I suspect this is due to the large size of the macrophage, it would be difficult for it to travel in the bloodstream, as it is quite big, compared to the small size of a monocyte. During inflammation, vascular dilation and permeability increase, which makes it easier for cells and proteins to diffuse across the endothelium.
A source that macrophages are present in all tissues: https://www.researchgate.net/publication/227897252_Macrophages_in_the_embryo_and_beyond_Much_more_than_just_giant_phagocytes
A source that talks about all the leukocytes and lymphocytes present in the blood normally: http://www.histology.leeds.ac.uk/blood/blood_wbc.php
The following is multiple choice question (with options) to answer.
White blood cells called what travel to areas of the body that are inflamed? | [
"phagocytes",
"gametocytes",
"platelets",
"spirochetes"
] | A | White blood cells called phagocytes travel to areas of the body that are inflamed. |
SciQ | SciQ-4288 | bond, structural-formula, carbon-allotropes
Title: Is the valency of carbon satisfied in graphite? Graphite has hexagonal parallel planes. In a hexagonal structure the carbon atom has three bonds. Since the valancy of carbon is 4 is the valency satisfied in graphite? Just as much as in benzene or any other $\mathrm{sp^2}$ carbon case.
The concept of valency doesn't mean that the given atom has to form bonds with the given number of neighbors, but refer to a simple way of counting electrons and formed bonds.
In organic chemistry, we often find carbon forming 4 (single) bonds to neighbors. For example you can find four $\ce{C-H}$ bonds from the central carbon in $\ce{CH4}$ or one $\ce{C-C}$ and three $\ce{C-H}$ bonds from each carbon in $\ce{C2H6}$.
However, in a benzene or ethene $(\ce{H2C=CH2})$ molecule there is only three neighbors of each carbons. In ethene the $\ce{C=C}$ is a double bond (unlike $\ce{C-C}$ in ethylene) which is formed by using two-two valence electrons of the carbons. When you count valence, you count these valence electrons, therefore a double bond counts twice.
The situation of benzene is a little trickier, as it does not have a double or a single bond between the carbons. If the carbons would form a single bond, there would be a extra dangling electron remaining on each of them. In reality these electrons are delocalized (shared) over the whole ring. If you count the valence electrons of a carbon, you should count this delocalized electron, too. You can understand graphite along this line: three bonds to the three neighbors plus the remaining one valence electron delocalized over the ring system (the whole graphite sheet) are together gives back the four valence electrons.
You can find more on hybridization in the other answer.
The following is multiple choice question (with options) to answer.
How many valence electrons can be found in a carbon atom? | [
"One",
"four",
"five",
"three"
] | B | Let’s briefly review the basics of covalent bonding as they pertain to carbon. Carbon has four valence electrons, which have a 2s 2 2p 2 configuration in isolated carbon atoms. These four electrons allow carbon to form four covalent bonds, which can mean four single bonds or some combination of single, double, and triple bonds. |
SciQ | SciQ-4289 | muscles, lungs, human-physiology
Title: Why is there smooth muscle in our bronchioles? Having muscle tissue in our bronchioles that can constrict seems like a poor choice for tissue. Why would our airway want to ever close up? Wouldn't it be more beneficial for our bronchioles to just remain open? There are at least two things to consider.
First, ability to limit airflow is a defense mechanism for animal. Imagine getting into area of some sort of toxic evaporation, e.g. CO2 cloud near volcano , then it makes sense to decrease delivery of toxin via lungs to minimum. As I understand, that is what an allergic asthma attack. (Sorry for not providing good enough source of that)
Secondly, you are incorrect in assuming that normal state is "dilated". Dilation of branchioles is sympathetic ("fight-and-fly") response of the nervous system to something like danger, that requires short-term boost in energy production. That is, by default, your airflow is limited. Probably, to limit amount of energy you effectively burn via oxygenation. But most importantly, you leave yourself a reserve in terms of oxygen supply for critical moments.
Some more information you might find here.
The following is multiple choice question (with options) to answer.
Diaphragm, lungs, and trachea take air deep into the body and provide oxygen gas to what? | [
"heart",
"brain",
"molecules",
"bloodstream"
] | D | (left) The human respiratory system is only part of the story of respiration. Diaphragm, lungs, and trachea take air deep into the body and provide oxygen gas to the bloodstream. The fate of that oxygen is the story of cellular respiration. (center) Spiracles in this Cluentius Sphinx ( Neococytius cluentius ) caterpillar connect to a system of internal tubes (tracheae), which carry oxygen throughout the animal's body. (right) Gills in this alpine newt larva, Ichthyosaura alpestris , bring blood close to an extensive surface area so that the newt can absorb dissolved oxygen gas from its watery habitat. |
SciQ | SciQ-4290 | biochemistry, gas-laws
Title: What is the state of aggregation (gas, liquid) of oxygen in blood? Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.
When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test
Also, how does the lungs convert the gas into something that is compatible to be in blood?
References:
Amount of Oxygen in the Blood Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.
Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See Wikipedia on this.
Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.
The following is multiple choice question (with options) to answer.
What gases move in and out of blood during gas exchange? | [
"oxygen, nitrogen",
"oxygen, carbon monoxide",
"oxygen, carbon dioxide",
"nitrogen, carbon dioxide"
] | C | User:helix84/Wikimedia Commons. Gas exchange is the movement of oxygen into the blood and carbon dioxide out of the blood . CC BY 2.5. |
SciQ | SciQ-4291 | 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 keeps various species from mating and reproducing outside their own species? | [
"reproductive organ incompatibility",
"cancer organ incompatibility",
"digestive system incompatibility",
"brain organ incompatibility"
] | A | Figure 18.19 The shape of the male reproductive organ varies among male damselfly species, and is only compatible with the female of that species. Reproductive organ incompatibility keeps the species reproductively isolated. |
SciQ | SciQ-4292 | thermodynamics, heat-engine
possibility of a “reverse-refrigerator” that cooks?
I just used that above image as a heating unit. But, the image's own title is "How Absorption Chillers Work" – not "How Absorption Heaters Work".
Which is fine! Because, as you suspected, you can do the same thing, sorta "in reverse", except it's more like we just flipped our heat sinks around.
I mean, technically, it's still a chiller. We're just chilling the waste heat source, and using the generated heat rather than dumping it (like typical refrigerators do).
The following is multiple choice question (with options) to answer.
A refrigerator must do work to reverse the normal direction of what? | [
"visible energy flow",
"coolant energy flow",
"spectral energy flow",
"thermal energy flow"
] | D | A refrigerator must do work to reverse the normal direction of thermal energy flow. Work involves the use of force to move something, and doing work takes energy. In a refrigerator, the energy is usually provided by electricity. You can read in detail in the Figure below how a refrigerator does its work. For an animation of how a refrigerator works, go to this URL: http://www. chemistry. wustl. edu/~edudev/LabTutorials/CourseTutorials/LabTutorials/Thermochem/fridge_movie. html. |
SciQ | SciQ-4293 | proteins, arachnology
MaSp1 and MaSp2 are large proteins of about 250 to 350 kDa that share
a general domain architecture. Both proteins contain a large, central, repetitive domain that
consists of approximately 100 tandem copies of a 30 to 40 amino acid
repeat sequence. The consensus repeat sequences for both MaSp1 and
MaSp2 are glycine-rich and end in poly-alanine motifs (usually four to
seven residues long). For MaSp1, the consensus repeat includes (GGX)n
motifs (where X = A, L, Q, or Y) and very low proline content. In
contrast, the MaSp2 consensus repeat has significant proline content
and characteristic motifs such as GPG and QQ.
The repetitive domains of different spidroins display a relatively
high level of amino acid sequence variation that has been implicated
in providing the elasticity and toughness that is characteristic of
the different fibers.
It is possible that different amounts of Sp-1 and Sp-2 are combined to tune the elasticity and toughness of the silk. I have no idea whether the mechanical properties of silk are changed by the spider to suit the context (e.g. elasticity in windy conditions, or whether the content changes seasonally in response to temperature differences). That would make for a cool research hypothesis.
The following is multiple choice question (with options) to answer.
The bone matrix consists of tough protein fibers—mainly what? | [
"tissues",
"hemoglobin",
"tendons",
"collagen"
] | D | Many people think of bones as being dead, dry, and brittle. These adjectives correctly describe the bones of a preserved skeleton, but the bones in a living human being are very much alive. As shown in Figure below , the basic structure of bones is bone matrix , which forms the underlying rigid framework of bones, formed of both compact and spongy bone. The bone matrix consists of tough protein fibers—mainly collagen—that become hard and rigid due to mineralization with calcium crystals. Bone matrix is crisscrossed by blood vessels and nerves and also contains specialized bone cells that are actively involved in metabolic processes. |
SciQ | SciQ-4294 | organic-chemistry, hydrocarbons, polarity
Title: Are alkynes weakly polar? I was reading about physical properties of alkynes in my Chemistry textbook.
One of the sentence states
Alkynes are weakly polar in nature.
I didn't understand how alkynes are weakly polar, so I tried to search about it on the internet but couldn't find any explanation.
Many sites (like this and this) rather state that alkynes are non-polar.
My question is: are alkynes weakly polar? If yes, why? Yes, alkynes can display a (small) permanent electric dipole moment, and thus are polar molecules by the usual definition. For example see https://cccbdb.nist.gov/exp2x.asp?casno=74997&charge=0 where the dipole moment for propyne is given as 0.780 Debye. Given such a molecule is asymmetric is it shouldn't be a surprise that there is a dipole moment.
The following is multiple choice question (with options) to answer.
Alkynes are what type of compound? | [
"unsaturated hydrocarbons",
"reversible hydrocarbons",
"proteins hydrocarbons",
"Split Hydrocarbons"
] | A | Unsaturated hydrocarbons that contain one or more triple bonds are called alkynes . The names of specific alkynes always end in –yne and have a prefix for the number of carbon atoms. The structural formula in the Figure below represents the smallest alkyne, named ethyne, which has two carbon atoms and two hydrogen atoms (C 2 H 2 ). Ethyne is also called acetylene. It is burned in acetylene torches, like the one pictured in the Figure below . The flame of an acetylene torch is so hot that it can melt metal. |
SciQ | SciQ-4295 | energy, photons, semiconductor-physics, solar-cells
In down-conversion one high energy photon promotes an electron from 1 to 3, and by falling to energy level 2 and then 1, two photons can be emitted. Thus one high energy photon in and two low energy photons out.
Of course the next step would be to use a solar cell to collect the converted photons. The up and down converters themselves don't generate power.
Other approaches
There are other approaches to reaching higher efficiency. In specially engineered materials high energy photons can generate multiple electron-hole pairs which provides more current per photon than normal solar cells.
Then there are the hot-carrier approaches. If a material and maintain a thermal gradient then this provides an additional thermodynamic potential allowing higher efficiencies to be achieved.
You can even use hot-carrier materials as a spectral converters! I've worked on this approach over the last few years.
The following is multiple choice question (with options) to answer.
Solar cells turn sunlight directly into what? | [
"gas",
"water",
"electricity",
"cold"
] | C | Solar energy is used to heat homes and water, and to make electricity. Scientists and engineers have many ways to get energy from the Sun ( Figure below ). One is by using solar cells. Solar cells are devices that turn sunlight directly into electricity. Lots of solar cells make up an individual solar panel. You may have seen solar panels on roof tops. The Sun’s heat can also be trapped in your home by using south facing windows and good insulation. |
SciQ | SciQ-4296 | zoology, species-identification, marine-biology, invertebrates
Title: Species identification - greenish blue ocean worm (nudibranch?) in Perhentian Islands, Malaysia We found this on a beach at the Perhentian Islands, Malaysia in March, 2016 and cannot identify it. It's some sort of worm-type creature with many legs and bluish back about 15cm long. The legs undulated along the body as it swam.
back:
belly side: It's hard to identify from the photos provided, but I think it is Chloeia flava (a species of polycaete worm, within the phylum Annelida), also known in English as the "Golden Fireworm".
The size is roughly similar to what you describe (they are typically about 7-10 cm long). The individual you observed looks like it lives in sandy bottom environments (not a typical environment for a nudibranch), and this worm does also. It is commonly found all across the warmer Indo-Pacific as well, and looks like the individual observed in your photo.
If it is not this species, I think it is another species of the same family, Amphinomidae.
The following is multiple choice question (with options) to answer.
What type of invertebrate typically has a single spiraled shell? | [
"arthropod",
"anthropod",
"gastropod",
"bipod"
] | C | |
SciQ | SciQ-4297 | food, nutrition, energy-metabolism
Title: What are the bare minimum nutrients required to survive as a human? I am trying to determine the bare minimum nutritional requirements to survive as a human, ignoring energy (caloric) requirements. Another way to ask this question is: What elements can humans not live without? I am not inquiring solely about what nutrients are needed, but also their approximate amounts.
Imagine pills that a person can take that covers all their base nutritional needs and that after taking this pill the person can eat whatever they want to meet their caloric requirements. Hypothetically, this pill could have some amount (how much?) fat, carbohydrates, protein, fiber, minerals, and vitamins, and the person could subsequently eat any other food to meet their caloric requirements knowing their nutritional needs would already be otherwise met. Lets ignore the possibility of the person suffering from health issues due to eating too much of any specific food to meet their caloric requirements (e.g., taking the magic pills and then eating only butter).
A person in this situation could think "Ok I've got most of my bases covered, now I just need to ingest another 1000 calories of (almost) anything I want).
What nutrients are absolutely necessary for humans to survive indefinitely, and how much of these nutrients are required?
I am hoping for a complete list with approximate amounts (e.g., 20g fat, 20g carbohydrates, 1mg Vitamin X, .05mg Vitamin Y, 10mg mineral X). Essential nutrients include (NutrientsReview):
Water
9 amino acids: histidine, isoleucine, leucine, lysine, methionine,
phenylalanine, tryptophan, threonine, valine
2 fatty acids (alpha linolenic and linoleic acid)
Vitamins: A, B1, B2, B3, B5, B6, folic acid, biotin, B12, C,
D, E and K (and choline, which is considered a vitamin-like substance)
Minerals: calcium, chromium, chloride, copper, iodine, iron,
manganese, molybdenum, phosphorus, potassium, selenium, sodium, zinc
The following is multiple choice question (with options) to answer.
What are nutrients the body needs in relatively large amounts called? | [
"abundances",
"macronutrients",
"vitamins",
"adulterants"
] | B | Nutrients the body needs in relatively large amounts are called macronutrients . They include carbohydrates, proteins, lipids, and water. All macronutrients except water can be used by the body for energy. (The energy in food is measured in a unit called a Calorie . ) The exact amount of each macronutrient that an individual needs depends on many factors, including gender and age. Recommended daily intakes by teens of three macronutrients are shown in Table below . Based on your gender and age, how many grams of proteins should you eat each day?. |
SciQ | SciQ-4298 | cell-biology, proteins, transcription, cell-signaling, intracellular-transport
Time is in minutes, and zeroed at first contact between the two cells. I've put a red dot on the T-cell and a blue one on the APC in the DIC images (left panes); hopefully that proves more informative than annoying. The right panes show GFP fluorescence and thus CD3 localization. As time progresses, CD3 is re-localized from one part of the membrane to another (the synapse). There is supposedly a video of this is in the supplementary information of the article, though I was unable to open it.
The rate and directionality of the movement implies that an active process is occurring, rather than simple diffusion. However, they did not find the actual mechanism for movement and I haven't found any follow-up papers in a brief search (though many subsequent papers implicate the cytoskeleton in this movement). Just to show that movement of transmembrane proteins can, in fact, be actively directed by the cytoskeleton, I refer you to this paper:
Grabham PW, Foley M, Umeojiako A, Goldberg DJ. 2000. Nerve growth factor stimulates coupling of beta1 integrin to distinct transport mechanisms in the filopodia of growth cones. J Cell Sci 113:3003-3012.
They show that membrane-spanning integrins are moved along actin filaments of the cytoskeleton by myosin motor proteins. Expectedly, the abstract does a good job of summarizing the paper:
The cycling of membrane receptors for substrate-bound proteins via their interaction with the actin cytoskeleton at the leading edge of growth cones and other motile cells is important for neurite outgrowth and cell migration. Receptor delivered to the leading edge binds to its ligand, which induces coupling of the receptor to a rearward flowing network of actin filaments. This coupling is thought to facilitate advance... [T]ransport was dependent on an intact actin cytoskeleton and myosin ATPase...
The following is multiple choice question (with options) to answer.
What is observed when two perpendicular flagella moves? | [
"pushing motion",
"shaking motion",
"turning motion",
"spinning motion"
] | D | Figure 23.12 The dinoflagellates exhibit great diversity in shape. Many are encased in cellulose armor and have two flagella that fit in grooves between the plates. Movement of these two perpendicular flagella causes a spinning motion. |
SciQ | SciQ-4299 | electrical-engineering, chemistry
Title: What is the field on engineering that combines chemistry and electronics together? I am looking for a career advice as I am interested in chemistry and electronics at the same time but the universities somehow have the two as different major. Is there any branch of engineering that combines the two? You could follow either Chemistry (Science), Chemical Engineering or Electrical Engineering and purse a career in Semiconductors. There are many variation in Semiconductor that fall either into chemistry or electronics. Below is small sample of options
Semiconductor Lithography Systems
MEMS Technology
Semiconductor Failure Analysis
Silicon Wafer Processing
Microfluidics and microfluidic devices
The following is multiple choice question (with options) to answer.
What is the name of a branch of the chemistry that deals with the interconversion of chemical energy and electrical energy? | [
"Biochemistry",
"Theoretical Chemistry",
"electrochemistry",
"Inorganic chemistry"
] | C | Chemical reactions either absorb or release energy, which can be in the form of electricity. Electrochemistry is a branch of chemistry that deals with the interconversion of chemical energy and electrical energy. Electrochemistry has many common applications in everyday life. All sorts of batteries, from those used to power a flashlight to a calculator to an automobile, rely on chemical reactions to generate electricity. Electricity is used to plate objects with decorative metals like gold or chromium. Electrochemistry is important in the transmission of nerve impulses in biological systems. Redox chemistry, the transfer of electrons, is behind all electrochemical processes. |
SciQ | SciQ-4300 | biochemistry, gas-laws
Title: What is the state of aggregation (gas, liquid) of oxygen in blood? Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.
When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test
Also, how does the lungs convert the gas into something that is compatible to be in blood?
References:
Amount of Oxygen in the Blood Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.
Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See Wikipedia on this.
Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.
The following is multiple choice question (with options) to answer.
Which system in the body exchanges gases with the outside air? | [
"vascular",
"respiratory",
"immune",
"digestive"
] | B | The respiratory system is the body system that exchanges gases with the outside air. It brings air containing oxygen into the body for the cells. It also releases carbon dioxide from the cells into the air. This exchange of gases is called respiration. |
SciQ | SciQ-4301 | 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 is a double membrane of the nucleus that encloses the genetic material? | [
"the nuclear compression",
"the complex envelope",
"the cell wall",
"the nuclear envelope"
] | D | The nuclear envelope is a double membrane of the nucleus that encloses the genetic material. It separates the contents of the nucleus from the cytoplasm. The nuclear envelope is made of two phospholipid bilayers, an inner membrane and an outer membrane. The outer membrane is continuous with the rough endoplasmic reticulum. Many tiny holes called nuclear pores are found in the nuclear envelope. These nuclear pores help to regulate the exchange of materials (such as RNA and proteins) between the nucleus and the cytoplasm. |
SciQ | SciQ-4302 | botany, terminology, nomenclature
Regnum Animale: the animals;
Regnum Vegetabile: the plants;
Regnum Lapideum: the minerals (you read it right).
Note that, in this classification, "animals" correspond to what nowadays we call animals and protozoans, and "plants" correspond to what nowadays we call plants, algae, fungi and bacteria.
You have to keep in mind that this book was first published in 1735, well before the evolutionary biology being proposed in the XIX century and established in the XX century. Therefore, it is a book published when fixism was the current paradigm, full of mentions to the scala naturae.
So, the plants (as well as the animals) showed a continuum of species, going to the lower plants (the bacteria) to the higher plants (the flowering ones). It's worth mentioning again that, by that time, bacteria were plants: Phylum Schyzophyta, to be more precise.
Thus, we have "lower plants" and "higher plants", "lower animals" and "higher animals", as well as "lower minerals" and "higher minerals"!
Unfortunately, this terminology is so embedded in the biological sciences that even today, as I mentioned, we struggle to get rid of it.
Just drop "higher plants", whatever it means
As your Wikipedia link says, "higher plants" is a synonym of vascular plants. However, there are a lot of problems here:
First, this is a remnant of the scala naturae and, just because of that, should be avoided. Think of it as a meaningless term, just like "more evolved organism".
Second, there is no clear and indisputable definition of what is a "higher" plant. Some authors used to define the "higher plants" as the Angiosperms only, or the seed plants (Angiosperms + Gymnosperms), or the vascular plants (Angiosperms, Gymnosperms and Pteridophyta).
For instance, in lusophone biology books, it was very common a division in three groups:
lower plants: bacteria and algae;
intermediate plants: bryophytes and pteridophytes;
higher plants: gymnosperms and angiosperms.
The following is multiple choice question (with options) to answer.
What is the highest taxon in the classification of living things? | [
"a family",
"a domain",
"a class",
"a phylum"
] | B | Prokaryotes are currently placed in two domains. A domain is the highest taxon in the classification of living things. It's even higher than the kingdom. |
SciQ | SciQ-4303 | species-identification, microbiology, microscopy
Title: Identification of protozoa under microscope I observed maybe Protozoa from standing FRESH water and from slowly flowing FRESH water. I am complete dilettante. Can you tell what these creatures are?
https://www.youtube.com/watch?v=6D5ck3zNJzA&t=474s
Thank you.
Added picture for to be more specific At first glance, the organisms may hold the appearance of protozoans like ciliates. However, I am of the belief that these 'totally tubular' micro organisms are in fact diatoms.
The diatoms are a diverse range of eucaryotic microalgae which comprise a large percentage of the phytoplankton group. (Diatomaceous earth is the residual remains of their calcareous walls)
They are likely diatoms because of their apparent hard membrane, and slight brown-green pigment, typical of heterokont diatoms.
I would be unable to specify the organism to family level. However, you may wish to complete your investigation by looking under the order 'Pennales'.
For general information regarding the Diatoms, you may visit https://en.wikipedia.org/wiki/Diatom
Morphology and description available from: https://books.google.co.uk/books?id=xhLJvNa3hw0C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Good luck
The following is multiple choice question (with options) to answer.
Animal-like protists are called what? | [
"genus",
"protozoa",
"larvae",
"bacteria"
] | B | Animal-like protists are called protozoa. Protozoa are single-celled eukaryotes that share some traits with animals. Like animals, they can move, and they are heterotrophs . That means they eat things outside of themselves instead of producing their own food. Animal-like protists are very small, measuring only about 0.01–0.5mm. Animal-like protists include the flagellates, ciliates, and the sporozoans. |
SciQ | SciQ-4304 | 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.
Mating with no strong pair-bonds is called? | [
"mutual",
"covalent",
"heterogeneous",
"promiscuous"
] | D | |
SciQ | SciQ-4305 | 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.
Rna is especially important during synthesis of what? | [
"mitochondria",
"sulfur",
"glucose",
"protein"
] | D | RNA, the other nucleic acid. RNA has many important functions, especially during protein synthesis. And what allows it to be involved in protein synthesis is its ability to fold into three-dimensional structures, giving the molecule specific functions. This structure depicts an RNA molecule. the numerous secondary structures, such as the helices, are visible. |
SciQ | SciQ-4306 | plant-anatomy
Title: Are bryophyte sporangia multicellular? My research on the matter can be summarized in a sentence: "It [sporangium] can be composed of a single cell or can be multicellular" (Source: https://en.wikipedia.org/wiki/Sporangium). Yet there shouldn't be a reply placed between "They are" and "They aren't" test options, speaking of "Are bryophyte sporangia multicellular?". A link to the source where I could ascertain whether the bryophyte sporangia is multicellular (if I could ascertain) is highly appreciated. In Embryophyta (land plants), including bryophytes, the sporangium is usually a multicellular structure.
Perhaps you meant to ask about the number of spore mother cells (SMCs) in each sporangium? That varies across groups. In bryophytes, each sporangium has many SMCs, and accordingly produces a large number of spores. (Contrast this with angiosperms, where a megasporangium [called an ovule] has only one megaspore mother cell.)
References and further reading:
https://courses.lumenlearning.com/boundless-biology/chapter/bryophytes/
https://www.britannica.com/science/plant-development
Image attribution:
By LadyofHats. (Public domain;
https://commons.wikimedia.org/wiki/File:Hornwort_structures.jpg)
The following is multiple choice question (with options) to answer.
Like other bryophytes, moss plants spend most of their life cycle as what? | [
"protozoa",
"zygotes",
"gametophytes",
"copepods"
] | C | Eleutherozoa are the echinoderms that can move. This group includes the starfish and most other echinoderms. |
SciQ | SciQ-4307 | parasitology
Title: Tapeworms and their effect on humans I've read that some people in some countries actually use tapeworms as a form of losing weight. What are the dangers to these people? I haven't really found much on this topic (besides popular sites) but I can summarize it here:
There are quite some tapeworms (or cestoda), I found numbers of up to 3500 species. They attach to the intestinal wall of the humans and then start to take up predigested food through their skin. With that, they reduce food from their host and start to grow, some get as long as 15 meters!
Some of the worms seem to be relatively harmless (besides stealing food), but this is more true for the first world. In poor countries, where there is not enough food, tapeworms can cause severe malnutrition.
Some tapeworms can migrate into the blood stream and from there into other tissues or organs like muscles, eye and brain. There they can cause cysts which can lead to organ failure and death.
For more information see this CDC webpage and this article: "Biochemistry and physiology of tapeworms.". This popular article is probably also interesting.
The following is multiple choice question (with options) to answer.
What is the ring of hooks tapeworms use to attach themselves? | [
"cilia",
"dewlap",
"scolex",
"flagella"
] | C | Tapeworms and flukes have suckers and other structures for feeding on a host. Tapeworms also have a scolex , a ring of hooks on their head to attach themselves to the host (see Figure below ). Unlike other invertebrates, tapeworms lack a mouth and digestive system. Instead, they absorb nutrients directly from the host’s digestive system with their suckers. |
SciQ | SciQ-4308 | ocean, waves
Title: What causes waves to form the characteristic "breaking" shape as they approach the shoreline? We all know that as waves approach the shallow shores, the waves begin to form a characteristic shape. The upper portion of these breaking waves appears to curl forward and downwards over the bottom segment of the wave, before breaking into "white wash". The image below illustrates what this characteristic shape looks like:
The following is multiple choice question (with options) to answer.
What form because water erodes the outside of curves and deposits eroded material on the inside? | [
"inlets",
"cascades",
"caverns",
"meanders"
] | D | Meanders form because water erodes the outside of curves and deposits eroded material on the inside. Over time, the curves shift position. |
SciQ | SciQ-4309 | acceleration, water, speed, distance
Title: Modeling a waterfall I'm modeling a waterfall, the water streams out of a rectangular box with a width of $\text{W}$, a length of $\text{L}$ and a hight of $\text{H}$, so the volume of the water that is streaming from a higher point to the lower point equals $\text{V}_\text{water}=\text{W}\times\text{L}\times\text{H}$. To calculate the acceleration of the water I used:
$$\text{a}(t)=\frac{\text{d}\text{v}(t)}{\text{d}t}=\frac{\text{d}^2\text{x}(t)}{\text{d}t^2}=\frac{\gamma}{\text{m}}\times \text{v}(t)^2-\text{g}$$
Where $\gamma$ is the drag coefficient (in kg/m) and $\text{m}$ is the mass of the water and $\text{g}$ is the acceleration due to gravity. Am I right about this equation?
For example, when I want to find $\text{x}(t)$ (all the initial conditions I assmumed to be zero). I have 6kg of water and the drag coefficient of water I set $7.0\cdot10^{-6}$ and $\text{g}=9.81$. Then I find for $\text{x}(t)$ (when I plot it):
The following is multiple choice question (with options) to answer.
Which waterfall series is the largest on the planet? | [
"iguassu falls",
"niagara falls",
"yosemite falls",
"angel falls"
] | A | Another name for this compound is…water. Water can create some absolutely beautiful sights. Iguassu Falls is the largest series of waterfalls on the planet, located in Brazil, Argentina, and Paraguay. And water is necessary for life. Water, like carbon, has a special role in biology because of its importance to organisms. Water is essential to all known forms of life. Water, H 2 O, such a simple molecule, yet it is this simplicity that gives water its unique properties and explains why water is so vital for life. |
SciQ | SciQ-4310 | botany, terminology, fruit
Title: What is the name of this part in plants, fruits, vegetables? What is the name of this part of the plant, fruit, vegetable? The thing that the plant is connected with the tree and gets nutrients with? The part we usually cut out when eat fruit.
Examples below
Papaya
Banana
Mango 'Stalk' or 'pedicel' would be an appropriate term (see, for example, this paper or this one). Specifically, you could say 'terminal part of the stalk/pedicel', though I don't know if there is a word for that.
Note that the term pedicel is commonly used for the stalk of a flower; it makes sense to use it for fruits too as they are derived from flowers.
The following is multiple choice question (with options) to answer.
What term is used to describe modern seed plants that produce seeds in cones? | [
"deciduous",
"perennials",
"gymnosperms",
"angiosperms"
] | C | Some modern seed plants are gymnosperms that produce seeds in cones. |
SciQ | SciQ-4311 | 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 kind of joints does the skull have that do not allow any movement? | [
"fixed cells",
"fixed joints",
"fixed particles",
"fixed plates"
] | B | Image copyright Vasiliy Koval, 2013, modified by CK-12 Foundation. The skull has fixed joints that do not allow any movement . Used under license from Shutterstock. com. |
SciQ | SciQ-4312 | human-anatomy
Atraumatic dislocation.
This occurs when the shoulder dislocates with minimal force such as reaching up for an object or turning over in bed. Usually it will 'pop' back in itself or with a little help. Normally this type of dislocation does not need reducing in A&E. It can occur regularly throughout the day and will be associated with certain positions the arm is placed into. This type of dislocation is associated with people that have 'lax' joints, for example people who hyper-extend their knees and elbows and can get the palms of both hands onto the floor with ease. This joint laxity is normal for these people and the onset of dislocation can be associated with a change in how the muscles around the shoulder are interacting with each other or a change in posture/ position of the arm. This can produce an imbalance in the control of the joint. Referral for appropriate physiotherapy is the initial form of management. The physiotherapist should look at the way in which the muscles and shoulder joint is moving and posture aiming to restore the balance. Treatment can 'cure' the problem as long as the exercises and advice is continued, but in some cases there is only minimal or nil benefit. At this point surgical intervention is indicated.
Positional Non-traumatic dislocations.
This group of people can dislocate their shoulders without any form or history of trauma. Some may have started out dislocating their shoulder as a party trick; others may have always had shoulders that just 'fall' out of joint. This type of dislocation is usually painless and can be put back in easily. Both shoulders are typically involved. The cause of this type of dislocation is usually a result of what we call 'abnormal muscle patterning' which means the strong muscles around the shoulder joint are not working in the correct order causing them to pull the shoulder out of joint with active movement in the particular direction such as lifting the arm forward above the head or out to the side and above the head. The main treatment for this is physiotherapy that looks at re-sequencing the muscles in order to prevent further dislocations. Occasionaly surgery in the form of thermal capsular shrinkage or plication may be neccessary.
The following is multiple choice question (with options) to answer.
The shoulder and hip are examples of what type of joints? | [
"lever",
"ball and socket",
"hinge",
"pivot"
] | B | This type of joint is found between the articular processes of adjacent vertebrae, at the acromioclavicular joint, or at the intercarpal joints of the hand and intertarsal joints of the foot. Ball-and-socket joints, in which the rounded head of a bone fits into a large depression or socket, are found at the shoulder and hip joints. Both plane and ball-and-sockets joints are classified functionally as multiaxial joints. However, ball-and-socket joints allow for large movements, while the motions between bones at a plane joint are small. |
SciQ | SciQ-4313 | solar-system, space, comets, radiation, dust
Title: How can comets have tails if there's no air resistance in space? I understand that solar radiation causes material to vaporize out of a comet into dust but why does the dust then trail behind the comet like a "tail"?
Assuming gravity is the only applied force acting on the comet, shouldn't all of the material, including the dust, be travelling at the same speed due to conservation of momentum? What causes the dust to travel slower than the comet's nucleus? In other words, why does the dust form a "tail" and not a "cloud"? There are two forces that can cause the formation of a tail: the solar wind and radiation pressure.
The first misconception in your question is "the dust [travels] slower than the nucleus". The tail is not left trailing behind the comet, it is pushed away from the comet by the sun. When the comet is moving away from the sun, the tail is in front of the comet.
Now radiation pressure is small but real. When light shines on something there is a small force. This pushes dust back from the comet in the direction opposite to the sun. The dust is still affected by gravity and a curved dust tail results.
The ultraviolet light from the Sun ionises the gas and gives it an electric charge. The solar wind carries magnetic fields and the gas (or more properly plasma) follows these fields in a straight line back from the sun.
So space around the Sun is not empty. There is powerful light and magnetic fields that are strong enough to push the dust and gas released by the comet away from the coma, and form the tail.
The following is multiple choice question (with options) to answer.
The tails of the hale-bopp comet point away from the sun, evidence that light has what property of motion? | [
"velocity",
"inertia",
"acceleration",
"momentum"
] | D | Figure 29.17 The tails of the Hale-Bopp comet point away from the Sun, evidence that light has momentum. Dust emanating from the body of the comet forms this tail. Particles of dust are pushed away from the Sun by light reflecting from them. The blue ionized gas tail is also produced by photons interacting with atoms in the comet material. (credit: Geoff Chester, U. Navy, via Wikimedia Commons). |
SciQ | SciQ-4314 | virology, infection
Title: Why don't viruses cause wounds? A simple mental model of a viral infection is that an infected cell emits a lot of virions and eventually dies. The emitted virions have a chance of infecting other cells. Nearby cells are at a higher risk of infection.
Based on this model, if one cell in my nose gets infected, I would expect a large part of my nose to be destroyed, as the infection spreads and destroys more and more cells in the same area.
This does not happen! I survived a number of infections and still have my nose. Why?
I know there are "flesh eating" bacteria. Why isn't this the norm for infections? Does a common cold virus or SARS-CoV-2 not infect a lot of cells within the same area? A virus does not destroy that many cells before it is exterminated by the immune system or before the host dies.
Perhaps even more crucially, viruses typically target a very specific type of cell — those on the inner mucal surface of the nose in the case of cold or flu, those of the gastrointestinal tract in the case of stomach viruses, CD4 immune cells in the case of HIV, etc.
Update
As an example of how much time it takes for a virus to eat a noticeable wound, one could take the extermination of the immune cells by HIV - although it does not look as a physical wound, it is one, in the sense that enough of the specific tissue is destroyed to cause a life-threatening condition. It takes about a decade(!) - from the initial infection to the immune system failure.
On the other hand, the lethal effect of typical respiratory viruses is typically via obstructions of the respiratory ways due to inflammation or secretions resulting from the immune response, or via creating suitable conditions for a more serious bacterial infection.
The following is multiple choice question (with options) to answer.
What type of virus can cause painful sores on the mouth and genitals? | [
"herpes",
"syphilis",
"Aids",
"gonorrhea"
] | A | This lip blister, or cold sore, is caused by a herpes virus. The virus is closely related to the virus that causes genital herpes. The genital herpes virus causes similar blisters on the genitals. If you’ve ever had a cold sore, you know how painful they can be. Genital herpes blisters are also painful. |
SciQ | SciQ-4315 | biochemistry, cell-biology, metabolism, photosynthesis
Title: How are ions 'pumped' across a membrane during electron transport? A number of sites (including this one) that provide descriptions of photosynthesis state that high energy electrons 'pump' ions across a membrane. What is the actual 'pumping' mechanism? I've looked at Wikipedia and at a number of YouTube lectures/tutorials but so far have only found statements as to the where and when but not the how of this important process. Short answer:
Electrons flow through membranes by floating through kind of channels made out of iron-sulfur clusters.
Long answer:
Let's take a look at the electron transport chain in the inner mitochodrial membrane. There is a proton gradient across the membrane building up a potential difference by pumping protons across the membrane as electeons flow through the respiratory chain. They (electrons) like to flow throught the respiratory chain because they can go from enzyme to enzyme each with a lower standart free energy. These enymes together form one big complex within the inner membrane with Fe-S clusters enabeling electrons to flow through the membrane by giving them a kind of a power stroke (see here).
This as an simplyfied answer on a example.
The following is multiple choice question (with options) to answer.
The flood of sodium ions through the symporter provides the energy that allows what to move through the symporter and into the cell? | [
"sucrose",
"insulin",
"mitochondria",
"glucose"
] | D | Active transport pumps can also work together with other active or passive transport systems to move substances across the membrane. For example, the sodium-potassium pump maintains a high concentration of sodium ions outside of the cell. Therefore, if the cell needs sodium ions, all it has to do is open a passive sodium channel, as the concentration gradient of the sodium ions will drive them to diffuse into the cell. In this way, the action of an active transport pump (the sodiumpotassium pump) powers the passive transport of sodium ions by creating a concentration gradient. When active transport powers the transport of another substance in this way, it is called secondary active transport. Symporters are secondary active transporters that move two substances in the same direction. For example, the sodiumglucose symporter uses sodium ions to “pull” glucose molecules into the cell. Because cells store glucose for energy, glucose is typically at a higher concentration inside of the cell than outside. However, due to the action of the sodiumpotassium pump, sodium ions will easily diffuse into the cell when the symporter is opened. The flood of sodium ions through the symporter provides the energy that allows glucose to move through the symporter and into the cell, against its concentration gradient. |
SciQ | SciQ-4316 | electromagnetism, electricity
Title: Electric generators? When a magnet passes through a copper coil and electricity is induced into the coil, is there a magnetic resistance on the magnet as it passes through the coil? Yes, the resistance to the magnetic field is called RELUCTANCE. As the magnet moves through a copper coil (consider circular), the change in magnetic field induces current in the coil. Due to the current in the coil, another magnetic field is produced in the opposite direction to the magnet moving through the copper coil. Also, the magnetic strength of both the field are same. But, the directions are exact opposite.
The following is multiple choice question (with options) to answer.
Alternative current is produced when a magnet or coil does what? | [
"moves up and down repeatedly",
"moves in circles at faster rates",
"moves at faster velocities",
"moves back and forth repeatedly"
] | D | The current produced by electromagnetic induction is greater when the magnet or coil moves faster, the coil has more turns, or the magnet is stronger. If the magnet or coil is moved back and forth repeatedly, alternating current is produced. |
SciQ | SciQ-4317 | molecular-structure, covalent-compounds
Title: How to know it when I see a covalent network? This is a well-known (better said: well-discussed) question in the internet. When you look for answers for popular questions, you usually see them with a variable degree of reliability and complexity. Unfortunately, for this one, I only observed very very crude and general rules of thumb. So let's get a real answer:
A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal may be considered a macromolecule. Formulas for network solids, like those for ionic compounds, are simple ratios of the component atoms represented by a formula unit. Covalent network, wikipedia
Diamond and SiO$_2$ are really great examples of covalent networks-lattices. So enough with stories:
If you face a new chemical formula, how would you assume it's a covalent network? (In case it is) Is it somehow done by drawing the Lewis structure? Is there a rule for this? Or is it only possible to know such thing with experimental data?
The following is multiple choice question (with options) to answer.
What are the chemical formulas for covalent compounds referred to as? | [
"molecular formulas",
"magnetic formulas",
"Electron Formulas",
"nucleus formulas"
] | A | The chemical formulas for covalent compounds are referred to as molecular formulas because these compounds exist as separate, discrete molecules. Typically, a molecular formula begins with the nonmetal that is closest to the lower left corner of the periodic table, except that hydrogen is almost never written first (H2O is the prominent exception). Then the other nonmetal symbols are listed. Numerical subscripts are used if there is more than one of a particular atom. For example, we have already seen CH4, the molecular formula for methane. Naming binary (two-element) covalent compounds is similar to naming simple ionic compounds. The first element in the formula is simply listed using the name of the element. The second element is named by taking the stem of the element name and adding the suffix -ide. A system of numerical prefixes is used to specify the number of atoms in a molecule. Table 4.1 "Numerical Prefixes for Naming Binary Covalent Compounds" lists these numerical prefixes. Normally, no prefix is added to the first element’s name if there is only one atom of the first element in a molecule. If the second element is oxygen, the trailing vowel is usually omitted from the end of a polysyllabic prefix but not a monosyllabic one (that is, we would say “monoxide” rather than “monooxide” and “trioxide” rather than “troxide”). Table 4.1 Numerical Prefixes for Naming Binary Covalent Compounds Number of Atoms in Compound. |
SciQ | SciQ-4318 | homework, reproduction, embryology
Title: Which process is needed to complete male reproductive development? In order to properly complete male reproductive development:
A. primordial germ cells must begin Meiosis I in utero.
B. Sertoli cells must produce testosterone.
C. Dihydrotestosterone must masculinize Wolffian duct derivatives
D. the paramesonephric ducts must degenerate
E. the metanephros must form the genital epithelium
My attempt: I think the answer is C because testosterone turns into DHT which then masculinzing the wolffian duct. Other people I am studying with claim the answer is D (which is true) except that I dont think the loss of the paramesonephric duct is needed to complete male repro development. Regarding option C:
Although it is correct that testosterone is converted into DHT, it is the former, not the latter, which is responsible for differentiation of the mesonephric (a.k.a. Wolffian) ducts:
Between 8 and 12 weeks, the initial secretion of testosterone stimulates mesonephric ducts to transform into a system of organs—the epididymis, vas deferens, and seminal vesicle—that connect the testes with the urethra.*
DHT (dihydrotestosterone) is produced in the Leydig cells by the 5α-Reductase enzyme. It is required for induction of the external male genitalia (urethra, penis, and scrotum) and prostate from the embryonic ureteral groove, and for testicular descent into scrotum.
Regarding option D:
Sertoli cells secrete Anti Müllerian Hormone (AMH), which causes degeneration of the müllerian (a.k.a. paramesonephric) ducts between weeks 8 and 10. It is normal to speak about degeneration of the müllerian ducts as a defining aspect of male embryology, and thus I believe answer D is correct. Your point is taken, however:
Nevertheless, small müllerian duct remnants can be detected in the adult male, including a small cap of tissue associated with the testis, called the appendix testis, and an expansion of the prostatic urethra, called the prostatic utricle.*
The following is multiple choice question (with options) to answer.
What do secondary spermatocytes form when completing meiosis? | [
"pores",
"spermatids",
"semen",
"sporozoans"
] | B | Spermatogonia lining the seminiferous tubule undergo mitosis to form primary spermatocytes , which are also diploid. The primary spermatocytes undergo the first meiotic division to form secondary spermatocytes , which are haploid. Spermatocytes make up the next layer of cells inside the seminiferous tubule. Finally, the secondary spermatocytes complete meiosis to form spermatids . Spermatids make up a third layer of cells in the tubule. |
SciQ | SciQ-4319 | human-anatomy, muscles
Title: Contracting muscles in humans I study biology at school, and unfortunately for me, my program skips the muscles in humans chapter.
I know (and mainly, feel) that the movement in one direction isn't created by the same muscle as the movement in the opposite direction, e.g the Triceps ("front") and Biceps ("back").
I know that the triceps straightens the elbow, while the biceps contracts the elbow.
I also know that, instead of actually moving the arm, I can contract these two muscles (when I show off, for example...) without actually moving the arm. That area becomes hard. Both muscles, as I feel, are contracting. I cannot statically contract only one of them.
My question is whether this action is something "special", or simply both muscles working against each other, resulting in zero movement? The situation you are describing where muscles are situated on opposites sides of a joint and produce opposing movements is called "antagonism." Most joints are set up where one or more muscles on either sides will produce such movements (e.g., flexors vs. extensors). Here's a question about muscles without antagonists.
When you contract all the muscles crossing a joint (i.e., when you are "showing off"), the muscles balance each other. If not, the bones would move and the joint angles would change. So taking the elbow as an example, in the image below, Arnold is contracting the elbow flexors (biceps brachii, brachialis) as well as the elbow extensors (triceps brachii). In order for the bones to remain static, the forces must be equal and opposite.
The following is multiple choice question (with options) to answer.
What is the name of the muscle that contracts to cause the joint to straighten? | [
"opposing",
"abductor",
"extensor",
"flexor"
] | C | Muscles can only contract. They cannot actively extend, though they can move or relax back into the non-contracted neutral position. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. Each muscle in the pair works against the other to move bones at the joints of the body. The muscle that contracts to cause a joint to bend is called the flexor . The muscle that contracts to cause the joint to straighten is called the extensor . When one muscle is contracted, the other muscle from the pair is always elongated. |
SciQ | SciQ-4320 | bacteriology, antibiotic-resistance, research-process
Title: How do scientists kill the bacteria they themselves made resistant? I was reading this article on researching bacteria resistance to silver by removing some of their genes.
Researchers then used "colony-scoring" software to measure the differences in growth and size of each plate's bacterial colony. E. coli strains with genes deleted involved in producing sensitivity, or toxicity, to silver grew larger colonies. Strains with genes deleted involved with resistance grew smaller colonies.
Once you end up with some resistant bacteria and you're done researching it, you can't just flush it down the toilet. How do you safely dispose those colony plates in a way that ensures those bacteria don't get out into the wild and reproduce? You are absolutely right, flushing down the toilet (or the sink) or simply throwing them into the normal waste doesn't work for biosafety reasons. And it is also not allowed, depending on the country you would do this in, this can lead to hefty fines.
Biologically contaminated lab waste can be inactivated (=all potential dangerous organisms are destroyed) by two ways: Either by heat or chemically. Which ways is used, depends on the kind of waste.
The most commonly used way is autoclaving, meaning treating the waste with steam at high temperatures at higher pressure. The temperature used here is usually 121°C, the exposure time depends on the volume of the waste, since the temperature needs to be reached and kept for at least 20 minutes. See the references for more details.
Liquid wastes (like culture media) can also be inactivated chemically by adding chlorine bleach to decompose the cells. Bleach can also be used to decontaminate surfaces, although here more often alcoholic solutions (70% Ethanol or Isopropanol) are used. After chemical inactivation, the remaining solutions should not be autoclaved as the emerging fumes are either unhealthy (bleach) or explosive (alcoholic solutions) and this is unnecessary, too.
Liquid wastes can also be autoclaved to inactivate them.
Autoclaving has the main advantage that it is rather simple (put the waste into the autoclave, close it and run a appropriate program), the waste can afterwards simply be discarded as normal waste, which may not be the case for chemically inactivated waste, which may need special precaution for disposal.
References:
The following is multiple choice question (with options) to answer.
Name the process of removing wastes from the body. | [
"filtration",
"depletion",
"degradation",
"excretion"
] | D | Excretion is the process of removing wastes from the body. |
SciQ | SciQ-4321 | organic-chemistry, stoichiometry
Title: What is mol % and how do you calculate the mass of a compound needed to be a certain mol % relative to another compound at a particular volume? I know that there is some stoichiometry involved, but I am lost here. I know you need the molecular weight of both compounds and that's about it? Assuming we have a binary mixture, or equivalently, a mixture that only involves two different components $A$ and $B$, the total mass of the mixture is simply the sum of the individual masses:
$$m=m_A+m_B$$
The same logic applies to the total amount of the mixture:
$$n=n_A+n_B$$
When you divide the mass of $A$ and $B$ (separately) by the total mass of the mixture, you obtain the mass fraction of $A$ and $B$ in the mixture:
$$X_A=\frac{m_A}{m}\quad\quad X_B=\frac{m_B}{m}$$
When you divide the amount of $A$ and $B$ (separately) by the total amount of the mixture, you obtain the mole fraction of $A$ and $B$ in the mixture:
$$Y_A=\frac{n_A}{n}\quad\quad Y_B=\frac{n_B}{n}$$
In a binary mixture, the sum of fractions of $A$ and $B$ is equal to 1:
$$X_A+X_B=1$$
$$Y_A+Y_B=1$$
The molar mass of a binary mixture can be calculated with either the mass fractions or mole fractions, and the molar masses of each component:
$$M=\left(\frac{X_A}{M_A}+\frac{X_B}{M_B}\right)^{-1}$$
$$M=Y_A\;M_A+Y_B\;M_B$$
Finally, if you want to convert a mass fraction into a mole fraction or vice-versa, you can use these formulas:
The following is multiple choice question (with options) to answer.
What term means the percentage by mass of each element in a compound? | [
"percent composition",
"mass effect",
"elemental percent",
"biomass"
] | A | Percent Composition The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most succinct way of representing this elemental makeup. When a compound’s formula is unknown, measuring the mass of each of its constituent elements is often the first step in the process of determining the formula experimentally. The results of these measurements permit the calculation of the compound’s percent composition, defined as the percentage by mass of each element in the compound. For example, consider a gaseous compound composed solely of carbon and hydrogen. The percent composition of this compound could be represented as follows: mass H × 100% mass compound mass C %C = × 100% mass compound. |
SciQ | SciQ-4322 | geology, mineralogy
There is an adage amongst some geologists that states "gold is where you find it". There is no altitude preferable for finding gold deposits. It's found in mountains, in deserts, in forests, under salt lakes, even dissolved in the oceans. The oceans contain the largest quantities of gold, but it is uneconomic to extract it from sea water because the concentration are so low.
Biological indicators, such a vegetation may work for some base metals, such as copper, but not necessarily for gold.
Also, gold can occur as a deposit of just gold, but it can also occur in association with other metals in the form of polymetallic deposits which contain gold, silver, copper, lead or zinc, even uranium.
Finally, not all deposits of minerals, gold included, are reserves. To be classified as a reserve and an orebody, a deposit of mineralization must be economic to mine.
The following is multiple choice question (with options) to answer.
Beaches and deserts collect large deposits of what? | [
"water",
"sand",
"plants",
"animals"
] | B | Sediments are deposited in many different types of environments. Beaches and deserts collect large deposits of sand. Sediments also continuously wind up at the bottom of the ocean and in lakes, ponds, rivers, marshes, and swamps. Avalanches produce large piles of sediment. The environment where the sediments are deposited determines the type of sedimentary rock that can form. |
SciQ | SciQ-4323 | 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 is the name for animals that have a backbone? | [
"mammals",
"skeletates",
"vertebrates",
"invertebrates"
] | C | The first eight phyla listed in Table above include only invertebrate animals. Invertebrates are animals that lack a vertebral column , or backbone. The last phylum in the table, the Chordata, also includes many invertebrate species. Tunicates and lancelets are both invertebrates. Altogether, invertebrates make up at least 95 percent of all animal species. The remaining animals are vertebrates. Vertebrates are animals that have a backbone. All vertebrates belong to the phylum Chordata. They include fish, amphibians, reptiles, birds, and mammals. |
SciQ | SciQ-4324 | molecules, polarity
Title: Non polar molecular and attractive forces How come when a non polar molecule increases in size, the attractive forces between the molecules of a substance also increase?
I thought that when a molecule increases in size, the atomic radius increases, which creates a bigger space between particles; thus, the force of attraction would be weaker.
But, why does the force of attraction increase when a non polar molecule increases in size? There is more than one factor that matters in the forces between molecules. The tradeoff between these different factors is complex and can't be reduced to a single simple equation or factor. So some of the factors become more important because of molecular or atomic size counterbalancing the factor of distance between the entities.
The collective force that cause molecules and atoms to attract are often referred to as van der Waal's force (though some sources use a more narrow definition that doesn't include all of the components below). The key non-bonding forces involved are:
forces between permanent dipoles
forces between permanent dipoles and induced dipoles
forces between instantaneously induced dipoles caused by quantum fluctuations
In non-polar molecules it is the third of these that dominates. Crudely stated the force arises because of uneven distribution of the electron cloud in a molecule or atom that happens as a result of quantum fluctuations in the cloud. An uneven distribution of electron density is the equivalent of a dipole moment. These dipole moments create induced dipoles in neighbouring atoms and can interact with other quantum fluctuations in the neighbouring atoms. These create small electrostatic forces between the atoms or molecules.
The reason why larger atoms or molecules seem to have larger forces is two fold. Larger molecules, crudely, have larger electron clouds and more ways to interact (shape matters too and large flat molecules "stick" together more than irregular lumpy ones: compare the melting points of benzene and toluene).
In larger atoms the explanation is simpler. Larger electron clouds are less tightly held by there nuclei than those in smaller atoms. Crudely, larger, floppier clouds can have more scope for the quantum fluctuations than tighter-held smaller clouds (also they have a larger area and that maters to the total force). So the size effect increases the strength of the force rather than reducing it as might be expected from simpler arguments.
The following is multiple choice question (with options) to answer.
The attractive force between water molecules is what kind of reaction? | [
"aquatic reaction",
"symmetrical reaction",
"diffusion reaction",
"dipole reaction"
] | D | The attractive force between water molecules is a dipole interaction. The hydrogen atoms are bound to the highly electronegative oxygen atom (which also possesses two lone pair sets of electrons, making for a very polar bond. The partially positive hydrogen atom of one molecule is then attracted to the oxygen atom of a nearby water molecule (see Figure below ). |
SciQ | SciQ-4325 | atoms
Title: Conversion atom to another One child has claimed to have find a solution to all physical problems. On asking for details, he said that all periodic elements has common components, i.e. electrons, protons, neutrons.
The child has suggested a solution: convert atom to another by adding electron. This way one can get substance like $\ce{H2O, Au, He}$ in abundance.
How can it be done? While what you suggest may sound nice on paper, it has some serious problems.
Getting the elements. Let's say that we're talking about purifying water to remove toxic elements such as Hg or Cd. Extracting the elements out of the water is a feat by itself, for example using reverse osmosis methods. This is a method used for seawater desalination - to turn them from salt water filled with all kinds of elements into drinkable water. This process is very expensive, and a very polluting one as well. Desalination just the amount of water you need for drinking water is complicated, so desalinating an entire reservoir is simply not going to happen.
Let's say you did somehow manage to extract the element in question. Now you need nuclear reactions to transmute one element to another. Not all are possible. For some elements, like Tc or Am this is the only way you can produce them. However, you are going to end up with radioactive nuclear waste.
To sum it up, even if it was possible, you would need so much power and to do it and you will produce some much pollution that it's simply not worth it. Just going and mining the gold will be orders of magnitude cheaper (and probably cleaner) than producing it using nuclear reactions.
If you do manage to somehow extract the the polluting elements, you usually do something else with them (aka recycling) and you do not attempt being an alchemist. Another example is soils contaminated with lead. The solution is to just dig it up, put it somewhere where it is not hazardous to anyone and replace it with clean soil.
The following is multiple choice question (with options) to answer.
Which procedure helps modern nuclear physics convert lead into gold? | [
"matter fusion",
"evaporation",
"nuclear bombardment",
"nuclear fission"
] | C | The alchemists were never successful in changing lead into gold. But modern nuclear physics can accomplish this task. Lead is subjected to nuclear bombardment in a particle accelerator. A small amount of gold can be obtained by this process. However, the cost of the procedure is far more than the amount of gold obtained. So the dream of the alchemists has never (and will never) come true. |
SciQ | SciQ-4326 | molecules, polarity
Title: Non polar molecular and attractive forces How come when a non polar molecule increases in size, the attractive forces between the molecules of a substance also increase?
I thought that when a molecule increases in size, the atomic radius increases, which creates a bigger space between particles; thus, the force of attraction would be weaker.
But, why does the force of attraction increase when a non polar molecule increases in size? There is more than one factor that matters in the forces between molecules. The tradeoff between these different factors is complex and can't be reduced to a single simple equation or factor. So some of the factors become more important because of molecular or atomic size counterbalancing the factor of distance between the entities.
The collective force that cause molecules and atoms to attract are often referred to as van der Waal's force (though some sources use a more narrow definition that doesn't include all of the components below). The key non-bonding forces involved are:
forces between permanent dipoles
forces between permanent dipoles and induced dipoles
forces between instantaneously induced dipoles caused by quantum fluctuations
In non-polar molecules it is the third of these that dominates. Crudely stated the force arises because of uneven distribution of the electron cloud in a molecule or atom that happens as a result of quantum fluctuations in the cloud. An uneven distribution of electron density is the equivalent of a dipole moment. These dipole moments create induced dipoles in neighbouring atoms and can interact with other quantum fluctuations in the neighbouring atoms. These create small electrostatic forces between the atoms or molecules.
The reason why larger atoms or molecules seem to have larger forces is two fold. Larger molecules, crudely, have larger electron clouds and more ways to interact (shape matters too and large flat molecules "stick" together more than irregular lumpy ones: compare the melting points of benzene and toluene).
In larger atoms the explanation is simpler. Larger electron clouds are less tightly held by there nuclei than those in smaller atoms. Crudely, larger, floppier clouds can have more scope for the quantum fluctuations than tighter-held smaller clouds (also they have a larger area and that maters to the total force). So the size effect increases the strength of the force rather than reducing it as might be expected from simpler arguments.
The following is multiple choice question (with options) to answer.
Alkanes are nonpolar and therefore do not attract what? | [
"atoms",
"molecules",
"eons",
"ions"
] | D | Alkanes are nonpolar; they do not attract ions. |
SciQ | SciQ-4327 | atmosphere, wind, geography, troposphere, stratosphere
Title: Other than the South Pole where is the windless place on Earth? For this other question "Would this chambered cylinder be possible", preferably near the equator where is a calmest place from the troposphere to the stratosphere where is the windless place one Earth most of the year? Not just the south pole, but 'Ridge A' and many other parts of the high Antarctic Plateau, at or about 4000 metres altitude, are generally recognized as being the least windy. Otherwise, there are a many parts of the high pressure belts at about +/- 30 degrees which have little wind for most of the year. These tend to be very dry deserts where occasional winds have momentum from other regions. On a local scale there are some deep valleys in tropical rain forests. Once you get below the canopy turbulence level they seldom receive winds of any significance - just the lightest breeze from impeded convection. However, records are hard to find because anemometers in such locations are not really representative of anything.
There is an instagram which claims that Fern tree bus stop, in Hobart, Tasmania, is the 'calmest place on Earth'.
But my experience of Hobart is that icy winds in winter can be far from calm.
These things are relative. Compared to the 2100 km/hour winds of Neptune, everywhere on our planet is as close to windless as makes no difference.
The following is multiple choice question (with options) to answer.
What do we call the lowest layer of the atmosphere? | [
"troposphere",
"mesosphere",
"stratosphere",
"asthenosphere"
] | A | The troposphere is the lowest layer of the atmosphere. In it, temperature decreases with altitude. The troposphere gets some of its heat directly from the Sun. Most, however, comes from Earth's surface. The surface is heated by the Sun and some of that heat radiates back into the air. This makes the temperature higher near the surface than at higher altitudes. |
SciQ | SciQ-4328 | biochemistry, gas-laws
Title: What is the state of aggregation (gas, liquid) of oxygen in blood? Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.
When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test
Also, how does the lungs convert the gas into something that is compatible to be in blood?
References:
Amount of Oxygen in the Blood Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.
Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See Wikipedia on this.
Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.
The following is multiple choice question (with options) to answer.
Oxygenated blood is transported by what system? | [
"circulatory",
"nervous",
"skeletal",
"pulmonary"
] | A | Oxygenated blood is transported by the circulatory system from lungs to tissues throughout the body. |
SciQ | SciQ-4329 | electric-circuits, electric-current, electrical-resistance, voltage, batteries
Title: Voltage drop across battery with internal resistance Consider a battery with internal resistance connected to an external voltage source; there is a voltage difference along the battery
The voltage source is not drawn in the picture
The voltage difference is $\ V= E ± Ir$ where ± is determined by the direction of the current flow. The symbols have their usual meanings
V is the total voltage difference through the battery. As per the definition of resistance ; the resistance of some component is equal to the total voltage difference through that component divided by the total current that flows through it.
Accordingly, it would follow that $\frac{V}{r}=I$ Which is in contradiction to the aforementioned. E would be zero, which is clearly wrong
The second method implicitly assumes that the total voltage drop is only caused by the resistance alone. However to my knowledge resistance is defined as the ratio between the total voltage difference and the current that flows through it.
What is the correct definition of resistance of a component, if it is different from the above? Or is there something wrong in my reasoning?
Reading the answer I now consider the contexts where V=IR can be used as a definition for the resistance of a component.
https://en.m.wikipedia.org/wiki/Electrical_resistance_and_conductance The wiki article uses “object” implying, some sort of a generality. $V$-$I$ linear OR $V=IR$ is statement of Ohm's law? Too stresses how resistance is defined.
Where have I gone wrong?
You've gone wrong here:
the resistance of some component is equal to the total voltage
difference through that component divided by the total current that
flows through it.
It's not some component that Ohm's law applies to, it's specifically (ideal) resistors.
To model a physical cell, one starts by putting an ideal resistor in series with an ideal voltage source. You'll note that the voltage across the resistor is given by Ohm's law but the voltage across the voltage source is what it is regardless of the current through, i.e., the ideal voltage source does not obey Ohm's law.
Thus, the voltage across the series combination of the voltage source and resistor will not, and should not be expected to, obey Ohm's law.
The following is multiple choice question (with options) to answer.
Internal resistance, or (electrical) resistance in general, involves the resistance of the flow of what? | [
"water",
"force",
"current",
"protons"
] | C | Internal Resistance As noted before, a 12-V truck battery is physically larger, contains more charge and energy, and can deliver a larger current than a 12-V motorcycle battery. Both are lead-acid batteries with identical emf, but, because of its size, the truck battery has a smaller internal resistance r . Internal resistance is the inherent resistance to the flow of current within the source itself. Figure 21.9 is a schematic representation of the two fundamental parts of any voltage source. The emf (represented by a script E in the figure) and internal resistance r are in series. The smaller the internal resistance for a given emf, the more current and the more power the source can supply. |
SciQ | SciQ-4330 | atmospheric-chemistry
But some researchers have argued it does make a notable contribution in the lower atmosphere, but indirectly. There doesn't appear to be a consensus on how big this effect is (and the Wikipedia reference is old and obsolete). The argument for ozone being a notable contributor is based on the following. Hydrocarbon pollution in the lower atmosphere (often from vehicle emissions) leads to a variety of undesirable reactions some of which lead to the production of ozone (as well as many other irritating components of smog). We really don't want too much smog or ozone in the lower atmosphere because it is bad for health. Some have estimated that it also adds to the warming caused by hydrocarbon emissions (exacerbating the warming potential of methane, for example).
It is hard to judge the estimates of its contribution to warming not least because they rely on models of complex reactions caused indirectly by other pollutants. Also, the big issue with emissions leading to ozone are not its contribution to warming but its contribution to pollution which causes direct harm to people in the short term. In fact regulations around emissions has been striving to reduce those emissions since before we started worrying about global warming. And, many countries have sharply reduced them (this is a major reasons why most western countries insist on catalytic converters in their vehicles). We should reduce ozone pollution by reducing the other emissions that cause it and we have been doing that for decades.
I would argue that ozone is essentially irrelevant to global warming. We should strive to reduce it in the lower atmosphere even if we were not worried by global warming. So even if we can't agree on how big its contribution to warming is (which the literature isn't clear on) we should be reducing it as much as we can for more direct reasons.
And, even if we wanted to report its contribution to warming, the best place to account for it is to add it to the contribution of other emissions (eg methane) rather than to account for it separately as we don't directly emit it from anything.
The following is multiple choice question (with options) to answer.
What gas produced by fossil fuel use is a major cause of global warming? | [
"phosphorous",
"hydrogen",
"carbon dioxide",
"helium"
] | C | When fossil fuels burn, they release thermal energy, water vapor, and carbon dioxide. Carbon dioxide produced by fossil fuel use is a major cause of global warming. The burning of fossil fuels also releases many pollutants into the air. Pollutants such as sulfur dioxide form acid rain, which kills living things and damages metals, stonework, and other materials. Pollutants such as nitrogen oxides cause smog, which is harmful to human health. Tiny particles, or particulates, released when fossil fuels burn also harm human health. Natural gas releases the least pollution; coal releases the most (see Figure below ). Petroleum has the additional risk of oil spills, which may seriously damage ecosystems. |
SciQ | SciQ-4331 | habitable-zone
Title: Better than Earth habitability Earth undoubtly has very good conditions for supporting life. Although it is expected that many other planets on the outer space have conditions at least as good as Earth, the vast majority doesn't, making them unhospitable to life or probably being able to support only very simple lifeforms. Earth itself for some billions of years until the Ediacaran or Cambrian could only support very simple lifeforms.
There are many parameters that may influence the habitability of a planet and its ability to support complex life: Star type; star temperature; star luminosity; stellar activity; stellar stability; star age; planet age; planet composition; planet size; orbital excentricity; orbital length; rotation axis inclination; planet tectonics; planet magnetosphere; presence and influence of satellites; abundance of water; planet atmosphere; interactions with other planets; presence or absence of asteroids, comets and minor planets planets belts and their position, distribution and composition; galactic orbit; galactic neighborhood; mass-extinction events rate, probability and intensity; and hundred of other possible variables including some based on pure luck and random chance.
Many of the parameters are modeled after Earth itself, since Earth is the only place so far that we know that life exists, and even if we found some alien life somewhere, it will probably be limited only to very simple forms of life.
But, what combinations of those parameters could lead to a planet with better life support than Earth itself?
Ok, you may argue that the question is too broad, so by "good life support" we could say something that allows the planet to evolve plenty biodiverse multicellular life ranging from simple microscopic creatures to complex dozens-meters long creatures with many body-differentiated parts and organs in a short timespan. So, a planet that has an environment which allows the development of richly-diverse and complex plant-like and animal-like creatures in a billion years after formation and stay like this for another 10 billion years is expected to be more life-friendly than Earth.
Further, lets restrict the biochemistry to what we know: water-based and carbon-based life, but not necessarily oxygen-breathing.
By the way, I am not asking anything about intelligent life or humans, just complex multicellular and biodiverse life.
The following is multiple choice question (with options) to answer.
What supports most of earth's ecosystems? | [
"sun",
"moon",
"oceans",
"crust"
] | A | The Sun supports most of Earth's ecosystems. Plants create chemical energy from abiotic factors that include solar energy. The food energy created by producers is passed through the food chain. |
SciQ | SciQ-4332 | organic-chemistry, carbonyl-compounds, reactivity, carbohydrates, protecting-groups
Title: Reaction of glucose acetal with acetic anhydride The following problem was asked in JEE Mains 2020 (Sept 2, Shift 1),
Consider the following reactions:
$\ce{ (i) Glucose + ROH ->[dry HCl] Acetal ->[$x$ eq. of (CH3CO)2O] acetyl derivative }$
$\ce{ (ii) Glucose ->[Ni/H2] A ->[$y$ eq. of (CH3CO)2O] acetyl derivative }$
$\ce{ (iii) Glucose ->[$z$ eq. of (CH3CO)2O] acetyl derivative }$
What are $x, y,$ and $z$ in these reactions, respectively?
I know that the reaction in (i) is acetal formation (used to protect aldehyde), and that alcohol reacts with anhydrides to form acids. As, there are only 5 hydroxyl group in acetyl deriv. of (i), so $x=5$.
In (ii), carbonyl part of glucose reduces to hydroxyl group, so $y=6$. And, in (iii), glucose directly reacts with anhydride, so $z=5$.
But, my answer was wrong (x only), as per the key. What am I doing wrong?
The answer given is,
x = 4, y = 6, z = 5 I think there's nothing to discussed about this further as all comments directing to the correct answer: $x = 4, \ y = 6,$ and $ z = 5.$ I think it's better show in the structures:
The following is multiple choice question (with options) to answer.
Because carbohydrates have a carbonyl functional group and several hydroxyl groups, they can undergo a variety of biochemically important reactions. the carbonyl group, for example, can be oxidized to form a carboxylic acid or reduced to form this? | [
"sucrose",
"caffeine",
"glucose",
"alcohol"
] | D | Because carbohydrates have a carbonyl functional group and several hydroxyl groups, they can undergo a variety of biochemically important reactions. The carbonyl group, for example, can be oxidized to form a carboxylic acid or reduced to form an alcohol. The hydroxyl groups can undergo substitution reactions, resulting in derivatives of the original compound. One such derivative is Sucralose, an artificial sweetener that is six times sweeter than sucrose; it is made by replacing two of the hydroxyl groups on sucrose with chlorine. Carbohydrates can also eliminate hydroxyl groups, producing alkenes. |
SciQ | SciQ-4333 | solar-system, history
Earth at the center.
Moon orbiting the Earth.
Mercury orbiting the Earth farther than the Moon.
Venus orbiting the Earth farther than Mercury.
Sun orbiting the Earth farther than Venus.
Mars orbiting the Earth farther than Sun.
Jupiter orbiting the Earth farther than Mars.
Saturn orbiting the Earth farther than Jupiter.
The celestial sphere of stars rotating around the Earth, being the outermost sphere.
The following is multiple choice question (with options) to answer.
What do earth and the other planets in the solar system make around the sun? | [
"elevated orbits",
"elliptical orbits",
"smooth orbits",
"radial orbits"
] | B | Earth and the other planets in the solar system make elliptical orbits around the Sun. The ellipses in this image are highly exaggerated. |
SciQ | SciQ-4334 | fluid-mechanics, heat-transfer
Title: Can I make a fishing line going through a small hole waterproof? Here's the setup, going through those four valves will be some fluid, probably water, but I need some fishing line going through this cylinder to be sealed. The line is anchored at two points, the top and bottom, and will be used to draw two points together. This apparatus is to heat and cool wound up fishing line, as that can be used as a muscle fiber. When hot water is applied, it contracts, when cool water is applied, it expands. This does mean that the line will be moving some percentage of the length, which may also mean that the diameter will change slightly.
Fishing Line Makes for Superhuman Artificial Muscles A high-quality seal that diameter would be very difficult to fabricate. You always want to avoid seals in designs when you can help it. For example, you could fix one end inside the cylinder so that you only have one moving end to worry about.
If you allow for some leakage and run the water at low pressure (less than 12" of head) you could probably get away with melting a small cup of wax around the line. Have the wax be as tall as the diameter of your primary tube. The longer distance will reduce water leakage. Pull the line taught while it cools so the path is straight. It should pull free with very little force, and with little movement during operation, it should provide a fair amount of operating life.
A more robust solution would be to put a diaphragm (as mentioned in the comments) on the end cap instead of a seal. The diaphragm will act like a soft spring, and can be compensated for with other spring components if necessary.
A design that you may or may not have considered; would be to use a single tube as your tension member and run hot and cold fluid through this tube. The design would be simpler, the volume of fluid per tension force would be lower, and the heat transfer would be quicker. Something to think about.
The following is multiple choice question (with options) to answer.
What do anglerfish use their glow-in-the-dark, rod-like structure for? | [
"to find a mate",
"to keep warm",
"to attract prey",
"for protection"
] | C | Anglerfish. This anglerfish lives between 1000 and 4000 meters below sea level. No sunlight penetrates to this depth. The rod-like structure on its face has a glow-in-the-dark tip. It is covered with microorganisms that give off their own light. The fish wiggles the structure like a worm to attract prey. In the darkness, only the rod-like worm is visible. |
SciQ | SciQ-4335 | fluid-statics, surface-tension
So, it would be very helpful if you could explain why does a metal paper clip float even though it has an acute contact angle with water.
Please note that the question Surface tension: the paper clip experiment is not same as this one. It doesn't discuss about the obtuse contact angles observed between metal paper clip and water which is the central theme of this question. When there is no wetting, the contact angle is obtuse. When wetting takes place, the contact angle becomes acute. A certain amount of pressure is needed to break the surface of the liquid so that wetting takes place. If wetting were to take place, the paperclip would sink (likewise it would sink if there were no surface tension).
When wetting does not take place, the contact angle is obtuse. The paper clip can float because wetting does not take place (or only a small amount of wetting takes place) - the clip is light enough that does not push hard enough on the surface of the water to break surface tension. This is undoubtedly helped by contaminants, such as oils picked up from fingers (it is opposite to capillary action, in which wetting does take place).
The following is multiple choice question (with options) to answer.
Surface tension is responsible for the fact that small insects can do this on water? | [
"walk",
"float",
"sink",
"swim"
] | A | tension causes liquids to form spheres in free fall or zero gravity (see - ball-ch10_s02_f01: the “floating” water isn’t in the shape of a sphere by accident; it is the result of surface tension). Surface tension is also responsible for the fact that small insects can “walk” on water. Because of surface tension, it takes energy to break the surface of a liquid, and if an object (such as an insect) is light enough, there is not enough force due to gravity for the object to break through the surface, so the object stays on top of the water ( ball-ch10_s03_f07). Carefully done, this phenomenon can also be illustrated with a thin razor blade or a paper clip. The fact that small droplets of water bead up on surfaces does not mean that water—or any other liquid— does not interact with other substances. Sometimes the attraction can be very strong. Adhesion is the tendency of a substance to interact with other substances because of intermolecular forces, while cohesion is the tendency of a substance to interact with itself. If cohesive forces within a liquid are stronger than adhesive forces between a liquid and another substance, then the liquid tends to keep to itself; it will bead up. However, if adhesive forces between a liquid and another substance are stronger than cohesive forces, then the liquid will spread out over the other substance, trying to maximize the interface between the other substance and the liquid. We say that the liquid wets the other substance. Adhesion and cohesion are important for other phenomena as well. In particular, if adhesive forces are strong, then when a liquid is introduced to a small-diameter tube of another substance, the liquid moves up or down in the tube, as if ignoring gravity. Because tiny tubes are called capillaries, this phenomenon is called capillary action. For example, one type of capillary action—capillary rise—is seen when water or water-based liquids rise up in thin glass tubes (like the capillaries sometimes used in blood tests), forming an upwardly curved surface called a meniscus. Capillary action is also responsible for the “wicking” effect that towels and sponges use to dry wet objects; the matting of fibers forms tiny capillaries that have good adhesion with water. Cotton is a good material for this; polyester and other synthetic fabrics do not display similar capillary action, which is why you seldom find rayon bath towels. A similar effect is observed with liquid fuels or melted wax and their wicks. Capillary action is thought to be at least partially responsible for transporting water from the roots to the tops of trees, even tall ones. On the other hand, some liquids have stronger cohesive forces than adhesive forces. In this case, in the presence of a capillary, the liquid is forced down from its surface; this is an example of a type of capillary. |
SciQ | SciQ-4336 | neuroscience, cardiology, action-potential
Title: Do nerve cells cause action potential in cardiac muscle? I think the answer is no, but I am not 100% sure.
If it was yes, then the dendrite of the nerve cell should each time receive a stimulus causing Na+ channels to open, when the contraction happen.
Also, then it would mean that outside events could alter the function of hearth, which would be dangerous.
The heart has a special excitatory system and a contractile system - Sinoatrial node and Pacemaker cells, which control the action potentials in different portions of the heart.
So heart and primarily myocardium i.e. cardiac muscle can depolarise without any external influence with a slow, positive increase in voltage across the cell's membrane.
Do nerve cells cause action potential in cardiac muscle? The vagus nerve controls heart rate. This is the best example of a direct nerve action potential impacting cardiac muscle, although one could argue the adrenaline system to be an indirect mechanism.
The vagus nerve is part of the parasympathetic system, it acts to decrease heart rate. Resting heart rate is maintained by permanent vagal stimulation/tone by the release of acetylcholine.
The following is multiple choice question (with options) to answer.
What kind of muscle is responsible for making the human heart beat? | [
"deltoid",
"cardiac muscle",
"teres minor",
"respiratory muscle"
] | B | Muscle tissue consists of cells that can contract, or shorten. Examples include skeletal muscle, which is attached to bones and makes them move. Other types of muscle include cardiac muscle, which makes the heart beat, and smooth muscle, which is found in other internal organs. |
SciQ | SciQ-4337 | 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.
Channel proteins and carrier proteins help substances diffuse across what? | [
"cell membrane",
"cytoplasm",
"endoplasmic reticulum",
"ribosomes"
] | A | Facilitated Diffusion Across a Cell Membrane. Channel proteins and carrier proteins help substances diffuse across a cell membrane. In this diagram, the channel and carrier proteins are helping substances move into the cell (from the extracellular space to the intracellular space). |
SciQ | SciQ-4338 | evolution, natural-selection
In fact since civilization has started feeding the hungry, making the hunting of wild beasts less important, causing the shrinkage of the male physique (we used to be much more muscular), inventing medicine and schools where smarts can be selected for, and giving us all more choice when it comes to mates, evolution has accelerated for human beings. The authors specifically cite social factors as being more important in our evolution now.
The following is multiple choice question (with options) to answer.
Humans building communities to make survival easier is an example of humans as a species changing their what? | [
"climate",
"environment",
"instinctive behavior",
"evolution"
] | B | |
SciQ | SciQ-4339 | bond, quantum-chemistry, molecular-orbital-theory
This is why the energy levels of $E_+$ and $E_-$ are not symmetrical with respect to the energy level of $E_\text{1s}$.
Intuitive Explanation
The intuitive explanation goes along the following line: Imagine two hydrogen nuclei that slowly get closer to each other, and at some point start mixing their orbitals. Now, one very important interaction is the coulomb force between those two nuclei, which gets larger the closer the nuclei come together. As a consequence of this, the energies of the molecular orbitals get shifted upwards, which is what creates the asymmetric image that we have for these energy levels.
Basically, you have two positively charged nuclei getting closer to each other. Now you have two options:
The following is multiple choice question (with options) to answer.
When a lower energy level is ______ electrons are added to the next higher energy level. | [
"full",
"ready",
"empty",
"unbalanced"
] | A | Only when a lower energy level is full are electrons added to the next higher energy level. Electrons at higher energy levels, which are farther from the nucleus, have more energy. They also have more orbitals and greater possible numbers of electrons. |
SciQ | SciQ-4340 | forces, pressure, continuum-mechanics, stress-strain
Title: Why is a force distributed over an area? Why couldn't the stress be directly equal to the force? So, my question might seem silly. I know in real life when we apply a force with our hand and push on lets say a cylinder , we know the force will be distributed over the cross section of the area, so if we had a wider area, we need more force, and if we had smaller area, then we need less force to push the cylinder a certain distance.
So its intuitive. The stress will be the force divided by the given area.
But why? like what happens at the micro-scale, and what makes the force be divided?
Thanks. Actually as @trula said the external force you apply acts only at the contact point but since all atoms are connected to each other via "interatomic forces" , your external force gets distributed all along the surface and so we need to define force per unit area viz. Stress.
The spring model of atomic structure is quite self explanatory about the interatomic force distribution.
The following is multiple choice question (with options) to answer.
The amount of force applied per given area is called? | [
"power",
"energy",
"strength",
"pressure"
] | D | Bernoulli’s law states that the pressure of a moving fluid such as air is less when the fluid is moving faster. Pressure is the amount of force applied per given area. The law is named for Daniel Bernoulli, a Swiss mathematician who discovered it during the 1700s. Bernoulli used mathematics to arrive at his law. For an animation of the law, go to the URL below. |
SciQ | SciQ-4341 | atoms, mole
Title: How to calculate the number of atoms of each element in Mg(NO3)2? I'm working on chemistry and I'm not quite sure how to solve this question? I haven't worked with moles before and whenever I try to figure out how to do these types of question I only end up confusing myself more.
How many Mg atoms are in 5.7892 mol of $\ce{Mg(NO3)2}$?
How many N atoms does the sample contain?
How many O atoms does the sample contain?
I haven't any clue how to do this so a walkthrough on how to solve these types of problem would be nice. $\ce{Mg(NO3)2}$ has (Figure 1):
One $\ce{Mg}$ atom
Two $\ce{NO3}$ groups, which are composed of:
One $\ce{N}$ atom
Three $\ce{O}$ atoms
Figure 1: we have one $\ce{Mg}$, two $\ce{N}$ ($2 \times 1$) and six $\ce{O}$ ($2 \times 3$) in $\ce{Mg(NO3)2}$.
Now all you need is to know that 1 mole equals $6.022\,140\,76\times 10^{23} \approx 6.022 \times 10^{23}$ particles.
Just multiply:
How many Mg atoms are in 5.7892 mol of $\ce{Mg(NO3)2}$?
$$1 \times 5.7892 \text{ mol $\ce{Mg}$} = 1 \times 5.7892 \times 6.022 \times 10^{23} \text{ atoms $\ce{Mg}$} \\= 3.48625624 \times 10^{25} \text{ atoms $\ce{Mg}$}$$
And so on.
The following is multiple choice question (with options) to answer.
What is the atomic number of magnesium? | [
"25",
"17",
"8",
"12"
] | D | REVIEW QUESTIONS 2. Magnesium has an atomic number of 12. Which of the following statements is true of a neutral magnesium atom? a. |
SciQ | SciQ-4342 | genetics, gene-expression, mrna, protein-expression, microarray
You can think of the microarray and RNASeq approaches as a fishing expeditions. If you find mRNAs that are only present after the cell receives a stimulus or an insult, expression of the mRNA has occurred (whether or not the amounts are directly proportional to the rate of synthesis). If the mRNA is synthesised you can assume it is translated into the protein it encodes. In the case of gamma irradiation you might assume any mRNA that shows a large increase in quantity encodes a protein that involved in protecting the cell from the radiation. This will be of scientific interest, especially if it is not what one anticipated.
The following is multiple choice question (with options) to answer.
After the egg is fertilized the mrna is translated into what? | [
"mitochondria",
"DNA",
"protein",
"factor"
] | C | |
SciQ | SciQ-4343 | human-biology, breathing
Our lungs work off of pressure. Specifically our lungs inflate by using "negative pressure" (a word I've always hated). The pressure is not actually negative it is simply lower than the surroundings. Since there is less air in your lungs the air from the atmosphere rushes in because the pressure is higher outside your lungs. This is Boyle's Law (not the pressure outside being higher, but what happens when your lungs expand). Where an increase in Volume means a decrease in Pressure (if all else remains unchanged). In fact plants pull water up using negative pressure.
However to push out the air from our lungs we supply pressure using our muscles that overcomes the outside pressure and forces the air out.
The reason you feel your breathing change is because when that train passes by you correctly observed the strong gust of wind. This gust of wind has some force behind it that normally is not in the air you are breathing from the atmosphere. It has more force which increases the air's velocity. This actually decreases the pressure, but there's no need to get into that here (Bernoulli's).
The reason it feels like your body is "fighting to breath" is because the air is traveling in a direction with some force that you need to overcome by opening up your lungs just enough to "suck" the air in with negative pressure. This is more than the pressure you usually need to produce in order to breath in air that is "still".
What is funny to think about is we don't really have a muscle that "pulls" air in, even though it feels like you are actively doing that. The air actually rushes in on its own. All you do is expand your rib cage, which your lungs are attached to (look up on how, it's actually pretty cool), thereby making inhalation occur.
Now an interesting question for you to ask yourself is why is cold air harder to breathe?
The following is multiple choice question (with options) to answer.
What is the process that ventilates lungs called? | [
"reproduction",
"photosynthesis",
"perspiration",
"breathing"
] | D |
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