source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-5644 | embryology
Title: What is a zygote? During fertilization, the nuclear membrane of the pro-nucleus of the ovum and sperm degenerate. Is the cell is stage called a zygote?
After the dissolution, mitosis occurs and two cells are formed.Or is the cell is stage called a zygote?
I'm confused as i knew a zygote was single-celled. Conventionally, a zygote is considered to be formed the moment that a spermatozoum, penetrates the cell membrane of the ovum and yields its genetic material into the ovum. Effectually, however, there is a lag between the instant of fertilization and the fusion of the male and female pronuclei. In mammals, the duration of this lag period is ~12 hours. There are also additional actions that must be completed before the first mitosis as in most mammals, including humans, the ovum is actually in the second metaphase of meiosis at the time of fertilization.
The following is multiple choice question (with options) to answer.
When a sperm penetrates the egg, it triggers the egg to complete what? | [
"mutations",
"fertilization",
"lesions",
"meiosis"
] | D | When a sperm penetrates the egg, it triggers the egg to complete meiosis. The sperm also undergoes changes. Its tail falls off, and its nucleus fuses with the nucleus of the egg. The resulting cell, called a zygote, contains all the chromosomes needed for a new human organism. Half the chromosomes come from the egg and half from the sperm. |
SciQ | SciQ-5645 | mammals, sex-chromosome, gender
Title: What processes regulate the sex of offspring? It is known that some species are more likely to born male than female (and some maybe vice versa). I understand that it is due to evolutionary perspective (average number of adult males is close to that of females), I want to know about how it is regulated.
What I thought is that spermatozoa are made by half as Y and half as X chromosome. Then mitosis and meiosis and the probability that one of them will die is equal for both types. So, somewhere I feel lost.
Also, can it be regulated by female body or not? According to this paper claiming that hormone levels in women affect the likelyhood to born son. Possibly it is just because they choose males that are more likely to have more Y spermatozoa than X, but if it is some chemical mechanism to regulate that I'd like to know.
I'm not asking only about humans, mechanisms can be similar in almost all mammals. I'm not asking about other species: I know some are regulated by temperature, etc. This question is only about mammals.
What processes regulate the sex of offspring?
The processes rulating the sex of offspring may occur in both males and females and be direct or indirect.
What I thought is that spermatozoa are made by half as Y and half as X chromosome. Then mitosis and meiosis and the probability that one of them will die is equal for both types. So, somewhere I feel lost.
This may not be entirely true. The phenomenon called "Meiotic drive" may change the ratio from 1:1. Meiotic Drive occurs through selfish genes. See "Selfish-gene theory" for more info.
Also, can it be regulated by female body or not?
if it is some chemical mechanism to regulate that I'd like to know.
Possibly, there is such in mammals. There is a bunch of mechanisms called "Cryptic female choice". Some of them are chemical. Although, the article is about birds, it can be the case similar mechanism is present in mammals.
Given that higher androgen level exposure in mothers affect make their offspring more male-typical in playing behavior we might consider that in general makes offsrpings more masculine. This would be a good reason for female organisms with higher androgen levels to favor sperm with Y chromosome present.
The following is multiple choice question (with options) to answer.
What chromosome determines the sex of an organism? | [
"ribosome",
"autosome",
"sex chromosome",
"S chromosome"
] | C | A sex chromosome is a chromosome that determines the sex of an organism. Humans have two sex chromosomes, X and Y . Females have two X chromosomes ( XX ), and males have one X and one Y chromosome ( XY ). An autosome is any chromosome other than a sex chromosome. If a trait is autosomal it will affect males and females equally. |
SciQ | SciQ-5646 | everyday-chemistry, experimental-chemistry
Title: Confusing definition of the term precision According to the textbook, we say a measurement is precise when series of measures are close to each other.
But in real use, I feel like the term is used in a different meaning.
For example, scale A weighs to cube of lead and displays 10.5g while scale B displays 10.4977g.
In this case, one say the measurement made by scale B is more precise than that of A. That is, scale B can distinguish more fine weights than A.
Isn't this usage of the word precise different from textbook definition? Please explain clearly the real usage of the term precise. In colloquial English, precision is synonymous with accuracy. If you look it up on Google, the first definition is:
the quality, condition, or fact of being exact and accurate.
In the field of science, however, it takes on another meaning:
the degree to which repeated measurements under unchanged conditions show the same results
There is also measurement resolution:
the smallest change [an instrument] can detect in the quantity that it is measuring
Which is similar to the definition precision takes on in numerical analysis:
the resolution of the representation, typically defined by the number of decimal or binary digit
In short, precision can take on different meanings depending on how you choose to apply it. If you talk about the precision in a set of measured data, you will be using the scientific definition; if you talk about the precision of an instrument, you will be using the numerical analysis definition.
The following is multiple choice question (with options) to answer.
In contrast to precision, this term means how close a measurement is to the correct or accepted value of the quantity being measured? | [
"diversity",
"accuracy",
"frequency",
"deviant"
] | B | In everyday speech, the terms accuracy and precision are frequently used interchangeably. However, their scientific meanings are quite different. Accuracy is a measure of how close a measurement is to the correct or accepted value of the quantity being measured. Precision is a measure of how close a series of measurements are to one another. Precise measurements are highly reproducible, even if the measurements are not near the correct value. |
SciQ | SciQ-5647 | genetics, dna, dna-sequencing, human-genetics
Title: Do eukaryote cells contain DNA that isn't part of a chromosome or located in the mitochondria? I specify eukaryote in the title, but I'm also interested if this question isn't applicable to eukaryote cells in general but is to humans. I was reading "RNA-seq: An assessment of technical reproducibility and comparison with gene expression arrays" (John Marioni 2008).
In the results it states
"By these criteria, 40% of reads mapped uniquely to a genomic location, and of these, 65% mapped to autosomal or sex chromosomes (the remainder mapped almost exclusively to mitochondrial DNA)."
I couldn't help but notice the "almost exclusively to mitochondrial DNA". Almost exclusively? Can DNA be found in places other than chromosones or mitochondria? Perhaps I'm interpreting the sentence wrong. Any pointers would be appreciated
Thanks In plants, chloroplasts and other plastids contain DNA, but I suppose you are more interested in humans. Quoting from wikipedia,
In many cells cytoplasmic DNA is also found, which is different from
nuclear DNA, both in methylation levels (cytoplasmic has less), and in
sequence. EccDNA or extrachromosomal circular DNA is present in all
eukaryotic cells, derived from genomic DNA and consists of repetitive
sequences of DNA found in both coding and non-coding regions of
chromosomes. EccDNA can vary in size from less than 2000 more than
20,000 base pairs. In animals, eccDNA molecules have been shown to
contain repetitive sequences that are seen in satellite DNA, 5S
ribosomal DNA and telomere DNA. The function of eccDNA has not been widely studied, but it has been proposed that the production of elements of eccDNA from genomic DNA sequences adds to the plasticity of the eukaryotic genome and can influence genome stability, cell aging and the evolution of chromosomes
The following is multiple choice question (with options) to answer.
Where is most of the cell's dna contained? | [
"cell membrane",
"nucleus",
"vacuole",
"epidermis"
] | B | Although most of a cell's DNA is contained in the cell nucleus, mitochondria have their own DNA. Mitochondria also have the machinery to manufacture their own RNAs and proteins. The human mitochondrial DNA sequence has 16,569 base pairs encoding 37 total genes: 22 tRNA genes, 2 rRNA genes, and 13 peptide genes. The 13 mitochondrial peptides in humans are integrated into the inner mitochondrial membrane, along with proteins encoded by nuclear genes. |
SciQ | SciQ-5648 | physiology, nutrition, organic-chemistry
Title: How is it known that there are only three macronutrients: proteins carbohydrates and lipids? It is stated here that in human nutrition, micronutrients are nutrients required generally in less than 100 mg daily quantities whereas macronutrients are required in gram quantities. It is widely stated that our macronutrients are carbohydrates, lipids, and proteins. How was it shown that these are the human macronutrients and that we don't have other macronutrients?
One answer to this similar question on Quora suggests that ethanol or ketones could be considered macronutrients. Ethanol is mentioned in this article, though ketones are not. Other sources I saw didn't clarify. Summary
The question is based on the misconception that the term “macronutrient” originated as a scientific definition, to which entities satisfying this definition were assigned. In fact it was a default term used as a distinction from compounds falling into the earlier category, “micronutrient”, and was used initially to encompass the three specific classes of food that had been established to be sources of energy through decades of nutritional research. Hence there was no question of whether there “should” be more macronutrients. The term is not a scientific definition, and today is used in different ways so that anyone using the term needs to clarify what it should be taken to mean in that particular context.
Food Energy and the history of Nutrition
Scientific studies of nutrition, dating the late 18th century, were initially concerned with chemical structure, metabolic fate and energy produced by different foods, and this is described in a short readable article by Ned Stafford in Nature (2010) 468, S16–17.
By the end of the 19th century protein, fat and carbohydrate had been established as the chemical fuels that supplied energy from the diet, and the energy values (in terms of the, now obsolete, calorie) had been established by Atwood, using his respiration calorimeter.
Micronutrients
The following is multiple choice question (with options) to answer.
The four major classes of biological macromolecules include carbohydrates, lipids, proteins, and what else? | [
"nucleic acids",
"liquids",
"structural acids",
"fats"
] | A | 3.1 | Synthesis of Biological Macromolecules By the end of this section, you will be able to: • Understand the synthesis of macromolecules • Explain dehydration (or condensation) and hydrolysis reactions As you’ve learned, biological macromolecules are large molecules, necessary for life, that are built from smaller organic molecules. There are four major classes of biological macromolecules (carbohydrates, lipids, proteins, and nucleic acids); each is an important cell component and performs a wide array of functions. Combined, these molecules make up the majority of a cell’s dry mass (recall that water makes up the majority of its complete mass). Biological macromolecules are organic, meaning they contain carbon. In addition, they may contain hydrogen, oxygen, nitrogen, and additional minor elements. |
SciQ | SciQ-5649 | human-biology, digestive-system, immune-system, microbiome
The next level of defense comes from the cells of the innate immune system (14). In innate immunity, specialized cells monitor the area they are in for Pathogen-Associated Molecular Patterns (PAMPs). PAMPs can be sugars that make up the cell walls of the microbe or proteins that get expressed on the surface of the organism, such as Flagellin, a protein only found in the flagella of certain pathogen. The innate immune cells have pattern recognition receptors (PRR) that have a general specificity for recognizing and responding to the PAMPs. Our cells even have PRRs for DNA and Double Stranded RNA's, however those are usually found in vesicles on the inside of the cell. These interactions are very general, however once PRRs bind to the PAMP, they are able to signal into the cytoplasm, which can lead to the production of proteins, among other possible responses.
Here you can think of PRRs like a motion detector in a security system; the dog, or your two year old, or an intruder are going to set off the alarm just the same. It is not specific. The motion sensor "knows" that something that it is supposed to recognize, i.e. a moving object larger than a mouse passed by and it triggered the response, but it cannot tell you which moving object triggered it, only that it was triggered.
The innate immune cells are also able to respond by "eating" the pathogen in a process called phagocytosis. Here, they break up the bacteria, yeast, or the remnants of other dead host cells or large pathogens, things like worms, and put the broken up pieces on protein molecules on their surface.
When innate immune cells do this, they are presenting molecules to specialized immune cells (adaptive immune cells (14)), B-Cells and T-Cells, that are highly specific as to what they will react to. These cells can also cause a lot of damage to the host, so they are tightly regulated. Think of the interactions as keys and locks. A protein from a bacteria should turn a few of these cells on, but a protein from the host should not fit the lock.
The following is multiple choice question (with options) to answer.
What protects you from pathogens and keeps you healthy? | [
"immune system",
"health system",
"potent system",
"immunity system"
] | A | Your immune system usually protects you from pathogens and keeps you well. However, like any other body system, the immune system itself can develop problems. Sometimes it responds to harmless foreign substances as though they were pathogens. Sometimes it attacks the body’s own cells. Certain diseases can also attack and damage the immune system and interfere with its ability to defend the body. |
SciQ | SciQ-5650 | inorganic-chemistry, everyday-chemistry, experimental-chemistry, home-experiment, carbon-allotropes
1) Pencil lead isn't graphite (neither is it "lead" for that matter ;P); it's a mixture of graphite and clay. So unless you know for sure that the impurities in your sample are clay, this doesn't really serve as a good baseline. Besides, the graphite particles aren't all aligned in that plane I was talking about.
2) Your makeshift resistor ("thick line on a piece of paper") is a poor standard for another reason: dimensions. Your line has no uniform dimensions (length, breadth or even depth). If you need resistance from resistivity of a given material, or the other way around, you need the sample's dimensions. Neither your line nor your powder have fixed dimensions in this test.
Trying to figure out what your sample is by comparing its resistivity with that of another substance is a really neat idea, so don't get me wrong; the issue here is (1) the design of the experiment, (2) of the two substances you're trying to compare (graphite and charcoal), the latter's electrical properties are altered because it's been powdered and (3) your "control-test/sample" (the line-resistor) is neither graphite nor charcoal, making it a rather pointless "control sample".
Conclusion: No useful data.
Rubbing it into paper it has a much blacker colour than the graphite (which to me looks like a really dark gray). However, I don't know if that is a reliable indicator.
I don't need to tell you how poor a test this is (you already seem to doubt the validity of the test yourself)
Conslusion: No useful data.
EDIT: Ok, I've made a paste using Isopropyl Alcohol and the carbon powder and made a small "stick" or rod of the stuff. I have now been able to achieve solid continuity at around 2 centimeters in distance and the resistance dropped from the high 40 - 50 kOhms for the loose powder, to the low 10s (ie 40 Ohms). If this helps anyone.
The following is multiple choice question (with options) to answer.
Although they differ vastly in hardness, pencil lead and diamonds both contain what element? | [
"hydrogen",
"oxygen",
"carbon",
"graphite"
] | C | Hardness helps determine how an element (especially a metal) might be used. Many elements are fairly soft (silver and gold, for example) while others (such as titanium, tungsten, and chromium) are much harder. Carbon is an interesting example of hardness. In graphite (the “lead” found in pencils) the carbon is very soft, while the carbon in a diamond is roughly seven times as hard. |
SciQ | SciQ-5651 | physiology, respiration
Title: Why does a worm's skin need to be wet for oxygen to diffuse across it? Pages I've read about worms' respiratory systems says that the skin needs to be wet (covered in mucus) or oxygen won't diffuse across the skin. Why? If there is more oxygen outside the worm's skin than inside, what prevents it from diffusing across the skin, even if the skin is dried out? The quick answer: When the skin dries, the lipids in the cell membranes of the skin tissue undergo a phase transition which makes the membranes less permeable for oxygen.
Explanation: The lipids of the cell membrane can exist in different phase states. In the liquid disordered phase the lipids are relatively flexible and mobile, making this phase more oxygen permeable compared to the liquid ordered phase, in which the lipids are more rigidly packed.
The phase transition temperature of lipids increases upon dehydration (another reference), meaning that at the same ambient temperature, a dry lipid membrane is in the liquid ordered state and a wet lipid membrane is in the liquid disordered state.
Therefore, a dry cell membrane is less oxygen permeable than a wet one.
The following is multiple choice question (with options) to answer.
The majority of salamanders lack what organs, so respiration occurs through the skin or through external gills? | [
"mouths",
"noses",
"lungs",
"throats"
] | C | Modern Amphibians Amphibia comprises an estimated 6,770 extant species that inhabit tropical and temperate regions around the world. Amphibians can be divided into three clades: Urodela (“tailed-ones”), the salamanders; Anura (“tail-less ones”), the frogs; and Apoda (“legless ones”), the caecilians. Urodela: Salamanders Salamanders are amphibians that belong to the order Urodela. Living salamanders (Figure 29.16) include approximately 620 species, some of which are aquatic, other terrestrial, and some that live on land only as adults. Adult salamanders usually have a generalized tetrapod body plan with four limbs and a tail. They move by bending their bodies from side to side, called lateral undulation, in a fish-like manner while “walking” their arms and legs fore and aft. It is thought that their gait is similar to that used by early tetrapods. Respiration differs among different species. The majority of salamanders are lungless, and respiration occurs through the skin or through external gills. Some terrestrial salamanders have primitive lungs; a few species have both gills and lungs. Unlike frogs, virtually all salamanders rely on internal fertilization of the eggs. The only male amphibians that possess copulatory structures are the caecilians, so fertilization among salamanders typically involves an elaborate and often prolonged courtship. Such a courtship allows the successful transfer of sperm from male to female via a spermatophore. Development in many of the most highly evolved salamanders, which are fully terrestrial, occurs during a prolonged egg stage, with the eggs guarded by the mother. During this time, the gilled larval stage is found only within the egg capsule, with the gills being resorbed, and metamorphosis being completed, before hatching. Hatchlings thus resemble tiny adults. |
SciQ | SciQ-5652 | species-identification, entomology
Title: Bug ID? Lower New York Found it on the floor of my basement laundry room in a mostly wooden house in the woods in Westchester County, NY. However I had done a mountain hike (same general area) and I may have brought it from there on my pants or something, but I'm not sure.
When it noticed me it stopped moving, but it was still alive because when I put it in this cup for a pic I accidentally flipped it upside down and it started squirming to get itself upright. That's not an insect but a crustacean (it has more than 6 legs).
It is a woodlouse (plural woodlice). A woodlouse is one of the few terrestrial isopode crustacean. There are about 5000 known species of woodlice. I have no idea which one is the one you captured!
Woodlice are generally appreciated in gardens as they control pests. They sometimes get inside searching for moisture. While it may not be pleasant to have woodlice at home (just because they look disgusting to many, me including), they do not spread disease or cause much damage.
The following is multiple choice question (with options) to answer.
Crabs, lobsters, shrimp, krill, and woodlice are all? | [
"arthropods",
"porifera",
"crustaceans",
"sponges"
] | C | Crustaceans include crabs, lobsters, shrimp, krill, and woodlice. |
SciQ | SciQ-5653 | solutions, phase, evaporation
Title: What is the relationship between solutions and changes to states of matter? For example, when liquid water evaporates, my instinct is to say that of course it's become gas, but I'm a bit unsure because, if I understand correctly, evaporation occurs because air dissolves the water, and it's not clear to me whether that counts as a phase change. Intuitively it seems like it should should water dissolves in the air or salt dissolved in water, etc. have different properties before and after being dissolved. And yet, the way I've always heard it explained, phase changes are specifically due to changes in temperature and/or pressure, not due to chemical interactions with another another substance.
On the other hand, from what I remember from chem 101 and 102, when we considered chemical reactions occuring between solids dissolved in a liquid (usually acids and bases dissolved in water), we usually just labeled them as aqueous, meaning "in solution", whereas for non-aqueous substances, we'd label them with the relevant state of matter, solid, liquid, or gas. Does that mean dissolved substances constitute their own state of matter? Or that it's simply not meaningful to talk about the state of the solute independent of the solvent?
I also saw this thread, Is it appropriate to say "solid-in-gas solution" and "liquid-in-gas solution"?, where someone says, "Whenever there is only one phase, but there are two or more chemical species, then you have a solution", which heavily implies there's a fundamental relationship between phase changes and solutions, but it also doesn't seem quite right Water vapour in air is a solution, but not in the same sense as solutions in water.
Water vapour in air is solution in sense of homogenous mixture, where molecules move freely and independently.
Salts in water dissociate (are dissociated by water) to ions. Having a net charge, they form a nonhomogeneous electrostatic gradient.Ions are hydrated by water molecules that have an electric dipole and therefore attracted to the center of such a gradient. So here we see strong interaction and dependent motion.
The following is multiple choice question (with options) to answer.
What makes water change to a different state? | [
"pressure",
"time",
"temperature",
"gravity"
] | C | The state the water is in depends upon the temperature. Each state (solid, liquid, and gas) has its own unique set of physical properties. |
SciQ | SciQ-5654 | hybridization, bond, bent-bond
Sneaks off and checks Wikipedia. Wikipedia says $\ce{Al2(CH3)6}$ is similar in structure and bond type.
I guess we have less such compounds because there are comparatively few elements ($\ce{B}$ group pretty much) with $\leq3$ valence electrons which form covalent bonds(criteria for the empty orbital). Additionally, $\ce{Al}$ is an iffy case--it like both covalent and ionic bonds. Also, for this geometry (either by banana bonds or by dative bonds), I suppose the relative sizes matter as well--since $\ce{BCl3}$ is a monomer even though $\ce{Cl}$ has a lone pair and can form a dative bond.
*Maybe you're used to the view of tetrahedral structure with an atom at the top? Mentally tilt the boron atom till a hydrogen is up top. You should realize that this is tetrahedral as well.
The following is multiple choice question (with options) to answer.
What is a hydrocarbon in which there are only single covalent bonds? | [
"fullerene",
"combined",
"alkane",
"proline"
] | C | An alkane is a hydrocarbon in which there are only single covalent bonds. The simplest alkane is methane, with the molecular formula CH 4 . The carbon is the central atom and makes four single covalent bonds to hydrogen atoms. |
SciQ | SciQ-5655 | \\. Area of a parallelogram given base and height. Yes, that's right! where R is spherical cap radius, r is base radius, and h is height. where r is radius and h is height. Using the area calculators autoscale tool, you can set the drawing scale of common image formats such as PNG, GIF, and JPEG, along with PDF’s. Area of an Ellipse. Its diagonals bisect internal angles. A is area under the curve. Follow along to learn how to calculate yourself, or simply use the calculator above. Area of a regular polygon. Formula. side a: Note that the surface area of the bases of the cylinder is not included since it does not comprise part of the surface area of a capsule. Area of a rhombus. When she receives a box of Lindt truffles, she proceeds to calculate the surface area of each truffle in order to determine the total surface area she has to lick to decrease the probability that anyone will try to eat her truffles. Use the calculator below to calculate the segment area given the radius and segment's central angle, using the formula described above. The calculations are done "live": How to Calculate the Area. The equations to calculate each, as well as the total SA of a closed circular cone are shown below: base SA = πr2 However, she feels that the model does not exude the feeling of architectural wonder that the original does and decides that coating it with "snow" would at least impart an aspect of wonder. Area of a quadrilateral. https://www.gigacalculator.com/calculators/area-calculator.php. It may come in handy. You can measure the area of a space in square meters in a few simple steps. Step 1: Measure all sides of the area in one unit (Feet, Meter, Inches or any other). where r is radius and h is height. Rather than eating his vegetables, Coltaine's father stares dejectedly at his plate, and estimates the surface area of the elliptical cuts of zucchini with axes 0.1, 0.2, and 0.35 inches: SA ≈ 4π 1.6√(0.11.60.21.6 + 0.11.60.351.6 +
The following is multiple choice question (with options) to answer.
What is the measure of the amount of space occupied by an object? | [
"growth",
"volume",
"mass",
"liquid"
] | B | Volume Volume is the measure of the amount of space occupied by an object. The standard SI unit of volume is defined by the base unit of length (Figure 1.25). The standard volume is a cubic meter (m3), a cube with an edge length of exactly one meter. To dispense a cubic meter of water, we could build a cubic box with edge lengths of exactly one meter. This box would hold a cubic meter of water or any other substance. A more commonly used unit of volume is derived from the decimeter (0.1 m, or 10 cm). A cube with edge lengths of exactly one decimeter contains a volume of one cubic decimeter (dm3). A liter (L) is the more common name for the cubic decimeter. One liter is about 1.06 quarts. A cubic centimeter (cm3) is the volume of a cube with an edge length of exactly one centimeter. The abbreviation cc (for cubic centimeter) is often used by health professionals. A cubic centimeter is also called a milliliter (mL) and is 1/1000 of a liter. |
SciQ | SciQ-5656 | photosynthesis
Title: Photosystem I and the ETC In the light reactions of photosynthesis, Photosystem I receives electrons from the ETC after Photosystem II sends them to the ETC. Then, when Photosystem I receives light, the electron becomes excited and passes the electron back to the ETC. This leads me to my question: In the following question, are both $B$ and $E$ correct?
Which of the following are directly associated with photosystem I?
$A)$ harvesting of light energy by ATP
$B)$ receiving electrons from the thylakoid membrane electron transport chain
$C)$ generation of molecular oxygen
$D)$ extraction of hydrogen electrons from the splitting of water
$E)$ passing electrons to the thylakoid membrane electron transport chain It appears the author of the question is trying to use "thylakoid electron transport chain" in an overly specific way. The chain from which PS I receives electrons has far more components and is different from the shorter chain to which PS I passes its electrons. But according to my copy of Biology, Campbell & Reece 7th edition, both are called "electron transport chains" and both reside in, or on, the thylakoid membrane. Perhaps the "directly" in the question refers to the fact that PS I's electron is first captured by a "primary receptor" before being passed to ferredixon, the first member of the chain to which PS I passes electrons. But, again according to Campbell, this primary acceptor is considered part of the photosystem.
I used to teach this stuff. I'd toss out the question.
The following is multiple choice question (with options) to answer.
The energy that enters the chloroplasts as sunlight becomes stored as what type of energy in organic compounds? | [
"chemical energy",
"defect energy",
"thermal energy",
"radiation energy"
] | A | |
SciQ | SciQ-5657 | human-biology, human-anatomy, human-genetics
Title: Are males taller than females in humans? Is there any scientific evidence that in humans males are taller than females? And if so, what is the reason that they are taller (please include genes or hormones that accounts for human growth and how they are affected in males and females)? Are males taller than females?
Best data I could find come from the Statistical Abstract of the United States (1999) > Section 3. Here is a table reporting the percentage of the male and female population which height is lower than a given threshold
Note that this data collection was done among students in US universities and is therefore not representative of the whole world or even the whole country.
Does height follow a bimodal distribution?
A difference in height between males and females is often used as a classical example in introductory statistic class to exemplify a bimodal distribution as seen in this picture
and on these (a priori fake) data
However, Schilling et al. 2002 argued that while the difference in mean height between the sexes is real, this difference is too small relative to the variance in height within each sex to be clearly depicted on a graph.
Note that I found this non-peer-reviewed paper which shows real data that display a truly bimodal distribution of height.
Genetics of height
The question why are they taller? is very broad. I will just focus to give you some hints about the genetics of height in humans. First, you want to make sure you understand the concept of heritability.
Evoy and Vissher 2009 report a heritability coefficient of 0.8. This estimate is impressively high - only a few phenotypic traits have such high heritability. They also review articles discussing that 50 loci are correlated with variation in height (actually, today, more than 500 loci are known to contribute to height, see the link in AlexDeLarge's comment to this answer). However, these loci are not sufficient to explain the whole heritability observed (common missing heritability issue). Yang et al. 2010 provide evidence that the remaining heritability is due to incomplete linkage
disequilibrium between causal variants and loci of weak effects. In short, height is a highly polygenic trait.
Related post
You should have a look at Is there a genetic reason explaining the difference of the height of male and female? for more information.
The following is multiple choice question (with options) to answer.
Whose rules are too simple to explain the inheritance of human height? | [
"mendel",
"Pascal",
"Einstein",
"Darwin"
] | A | Unlike Mendel's peas, people do not all fall into two categories: short or tall. Most people, in fact, are somewhere in between. Obviously, Mendel's rules are too simple to explain the inheritance of human height. |
SciQ | SciQ-5658 | embryology
Title: What is a zygote? During fertilization, the nuclear membrane of the pro-nucleus of the ovum and sperm degenerate. Is the cell is stage called a zygote?
After the dissolution, mitosis occurs and two cells are formed.Or is the cell is stage called a zygote?
I'm confused as i knew a zygote was single-celled. Conventionally, a zygote is considered to be formed the moment that a spermatozoum, penetrates the cell membrane of the ovum and yields its genetic material into the ovum. Effectually, however, there is a lag between the instant of fertilization and the fusion of the male and female pronuclei. In mammals, the duration of this lag period is ~12 hours. There are also additional actions that must be completed before the first mitosis as in most mammals, including humans, the ovum is actually in the second metaphase of meiosis at the time of fertilization.
The following is multiple choice question (with options) to answer.
The fertilized egg that sexually reproducing organisms begin life as is known as what? | [
"infant",
"zygote",
"gamete",
"fetus"
] | B | Introduction The individual sexually reproducing organism—including humans—begins life as a fertilized egg, or zygote. Trillions of cell divisions subsequently occur in a controlled manner to produce a complex, multicellular human. In other words, that original single cell was the ancestor of every other cell in the body. Once a human individual is fully grown, cell reproduction is still necessary to repair or regenerate tissues. For example, new blood and skin cells are constantly being produced. All multicellular organisms use cell division for growth, and in most cases, the maintenance and repair of cells and tissues. Single-celled organisms use cell division as their method of reproduction. |
SciQ | SciQ-5659 | human-biology, hair
In most people this receptor functions as intended, and melanocytes in the skin produce varying degrees of brown-black eumelanin (the extent of which depending on one's ethnic background) while pheomelanin is switched on in the few key areas listed above. When both copies of the MC1R gene inherited from each of your parents are disfunctional, this switching mechanism no longer works and your melanocytes will produce primarily pheomelanin ubiquitously across your body. This is what we know as 'redheads'.
What isn't immediately obvious is that red-haired individuals are not unique in just the aspect of their hair. Their whole body presents with a deficiency in eumelanin and as such they also carry a pale/rosy complexion as well as an inability to tan and a propensity to sunburn easily. This is a consequences of the fact that eumelanin is our primary defense against UV radiation.
While melanocytes in the skin and eyes are responsible for the production of melanin, the melanin in one's hair gets there as a result of a handoff between melanocytes and the keratin producing keratinocytes. Melanin within melanocytes is produced and stored within organelles known as melanosomes and, through a complex formed by the 3 genes MYO5A, RAB27A, and MLPH, the transfer of these melanosomes through the tendrils of the melanocytes to the keratinocytes is facilitated. Defects in any of these 3 genes can result in a condition known as Griscelli syndrome (types 1, 2, and 3, respectively) where the transfer of melanin from melanocytes to keratinocytes is impaired.
The following is multiple choice question (with options) to answer.
People with red hair usually have what type of skin? | [
"light",
"dark",
"oily",
"dry"
] | A | 7. People with red hair usually have very light skin. What might be a genetic explanation for this observation?. |
SciQ | SciQ-5660 | cell-biology
Title: Structure of Cell Are cells spheres or ovals/circles bound by phospholipidbilayer?
If they are spherical how are we able to see the nucleus through the phospholipid bilayer under a microscope? Not exactly. That is a stereotype of cells. Muscle cells are not round nor oval, but rather elongated rods. If you were to look up epithelia cells, you can quickly see that cells are grouped based on their physical characteristics; simple (round/oval & single layer), columnar, and cuboidal to name a few. Cells come in many shapes and sizes. As Hans stated, stains are vital in viewing cellular components. There is a diverse amount of stains used - which all carry a purpose and benefit in a specific application.
The following is multiple choice question (with options) to answer.
What provides the shape of a cell? | [
"cytoplasm",
"nucleus",
"cytoskeleton",
"cellulose"
] | C | The cytoskeleton provides the shape of the cell. |
SciQ | SciQ-5661 | evolution, life-history
the relatedness of the actor to the recipient (note a relatedness is not necessarily symmetric)
The competition this recipient causes on the actor
The cost (energy cost, risk of being injured or killed) of killing
Many species (ants, wolves) might kill or injured individuals of the same species, when for example there is competition for reaching a status in the hierarchy.
I think that the definition of k-selected species is not very accurate. First because there are limit cases. But also because r and k can relate to the function that describes the population growth of a species or might describe the amount of energy the parents spend into one offspring which is not necessarily the same thing. If we think of the parental care, we can think of the lions. When a male win the right to access to the females of another male, he will kill the babies that might be potential competitors to his progeny (because they take energy from the females or because females are not fertile before having lost their babies).
Killing its own offsprings is certainly not less common in k-selected species. You might think it is such a big cost to kill one of its own offspring when one has few offspring but what is important is to think in percentage. Killing 50% of the progeny has the same cost of an r-selected species than for a k-selected species.
If one has a probability of 10% to be able to raise its offspring to adult age. But this probability raised to more than 20% if it accepts to kill an offspring to save energy for the next offspring, then it wins by doing so. THen we might ask: "so would one make an offspring if it intends to kill it?"
Well it does not necessarily intend to kill it. It might need to decide late in the season whether or not it has better to kill its own offspring.
Then, maybe offspring might be used as a reserve of energy and matter for its siblings or for its parents.
The following is multiple choice question (with options) to answer.
Competition between members of the same species is known as? | [
"interspecies competition",
"egregious competition",
"nuchal competition",
"intraspecific competition"
] | D | Intraspecific competition occurs between members of the same species. For example, two male birds of the same species might compete for mates in the same area. This type of competition is a basic factor in natural selection. It leads to the evolution of better adaptations within a species. |
SciQ | SciQ-5662 | acid-base, lewis-structure
Title: Why is carbon dioxide a Lewis acid? I know this has been asked before, but can anyone explain me in simpler terms? Why is $\ce{CO2}$ a Lewis acid? The carbon atom doesn't have any vacant orbitals to accept a lone pair. How can it be a Lewis acid? Suppose one of the doublets of one C=O bond moves to one of these two atoms. It will not be to the Carbon atom. The Oxygen atom is a better choice. And now this Oxygen atom would be negatively charged. As a consequence the Carbon atom is positively charged and has a vacant orbital able to accept a lone pair, for example from an $\ce{OH-}$ ion or from water. This will produce the ion $\ce{HCO3^-}$ (from $\ce{OH-}$) or $\ce{H2CO3}$ (from $\ce{H2O}$).
The following is multiple choice question (with options) to answer.
One molecule of carbon dioxide consists of 1 atom of carbon and 2 atoms of what element? | [
"hydrogen",
"oxygen",
"methane",
"nitrogen"
] | B | A molecular formula of the compound carbon dioxide is CO 2 . One molecule of carbon dioxide consists of 1 atom of carbon and 2 atoms of oxygen. We can calculate the mass of one molecule of carbon dioxide by adding together the masses of 1 atom of carbon and 2 atoms of oxygen. |
SciQ | SciQ-5663 | biochemistry
Hence more $\ce{Na+}$ enters the cell, leading to depolarisation of the membrane until the membrane potential reaches approximately +30 mV. At this stage, the voltage-gated $\ce{Na+}$ channels close and the voltage-gated $\ce{K+}$ channels open. Again, we need to consider the two factors that influence the diffusion of $\ce{K+}$:
The potential difference, which is now positive, favours efflux of $\ce{K+}$.
Since the intracellular concentration of $\ce{K+}$ is higher than the extracellular concentration, the concentration gradient also favours efflux of $\ce{K+}$.
The following is multiple choice question (with options) to answer.
What facilitates the diffusion of ions across a membrane? | [
"passive transport",
"photon channels",
"ion channels",
"ionic bonds"
] | C | |
SciQ | SciQ-5664 | discrete-signals, frequency, analog
This, in essence, is Frequency Division Multiplexing (FDM) -- the available spectrum is divided into frequency bands and each signal is combined with a "carrier" frequency to occupy the appropriate frequency band. (The original signal, before multiplexing, is referred to as a "baseband" signal, because it has not been combined with a carrier. This sort of contrasts with "broadband", where multiple signals have been multiplexed, but unfortunately the term "broadband" has multiple confusing definitions.)
FDM used to be used extensively in the phone system, for long-distance lines. A single pair of wires (and associated amplifiers), which might have a frequency response from 20Hz to 100KHz, carried a dozen or so audio signals, each at an assigned frequency just like broadcast radio or TV. Later coaxial cables were used, increasing the available bandwidth to several MHz and allowing several hundred audio signals per cable.
(A significant drawback of this scheme was that many amplifiers were required -- one every ten miles at least, and one every mile for some schemes.)
Now, it should be clear that, given that there's no fundamental difference (electrically) between an analog signal and a digital signal, digital signals can indeed be broadcast using FDM. In fact, if you have a cable modem, the cable, with over a hundred analog channels, is frequency multiplexed (just as over-the-air TV is). Your cable modem signal occupies (sharing with your neighbors) one of those "analog" channels. So your cable modem signal is being transmitted via FDM (though with several added twists).
Now for Time Division Multiplexing (TDM).
Time division multiplexing involves what it name implies -- the time axis of the combined signal is divided into discrete segments, and different individual signals are transmitted in the different segments.
TDM actually goes back to before regular digital data. The Bell Telephone company in the US experimented in the 50s with chopping up analog signals into lots of thin slices and interleaving the slices from several different analog signals together, allowing the several signals to be sent over a single pair of wires without having to resort to FDM. So in this case analog signals were transmitted via TDM.
The following is multiple choice question (with options) to answer.
What kind of fibers are used to transport telephone and television signals? | [
"process fibers",
"touch fibers",
"hair fibers",
"optical fibers"
] | D | Total internal reflection allows the light to travel down the optical fiber and not pass through the sides of the tube. The light continuously reflects from the inside of the tube and eventually comes out the end. Optical fibers make interesting lamps but they are also used to transport telephone and television signals. |
SciQ | SciQ-5665 | microscopy, fluorescent-microscopy, safety, research-tools
Title: What kind of microscope for ML/biological research? I am a computer science student, focusing on machine learning applications. I have been always interested in biology but I lack any training in it. Now, I had an idea that I could introduce myself to biology more by buying a microscope, and doing some small (still serious, if possible) experiments.
Now, the problem one I am facing is what kind of microscope should I get? Preferred answer would outline what kind of research is possible to do with such and such microscope, and what is the typical price range for the system.
If there are any safety (e.g. does any of the UV leak from fluorescence microscopes?) or ethical concerns I would like to hear about them too. Thanks! This really depends on the application you have in mind. As with other precision instruments there is a huge range of qualities and applications.
If you just want brigth field illumination and look at relatively big things ( approx 100 microns) then you could find something decent for the price you mention if you buy used.
But if you want more complex imaging techniques like confocal microscopy or fluorescence microscopy to image smaler strutures and cell imaging then your budget is probably not enough. There you probably won't get a decent microscope for less than 2500 Euro.
I think you should figure out what you want to do with your instrument not just buy one and then get started.
The following is multiple choice question (with options) to answer.
In what century was the microscope invented? | [
"17th",
"16th",
"15th",
"20th"
] | A | 7.2 History of cell knowledge The optical microscope was first invented in 17th century. Shortly thereafter scientists began to examine living and dead biological tissues in order to better understand the science of life. Some of the most relevant discovery milestones of the time period include: • The invention of the microscope11 , which allowed scientists for the first time to see biological cells • Robert Hooke12 in 1665 looked at cork under a microscope and described what he called cork "cells" • Anton van Leeuwenhoek13 called the single-celled organisms that he saw under the microscope "animalcules" • Matthias Jakob Schleiden14 , a botanist, in 1838 determined that all plants consist of cells • Theodor Schwann15 , a zoologist, in 1839 determined that all animals consist of cells • Rudolf Virchow16 proposed the theory that all cells arise from previously existing cells In 1838, the botanist Matthias Jakob Schleiden and the physiologist Theodor Schwann discovered that both plant cells and animal cells had nuclei. Based on their observations, the two scientists conceived of the hypothesis that all living things were composed of cells. In 1839, Schwann published 'Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals', which contained the first statement of their joint cell theory. |
SciQ | SciQ-5666 | neuroscience, neurophysiology, hearing, human-ear, senses
Title: Depolarization and hyperpolarization in stereocilia of the inner ear It’s a well mentioned fact that when the stereocilia of the cochlear hair cells bend in one direction, the hair cell depolarizes, and when the stereocilia bend in the other direction, the cell hyperpolarizes. When the basilar membrane vibrates, the stereocilia are bent back and forth, creating depolarizations in the hair cells followed by hyperpolarizations. What I’m having trouble understanding is why this is significant. This does not determine the frequency of the sound wave, as that is determined by the location along the basilar membrane that the wave impinges on. I don’t see how this would determine amplitude either, seeing as a greater amplitude would only create more drastic bending of a greater number of hair cells. Can anyone shed some light on this? There are roughly two modes of pitch coding in the cochlea: place-coding and temporal coding. The place-theory is the most prevalent accepted model of how the cochlea realizes pitch coding (e.g., Zwislocki, 1991). Basically, it is based on a frequency-to-place Fourier transformation on the incoming sound, where each frequency is coded on a different place on the basilar membrane, as described accurately in the question.
However, there is another, much overlooked way of coding pitch, namely temporal coding. Up until about 1 kHz, spiral ganglion cells in the auditory nerve and acoustical brain stem regions (such as the inferior colliculus) have been found to respond in a phase-locked pattern (Du et al., 2011). Electrophysiology in auditory nerve fibers illustrates the phase-locked activity in response to low-frequency sounds (Fig. 1). This phase-locking behavior of neurons in the auditory system is called the frequency-following response (FFR).
The following is multiple choice question (with options) to answer.
What do the hair cells in the cochlea release when they bend? | [
"receptors",
"hormones",
"neurotransmitters",
"lipids"
] | C | The oval window passes the vibrations to the cochlea . The cochlea is filled with liquid that moves when the vibrations pass through, like the waves in water when you drop a pebble into a pond. Tiny hair cells line the cochlea and bend when the liquid moves. When the hair cells bend, they release neurotransmitters. |
SciQ | SciQ-5667 | thermodynamics, equilibrium, proteins, chemical-engineering
Title: Chemical Equilibria - Fraction Bound equation based on Kd, [R], [L], [RL], is actually an average?
Let's say 150 stem cells express exactly 150 copies of the same mebrane antigen X. While all differentiated cells express exactly 15 copies of X. To the cell mixture you add a large amount of 0.2 μM solution of antibody to X. The $K_D=$ 4 μM.
If you experimentally analyze the number of antibodies bound per stem cell, you will find that it is not constant. Explain why, even for cases where the number of antigens expressed is the same, the binding follows a binomial distribution?
I found the fraction bound to be $\frac{1}{\frac{K_D}{\left[L\right]}+1\:}=f_{bound}$
I scaled the [L] contribution by the number of antigens expressed per cell, so for the differentiated case, I scaled 0.2 μM by 15, and for the normal case, I scaled 0.2 μM by 150.
the differentiated case has a lower $f_{bound}$ because it has less ligands.
To describe the binomial distribution for binding part
the antigens exist in the environment of the beaker (or wherever the reaction is taking place) so they can exchange antigens? resulting in some cells $f_{bound}$ being lower. How exactly the interaction takes place occurs stochastically. <--- want help clarifying this part When a reaction is at equilibrium, there will be stochastic fluctuations. These are usually not measurable (for example, if we have more than a mole of products and reactants in our reaction mixtures).
In this specific case, the fluctuations are easy to measure because the total number of antigen molecules per cell is countable, and you are separating cells (I presume) before analyzing the number of antibodies bound.
If you expect a fluctuation of $\sqrt{N}$ for N objects, that is significant for $N= 150$ but not for $N = \pu{6.022e23}$ when expressed relative to $N$.
The following is multiple choice question (with options) to answer.
Receptor clustering happens when what binds to the receptors? | [
"carbohydrates",
"lipid molecules",
"fas molecules",
"enzymes"
] | C | |
SciQ | SciQ-5668 | human-biology, human-anatomy
However they don't give actual experimental results. So my question is which of the above is the real cause of this difference in the growth rate of nails; or simply why toenails grow much slower than fingernails?
P.S. The season dependence and the lefthand-righthand asymmetry were news to me; it would be really nice if the answer explains them as well. Going on the abstract of a study by J.P. Pessan, et al., fluoride intake, as well as "the fact that toenails are less prone to environmental contamination," constitutes a lesser need for growth in toenails than that in fingernails. Also, fluorine being a crucial component in maintaining the solidity of bones, the body may redirect more fluorine that is ingested by various means, to the hands than to the feet, due to the arguably more necessary functions of the hands (in that they are used them for agile and precise motions that tend to influence our survival), meaning less growth in toenails as evidenced in the first citation.
The following is multiple choice question (with options) to answer.
What makes toenails and fingernails hard? | [
"keratin",
"cellulose",
"taurine",
"guanine"
] | A | Fingernails and toenails consist of specialized epidermal cells that are filled with keratin. The keratin makes them tough and hard, which is important for the functions they serve. Fingernails prevent injury by forming protective plates over the ends of the fingers. They also enhance sensation by acting as a counterforce to the sensitive fingertips when objects are handled. |
SciQ | SciQ-5669 | 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.
Producing sperm and secreting testosterone are the main functions of what system? | [
"male reproductive system",
"female reproductive system",
"endocrine system",
"pollination"
] | A | The main functions of the male reproductive system are to produce sperm and secrete testosterone. |
SciQ | SciQ-5670 | biochemistry
Title: educational sources for learning biochemistry I just finished high school and am going into a biology undergraduate degree, I'm getting into biochemistry too and would like to learn more about it through online platforms or even non-fiction books to use my time effectively this summer. So far I've been using online flash cards to learn more about the jargon and would like to hear some suggestions of platforms or books to read that teach concepts strongly tied to biochemistry beyond what a basic high school curriculum would teach. There are several reference books for biochemistry, some more readable than others. I personally recommend two of them: (1) Lehninger et al. Principles of Biochemistry and (2) Voet, D., Voet, J., et al. Fundamentals of Biochemistry: Life at the molecular level. Both books contain the most important and basic features of each subject. The chapters are generally well written. I have to say that, from my own experience, I consider that Voet's book is more enjoyable, given that some of the sections of Lehninger's can be a bit tricky. Whichever book you choose, make sure you get relatively new editions. Good luck!
As a side note, even though biochemistry is one the first proper biology classes one takes in undergrad, there are some background requirements. Taking organic and inorganic chemistry courses before is important and some understanding of thermodynamics will certainly come in handy.
The following is multiple choice question (with options) to answer.
Biochemistry is the study of the chemistry of? | [
"living systems",
"the Earth",
"abiotic factors",
"inorganic matter"
] | A | The related field of biochemistry overlaps to some extent with organic chemistry. Biochemistry is the study of the chemistry of living systems. Many biochemical compounds are considered to be organic chemicals. Both of the molecules shown above are biochemical materials in terms of their use in the body, but organic chemicals in terms of their structure and chemical reactivity. |
SciQ | SciQ-5671 | thermodynamics, heat
where $c_p$ is the (molar) heat capacity of the mixture, $c_{p,\mathrm{solv}}$ and $c_{p,\mathrm{solute}}$ are the (molar) heat capacities of solvent and solute, respectively, and $x_\mathrm{solv}$ is the mole fraction of solvent in the mixture. Since for dilute solution we can often make the approximation $x_\mathrm{solv}\approx 1$, the second term on the right is approximately zero and can be ignored. Then
$$c_p\approx c_{p,\mathrm{solv}}$$
So for many examples, in particular those involving dilute solutions, you can safely ignore the effect of the added solute and assume that the heat capacity of the mixture is equivalent to that of the pure solvent.
To give a slightly more quantitative example, consider the molar heat capacity of solutions of sodium chloride in water, data from the Dortmund Data Bank:
The following is multiple choice question (with options) to answer.
Color, temperature, and solubility are examples of what type of property? | [
"severe",
"minimal",
"intensive",
"susceptible"
] | C | Color, temperature, and solubility are examples of intensive properties. |
SciQ | SciQ-5672 | 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 is the term for nutrients the body needs in relatively small amounts, including vitamins and minerals? | [
"trace nutrients",
"minor nutrients",
"insignificant nutrients",
"micronutrients"
] | D | Nutrients the body needs in relatively small amounts are called micronutrients . They include vitamins and minerals. Vitamins are organic compounds that are needed by the body to function properly. Several vitamins are described in Table below . Vitamins play many roles in good health, ranging from maintaining good vision to helping blood clot. Vitamin B12 is produced by bacteria in the large intestine. Vitamin D is synthesized by the skin when it is exposed to UV light. Most other vitamins must be obtained from foods like those listed in Table below . |
SciQ | SciQ-5673 | immunology
Title: Is Plasmablast a precursor of Plasma cell? I read it in Roitt's Essential Immunology.
Plasmablasts are precursor cells of short- and long-lived plasma cells and
are generally described as a proliferating fraction of
antibody-secreting cells, often found in the bloodstream
emigrating to organs such as the bone marrow.
I coudn't find any authentic source repeating the same.
Is it true? Is this book authentic enough to follow? Antigen activated B-cells enter the germinal centre dark zone to form centroblasts which undergo somatic hypermutation. These then form centrocytes in the light zone. The various possibilities/routes the centrocyte can take are shown in the following figure. If the centrocyte undergoes a class switch recombination, it becomes a plasmablast.
A plasmablast is defined as
Plasmablast
The B-cell lineage precursor of non-dividing plasma cells, which has the capacity to divide and that has migratory potential.
Once it matures as a plasma cell, it is out in the blood secreting soluble immunoglobulins or antibodies.
Another important definition to mentioned here would be of antibody secreting cells.
Antibody-secreting cells
A term that denotes both proliferating plasmablasts and non-proliferating plasma cells. The term is used when both cell types might be present
So, yes, they indeed are a precursor of plasma cells.
Also, it is necessary to clarify here that although both plasma cells and plasmablasts are antibody secreting cells, plasma cells lack membrane bound antibodies while plasmablasts retain them.
Finally, this is just the germinal centre response that is shown over here. Plasma cells and plasmablasts can also form in an extrafollicular response in extrafollicular sites in the spleen or in the medullary cords of the liver. That's another story altogether!
For a more detailed explanation, have a look at my other answer.
Image and reference: http://www.nature.com/nri/journal/v8/n1/full/nri2217.html
The following is multiple choice question (with options) to answer.
What do corals secrete that builds up to become a coral reef? | [
"exoskeletons",
"saliva",
"actuators",
"tentacles"
] | A | Many corals secrete an exoskeleton that builds up to become a coral reef. |
SciQ | SciQ-5674 | # Mathematical Physics: Differential equation of a raindrop
I hope this is a suited question for this site since it contains a mix of physics and mathematics. In case I should post this on the physics stackexchange site, please let me know.
A spherical raindrop is falling from the sky. Because of the humid atmosphere the raindrop will gain mass during his fall. The increase in mass per time is proportional to the current surface area.
1. Find an equation for the radius of the drop as a function of time ($r(t)$). ($r(0) =r_0$)
2. Find and solve the equation of motion for the raindrop. The equation of motion should depend on $r_0$
My work so far:
Mass: $m(t)=\frac{4}{3} \pi r(t)^3 \rho$
Sufrace Area: $A(t)=4\pi r(t)^2$
\begin{aligned} & \implies \frac{dm(t)}{dt}=\frac{d}{dt}(\frac{4}{3}\pi r(t)^3 \rho)=4 \pi r(t)^2 r'(t)\rho\\ & \iff 4 \pi \rho r(t)^2 r'(t)=\lambda 4 \pi r(t) ^2 \iff r'(t)=\frac{\lambda}{\rho} \iff \frac{dr}{dt}=\frac{\lambda}{\rho} \\ & \iff \int dr = \frac{\lambda}{\rho} \int dt \iff r(t)=\frac{\lambda}{\rho}t+c \\ & \color{blue}{\implies r(t)=\alpha t+r_0} \space \space \space \space \space \space \space \space \space \space \space \text{where}\space \space\alpha=\frac{\lambda}{\rho} \end{aligned}
Equation of motion:
Gravitational Force: $mg$
The following is multiple choice question (with options) to answer.
Solid balls of water and dust falling from the sky are known as? | [
"rain",
"golf balls",
"hail",
"snow"
] | C | |
SciQ | SciQ-5675 | neuroscience, brain
Davis, Z. W., Muller, L., Martinez-Trujillo, J., Sejnowski, T., & Reynolds, J. H. (2020). Spontaneous travelling cortical waves gate perception in behaving primates. Nature, 1-5.
Harris, K. D. (2005). Neural signatures of cell assembly organization. Nature Reviews Neuroscience, 6(5), 399-407.
Liu, X., Ramirez, S., Pang, P. T., Puryear, C. B., Govindarajan, A., Deisseroth, K., & Tonegawa, S. (2012). Optogenetic stimulation of a hippocampal engram activates fear memory recall. Nature, 484(7394), 381-385.
Luczak, A., McNaughton, B. L., & Harris, K. D. (2015). Packet-based communication in the cortex. Nature Reviews Neuroscience, 16(12), 745-755.
The following is multiple choice question (with options) to answer.
What brain structure is important in recognizing and recalling emotions? | [
"cerebral cortex",
"thalmus",
"pituitary",
"amygdala"
] | D | |
SciQ | SciQ-5676 | biochemistry, plant-physiology, plant-anatomy
Title: Why do plants store energy as carbohydrates and not as fats? In my introductory biology class, we are learning about biomolecules. The textbook says fats are a more efficient energy store than carbohydrates.
So my question is - why would plants store their energy as carbohydrates and not as fats, if fats are a more efficient energy store? There are quite some reasons for why plants prefer carbohydrates for energy storage rather than fats. I will reach some of them one at a time.
The following is multiple choice question (with options) to answer.
Oils are liquid lipids that plants use for storage of what? | [
"glucose",
"energy",
"oxygen",
"fat"
] | B | In unsaturated fatty acids, there is at least one double bond between carbon atoms. As a result, some carbons are not bonded to as many hydrogen atoms as possible. Unsaturated fatty acids are found in oils. Oils are liquid lipids that plants use to store energy. |
SciQ | SciQ-5677 | entomology, pathology, parasitology
Title: Why is the species-diversity of deadly parasites greatest in the tropics? There are so many parasites living in tropical regions of Africa, South America, or Asia, but very few in Europe or North America.
Is this due to climate, or are there other reasons?
Many of the tropical diseases and parasites are transmitted by insects, such as flies and mosquitoes. Well there are flies and mosquitoes in Europe as well.
There might be malaria-transmitting mosquitoes in the very south of Europe, and there is encephalitis transmitted by ticks. But that's it. Why don't the hundreds of different parasitic species from Africa spread to Europe ? The diversity of parasites shows a gradient with increasing diversity from the poles to the equator. Several reasons have been brought forth to explain the latitude-dependency of parasite diversity:
An increased diversity overall around the equator; species diversity in general is greater in the rain forests and hence more hosts are available and thus more parasitic species can develop that target specific hosts;
Larger amounts of precipitation and higher temperatures around the equator may favor the development and transmission of parasites (Nunn et al., 2005);
Increased available energy overall around the equator (Guernier et al., 2004).
References
- Guernier et al., PLOSone (2004): 0020141
- Nunn et al., Diversity and Distrib (2005); 11: 249–56
The following is multiple choice question (with options) to answer.
Where do the majority of arthropods live? | [
"in air",
"in hives",
"in water",
"on land"
] | D | The majority of mollusks and annelids live in the water or inside hosts. Arthropods are invertebrates that include insects. The majority of arthropods live on land. |
SciQ | SciQ-5678 | proteins, amino-acids, classification
Title: Classifying Polypeptides (and/or Proteins) Since polypeptides are a linear chain of twenty amino acids, each having a single letter abbreviation (e.g. Alanine = A). So can a polypeptide be represented as just the sequence (say: ADN for an Alanine, Aspartic acid, Asparagine polypeptide)?
This method of classifying polypeptides would lead to a possible 8000 (20**3) variations just for 3-amino-acid-polypetides (3200000 for 5-amino-acid-polypeptides, etc.) and that there would be many variations; and for longer polypeptides - that is, proteins - there would be even more variations.
Or are only the important polypeptides and proteins named, since not every variation of polypeptides and proteins are found in the body? I would've thought that many proteins (and enzymes, etc.) are incredibly specific and so they could be classified in some methodological way, as opposed to just 'lipase' or 'carbohydrase' which provides no structural information (though it would have a long methodological name). You can certainly refer to short peptides by their sequence. I don't know of any exact boundaries, but I've seen tripeptides referred to by either their three letter codes (Ala-Asp-Asn) or even the chemical name (alanylaspartylasparagine) although obviously that gets ridiculous pretty quickly.
As the largest known protein, titin also has the longest IUPAC name of
a protein. The full chemical name of the human canonical form of
titin, which starts methionyl... and ends ...isoleucine, contains
189,819 letters and is sometimes stated to be the longest word in the
English language, or any language. However, lexicographers regard generic names of chemical compounds as verbal formulae rather than English words
The following is multiple choice question (with options) to answer.
Protein chains containing 10 or fewer amino acids are usually referred to as what? | [
"polypeptides",
"peptides",
"protons",
"carboxyl"
] | B | the conditions, amino acids can act as either acids or bases, which means that proteins act as buffers. The pH at which an amino acid exists as the zwitterion is called theisoelectric point (pI). The amino acids in a protein are linked together by peptide bonds. Protein chains containing 10 or fewer amino acids are usually referred to as peptides, with a prefix such as di- or tri- indicating the number of amino acids. Chains containing more than 50 amino acid units are referred to as proteins orpolypeptides. Proteins are classified globular or fibrous, depending on their structure and resulting solubility in water. Globular proteins are nearly spherical and are soluble in water; fibrous proteins have elongated or fibrous structures and are not soluble in water. Protein molecules can have as many as four levels of structure. The primary structure is the sequence of amino acids in the chain. The secondary structure is the arrangement of adjacent atoms in the peptide chain; the most common arrangements are α-helices or β-pleated sheets. The tertiary structureis the overall three-dimensional shape of the molecule that results from the way the chain bends and folds in on itself. Proteins that consist of more than one chain have quaternary structure, which is the way the multiple chains are packed together. Four types of intramolecular and intermolecular forces contribute to secondary, tertiary, and quaternary structure: (1) hydrogen bonding between an oxygen or a nitrogen atom and a hydrogen atom bound to an oxygen atom or a nitrogen atom, either on the same chain or on a neighboring chain; (2) ionic bondingbetween one positively charged side chain and one negatively charged side chain; (3) disulfide linkages between cysteine units; and (4) dispersion forcesbetween nonpolar side chains. Because of their complexity, protein molecules are delicate and easy to disrupt. Adenatured protein is one whose conformation has been changed, in a process called denaturation, so that it can no longer do its physiological job. A variety of conditions, such as heat, ultraviolet radiation, the addition of organic compounds, or changes in pH can denature a protein. Saylor URL: http://www. saylor. org/books. |
SciQ | SciQ-5679 | human-biology, biochemistry, metabolism, food
Which seem to go in different, rather contradictory directions.
Also, Studies partially supporting either viewpoint can be found:
Study considering hemoglobin A1c levels
Study considering peak glucose levels
Study considering snacking
Which leaves the non-biologist asking themselves which is the "major effect" (certainly, there will be some truth to each position, but the question is which one(s) got the "main point"), and if there are any other important effects to be considered, hence this broad question here, so I understand, from a biological standpoint, what happens to the carbohydrates when I eat them, so I can conclude for myself how to adapt my diet for "optimal" health. Scope of Answer
The original poster provided ample context for his question, which related to health considerations. It was perhaps for this reason, among others, that the question had not received an answer at the time of writing: questions relating to medical or health advice are off-topic here. However, his actual question is primarily biochemical:
What are the biological differences between the digestion of sugar and
different types of carbs as constituents of different types of food in
humans?
Although this might be answered with a little internet search, I felt it would be hospitable if someone offered him an answer to this — and this only.
Definitions
The basic sugar unit is a mono-saccharide, those of relevance to this question being hexoses or pentoses, having six or five carbon atoms, respectively.
What in non-technical language is called sugar, refers to a specific molecule, sucrose, which is a disaccharide of covalently-bonded glucose and fructose.
What in non-technical language are referred to as dietary carbohydrates generally refers to the storage polysaccharide of plants such as potato and other root vegetables, rice, and other cereal crops used to make bread. This is a homo-polymer composed solely of glucose units.
Summary of the differences in metabolism
Arising from these definitions, the following differences in metabolism emerge:
Different enzymes (amylase for these polysaccharides, sucrase for saccharose) are used to catalyse the hydrolysis of the linkages between the monomeric units.
Absorption in the gut is different for glucose and fructose, as is transport into cells.
The following is multiple choice question (with options) to answer.
The primary site of carbohydrate digestion is in the? | [
"large intestine",
"mouth",
"stomach",
"small intestine"
] | D | The primary site of carbohydrate digestion is the small intestine. The secretion of αamylase in the small intestine converts any remaining starch molecules, as well as the dextrins, to maltose. Maltose is then cleaved into two glucose molecules by maltase. Disaccharides such as sucrose and lactose are not digested until they reach the small intestine, where they are acted on by sucrase and lactase, respectively. The major. |
SciQ | SciQ-5680 | zoology, ecology, population-biology, ecosystem, predation
Title: Predator prey interaction I went through a line in my textbook which read:
"But for predators, prey species could achieve very high population densities and cause ecosystem instability."
I was not able to understand the meaning 'but for predators'. Can anyone please help me to interpret it's meaning?link to page where this line is mentioned
Edit: In terms of biology, I was unable to understand the meaning of the sentence, and I wanted to make sure that I don't misunderstand things... And this is why I posted the question.. I feel that the answer given is correct and in case, you find better explanation, please do post. I disagree with GForce's explanation; the meaning is not that growth of prey populations causes instability in predator species.
The sentence is merely saying that without predation, prey population growth is more likely to be at a level which leads to ecosystem instability. The term "but for predation" means "if it wasn't for the effects of predation". In other words:
"Ecosystem instability can occur when population growth of some species goes unchecked by predation."
See here for more explanation, where this example comes from in which it says that running a red light caused a crash:
"but for running the red light, the collision would not have occurred"
Biologically this makes sense in the sentence you show; without predators a species is limited by its supply of resources, and it can use these resources at an unsustainable level, whereas if you add predators to the mix there is additional extrinsic effects on population size, not determined by ecosystem properties such as space or nutrients.
The following is multiple choice question (with options) to answer.
A potential cause of extinction, competition between different species is called what? | [
"parasitism",
"interspecific competition",
"mutualism",
"intraspecific competition"
] | B | Competition between different species is called interspecific competition. It might lead to the less well-adapted species going extinct. Or it might lead to one or both species evolving specialized adaptations. For example, competing species might evolve adaptations that allow them to use different food sources. You can see an example in Figure below . |
SciQ | SciQ-5681 | 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.
Within the microsporangium, the microspore mother cell divides by meiosis to give rise to four microspores, each of which will ultimately form this? | [
"ova",
"sperm cell",
"zygote",
"pollen grain"
] | D | Within the microsporangium, the microspore mother cell divides by meiosis to give rise to four microspores, each of which will ultimately form a pollen grain (Figure 32.7). An inner layer of cells, known as the tapetum, provides nutrition to the developing microspores and contributes key components to the pollen wall. Mature pollen grains contain two cells: a generative cell and a pollen tube cell. The generative cell is contained within the larger pollen tube cell. Upon germination, the tube cell forms the pollen tube through which the generative cell migrates to enter the ovary. During its transit inside the pollen tube, the generative cell divides to form two male gametes (sperm cells). Upon maturity, the microsporangia burst, releasing the pollen grains from the anther. |
SciQ | SciQ-5682 | physiology, neurophysiology, respiration, breathing, pulmonology
Title: Is breathing a reflex action or is it an intrinsic process? The process of breathing is controlled by respiratory centers in the brain stem. Do these centers have an innate activity, i.e., just send out signals to breathing muscles intrinsically, and have the rate and manner in which they do so modified by various regulatory factors?
Or are they driven by imbalances (in levels of oxygen, carbon dioxide, hydrogen ions) like a reflex? Let's say that hypothetically these levels remain static in an acceptable state such that this reflex is no longer needed, would breathing stop since there's no longer a driving motive or would it continue because the respiratory centers have an intrinsic activity? While the ultimate purpose of breathing could be considered to be the maintainance of a balance of the substances you are referring to (such as blood oxygen, carbon dioxide, and hydrogen ions), the blood levels of these substances do not directly control the production of action potentials within the motor neurons that promote the contraction of the diaphragm and intercostal muscles.
The propagation of these action potentials is initiated by signals from the medullary respiratory center, specifically the neurons in the dorsal respiratory group (DRG) and the ventral respiratory group (VRG). In the VRG, a complex of neurons known pre-Bötzinger complex is responsible for generating the signals that cause the rhythmic muscle contractions involved in breathing:
The respiratory rhythm generator is located in the pre-Bötzinger complex of neurons in the upper part of the VRG. This rhythm generator appears to be composed of pacemaker cells and a complex neural network that, acting together, set the basal respiratory rate.
The following is multiple choice question (with options) to answer.
What is regulated by the reticular formation? | [
"anxiousness",
"wakefulness",
"awkwardness",
"sleepiness"
] | B | Wakefulness is regulated by the reticular formation, which is present in the. |
SciQ | SciQ-5683 | genetics, botany, seeds
Title: What DNA does a self-fertile plant's seedling have? Some plants are said to be self-fertile. An example is Prunus tomentosa.
Assuming that no cross-pollination happened with other plants, if a self-fertile plant such as prunus tomentosa produces a seedling, what DNA will the seedling have? Is the seedling's DNA an exact copy of the parent plant's DNA, or do the genes get rearranged? Selfing (aka self-fertilizing) differs from cloning. When selfing occurs, the offspring is not an exact copy of the parent. When cloning occurs, the offspring is an exact copy (except for a few mutations) of the parent.
Selfing implies that an individual will produce two gametes (typically a spermatozoid and an ovule but that might be a bit more complicated) and these two gametes are fusing to give the zygote (egg or offspring if you prefer).
As a consequence, when selfing, meiosis is occurring (and therefore segregation and recombination) so that the offspring is not an exact clone of the parent but rather some kind of a rearrangement of the parent genome (with a few mutations of course).
The following is multiple choice question (with options) to answer.
All living things are capable of what process whereby living things give rise to offspring? | [
"cell division",
"mitosis",
"differentiation",
"reproduction"
] | D | All living things are capable of reproduction, the process by which living things give rise to offspring. |
SciQ | SciQ-5684 | climate-change, climate, paleoclimatology, carbon-cycle
Title: Did climate cool down when underground hydrocarbons stocks formed? As far as I understand, the dominant theory of modern climate change says that recent warming is mainly caused by the massive burning of hydrocarbons that used to be stored in solid form mostly underground as petroleum, coal, etc.
This suggests that the reverse process should contribute to a cooling of the climate (or to a slowed down warming if other processes are at play at the same time).
In particular, a cooling should have occurred throughout the period when the stocks of underground hydrocarbons were formed by the "pilling" of organic remains.
My questions:
The following is multiple choice question (with options) to answer.
What is the common name of mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms? | [
"fossil record",
"renewable resources",
"non-renewable fuel",
"fossil fuels"
] | D | Fossil fuels are mixtures of hydrocarbons that formed over millions of years from the remains of dead organisms. They include petroleum (commonly called oil), natural gas, and coal. Fossil fuels provide most of the energy used in the world today. They are burned in power plants to produce electrical energy, and they also fuel cars, heat homes, and supply energy for many other purposes. You can see examples of their use in Figure below . |
SciQ | SciQ-5685 | universe, cosmology
Title: Is there any other theory, apart from the Big Bang paradigm, which describes the birth of universe? The Big Bang theory is the approved theory of the "birth" of Universe. Are there any other theories which can explain how our Universe came into existence? This is not an answer but a comment which is too long to post as such.
There is no such thing as a scientifically approved theory, there are theories consistent with the evidence some of which are simpler in some sense than others, and philosophy of science tells us that we should prefer those that are simpler.
Also I doubt that the big-bang theory is what you think it is, which is simply that at a certain time in the past the Universe was in a hot dense state which then expanded, forming the lightest chemical elements... The first part of this is a simple extrapolation of the observation of the way that galactic Doppler shift increases with distance and the observed cosmic microwave background. The second part is the consequence of the application of well know nuclear properties of matter.
Now there are plenty of more-or-less widely accepted additions to this, mainly to explain the uniformity and fluctuations in the microwave background, and the emergence of first stars and galaxies etc. But all of these are to some extent speculative since we have no generally accepted unification of Quantum Mechanics and General Relativity or require physics that has no predicted consequence (so far) beyond the phenomena it has been proposed in order to explain.
To make this approximate an answer I will point you to the Wikipedia page on Non-Standard Cosmologies
The following is multiple choice question (with options) to answer.
What branch of science is the study of the universe, not of cosmetics? | [
"cosmology",
"epistemology",
"theology",
"astronomy"
] | A | The study of the Universe is called cosmology . Cosmologists study the structure and changes in the present Universe. The Universe contains all of the star systems, galaxies, gas, and dust, plus all the matter and energy that exists now. Plus all that existed in the past, and all that will exist in the future. The Universe includes all of space and time. |
SciQ | SciQ-5686 | circulatory-system, lymphatic-system, veins
Title: How does most of lymph get back into the blood stream? (I don't mean the lymphatic system) I once read that it was because of osmotic pressure that it returns to the blood stream, by entering the venules. But why? If lymph originated as plasma how come that the solute concentration is higher in the venule? Doesn't plasma contain solutes such as salts, nutrients, oxygen, etc. ? Technically 'lymph' is used to refer to the fluid found within the lymphatic system. If it's not in the lymphatic system, it is not lymph fluid. Thus, your question is really asking about interstitial fluid or the plasma that was filtered out of blood capillaries.
The answer to your question is based on the Starling equation. Normally fluid leaves a capillary due to a net pressure that favors the interstitium. This net pressure is based on the hydrostatic pressure within the capillary being greater than the interstitial pressure of the surrounding tissues, and the oncotic pressure of the capillary (that draws fluid in) being weaker than the hydrostatic pressure of the capillary (that pushes fluid out). At the venule end of this system, the capillary oncotic pressure is stronger than the capillary hydrostatic pressure, drawing fluid back into the circulatory system.
Remember that albumin is the most important component which establishes the oncotic pressure within a vessel, and that this protein is normally NOT released out of a vessel during filtration. Thus, it passes from the capillary into its corresponding venule directly.
The following is multiple choice question (with options) to answer.
Which blood leaves the placenta through veins leading back to the fetus? | [
"immunity",
"fetal",
"pelvic",
"molecular"
] | B | |
SciQ | SciQ-5687 | states-of-matter, matter
Title: What distinguishes the difference states of matter from solid to BEC and perhaps fermionic condensate? Is it something to do with the behavior of electrons? How many states are there either discovered or predicted? 無
'States of matter' is a question of taxonomy, not of reality, and moreover, it's a result of the conditions surrounding the matter, not its internal properties. Certain combinations of properties give us a hint towards calling something 'solid' or 'liquid', but in truth there are no lines, just a continuous spectrum, and under certain conditions, matter transitions seamlessly through all sorts of states, both mundane and exotic:
Behold: Jupiter
A perfect example of this is Jupiter. Composed primarily of hydrogen, this gas giant consists (conjecturally) of a core of high-temperature hydrogen ice, floating in liquid hydrogen, enveloped in hydrogen gas, moving through interplanetary medium composed of hydrogen plasma.
Except not really: Under these conditions, the classical notions of states of matter break down entirely: Between these states of matter there are no interfaces, just a gradual, continuous transition.
In other words: The distinctive line to separate one state from another you are after doesn't really exist.
The following is multiple choice question (with options) to answer.
Matter can be classified on the basis of how what interacts with it? | [
"gravity",
"water",
"air",
"light"
] | D | Matter can be classified on the basis of how light interacts with it. Matter may be transparent, translucent, or opaque. Each type of matter is illustrated in Figure below . |
SciQ | SciQ-5688 | experimental-chemistry
Title: How to determine Acid-Base Indicator How do we determine which is the best indicator to use when given the initial pH’s of both the acids and bases and the endpoint value of our base? All acid-base indicators are weak acids or bases themselves. They have a pKa value associated with them. The pH at which they change color "quickly" is
pH of abrupt color change = pKa-1 to pKa+1;
For example phenolphthalein has a pKa of 9.3, so it will quickly change colors in the pH range of 8.3 to 10.3, whichever side your are approaching this range. This is how those numbers are listed for your indicators.
So how do we choose an indicator? The punchline is that your end-point* must lie close the pH range of abrupt color change. Take the titration of HCl (in a flask)and NaOH (in a burette). Now you see that pH has reached 7; in order to ensure that there is no trace of acid remaining, you would add a fraction of a drop of a base to the flask; the pH will quickly jump to an alkaline pH because there is no acid anymore. Which indicator would abruptly change color as it sees a slightly excess of base? Phenolphthalein (8.2 to 10.2 as per your text)
You can do the rest using similar logic.
* Finer details: Your text is wrong in the sense of using the word endpoint. End point in a classical sense means that you have added a slight excess (fraction of a drop) to the titration flask. This indicates end of the titration. The correct term in your scanned image should be "equivalence point" where the titration has just been completed (equivalent amounts of base and acids have reacted); so the end point of a strong acid- base titration is not at pH of 7.0, it is slightly basic if the base is being added from the burette. Ask your teacher to clarify further.
The following is multiple choice question (with options) to answer.
What scale is used to succinctly communicate the acidity or basicity of a solution? | [
"ph",
"Richter scale",
"solvent scale",
"ions"
] | A | The pH scale is used to succinctly communicate the acidity or basicity of a solution. |
SciQ | SciQ-5689 | human-biology
Title: Stopping the effect of hormone Many hormones released by endocrine organs travel down in the blood and bind to specific receptors on the target cells. What then breaks that binding of the molecule with the receptor ? ( thus inactivating further stimulation of the target cell ) The binding is reversible typically; part of the potency of a drug is ow well and for how long it binds to its target. There's a natural equilibrium of binding and dissociation. Many drugs, once bound to their cognate receptor, cause a down regulation of their cognate receptor on the target cell. The bound/activated downstream signalling pathways may be inhibited by ubiquitination of the downstream signals themselves or upregulation of antagonists etc. The hormone itself has a half life, which is very important, thus levels naturally decrease and for some hormones this is incredibly rapid. Levels may decrease due to breakdown or excretion. Increase of binding hormones may decrease free hormone thus it's effect also.
The following is multiple choice question (with options) to answer.
Hormones often regulate what through antagonistic functions? | [
"homeostasis",
"breathing",
"hypothesis",
"consciousness"
] | A | |
SciQ | SciQ-5690 | acid-base, aqueous-solution, solubility, titration, conductivity
\cdots&\cdots\\
\ce{V_{b} &=\frac{\left([H+] - \frac{K_{w}}{[H+]}-\frac{C_{a}K_{a}}{K_{a} + [H+]}\right)\times V_{a}}{\frac{K_{w}}{[H+]} -[H+] - \frac{K_{b}C_{b}}{K_{b} + \frac{K_{w}}{[H+]}}}}
\end{align}
$$
I used this to generate a pH curve and conductivity curve for the titration using the concentration of the various chemical species in solution:
The following is multiple choice question (with options) to answer.
The potential of what can be used to measure the ph of a solution? | [
"stimulation cell",
"galvanic cell",
"symbiotic cell",
"electrodes cell"
] | B | Thus the potential of a galvanic cell can be used to measure the pH of a solution. Exercise Suppose you work for an environmental laboratory and you want to use an electrochemical method to measure the concentration of Pb2+ in groundwater. You construct a galvanic cell using a standard oxygen electrode in one compartment (E°cathode = 1.23 V). The other compartment contains a strip of lead in a sample of groundwater to which you have added sufficient acetic acid, a weak organic acid, to ensure electrical conductivity. The cell diagram is as follows”. |
SciQ | SciQ-5691 | thermodynamics, statistical-mechanics
Title: Why do particles of an ideal gas move in random motion? Suppose we imagine that the particles (no molecules) of a helium gas are all initially moving horizontally at the same speed.(there is no interaction among them, and the container is ideal, in the sense that the particles scatter horizontally when they hit it) Would at least some later be moving vertically?
If they were completely organized in the beginning, would they get sprayed around at all angles, and then would the sprayed ones get sprayed some more, and sprayed some more, and sprayed some more?
What would be the origin of the random motion of the particles of a helium gas , for example, in a perfect box? Uncertainty principle? You could design initial conditions for a gas for which it doesn't move in brownian motion, just like you described. It's just that that takes some really particular initial conditons, and life is way too messy for that to happen frequently. Not only that, considering that there are on the order of $~10^{23}$ particles in a macroscopic object, the word "infrequently" here becomes "so rare that it has most likely never happened anywhere in the visible universe".
For example, start with your suggestion, and imagine you trap the particles in a box. They will hit a wall, ricochet off at different angles, collide into each other, and soon you will once again have a mess of particles moving unpredictable directions. This kind of thing is very typical and that's why any gas you see in real life will have random motion with probability which is unfathomably close to 100%.
The following is multiple choice question (with options) to answer.
What theory says atoms of matter are in constant random motion? | [
"modern residual theory",
"sound kinetic theory",
"modern kinetic theory",
"the theory of relativity"
] | C | A: The modern kinetic theory of matter is remarkably similar to Democritus’ ideas about the motion of atoms. According to this theory, atoms of matter are in constant random motion. This motion is greater in gases than in liquids, and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place. |
SciQ | SciQ-5692 | cosmology, astrophysics, antimatter, galaxies, baryogenesis
Title: How would we tell antimatter galaxies apart? Given that antimatter galaxies are theoretically possible,
how would they be distinguishable from regular matter galaxies?
That is, antimatter is equal in atomic weight and all properties, except for the opposite reverse charge of the particles, identical to regular matter. Hence a star composed of antimatter hydrogen would fuse to anti-helium in an analogous way to our own Sun, and it would emit light and radiation at the same wavelengths as any regular matter star and would cause the same gravitational forces for planetary systems to form as in any other star system.
Hence, what would be a telltale sign if you were observing a galaxy made up entirely of antimatter?
Also, is there any evidence for that half of all galaxies are not made of antimatter -- while general theories currently assume that there is an imbalance of matter over antimatter in the universe, then what is the rationale for not assuming that there is in fact an even balance between the two? You're right - for isolated galaxies, there is no obvious way of discerning whether they are made of matter or antimatter, since we only observe the light from them. But if there are regions of matter and antimatter in the universe, we would expect to see HUGE amounts of radiation from annihilation at the edges of these regions. But we don't. You could also make the case that galaxies are well-separated in space, and there's not much interaction between them. But there are plenty of observed galaxy collisions even in our own small region of the universe, and even annihilation between dust and antidust in the intergalactic medium would (probably) be observable.
The following is multiple choice question (with options) to answer.
The laws of what field of science apply to galaxies and atoms, an indication of the underlying unity in the universe? | [
"geology",
"astronomy",
"anthropology",
"physics"
] | D | Figure 1.1 Galaxies are as immense as atoms are small. Yet the same laws of physics describe both, and all the rest of nature—an indication of the underlying unity in the universe. The laws of physics are surprisingly few in number, implying an underlying simplicity to nature’s apparent complexity. (credit: NASA, JPL-Caltech, P. Barmby, Harvard-Smithsonian Center for Astrophysics). |
SciQ | SciQ-5693 | soil, minerals, terminology, soil-science
Title: "Down wash" as a source for mineral particles in the soil In a previous IGCSE examination paper$^1$, the following question was asked and answer provided:
State one source of mineral particles in soil.
Marking Scheme:
Accept any one of:
rock;
down wash;
What's "down wash" and how is it responsible for providing minerals to soil? Googling the term lead me to an aerodynamics definition, which I doubt is the one referred to by the marking scheme.
$^1$ UCLES. Environmental Management, 0680/12, Paper 1. Cambridge International General Certificate of Secondary Education, February/March 2017. Downwash can be part of some erosion environments where minerals are moved down from their host rock environment to another location.
Black Snake Range - Granite Slopes, Victoria, Australia
The crest of the divide rises to almost 400 metres and at this site there are numerous exposed granite slopes and large boulders near the ridge crest. The lower slopes have a cover of granite downwash and the minor valleys have become partly infilled with this granitic sand wash, and hence they are swampy
Southdowns, UK, page 4
Overlying the bedrock geology are drift deposits of alluvium (along the numerous
streams) and ‘head’ (downwash deposits at the base of the Greensand Hills around
Liss and Petersfield).
In the Discussion section of Slope Stability and Slope Formation in the Flysch Zone of the Vienna Forest (Austria)
The downwash of the basal clays and marls, uncovering the solid bedrock, has to be regarded as the main aspect of this phase
The following is multiple choice question (with options) to answer.
What makes soil and rock particles move gradually down the slope during each thaw? | [
"heat",
"rain",
"gravity",
"wind"
] | C | Hot spots may also be active at plate boundaries. This is especially common at mid-ocean ridges. Iceland is formed by a hot spot along the Mid-Atlantic Ridge. |
SciQ | SciQ-5694 | species-identification, microbiology, microscopy
Title: Identification of protozoa under microscope I observed maybe Protozoa from standing FRESH water and from slowly flowing FRESH water. I am complete dilettante. Can you tell what these creatures are?
https://www.youtube.com/watch?v=6D5ck3zNJzA&t=474s
Thank you.
Added picture for to be more specific At first glance, the organisms may hold the appearance of protozoans like ciliates. However, I am of the belief that these 'totally tubular' micro organisms are in fact diatoms.
The diatoms are a diverse range of eucaryotic microalgae which comprise a large percentage of the phytoplankton group. (Diatomaceous earth is the residual remains of their calcareous walls)
They are likely diatoms because of their apparent hard membrane, and slight brown-green pigment, typical of heterokont diatoms.
I would be unable to specify the organism to family level. However, you may wish to complete your investigation by looking under the order 'Pennales'.
For general information regarding the Diatoms, you may visit https://en.wikipedia.org/wiki/Diatom
Morphology and description available from: https://books.google.co.uk/books?id=xhLJvNa3hw0C&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false
Good luck
The following is multiple choice question (with options) to answer.
What is the protist kingdom sometimes called as? | [
"fossil can kingdom",
"flora can system",
"plant can kingdom",
"trash can kingdom"
] | D | The protist kingdom is sometimes called the “trash can” kingdom. It includes all eukaryotes that don’t fit in one of the other three eukaryote kingdoms: Animalia, Plantae, or Fungi. There are thought to be between 60,000 and 200,000 protist species. Many have yet to be identified. The protist kingdom is very diverse, as shown in Figure below . |
SciQ | SciQ-5695 | Last edited: Jul 7, 2011
9. Jul 7, 2011
### Superstring
You forgot about the constant of integration (and units). It should read:
$$v(t) = \frac{1}{2} st^2+C$$
Now you need to figure out what C is equal to with the initial condition that v(0)=3 m/s
You can't use that equation unless a is constant, which it is not. You ALREADY have an equation that tells you the velocity at any point in time (or, at least you will once you solve for C) - you just need to solve for t when v(t)=21.
10. Jul 7, 2011
### SammyS
Staff Emeritus
I see there have been quite a few posts since my first reply. But you seem to have missed the whole point of what I stated in the quoted text above.
You have in the original problem statement that the acceleration is given by: a(t) = s·t .
Therefore, taking the integral (anti-derivative) gives: $\displaystyle v(t)=\int st\,dt$, where s is a constant, namely s = 2 m/s3.
Therefore, v(t) = (1/2)s t2 + C .
At t=0, we have v(0) = 3 m/s. So, what is C ?
Using that value for C and plugging-in s = 2, should give you v(t) .
Then solve v(T) = 21 m/s for T .
11. Jul 8, 2011
### rjs123
thanks i got it now...I just started 8 days ago...so this is all new to me.
c = 3
21 = t^2 + c
18 = t^2
t = 4.2 s
12. Jul 8, 2011
Correct
The following is multiple choice question (with options) to answer.
The constant "c" can be specifically used to represent the (extremely fast) speed of what? | [
"sound",
"gravity",
"electricity",
"light"
] | D | n = cv , where v is the observed speed of light in the material. Since the speed of light is always less than only in a vacuum, the index of refraction is always greater than or equal to one. |
SciQ | SciQ-5696 | atmosphere, ocean, hydrology, climate-change
Comment: I strongly endorse the use of wind and hydropower as sources of energy over the further use of fossil fuels. However, I still think it is important to do research into the actual renewability of presumed-renewable energy sources, as we don't want to end up with another fossil fuel-type situation, in which we become aware of dependency on these energy sources and their malignant environmental side-effects long after widespread enthusiastic adoption. Electricity from waves, from hydro (both run-of-river and storage) and from wind, are all indirect forms of solar power. Electricity from tides is different, and we can deal with that in a separate question. Global tidal electricity generation is not yet at the scale of gigawatts, so it's tiny for now.
Winds come about from the sun heating different parts of the planet at different rates, due to insolation angles, varying cloud cover, varying surface reflectivity, and varying specific heat of surface materials. Temperature differentials create wind currents.
Waves come about from wind, so they're a twice-indirect form of solar power.
Sunlight on water speeds up evaporation, lifting the water vapour into clouds, giving them lots of gravitational potential. That rain then falls, sometimes onto high land, from where it can be gathered into storage reservoirs that are tapped for electricity, or where it flows into rivers that are then harnessed in run-of-river hydro.
How much power is there? Well, the insolation from the sun is, at the outer boundary of the Earth's atmosphere, at an intensity of about 1400 Watts per square metre. The Earth's albedo is roughly about 30% - i.e. on average about 400 Watts are reflected back into space, giving an average irradiation into the Earth of about 1000 Watts per square metre. Picture the Earth's surface as seen from the Sun: wherever the Earth is in its orbit on its own axis, and around the Sun, the Sun sees a disc that has the Earth's diameter, so the surface area exposed to the Sun is just $\pi$ times the square of Earth's radius, which is about 6 300 kilometres.
So the incoming solar radiation is $1000 \times 6,300,000^2 \times \pi \approx 125 \times 10^{15} \rm \ W$
The following is multiple choice question (with options) to answer.
What are non-renewable sources of energy that produce environmental damage? | [
"fossil fuels",
"crop fuels",
"wind",
"sunlight"
] | A | Fossil fuels are non-renewable sources of energy that produce environmental damage. |
SciQ | SciQ-5697 | cancer, mutations
Here is another great paper that specifically addresses your question, linking increased cell division with the accumulation of both significant and insignificant mutations, which over time, lead to an accumulation of mutations needed for cancer to develop.
The following is multiple choice question (with options) to answer.
What causes cancer cells to avoid elimination and continue to multiply? | [
"chronic cell division",
"continuous cell division",
"uncontrolled cell division",
"persistent cell division"
] | C | When normal cells are damaged beyond repair, they are eliminated. The upper diagram depicts damaged cells being destroyed. Cancer cells avoid elimination and, because of uncontrolled cell division, continue to multiply in an unregulated manner. The lower diagram depicts damaged cells dividing in an uncontrolled fashion. |
SciQ | SciQ-5698 | atomic-physics
Title: What gives covalent bond its strength? I came across the following passage from Structure and Properties chapter of Morrison-Boyd Organic Chemistry:
What gives the covalent bond its strength? It is the increase in electrostatic attraction. In the isolated atoms, each electron is attracted by-and attracts-one positive nucleus;in the molecule, each electron is attracted by two positive nuclei.
However, I don't think it refers to the force holding each atom together. It rather, merely describes the increase in the electrostatic force of attraction between the electrons and the nuclei. I believe that bond strength is a measure of the difficulty in pulling apart the component atoms, not the electrons from the positive nuclei.
What exactly is the pattern or picture of the forces on the nuclei and the electrons, due to one another, that holds the component atoms together? (I am aware that the decrease in overall energy or increase in stability is definitely not a reason to account for the strength of covalent bond, but rather a consequence of the action of such forces.) It probably helps to define what a covalent bond really is. Covalent bonds occur when one or more Atomic Orbitals (AO) of the participating atoms constructively interact and form a (bonding) Molecular Orbital (MO). The figure below schematises the formation of a $\sigma_{ss}$ MO when two hydrogen atoms combine to form a dihydrogen molecule:
The following is multiple choice question (with options) to answer.
Electronegativity is a qualitative measure of how much an atom attracts what in a covalent bond? | [
"electrons",
"protons",
"neutrons",
"isotopes"
] | A | Electronegativity is a qualitative measure of how much an atom attracts electrons in a covalent bond. |
SciQ | SciQ-5699 | photons, material-science, absorption, optical-materials, glass
Funny thing is, as I wrote this long question, I feel like I answered my own question. Is it basically that whereas the molecules in opaque materials generally convert photons to heat after absorption, those in transparent materials such as glass/water are unable to do so and so must re-emit them? This is a really interesting question, and I worry that you are getting overly bogged down by being unable to focus individually on the different perspectives which are happening at multiple scales. First, let's tackle the more microscopic quantum scale. If we want to understand how light is (or is not) being absorbed by a material, we must first understand what would cause that absorption in the first place. You hit the nail on the head by giving an example of a process that would allow light to be absorbed; absorption of UV-visible light often leads to the excitation of electrons about the various energy levels within the material. A related phenomena might be the absorption of IR light by molecules because of the excitation of the vibrational degrees of freedom into excited states. All together, the various ways that a material may absorb light are collectively determined by the quantum mechanical structure of the material and what levels and states are available. Of course, describing these levels gets increasingly complicated the more complex the material becomes (which is why I have a job!). But there is one key thing you are missing.
While there may be levels present to allow an absorption of light, we still have to ask how likely it is that the light is absorbed! The classic example of such a calculation is Fermi's Golden Rule in perturbation theory for a two level system which relates the probability of absorption to the transition dipole moment between the two states. See MacQuarrie's Physical Chemistry A Molecular Approach, or his Statistical Mechanics for derivations and details. So we not only have to worry about whether there are levels for the light to cause transitions between, but also the probability of this happening at all. This probability analysis becomes more difficult when we then have to consider how frequently the light will actually get an opportunity to be absorbed on its journey.
The following is multiple choice question (with options) to answer.
Depending on how matter interacts with light, it can be classified as transparent, translucent, or what? | [
"opaque",
"reflective",
"reactive",
"protective"
] | A | Matter can be classified as transparent, translucent, or opaque depending on how it interacts with light. |
SciQ | SciQ-5700 | physiology, senescence, organs
Kidney: 7.2 years
Liver: 16.9 years
Lung: 2.1 years
Heart: 14.5 years
Kidney-Pancreas: 12.9 years
These numbers are not definite, since the life style of the donor and the receiver as well as infections of the transplated patient (who has a severely suppressed immune system – this is critical) also play an important role in determining the lifetime of the organ.
The following is multiple choice question (with options) to answer.
Kidneys, large intestine, liver, skin, and lungs comprise which system? | [
"excretory system",
"Lymphatic system",
"Muscular system",
"Digestive system"
] | A | Organs of excretion make up the excretory system. They include the kidneys, large intestine, liver, skin, and lungs. |
SciQ | SciQ-5701 | cell-biology, microbiology
Title: Are there any organisms that are made of more than one (~5-12) cell? Prokaryotes and eukaryotes are unicellular, made of one cell. Great. Eukaryotes are unicellular or multicellular. But the typical examples of multicellular eukaryotes we have are made of, often, trillions of cells, like us humans. Ants must still be made of many millions of cells. Are there known eukaryotes with very few cells that make them up? Like, 5, or something? Or maybe a dozen cells making up the whole organism in its fully developed state? There's Trichoplax adhaerens, a Placozoa, made of a few thousand cells. Then there is Dicyema japonicum, a simple mesozoan, made up of 9 to 41 cells. Arguably, the simplest multicellular organism is the algae Tetrabaena socialis, whose body consists of 4 cells. Then, there's the parasitic Myxozoa which have 7 cells.
The following is multiple choice question (with options) to answer.
What group of single-celled organisms lacking a nucleus comprises the most numerous organisms on earth? | [
"fungi",
"eukaryotes",
"carbohydrates",
"prokaryotes"
] | D | No doubt you’ve had a sore throat before, and you’ve probably eaten cheese or yogurt. If so, then you’ve encountered the fascinating world of prokaryotes. Prokaryotes are single-celled organisms that lack a nucleus. They also lack other membrane-bound organelles. Prokaryotes are tiny and sometimes bothersome, but they are the most numerous organisms on Earth. Without them, the world would be a very different place. Prokaryotes are the simplest organisms. The first cells and organisms to evolve would be classified as prokaryotic. |
SciQ | SciQ-5702 | crystal-structure, carbon-allotropes
Title: Why is the buckminsterfullerene the purest form of carbon? Other websites say that $\ce{C60}$ doesn't have surface bonds that are attracted by other atoms as in graphite and diamond.
I understand that graphite may be attracted by other atoms because of its dangling electron. But why diamond? Each carbon in diamond is covalently bonded to $4$ other carbon atoms in a tetrahedral fashion. Diamond has dangling bonds on the outer surface of the crystal for pretty much the same reason as graphite. If you understood graphite differently, then you understood it wrong.
See, a molecule of oxygen contains 2 atoms, a molecule of sulfur has 8; but how many atoms are there in a "molecule" of diamond or graphite? Try drawing one to the end, so as to count them. You won't be able to do that. There is no end. The thing is infinite. But the real-world objects are finite, which means that at some point you have to say "Enough" and crop your ideal structure, and in doing so, you leave dangling bonds which attract other atoms. Fullerene lacks those, and hence is "more pure".
There is an altogether different dimension to the problem. Our thought experiment implied that we are able to produce a huge crystal without defects except maybe some on the surface. This is not true. Real-world compounds always contain impurities, and once you have a wrong atom built into the crystal lattice of graphite or diamond, it is stuck there forever. You'll never remove it, short of destroying the entire crystal. Fullerenes, on the other hand, are molecular compounds. They can be dissolved. They can be put through chromatography, sublimation, and other purification techniques. We can always remove any impurity (not that we can remove all of them, because nothing is ideal).
Either way, fullerenes win.
The following is multiple choice question (with options) to answer.
Diamond, graphite and fullerene are examples of what form of carbon? | [
"crystalline",
"faceted",
"zirconia",
"magnesium"
] | A | Pure carbon can form different types of crystals. Crystalline forms of carbon include diamond, graphite, and fullerenes. |
SciQ | SciQ-5703 | thermodynamics, absorption
When you want to boil water efficiently, you do two things: cover the pot (limit loss due to evaporation) and put the heat inside if you can: for example the submerged heater element in electric kettles. Other forms of boilers also put the heat in the middle of the water (think water heaters for homes) so most of the hot gas gets to give off its energy to the water.
But if you have a flame, the best you can hope to to is transfer all it's internal energy to the water - so when the water is hotter a flame is always less efficient.
Very efficient systems use counter flow - the hot air moves left to right, and the water to be heated right to left: in that way the colder gas meets even colder water so when the gas finally is exhausted it has no heat left. Same principle is used in efficient gas furnace for homes, etc.
The following is multiple choice question (with options) to answer.
A hot-water heating system uses what type of energy to heat water? | [
"atmospheric energy",
"negative energy",
"potential energy",
"thermal energy"
] | D | A hot-water heating system uses thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a diagram of this type of heating system in Figure below . Typically, the water is heated in a boiler that burns natural gas or heating oil. There is usually a radiator in each room that gets warm when the hot water flows through it. The radiator transfers thermal energy to the air around it by conduction and radiation. The warm air then circulates throughout the room in convection currents. The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats. |
SciQ | SciQ-5704 | nuclear-physics, radioactivity
Title: Carbon-14 formation in atmosphere Wikipedia says Carbon-14 is formed in the atmosphere by the reaction:
1n + 14N → 14C + 1p
This looks like neutron capture. However, I would expect neutron capture to result in 15N. However, "proton emission" seems to be a rare phenomenon:
15N → 14C + 1p
So, my first question is, does the reaction happen in two stages, or is the proton ejected "immediately"?
Secondly, is this overall type of reaction 1n + → + 1p common? Are there any other examples of such reactions, other than with 14N? It is a prompt (immediate) reaction, and is more usually written something like N14(n,p)C14 to indicate that. It is far from the only such reaction.
EDIT - To quantify my statement that there are many similar reactions, I went to the Evaluated Nuclear Data Files site hosted at Brookhaven (ENDF), entered 'n,p' for the reaction, 'sig' for the desired quantity (sig = sigma = cross-section in barns for the reaction). This returned 308 separate data sets, from He3(n,p)H3 to Bi209(n,p)Pb209. So, indeed, the existence of the N14(n,p)C14 reaction is no great surprise.
The following is multiple choice question (with options) to answer.
What captures carbon dioxide as it is emitted by a power plant before it enters the atmosphere? | [
"nitrogen sequestration",
"oxide sequestration",
"carbon sequestration",
"chemical sequestration"
] | C | Carbon sequestration captures carbon dioxide as it is emitted by a power plant before it enters the atmosphere. The carbon dioxide is then stored in another form. Carbon is sequestered naturally by forests. Trees take in carbon dioxide for photosynthesis. Artificial methods of sequestering carbon underground are being researched. This is just one of the geoengineering methods that are being researched for reducing carbon dioxide. |
SciQ | SciQ-5705 | pumps, safety, vacuum, vacuum-pumps
Title: Replace mercury with silicone oil in diffusion pump We have obtained an old mercury-vapor diffusion pump for high vacuum. However, we do not want to operate it with mercury in our lab due to health concerns (which is presumably the reason it was scrapped by the original owner).
Instead, we plan to fill it with a silicone oil of the DC-704 type or similar. The pump has thermal regulation and a large baffle to stop oil vapor counter-propagation.
Has anybody tried replacing mercury with oil? What are possible problems with this approach? I did some internet searching and did not find anyone that had done a direct swap out. Granted, probably the majority of these replacements occurred before the existence of the internet ;-). As I am sure you are already aware (but to be thorough), modern diffusion pump designs do use synthetic working fluids.
It will probably take some fine tuning of the temperatures of the heater and cooler, but I don't see any reason why it wouldn't work. If you have means of measuring the vacuum level, you could run through some different temperatures to empirically find its new ideal operating conditions.
Worst case, the pumping efficiency will be less because the nozzle diameter was designed for higher density particles. I am not a vacuum physicist however, so who knows, it may work even better than before ;-)
Another possible issue is that it may have more backstreaming of the oil into the vacuum chamber resulting in unacceptable levels of oil contamination. Maybe the baffle you mentioned will take care of this; hard to say without some experimentation.
Just as long as no oxygen reaches the oil during operation, it wont fail catastrophically, so give it a try and let us know how it went!
Reference:
Good overview of diffusion pump working fluids
Some good history or mercury as a diffusion pump working fluid
The following is multiple choice question (with options) to answer.
What type of oil is being explored to replace petroleum products in lubricants? | [
"whale oil",
"diesel",
"vegetable",
"essential oil"
] | C | Vegetable oils are being explored for a variety of uses in which they could replace petroleum products. One such application is in the field of lubricants. Every moving part in machinery (such as engine pistons) needs lubrication to decrease friction and prolong the life of the equipment. Petroleum products serve this purpose now, but are not good for the environment. New techniques for making specialized esters from vegetable oil are being explored that will make the compounds more stable and more useful as lubricants. |
SciQ | SciQ-5706 | newtonian-mechanics, work, string
Title: Why pulley systems give mechanical advantage? In a system with 2 pulleys, to lift a x kg object y meters I would need half the force that the object exerts due to gravity but pull the rope double the distance, why does this happen this way? This can be viewed as a requirement of the work-energy theorem and the conservation of energy. Assuming you alter the system slowly enough that parts don't gain a significant kinetic energy, the work you do by pulling the rope must be equal to the work done against gravity or any other forces that may be applicable. If you pull the rope with a force $F$ by a distance $a$, and the object of interest with weight $W$ is lifted a distance of $b$, we have
$$ F a \ge W b, $$
where equality holds in idealized systems where work is only being done by pushing the weight $W$ against gravity. For a pulley system, this means having no friction, massless strings and massless pulleys. If $ a = 2b $ in such an idealized system, then $ F = W/2 $.
The following is multiple choice question (with options) to answer.
What advantage equals the distance of effort divided by the distance the object moves and is also equal to the output force divided by the input force? | [
"potential",
"constant",
"mechanical",
"atomic"
] | C | Mechanical advantage equals the distance of effort divided by the distance the object moves. It is also equal to the output force divided by the input force. |
SciQ | SciQ-5707 | zoology
Title: What is right below skin? I was skinning a gopher so my cat can eat it (it was a pest and we didn't want to waste it). I thought its organs would fall out and make a mess, but that didn't happen. There was this sticky, transparent substance that surrounded its insides. What is this casing called? My dad said it was mucus but that isn't specific enough since there is mucus inside the stomach so I don't think they are the same.
I think this casing is found in all multicellular animals but I couldn't be sure. Based on your reference to organs falling out and the overall description, I presume you're thinking of the abdominal cavity primarily, so there you'd be looking at the peritoneum or possibly the serous membranes of other organs (e.g., pleura, pericardium). These are membranous (in the general sense, not as a cell membrane) connective tissues covering the organs found in the abdomen and chest.
Other things you'll find underneath skin would include layers of fat, other connective tissues, muscle.
Here's a labeled image of a mouse dissection from Friedrich, L., Schuster, M., de Celis, M. F. R., Berger, I., Bornstein, S. R., & Steenblock, C. (2021). Isolation and in vitro cultivation of adrenal cells from mice. STAR protocols, 2(4), 100999.:
You might also look for dissections of fetal pigs or cats, which are commonly used in laboratory demonstrations for students (more often cats longer ago, more often fetal pigs these days).
The following is multiple choice question (with options) to answer.
What is the outer layer of skin, consisting almost entirely of epithelial cells? | [
"hypodermis",
"dermis",
"connective tissue",
"epidermis"
] | D | The epidermis is the outer layer of skin, consisting of epithelial cells and little else (see Figure below ). For example, there are no nerve endings or blood vessels in the epidermis. The innermost cells of the epidermis are continuously dividing through mitosis to form new cells. The newly formed cells move up through the epidermis toward the skin surface, while producing a tough, fibrous protein called keratin. The cells become filled with keratin and die by the time they reach the surface, where they form a protective, waterproof layer called the stratum corneum. The dead cells are gradually shed from the surface of the skin and replaced by other cells. |
SciQ | SciQ-5708 | molecular-biology, cell-biology
This rate decreases dramatically as radius of the cell increases. For example a cell with double the diameter (2 micrometers) has a volume eight times larger, so collisions between any two molecules take 8 times ($2^3$) as long to occur (in other words, it takes molecules 8 times longer to "find" each other). This is one reason why there is a kind of upper limit on the size of an individual cell. Bigger organisms are bigger because they have more cells, not because they have larger cells.
The field of biology concerned with how likely it is for a reaction to occur is called enzyme kinetics. A related field, which deals with how frequently molecules collide is called statistical mechanics.
The following is multiple choice question (with options) to answer.
What is the accumulated total of all the biochemical reactions occurring in a cell or organism called? | [
"circulation",
"expansion",
"metabolism",
"respiration"
] | C | All living things—even the simplest life forms—have a complex chemistry. Living things consist of large, complex molecules, and they also undergo many complicated chemical changes to stay alive. Thousands (or more) of these chemical reactions occur in each cell at any given moment. Metabolism is the accumulated total of all the biochemical reactions occurring in a cell or organism. Complex chemistry is needed to carry out all the functions of life. |
SciQ | SciQ-5709 | water, ions
Title: Nitrates in water In my previous question, someones answer among other things, said that boiling the water increases the concentration of nitrates and nitrites. I searched on google and it's true, but how does that happen ? What is the reaction that leads to an increasing level of nitrates?
Im very courious because nitrates are too dangerous to be high in concentration, i would appreciate your help.
boiling the water increases the concentration of nitrates and nitrites.
Yes.
how does that happen? What is the reaction that leads to an increasing level of nitrates?
It happens because you boil away the water, and the nitrates and nitrites stay in what's left of the water, thus raising the concentration of those species in the now reduced amount of water. There is no "reaction," per se, just you are concentrating dissolved species by removing the water.
The following is multiple choice question (with options) to answer.
When fertilizer ends up in bodies of water, the added nutrients cause excessive growth referred to as what, which can render the water unfit for human consumption or recreation? | [
"algal bloom",
"agricultural bloom",
"chemical bloom",
"caustic bloom"
] | A | When fertilizer ends up in bodies of water, the added nutrients cause excessive growth of algae. This is called an algal bloom. You can see one in Figure below . The algae out-compete other water organisms. They may make the water unfit for human consumption or recreation. |
SciQ | SciQ-5710 | cell-biology, organelle
Title: Univocal identifying of a plant cell We yesterday got our biology-exams back and there's one exercise where I don't agree with my teacher. However, since he is the expert and not me, I need the support of external sources, i.e. experts in order to justify my statement.
Now in the exercise, we first had to identify the parts of a cell (which was shown in form of an image) and then in part b) reason whether it was an animal or plant cell.
I had identified a chloroplast and a vacuole and stated that the only cell with this organelles was the plant cell. My teacher answered that I had missed the fact, that the cell had also a cell wall (which is indeed a difference between plant and animal cells).
My question is
Is the fact that the cell had a cell wall necessary in my argumentation, i.e. are there other cells having chloroplasts and a vacuole without being a plant cell?
Could you provide a source which supports, or doesn't support my statement so that I can show it to my teacher?
Thanks in advance Your teacher is right, chloroplasts and vacuoles are not sufficient to define a plant cell.
Amoeba have both chloroplasts (McFadden et al, PNAS, 1994) and vacuoles (Day, J. Morphology, 1927) but they are not plants - and they do not have a cell wall.
Sea slugs eat algae and can "steal" their plastids and keep them working for weeks/months, effectively becoming photosynthetic animals for a while. This is called kleptoplastidy (Pillet, Mob. Genet. Elements, 2013).
The following is multiple choice question (with options) to answer.
What part of the cell controls what enters and leaves? | [
"membrane",
"nucleus",
"protein",
"organism"
] | A | Like all other living cells, prokaryotes have a cell membrane. It controls what enters and leaves the cell. It's also the site of many metabolic reactions. For example, cellular respiration takes place in the cell membrane. |
SciQ | SciQ-5711 | cardiology, embryology, pain, central-nervous-system
Title: At what stage is the nervous system developed enough to interpret neuronal signals as 'pain'? According to this article in Live Science, one of the reasons the fetus can't feel pain until 19 weeks is because the nervous system isn't fully developed.
But according to this article, the heart starts beating at day 16.
And according to this article, the nervous system controls the rate beating of the heart.
Then my question is, **how can it be assured that the nervous system isn't developed until 19 weeks, when the nervous system controls the heart beating rate since day 16? First, there is some confusion on your part about heart cells and pain perception. Heart cells generate an action potential intrinsically; they do not need the central nervous system to beat (your second article explains this; read the part about the importance of calcium.) So yes, long before a fetus can feel pain, the heart is beating, because there must be circulation of nutrients throughout the embryo.
Secondly, the vagus nerve and sympathetic nerves can affect heart rate (the former by slowing it down when firing). These nerves start to reach their endpoints late in week 4 of development. So 19 days is not correct.
Cardiac sympathetic system
Although the primitive human heart starts to beat at 21 to 22 d, heart development continues to day 50, and it is near the end of this period, during the fifth week, that thoracic neural crest cells migrate from the neural tube through the somites and form aggregations (ganglia) near the dorsal aorta. [emphasis mine]
To experience pain, however, requires maturation of certain parts of the brain, most importantly, part of the thalamus and the cerebral cortex:
Current theories of pain consider an intact cortical system to be both necessary and sufficient for pain experience. In support are functional imaging studies showing that activation within a network of cortical regions correlate with reported pain experience. Furthermore, cortical activation can generate the experience of pain even in the absence of actual noxious stimulation. These observations suggest thalamic projections into the cortical plate are the minimal necessary anatomy for pain experience. These projections are complete at 23 weeks' gestation. [emphasis mine]
The following is multiple choice question (with options) to answer.
Where does the development of a fetus take place? | [
"The kidney",
"the female reproductive system",
"The vagina",
"The bladder"
] | B | Earth has a tremendous amount of water. So why is water sometimes a scarce resource?. |
SciQ | SciQ-5712 | entomology
Title: The death of Earthworm In rainy season when children sprinkle salt on earthworm ,it dies.But salt is not dangerous.We use it daily.Then why earthworm dies? It's because on the earth worm skin's special mucous. Acording to this article: Why do earthworms die when salt is sprinkled on them? the mucous makes moist to the worm's skin, which is vital for their survival. Moreover, the worms don't have a respiratory organs, like lungs, gills, etc. This means that Carbon Dioxide and other characterized as "dump" gases can not be exchanged with the Oxygen. But worms breath through their skin, with the help of these special mucous that are developed on its skin. If their skin dries out the result will be death, because the gas exchange will not last without the mucous help. Similarly, the circulatory system won't function, because its main role is to trade gasses with the cells via red blood cells.
What about salinity?
Salinity is a very important factor for the earthworms health, because high salinity destroy their valunable and sensitive skin and kills the mucous that in fact help the worm to "breathe". Low salt concentrations are very beneficial for the worm, because not only their mortarity level is increaced, there are size changes to the worm's body (noticeable bigger size).
Here are and some photos of a worm that its enviroment has low salinity and high salinity:
High salinity:
Low-to-medium salinity
Source: Why do earthworms die when salt is sprinkled on them?.
The following is multiple choice question (with options) to answer.
What is the critical factor for the survival of segmented worms? | [
"sunlight and water",
"water and humidity",
"humidity and sunlight",
"sunlight and warmth"
] | B | Phylum Annelida Phylum Annelida includes segmented worms. These animals are found in marine, terrestrial, and freshwater habitats, but a presence of water or humidity is a critical factor for their survival, especially in terrestrial habitats. The name of the phylum is derived from the Latin word annellus, which means a small ring. Animals in this phylum show parasitic and commensal symbioses with other species in their habitat. Approximately 16,500 species have been described in phylum Annelida. The phylum includes earthworms, polychaete worms, and leeches. Annelids show protostomic development in embryonic stages and are often called “segmented worms” due to their key characteristic of metamerism, or true segmentation. Morphology Annelids display bilateral symmetry and are worm-like in overall morphology. Annelids have a segmented body plan wherein the internal and external morphological features are repeated in each body segment. Metamerism allows animals to become bigger by adding “compartments” while making their movement more efficient. This metamerism is thought to arise from identical teloblast cells in the embryonic stage, which give rise to identical mesodermal structures. The overall body can be divided into head, body, and pygidium (or tail). The clitellum is a reproductive structure that generates mucus that aids in sperm transfer and gives rise to a cocoon within which fertilization occurs; it appears as a fused band in the anterior third of the animal (Figure 28.28). |
SciQ | SciQ-5713 | human-biology, sex, reflexes
Title: In males, why it is difficult to control orgasm? Why it is difficult to control orgasm in male humans? How are orgasms controlled and what is different between males and females?
We can control urine for few minutes, but we can't control orgasm for more than a few seconds, but both are discharging though same organ (penis). The sphincter of the bladder is under voluntary control (that's what toilet training is about). That's why you can hold your urine even when the stretched bladder is sending messages to your brain that you really have to go. That's not to say there aren't involuntary effects on the bladder during orgasm.
Orgasm is a separate entity. It is a complex neurological response with four stages. Orgasm is controlled by the autonomic nervous system and is a response that can be controlled as easily as pupillary dilation/contraction in response to light (that is, not at all). However, there is some measure of voluntary control over the plateau phase of orgasm.
In a bit more detail,
expulsion is a spinal cord reflex that occurs as the ejaculatory process reaches a ‘point of no return’. During expulsion, the smooth muscle fibers of the bladder neck contract to prevent the backward flow of semen into the bladder; the pelvic floor muscles, along with the bulbospongiosus and ischiocavernosus muscles, have primary roles in this function, and display stereotypical rhythmic contractions to propel semen distally throughout the bulbar and penile urethra. During this process, the external urinary sphincter is normally relaxed. The bladder neck and proximal portion of the urethra, which both contain abundant smooth muscle fibers, receive dual sympathetic and parasympathetic innervation. Besides the cholinergic and noradrenergic components, the principal mediators found in these nerve terminals are NPY, VIP, and NO. The external urethral sphincter and pelvic floor striated muscles are solely regulated by the somatic nervous system, but there is no definitive evidence that a voluntary control of the expulsion phase exists in humans.[1]
Human sexual response cycle
Physiology of male sexual function
[1] Ejaculatory Disorders: Pathophysiology and Management: Physiology of Ejaculation
The following is multiple choice question (with options) to answer.
During sexual arousal what does the clitoris, vagina, and labia minora all engorge with? | [
"bacteria",
"urine",
"blood",
"fluid"
] | C | |
SciQ | SciQ-5714 | units, notation, unit-conversion
These are just a few examples where electrical engineering is chock full of "A rate of something happening in a time period of one second" is basically defined as that something multiplied by time, as opposed to divided by time as in the case of velocity.
As far as I can tell the phrasing is effectively equivalent, but mathematically, the difference is profound, and very, very confusing. Can someone explain the difference between the two? Velocity, $m/s$, is a measure of the rate at which something moves. I guess you could define displacement as velocity-seconds, a measure of how far something moves at a given rate over a second. In your examples, it is not rates being defined, but the effect of going at a certain rate over a period of time. Amps are Coulombs per second, so you can define Coulombs as the amount of charge moved over a second at a rate of one amp. If you multiply the rate at which something happens by how long that something happens, you will get how much of that something happened.
The following is multiple choice question (with options) to answer.
What is another term for joules per second? | [
"watts",
"parsons",
"jacobs",
"jiffies"
] | A | Electric energy is measured in joules per second, or watts. |
SciQ | SciQ-5715 | inorganic-chemistry, separation-techniques
Title: How to separate manganese(IV) oxide and chromium(III) hydroxide? I am trying to find a reagent that keeps either $\ce{MnO2}$ or $\ce{Cr(OH)3}$ solid and make other soluble so I can centrifuge or use filtration. I thought of $\ce{NaOH},$ but I could not find any information about how $\ce{MnO2}$ reacts with $\ce{NaOH}.$ Add at least twice its volume of $\pu{2 M}$ $\ce{NaOH}$ and stir. The $\ce{Cr(OH)3}$ precipitate will be dissolved if the solution is cold. It will make a solution of sodium chromite $\ce{Na[Cr(OH)4]},$ and $\ce{MnO2}$ will not react.
$$\ce{Cr(OH)3 + OH- <=> [Cr(OH)4]^-}$$
After filtration, $\ce{MnO2}$ is not easy to filtrate on paper. It can be centrifuged. The solution of chromite is then heated and diluted with a volume of water equal to four times the volume of the solution. The last equation is an equilibrium and will be reversed at high temperature, so that $\ce{Cr(OH)3}$ will precipitate again, and can be filtrated.
The following is multiple choice question (with options) to answer.
What is extracted from rock by heap leaching, flotation, or smelting? | [
"ore",
"copper",
"methane",
"fuel"
] | A | Ore is extracted from rock by heap leaching, flotation, or smelting. |
SciQ | SciQ-5716 | measurements, ocean, remote-sensing
Title: What methods exist for remote profiling of oceanic columns? Remote sounding of the atmosphere is a well-established method used extensively used extensively for operational weather forecasting and scientific research. Active or passive instruments carried on satellites (or aircraft) can measure profiles of temperature, pressure, trace gases, and particulate matter.
Is anything similar possible for a ship sailing on the ocean? What methods exist, in theory and in practice, to remotely sense a profile of temperature, density, salinity, etc., from the ocean floor to the ship? Or can such profiles only be obtained in-situ? There are a number of programs and instruments that sample the ocean autonomously. Examples of such programs are:
The ARGO program (http://www.argo.net/): Currently around 3000 floats are freely drifting in the ocean measuring temperature, salinity and in some cases velocity of the upper 1000-2000 meters of the ocean. The floats drift for around 10 days most commonly at 1000 or 2000 meters and then conduct a vertical profile to the surface where they transfer the data to a satellite.
RAFOS floats (http://www.whoi.edu/instruments/viewInstrument.do?id=1061): They map the ocean currents using the SOFAR channel (a horizontal layer in the ocean where sound speed is minimum).
Gliders (http://www.ioos.noaa.gov/glider/): A type of autonomous underwater vehicle (AUV) that uses buoyancy to control its vertical position in the ocean. They sample along predetermined routes and can be equipped with instruments to measure temperature, salinity, turbidity, velocity...
Other AUVs: Most other AUVs use propellers powered by rechargeable batteries and are able to carry a lot more instruments, but are limited to shorter missions.
The following is multiple choice question (with options) to answer.
What tool is useful for studying the ocean floor because the environment is remote and underwater? | [
"scale",
"microscope",
"sonar",
"telescope"
] | C | Studying the ocean floor is difficult because the environment is so hostile. The seafloor can be studied indirectly with tools such as sonar. It can be studied directly using special vehicles. Some vehicles carry scientists and their devices to the ocean floor. Other vehicles are operated remotely. |
SciQ | SciQ-5717 | human-biology, physiology, psychology
If your thoughts (Activated neurons) end with unsolved vital problem, it activates parts of your brain that is related to anxiety and stress and these neurons activate hypothalamus.
Hypothalamus turns sympathetic nerves on.
The sympathetic nerves release adrenaline (epinephrine).
And adrenaline cause more urine flow.
This example shows two more kinds of polyuria
If you are interested in how increasing level of adrenaline results in more urine flow read this and this and this.
The following is multiple choice question (with options) to answer.
What is the functional unit of the kidney which actively filters blood and generates urine? | [
"epithelial",
"sechron",
"nephron",
"mecrophron"
] | C | 41.2 The Kidneys and Osmoregulatory Organs The kidneys are the main osmoregulatory organs in mammalian systems; they function to filter blood and maintain the osmolarity of body fluids at 300 mOsm. They are surrounded by three layers and are made up internally of three distinct regions—the cortex, medulla, and pelvis. The blood vessels that transport blood into and out of the kidneys arise from and merge with the aorta and inferior vena cava, respectively. The renal arteries branch out from the aorta and enter the kidney where they further divide into segmental, interlobar, arcuate, and cortical radiate arteries. The nephron is the functional unit of the kidney, which actively filters blood and generates urine. The nephron is made up of the renal corpuscle and renal tubule. Cortical nephrons are found in the renal cortex, while juxtamedullary nephrons are found in the renal cortex close to the renal medulla. The nephron filters and exchanges water and solutes with two sets of blood vessels and the tissue fluid in the kidneys. There are three steps in the formation of urine: glomerular filtration, which occurs in the glomerulus; tubular reabsorption, which occurs in the renal tubules; and tubular secretion, which also occurs in the renal tubules. |
SciQ | SciQ-5718 | genetics, evolution, human-evolution, retrovirus
Title: Endogenous retroviral insertions as evidence for evolutionary relationships among primates A synopsis of a 2005 paper in PlosBiology by Yohn et al. states that:
Searching the genomes of a subset of apes and monkeys revealed that
the retrovirus had integrated into the germline of African great apes
and Old World monkeys—but did not infect humans and Asian apes
(orangutan, siamang, and gibbon). This undermines the notion that an
ancient infection invaded an ancestral primate lineage, since great
apes (including humans) share a common ancestor with Old World
monkeys.
Also, Micheal Lynch writes :
"Remarkably, we have found many cases of parallel intron gains at
essentially the same sites in independent genotypes," Lynch said.
"This strongly argues against the common assumption that when two
species share introns at the same site, it is always due to
inheritance from a common ancestor."
Since shared ERVs in humans and chimps is touted as one of the proofs of humans and chimps sharing ancestry (like by Ken Miller here), does the above paper (and quote) undermine this line of reasoning?
Is there any good (recent) source which discusses proof of common descent using ERVs? The Yohn et. al. (2005) paper (from Evan Eichler's lab) is describing a single type of endogenous retroviral element (loosely think of it as a 'species'), called PTERV1. They show that there were multiple independent infection events that resulted in permanent integrations in the ancestors of modern species (~3-4 MYA in the ancestors of gorillas and chimps, ~1.5 MYA in the ancestors of baboons and macaques). This in no way contradicts the notion of common ancestors among the apes/monkeys; indeed, they state this as a given in their analysis (emphasis mine):
A total of 275 of the insertion sites mapped unambiguously to
non-orthologous locations (Table 2), indicating that the vast majority
of elements were lineage-specific (i.e., they emerged after the
divergence of gorilla/chimpanzee and macaque/baboon from their common
ancestor).
The following is multiple choice question (with options) to answer.
Name two candidates for the original sources of viral genomes. | [
"macrophages and transposons",
"plasmids and transposons",
"ediacara and transposons",
"chloroplasts and transposons"
] | B | |
SciQ | SciQ-5719 | acid-base, ionic-compounds, erratum
Title: Are all ionic compounds salts? According to Wikipedia:
A salt is an ionic compound that can be formed by the neutralization
reaction of an acid and a base.
Are all ionic compounds salts? Are all salts ionic compounds? Interestingly, IUPAC states that a "salt" is "a chemical compound consisting of an assembly of cations and anions". Under this definition, all ionic compounds are salts, and all salts are ionic compounds.
Therefore, something like sodium hydroxide ($\ce{Na+OH-}$, definitely an ionic compound) could actually be correctly called a salt. This clashes with the commonly taught high-school level definition of a salt ("the product of an acid-base reaction"), unless you consider very general definitions of acids and bases such as the Usanovich definition, whereby sodium metal $\ce{Na^0}$ is an electron donor (and therefore a base) and water is an electron acceptor (and therefore an acid).
That said, the high-school definition is too simplistic. It is common for compounds to be an acid, a base and a salt all at the same time; consider for example sodium bicarbonate ($\ce{Na+HCO3-}$). It is made of cations and anions, and therefore is definitely a salt. Furthermore, it can act as both a Brønsted–Lowry acid ($\ce{NaHCO3 + OH- -> H2O + Na+ + CO3^2-}$) and as a Brønsted–Lowry base ($\ce{NaHCO3 + H+ -> Na+ + H2CO3}$). Another amusing example is hydrazinium sulfate, a salt, acid and base, where both the cation and anion are also both acids and bases!
The following is multiple choice question (with options) to answer.
What do you call a substance that is not an acid or a base? | [
"oxidic",
"neutral",
"equivalent",
"toxic"
] | B | What is one of the most important characteristics of a referee? A referee must be neutral. He can’t favor one team over the other. In chemistry, being neutral means not being an acid or a base. Pure water is an example of a neutral substance. In some chemical reactions, an acid and a base combine to form neutral products, including water. You’ll see how this happens when you read this article. |
SciQ | SciQ-5720 | organic-chemistry, bond, covalent-compounds
Title: The difference between peptide bonds and the bonds between polypeptides? I was doing some tests for the multiple-choice final we've got ahead. And it was on me to count the peptide bonds in an Insulin hormone with 51 aminoacids arranged in two polypeptides with 30 and 21 aminoacids. (these are not true in reality) the number of bonds were 49, not 50, and that means the bond between two polypeptides doesn't count as a peptide bond. Additionally, I know that polypeptide bonds make the proteins' molecular structure, as it is now. (just look at that shape.) PEPTIDE COVALENT BONDS CAN NEVER cause that kind of 3d orientation in space. So there must be some fundamental difference between those bonds. What is it?
My research couldn't find any results as simple things have jammed the internet. Aside from covalent bonds (amide and disulfide), the sturcture of a protein is determined by hydrogen bonds, salt bridges, and less specific interactions such as hydrophobic and hydrophilic effects. Hydrophobic portions of the protein chain tend toward the interior of the folded protein and hydrophilic regions to the exterior, in aqueous solution.
The following is multiple choice question (with options) to answer.
An amide bond joining two amino acid units is called a what? | [
"peptide bond",
"carboxyl bond",
"ammonia bond",
"precipitate bond"
] | A | An amide bond joining two amino acid units is called a peptide bond. Note that the product molecule still has a reactive amino group on the left and a reactive carboxyl. |
SciQ | SciQ-5721 | galaxy, gravity, star-systems
Title: Why are stars still distant from one another? Why are stars so far from each other? Shouldn't gravity pull them closer over time? And if the effects of gravity are negligible is there an explanation why stars have to be so distant from one another?
The closest star is Alpha Centauri (I think) and it is 4.4 light years away. The initial star formation regions were regions that have a high enough mass density to form a star. The density of the early universe was not constant at different locations. Some regions had high enough density to form a star, and some didn't.
When a star forms it draws in matter from a large distance away. This forms an accretion disk and leaves a temporary relatively empty space around the star at a large distance away. There is no way a star can form in this low mass region. Once you get further away from this region the matter density may return to a level where a star can form. But this region is far from a star.
Yes, gravity from a particular star is pulling at other stars but there are many stars pulling on the particular star of interest. So the net force on the star may be very small.
The following is multiple choice question (with options) to answer.
What is the name for spherical groups of old stars held tightly together by gravity? | [
"elliptical clusters",
"globular clusters",
"dark matter",
"nebula"
] | B | Globular clusters are spherical groups of old stars held tightly together by gravity. |
SciQ | SciQ-5722 | species-identification, mycology
Title: What is these mushrooms in my indoor pot? I am living in Japan and in summer, it's very hot and humid even inside my room.
Today, I've found two mushrooms in the pot of a plant.
What is this species? It's very surprising than within one day they grew like this. They do look a lot like a common mushroom called "shaggy mane" mushroom (Coprinus comatus). This may not be a correct identification though, so do not eat them. They are widespread around the world, but usually grow outside.
Yes it is amazing how rapidly the fruiting body of many fungi can grow. I am providing an interesting Wikipedia link with more information. You can also search to find other images using Google images online.
https://en.wikipedia.org/wiki/Coprinus_comatus
The following is multiple choice question (with options) to answer.
What type of state do most fungi spend their lives in? | [
"diploid",
"triploid",
"meiosis",
"haploid"
] | D | Most fungi are multicellular, but some exist as single cells. Fungi spend most of their life cycle in the haploid state. They form diploid cells only during sexual reproduction. Like the cells of protists and plants, the cells of fungi have cell walls. But fungi are unique in having cell walls made of chitin instead of cellulose. Chitin is a tough carbohydrate that also makes up the exoskeleton (outer skeleton) of insects and related organisms. |
SciQ | SciQ-5723 | electroplating
I'm not a chemist, so I won't understand anything clever or those molecular spider diagrams... I haven't found much in literature about this process, we can try to find the solution reasoning, but some experiments should helpful.
What is being deposited?
If he connects the positive terminal to the object it means that the object is the anode. So something is reduced on the anode. Copper(II) oxide quite common oxide used for balckening. How can we obtain this by reduction? I would say that it could be the reduction of copper acetate to copper(II) oxide.
So where the copper acetate come from?
In fact, to the cathode there is also a copper wire wrapped around the steel, it could be that the copper ions are produced from that wire on the cathode:
$$\ce{Cu + 2H^{+} -> Cu++ + H2 }$$
Vinegard contains acetic acid and reacts with copper:
$$\ce{2CH3COO- +Cu++ -> Cu(CH3COO- )2}$$
Or directly from the acid attack of acetic acid:
$$\ce{2CH3COO- + 2H+ + Cu ->Cu(CH3COO- )2 +H2}$$
What could happen is the following (decribed here):
$$\ce{Cu(CH3COO- )2 +H2 -> (CH3COO- )2CuH2}$$
$$\ce{(CH3COO- )2CuH2 + Cu(CH3COO- )2 +H2O -> Cu2O +4CH3COOH}$$
Is the deposit related directly to the cathode material?
If this is true there is no relationship with the steel used at the cathode.
What happens if I change the cathode to say normal steel /copper wire?
The cathode may oxidize. If the copper wrapped around the steel has a part on the process, the process could not work if you don't use copper.
Do we not understand the role vinegar and some salt plays?
Salt is probably used to increase the conductivity of the solution.
The following is multiple choice question (with options) to answer.
What is the white solid that forms on corroded battery terminals? | [
"ammonia sulfate",
"copper sulfate",
"lead sulfate",
"straight sulfate"
] | C | Pb(s) + 2H+(aq) + SO42−(aq) → PbSO4(s) + H2(g) Lead(II) sulfate is the white solid that forms on corroded battery terminals. Exercise Using the activity series, predict what happens in each situation. If a reaction occurs, write the net ionic equation. |
SciQ | SciQ-5724 | human-biology, cell-biology
Title: Body's decomposition Does a human body decompose in a completely sterile environment ? If yes, what decomposes it ? And how fast ? What happens in vacuum ? Can it remain exactly the same ?
Thanks
Does a human body decompose in a completely sterile environment ?
No it wont. Unstable molecules like ATP will quickly degrade spontaneously. The stable ones like many proteins and lipids wont degrade spontaneously. Enzymes are essential to degrade them and are to be supplied extraneously.
What happens in vacuum ?
Body will dry up :P
The following is multiple choice question (with options) to answer.
What does the decomposition of dead organisms and organic waste release into the atmosphere, soil, or ocean? | [
"hydrogen",
"carbon",
"nitrogen",
"oxygen"
] | B | Decomposition of dead organisms and organic wastes releases carbon back to the atmosphere, soil, or ocean. |
SciQ | SciQ-5725 | energy, nuclear-physics, mass-energy, fusion
2.2 scenario: The nucleus is that of the kind initial nucleus => lighter element + lighter element, and lighter element + lighter element => initial nucleus. Then it is very possible, and it even happens in nature itself. Remember the cycle Be-8 => He-4 + He-4 => Be-8 =>...? There you have it, smash two Helium-4's together and you have Be-8, which will undergo fission to generate two He-4, which could be fused again to finally create a cycle of fusion-fission; actually, this already happens in Helium-fusing stars, until the Be-8 successfully fuses with another He-4 to form Carbon. Other examples are possible, such as Lithium-4 => Helium-3 + proton => Lithium-4.
The following is multiple choice question (with options) to answer.
In which process do two light nuclei combine to produce a heavier nucleus and great energy? | [
"general fusion",
"light fusion",
"nuclear fusion",
"certain fusion"
] | C | Summary Nuclear reactions are accompanied by large changes in energy, which result in detectable changes in mass. The change in mass is related to the change in energy according to Einstein’s equation: ΔE = (Δm)c2. Large changes in energy are usually reported in kiloelectronvolts or megaelectronvolts (thousands or millions of electronvolts). With the exception of 1H, the experimentally determined mass of an atom is always less than the sum of the masses of the component particles (protons, neutrons, and electrons) by an amount called the mass defect of the nucleus. The energy corresponding to the mass defect is the nuclear binding energy, the amount of energy released when a nucleus forms from its component particles. In nuclear fission, nuclei split into lighter nuclei with an accompanying release of multiple neutrons and large amounts of energy. Thecritical mass is the minimum mass required to support a self-sustainingnuclear chain reaction. Nuclear fusion is a process in which two light nuclei combine to produce a heavier nucleus plus a great deal of energy. |
SciQ | SciQ-5726 | bacteriology, food, hematology, toxicology, parasitology
Title: Blood consumption Is consumption of blood more "dangerous" compared to meat?
There was a news-article about unnatural chemicals found in the blood of mothers. This reminded me about a question I have pondered upon from time to time. Now, I am not a vampire, but curious as to the nature of blood vs meat in animals. More specifically unhealthy components.
There are various examples of viruses being in danger of spreading by consumption of raw blood like ebola, H5N1 etc. (But then also meat etc.)
Perhaps easier if I throw out some questions to show what I am asking:
Are there more of such in blood then meat?
Are there other things that can be worse in blood even after preparing? Like cooking, conservation etc.
Are parasites etc. more frequently found in blood?
Are there organisms that are highly resilient to heat treatment found in blood?
Are there more heavy metals in blood then meat? (Which I assume cooking does not give much of a difference.)
Other toxins?
Some references:
http://www.eufic.org/article/en/food-safety-quality/animal-health/expid/review-animal-diseases/
http://www.fao.org/avianflu/en/qanda.html
Is consumption of blood more "dangerous" compared to meat?
Actually yes, a simple high dose of blood is enough to kill. The cause is, though it is most important thing to live when flowing the vessel, it's highly toxic when consumed. There are high chances of getting haemochromatosis or Iron overload.
Source and More on this:
http://www.livescience.com/15899-drinking-blood-safe.html
Composition of Blood
(source: snmjournals.org)
The following is multiple choice question (with options) to answer.
What results from the consumption of pathogenic bacteria, viruses, or parasites that contaminate food? | [
"parabens diseases",
"hidebound diseases",
"foodborne diseases",
"airborne diseases"
] | C | 22.4 Bacterial Diseases in Humans Devastating diseases and plagues have been among us since early times. There are records about microbial diseases as far back as 3000 B. Infectious diseases remain among the leading causes of death worldwide. Emerging diseases are those rapidly increasing in incidence or geographic range. They can be new or re-emerging diseases (previously under control). Many emerging diseases affecting humans, such as brucellosis, are zoonoses. The WHO has identified a group of diseases whose re-emergence should be monitored: Those caused by bacteria include bubonic plague, diphtheria, and cholera. Biofilms are considered responsible for diseases such as bacterial infections in patients with cystic fibrosis, Legionnaires’ disease, and otitis media. They produce dental plaque; colonize catheters, prostheses, transcutaneous, and orthopedic devices; and infect contact lenses, open wounds, and burned tissue. Biofilms also produce foodborne diseases because they colonize the surfaces of food and food-processing equipment. Biofilms are resistant to most of the methods used to control microbial growth. The excessive use of antibiotics has resulted in a major global problem, since resistant forms of bacteria have been selected over time. A very dangerous strain, methicillin-resistant Staphylococcus aureus (MRSA), has wreaked havoc recently. Foodborne diseases result from the consumption of contaminated food, pathogenic bacteria, viruses, or parasites that contaminate food. |
SciQ | SciQ-5727 | thermodynamics, definition
Title: Definition of "intensive" and "extensive" properties Today I was asked what does it mean for a physical property of a system to be intensive.
My first answer, loosely speaking, was:
"It is a property that is local."
I was specifically thinking about density and, by "local", I meant "that is unaffected by the dimension of the system".
Ofcourse this is a very ambiguous answer, so after that I said (shifting to extensivity's definition):
"A property is extensive if it depends on the volume of the system observed."
To be honest, I said if it's proportional to the volume, but I'm not sure the this is correct. Now, that I'm still thinking about it, I've come to the conclusion that a good definition could be:
"A property is extensive if it depends on the quantity of matter of the system observed."
Looking on wikipedia I realized that this is exactly the definition given. But I'm somewhat still uncomfortable with that: if a gas is kept in a recipient of volume $V$ at a temperature $T$, his pressure is function of the number of moles of the gas:$$p=n(RT/V).$$
And, as we know, pressure is an intensive property. So (to me) it is not really clear what does "does not depend on the quantity of matter" mean.
I also thought that one could use an operational definition (if this is the good term) of extensivity/intensivity: one example might be:
"Suppose to measure a quantity $q(S)$ relative to a system $S$. Now reproduce a copy of $S$ and measure the same quantity for the system $S+S$ given by the two identicaly systems joined. If $q(S+S)=q(S)$, then $q$ is an intensive quantity."
This seems to give a more precise sense to the "does not depend on the quantity of matter" in the above definition, but there are gaps to fill. Maybe I will try to develop better this in a second time. Now, ofcourse, the question is: what is the definition of extensivity/intensivity in rigorous and unambiguous terms? Personally, your last example is exactly how I would define intensive quantities:
The following is multiple choice question (with options) to answer.
What type of physical properties of a substance do not depend on amount? | [
"inherent",
"intensive",
"extensive",
"stable"
] | B | All matter has physical and chemical properties. Physical properties are characteristics that scientists can measure without changing the composition of the sample under study, such as mass, color, and volume (the amount of space occupied by a sample). Chemical properties describe the characteristic ability of a substance to react to form new substances; they include its flammability and susceptibility to corrosion. All samples of a pure substance have the same chemical and physical properties. For example, pure copper is always a reddish-brown solid (a physical property) and always dissolves in dilute nitric acid to produce a blue solution and a brown gas (a chemical property). Physical properties can be extensive or intensive. Extensive properties vary with the amount of the substance and include mass, weight, and volume. Intensive properties, in contrast, do not depend on the amount of the substance; they include color, melting point, boiling point, electrical conductivity, and physical state at a given temperature. For example, elemental sulfur is a yellow crystalline solid that does not conduct electricity and has a melting point of 115.2°C, no matter what amount is examined (Figure 1.12 "The Difference between Extensive and Intensive Properties of Matter"). Scientists commonly measure intensive properties to determine a substance’s identity, whereas extensive properties convey information about the amount of the substance in a sample. Figure 1.12 The Difference between Extensive and Intensive Properties of Matter. |
SciQ | SciQ-5728 | electromagnetism, special-relativity, electromagnetic-radiation, vacuum, aether
The trick is that these disturbances do not imply the movement of any particle and there is no rest frame for a medium in which the waves propagate. But it turns out this is just extra baggage that our common experience causes us to expect, but which is not really necessary. If you look at the equations (Maxwell's equations) defining the laws of motion for the electric and magnetic fields, you can show that the electric and magnetic fields obey a wave equation (ie -- the same equation obeyed by small ripples on a pond, or waves on a string). This equation has exactly the same form in any reference frame. The modern point of view is to take these governing equations as the definition of a wave -- even though this is an abstraction from our common sense intuition that waves should involve a disturbance in a medium.
The following is multiple choice question (with options) to answer.
A wave that consists of vibrating electric and magnetic fields is called what? | [
"thermal wave",
"electromagnetic wave",
"mechanical wave",
"propagate wave"
] | B | An electromagnetic wave is a wave that consists of vibrating electric and magnetic fields. A familiar example will help you understand the fields that make up an electromagnetic wave. Think about a common bar magnet. It exerts magnetic force in an area surrounding it, called the magnetic field. You can see the magnetic field of a bar magnet in Figure below . Because of this force field, a magnet can exert force on objects without touching them. They just have to be in its magnetic field. An electric field is similar to a magnetic field (see Figure below ). An electric field is an area of electrical force surrounding a charged particle. Like a magnetic field, an electric field can exert force on objects over a distance without actually touching them. |
SciQ | SciQ-5729 | biochemistry, cell-biology, neurotransmitter, membrane-transport, synapses
Title: Exocytosis of synaptic vesicles I'm reading the following paper:
http://jcs.biologists.org/content/123/6/819
The part I am really confused about is when they say:
Exocytosis appears to use two alternative pathways: clathrin-mediated endocytosis (CME), which is well established by numerous lines of evidence, and the more controversial ‘kiss-and-run’ pathway, which involves direct retrieval of a vesicle at the site of fusion
My question is .. How can exocytosis (contents inside of cell are transported to outside of cell) use clathrin mediated endocytosis?
I thought endocytosis is the opposite of exocytosis, so why do synaptic vesicles use clathrin mediated endocytosis as a method of exocytosis? That sentence is located in a paragraph titled "Stages 5-7: Endocytosis and recycling": it's talking about recycling exocytosed membrane which is necessary for making vesicles for further exocytosis.
The sentences before the part you quoted are:
Synapses possess highly efficient mechanisms for retrieving SVs from the plasma membrane of the presynaptic terminal after exocytosis. Fast regeneration of functional SVs is a prerequisite for synapses to function during prolonged activity.
I think the passage is just somewhat confusingly worded, in that "exocytosis" is used as the subject of the sentence which is strange in this context. You could rewrite that sentence:
There appear to be two alternative pathways to recycle membrane for exocytosis: clathrin-mediated...
The following is multiple choice question (with options) to answer.
Both endocytosis and ______ are active transport processes. | [
"proteolysis",
"exocytosis",
"biosynthesis",
"cellular respiration"
] | B | Both endocytosis and exocytosis are active transport processes. |
SciQ | SciQ-5730 | structures
Title: Siding for Industrial Shed: Rain protection vs Ventilation When building a 12 m tall industrial shed with a peaked roof it is desirable that the sides of the shed should stay open as much as possible for ventilation / safety / access concerns.
On the other hand, an entirely open side from top to bottom might cause a lot of rain exposure when the rain comes in angled?
Is there a trade-off possible? Perhaps to enclose sides till a certain distance below the roof edge? Any heuristics about how much? (I've shown 4000 mm in the sketch below)
The contents inside the shed are relatively robust / waterproof & hence absolute rain protection is not needed. This will very much depend on the exposure of the building to wind as this is what will drive the rain in at an angle. So you really need to consider the prevailing wind direction and how sheltered the building is by other nearby structures etc.
If may be that if the prevailing wind direction is fairly consistent you can have one side more open than another.
Another option is to have panels which can be folded down when required eg if you have 4000mm of fixed cladding, you could have the same in fold-down form (this arrangement is fairly common in barns).
Also it depends what access you need obviously forklifts will need more height clearance than pedestrians.
You could also consider using strip curtains for at least part of the height.
The following is multiple choice question (with options) to answer.
What type of roads and parking lots prevent rainwater from soaking into the ground? | [
"gravel",
"dirt",
"shaded",
"paved"
] | D | Paved roads and parking lots prevent rainwater from soaking into the ground. This increases runoff and the potential for soil erosion. |
SciQ | SciQ-5731 | organic-chemistry, acid-base, everyday-chemistry
Title: Explanation of Lemon Juice-Invisible Ink A cute homegrown spy-trick we all know: lemon juice invisible ink. But there is no scholary article available in the internet about this phenomenon.
A rough explanation I found in Scientific American:
Lemon juice—and the juice of most fruits, for that matter—contains carbon compounds. These compounds are pretty much colorless at room temperature. But heat can break down these compounds, releasing the carbon. If the carbon comes in contact with the air, a process called oxidation occurs, and the substance turns light or dark brown.
But, this is not the type of explanation to be content with.
Question: What is the mechanism going on here? Please, support your answer with sufficient information and references, don't give a rough explanation.
Edit: I don't think my question is duplicate as I am asking for a well-referenced and informative answer which the other question doesn't have. Lemon juice works as a sympathetic ink partially due to its caramelization, as @Mithoron profoundly noticed -- especially upon extreme heating.
Recent review of the degradation process of lemon juice [1] suggests that browning of lemon juice is associated with 3 processes:
ascorbic acid degradation;
Maillard reaction;
caramelization.
One of the first in-depth investigations revealed the major role of ascorbic acid degradation referring to the browning phenomena [2]:
Compared with other fruit products, lemon juice contains few natural pigments to mask.
...
Because of the high acidity (pH 2.5) of this product, it was unlikely that browning was due to sugar-amine condensation and the results showed that ascorbic acid was the main precursor. Browning of lemon juice and model systems was proportional to the level of ascorbic acid; the presence of amino-acids in model systems increased the intensity of browning.
The principal role of amino-acids in the non-enzymic browning of fruit products appears not to be in the initial reaction leading to the formation of reactive compounds, but to increase the browning potential after the oxidation of the ascorbic acid to reactive carbonyl compounds. Thus, the pathway for the build-up of carbonyls depends on the pH and nature of the product, but in all cases the formation of melanoidin complexes originates from the polymerisation of carbonyl and $\alpha$-amino-groups.
The following is multiple choice question (with options) to answer.
What type of acid is often used as a preservative for acidic foods such as fruit juices? | [
"hydrochloric acid",
"benzoic acid",
"sulfuric acid",
"citric acid"
] | B | Benzoic acid crystals in polarized light are pictured above. Benzoic acid is widely used as a food preservative, either as the carboxylic acid or as the sodium benzoate salt. This compound is most effective when added to acidic foods such as fruit juices and soft drinks. The major industrial source of benzoic acid is the partial oxidation of toluene with oxygen. The process is inexpensive and environmentally benign. |
SciQ | SciQ-5732 | homework, plant-physiology, plant-anatomy
and 'Vascular Plants = Winning! - Crash Course Biology #37'
https://youtu.be/h9oDTMXM7M8?t=373
[5] Osmosis (water compensating solutes) "In Da Club - Membranes & Transport: Crash Course Biology #5"
https://youtu.be/dPKvHrD1eS4?list=PL3EED4C1D684D3ADF&t=148
Ian (and dad <= all errors and approximations are his :) ).
The following is multiple choice question (with options) to answer.
Vascular plants evolved what basic structures to collect sunlight? | [
"flowers",
"roots",
"stems",
"leaves"
] | D | Vascular plants evolved leaves to collect sunlight. At first, leaves were tiny and needle-like, which helped reduce water loss. Later, leaves were much larger and broader, so plants could collect more light. |
SciQ | SciQ-5733 | homework-and-exercises, thermodynamics, entropy, ideal-gas
So, as we can see, for a constant pressure $P$, the entropy of the ideal gas is a monotonically decreasing function with respect to decreasing $T$; if we decrease $T$, we decrease $S$.
I suspect your confusion comes from thinking that $S$ can never decrease, but this is only the case for isolated systems. If you are forcing an ideal gas to undergo an isobaric compression, then the system is no longer isolated, and so the entropy can decrease (entropy will increase elsewhere though).
As a separate argument, the entropy is a state function, meaning its value only depends on the state, not how you got there. Now, let's consider your isobaric process, and let's say we do an isobaric expansion and then an isobaric compression back to the original state (this is the original state of the system, not the original state of the system as well as the surroundings, which is impossible to achieve). Since entropy is a state function, the entropy ends at where it started. But this means one of two things happened
The following is multiple choice question (with options) to answer.
The entropy is decreasing because a gas is becoming a what? | [
"vapor cloud",
"solid",
"liquid",
"swirl"
] | C | The entropy is decreasing because a gas is becoming a liquid. |
SciQ | SciQ-5734 | organic-chemistry, redox, carbohydrates
That's all fine and dandy, but the thing is, I can't seem to find any source that (explicitly) explains why this whole 'ring-opening' business even happens in disaccharides like maltose, but not in sucrose.
The Wikipedia article probably implies that this has to do with the fact that both the monomers of sucrose are bound through their anomeric carbons, which is not the case with maltose. A quick look at the structures of maltose and sucrose confirms this, however; pardon me if I'm being dense here, but I don't see how that piece of information helps.
Can anyone explain this discrepancy? The difference in stability between maltose and sucrose boils down to the different structural elements their aldehyde/ketone groups have been turned into during the formation of the disaccharide.
In maltose, you combine two glucose units using the 1-hydroxy group of one and the 4-hydroxy group of the other. The 1-hydroxy group has been created in a process called acetal formation by the attack of what used to be the 5-hydroxy group and is now the ring oxygen. This is shown in equation $(1)$, the explicit carbon atom being carbon-1; the aldehyde.
$$\ce{R'-OH + RCHO <=>> R'-OH+-CHRO- <=>> R'-O-CHR-OH}\tag{1}$$
Notice that there are two oxygens bound to that carbon after the reaction; if we wanted, we could label it $\ce{RCH(OR)(OH)}$; this structure is called hemiacetal. If we use that hemiacetalic hydroxy group to bond to a second glucose unit,[1] we have replaced the hydrogen with an alkyl residue. Like the difference between alcohols ($\ce{R-OH}$) and ethers ($\ce{R-OR'}$), this group has a different reactivity and is termed full acetal or O,O-acetal.
The following is multiple choice question (with options) to answer.
Sucrose does not undergo reactions that are typical of aldehydes and ketones, therefore it is a nonreducing what? | [
"juice",
"salt",
"sugar",
"wheat"
] | C | solution. In addition, sucrose does not undergo reactions that are typical of aldehydes and ketones. Therefore, sucrose is a nonreducing sugar. The hydrolysis of sucrose in dilute acid or through the action of the enzyme sucrase(also known as invertase) gives an equimolar mixture of glucose and fructose. This 1:1 mixture is referred to as invert sugar because it rotates plane-polarized light in the opposite direction than sucrose. The hydrolysis reaction has several practical applications. Sucrose readily recrystallizes from a solution, but invert sugar has a much greater tendency to remain in solution. In the manufacture of jelly and candy and in the canning of fruit, the recrystallization of sugar is undesirable. Therefore, conditions leading to the hydrolysis of sucrose are employed in these processes. Moreover, because fructose is sweeter than sucrose, the hydrolysis adds to the sweetening effect. Bees carry out this reaction when they make honey. The average American consumes more than 100 lb of sucrose every year. About twothirds of this amount is ingested in soft drinks, presweetened cereals, and other highly processed foods. The widespread use of sucrose is a contributing factor to obesity and tooth decay. Carbohydrates such as sucrose, are converted to fat when the caloric intake exceeds the body’s requirements, and sucrose causes tooth decay by promoting the formation of plaque that sticks to teeth. |
SciQ | SciQ-5735 | electricity, electric-circuits, electrons, electric-current, charge
Title: Electrons in an electric circuit , its movement and power delivered Does an electrical appliance convert electrons into its respective work , I mean is electron being consumed by appliance (say bulb ) and then this mass gives us energy.
or the same number of electron , just revolve around the circuit, then from where does power comes from, Electrons have charge and so when there is a potential difference across a circuit, this charge moves through it. In an incandescent light bulb, there is a high resistance, meaning that there are many atoms with which the charges collide, transferring some of their kinetic energy. No electrons are being "consumed" by the light bulb, i.e. the number of electrons in the circuit does not change. The ability of the charges to do work is because of a potential difference, which can be achieved through a number of means, e.g. using voltaic cells or electromagnetic induction.
To gain a better idea of why potential difference moves charges, consider two isolated point charges of opposite charges, one positive and one negative. If you pull the negative charge away from the positive one, you are doing work on it in the form of potential energy, as you are opposing the electric field of the positive charge. If you let go, the negative charge will convert this potential energy into kinetic energy, as it is attracted to the positive test charge. A potential difference across a circuit, albeit simplified, essentially does this – it brings electrons from a higher potential to a lower potential, converting potential energy into the kinetic energy in the process.
The following is multiple choice question (with options) to answer.
An electric stove changes electric current to what form of energy? | [
"thermal",
"thermodynamic",
"kinetic",
"nuclear"
] | A | Electric devices, such as lights and household appliances, change electric current to other forms of energy. For example, an electric stove changes electric current to thermal energy. Other common devices, such as mobile phones and computers, use electric current for another purpose: to encode information. A message encoded this way is called an electronic signal , and the use of electric current for this purpose is called electronics . For an overview of electronics and electronic signals, read the short article at this URL: http://www. bbc. co. uk/scotland/learning/bitesize/standard/physics/electronics/overview_rev1. shtml . |
SciQ | SciQ-5736 | cellular-respiration
Title: Do cold blooded animals generate any heat? In explaining energy and work to an 8 year-old I said that all conversion of energy generates heat as a by-product. For example, cars generate heat in their engines and running generates heat in our bodies. Then the 8 year-old said, except for cold-blooded animals.
So my question is, do cold-blooded animals generate any heat in their conversion of stored energy (food, fat, etc) into motion? If they generate heat, why are they cold-blooded? They do generate heat. They just do not SPEND energy specifically on heating their bodies by raising their metabolisms. This is a form of energy conservation. The metabolic rate they need to live is not nearly enough to heat their bodies.
An example of spending energy to heat the body is seen in humans shivering. Here muscle is activated not for its usual purpose, but to function as a furnace. "Warm-blooded" and "cold-blooded" is somewhat a misnomer. The correct way to think of it is...
Endotherm or ectotherm. Does the heat primarily come from within (endo) or from the surroundings (ecto). Endothermic animals include mammals. Most of their body heat is generated by their own metabolisms. Ectothermic animals include reptiles and insects. They absorb most of their body heat from the surroundings. This is not the same as saying they let their body temperature fluctuate with their surroundings, some avoid this by moving around to accomodate themselves.
Homeotherm or poikilotherm. Homeotherms want to maintain homeostasis for their body temperatures. They don't want it to change. Poikilotherms do not exhibit this behaviour, instead their body temperatures vary greatly with the environment.
We can have endotherm poikilotherms, such as squirrels, who let their body temperature drop while hibernating. Endotherm homeotherms, such as humans, where temperature is constant by means of complex thermoregulation. Ectotherm homeotherms, such as snakes (moving into shadow or into the sun to regulate temperature), and ectotherm poikilotherms, such as maggots.
The following is multiple choice question (with options) to answer.
Mammals are endothermic vertebrates that have four limbs and produce what type of eggs? | [
"umbilical",
"epithelial",
"amniotic",
"gymnoic"
] | C | Mammals are endothermic vertebrates that have four limbs and produce amniotic eggs. Defining traits of mammals are fur or hair and mammary glands. Mammals are noted for the many different ways they can move and their specialized limbs. |
SciQ | SciQ-5737 | ions, elements
The book uses Potassium as an example. Looking at my table, the closest noble gas to Potassium is Argon, which has $18$ electrons. Therefore Potassium wants to lose one electron...
$$\ce{K^+}$$
Nice, I get that. But then I noticed something odd about all the examples in my book: all the elements they picked are elements conveniently one or two steps away from a noble gas. They never picked an element in the middle of the table like, say, iron.
Iron has $26$ electrons. Its closest noble gas is Argon, which has $18$ electrons. So iron wants to lose $8$ electrons (becoming a cation):
$$\ce{Fe^{8+}}$$
Is this correct? My book literally avoids picking elements in the middle of the table, so I feel there's something weird about this.
Also, I noticed that in every example, the book mentions the Group of the element (Potassium is group 1A, etc...). How is that even relevant? All you have to do is count the number of electrons, no? The book's explanation about a noble gas configuration is somewhat accurate, but fairly incomplete.
The elements on the right and on the left of the periodic table (the alkali (earth) metals, the halogens, the chalcogens (the group that starts with Oxygen) and the pnictogens (Nitrogen group)) have electron configurations that make it somewhat easier to lose/gain electrons to "look" like noble gasses (this is why alkali metals and halogens are so reactive: the destabilization from the charge is very minimal compared to the stability of the electron configuration).
However, as you have observed, the book goes to some effort to avoid talking about transition metals. There is a reason for that.
Noble gas configurations are a subset of the stable configurations of electrons. In reality, what's actually being aimed for is an element with no incomplete electron shells.
What is an electron shell? The actual quantum mechanical definition may be a bit more complicated than you need, but for your purposes, it suffices to say that it's how electrons will tend to be distributed around a nucleus. Note that this is extremely distinct from saying that the electron "orbits" the nucleus.
If you look at a periodic table, there are four general regions to look at:
The following is multiple choice question (with options) to answer.
Which group of metals in the periodic table include elements such as sodium and potassium? | [
"igneous metals",
"actinides",
"alkali metals",
"lanthanides"
] | C | The first step in the process of inductive reasoning is making specific observations. In the periodic table of elements, which we will discuss later, there is a group of metals with similar properties called the alkali metals. The alkali metals include elements such as sodium and potassium. If I put sodium or potassium in water, I will observe a very violent reaction every time. I draw a general conclusion from these observations: all alkali metals will react violently with water. |
SciQ | SciQ-5738 | homework-and-exercises, newtonian-mechanics, forces
Title: Force between two blocks on a friction-less surface The question is,
A single horizontal force $F$ is applied to a block of mass $M_1$ which is in contact with
another block of mass $M_2$ as shown in the figure.
The surfaces are friction-less.
What will be the force between the blocks?
I have another question. If the blocks are in contact and they do not have elasticity, should not the force between them be $F$ ? Not quite. The key is that both the bodies move with the same acceleration. This is proven by Newton's first law and that both the bodies are perfectly rigid.
If they move with the same acceleration we can consider both the bodies as one body of mass $M_1 + M_2$. Newtons second law is $\Sigma$$F=ma$, so the acceleration of both the bodies is $F/(M_1+M_2)$.
Now think of them as two separate bodies. $M_2$ has to move with an acceleration of $F/(M_1+M_2)$. Normal force of $M_1$ on $M_2$ is what accelerates $M_2$. So force of $M_1$ on $M_2$ is given by $M_2*F/(M_1+M_2)$.
The following is multiple choice question (with options) to answer.
What is the term for force that opposes motion between any touching surfaces? | [
"stress",
"friction",
"tension",
"gravity"
] | B | All machines make work easier, but they don’t increase the amount of work that is done. You can never get more work out of a machine than you put into it. In fact, a machine always does less work on an object than the user does on the machine. That’s because a machine must use some of the work put into it to overcome friction. Friction is the force that opposes motion between any surfaces that are touching. All machines involve motion, so they all have friction. How much work is needed to overcome friction in a machine depends on the machine’s efficiency. |
SciQ | SciQ-5739 | taxonomy, mammals, cladistics
Title: Why aren't mammals and reptiles considered amphibians? We've all heard it: birds descend from dinosaurs, so they're dinosaurs too. But this got me thinking: doesn't this mean that, for instance, all terrestrial vertebrates – including humans – are technically fish? A recent video by MinuteEarth and the Wikipedia article for "Fish" confirmed my shower thought hypothesis.
Interesting. But... all amniotes, i.e. reptiles (and, by extension, birds) and mammals, descend from amphibians, right? If so, then why aren't they considered amphibians too? Mammals and reptiles aren't considered amphibians, because amniotes are not hypothesized to descend from Amphibia. That is to say that Amphibia did not evolve into Amniota. They are sister clades (actually Reptiliomorpha in the Tree of Life tree below).
The following is multiple choice question (with options) to answer.
Most animals are in which clade? | [
"synapsids",
"eutheria",
"bilateria",
"metazoa"
] | C | |
SciQ | SciQ-5740 | human-biology, digestive-system, food
Title: Does sour food cause sweating? While eating sour food or candy, I start to sweat if it's sour enough. My body feels much hotter although my actual temperature is the same, my forehead starts sweating a lot and I feel like it just got twice as hot wherever I am.
Is this a biological phenomena or is my DNA just stupid? Is it somehow related to the digestive system, that sour food is harder to digest? In general, sweating is caused by too much heat, even if you're not aware of the heat. This can happen if the bowel moves and so raises the core temperature. Such movement is often accompanied with sweating, and since you only feel the normal temperature on the skin, it is cold sweat. But at the same time your core is hot so you think it's cold, but it will later mix to normal.
Anyway, it points to unusual bowel movement. This can be due to food allergy or, in a milder form, in food intolerances which are quite common. When it comes to sour ingredients, they are often in fruits, so I'll make a shot in the blue and say that you have a food intolerance against some fruits. You can check this hypothesis by trying chemically pure acetic acid to sour your food. If that doesn't result in sweat/hotness then it's probably the fruits.
http://en.wikipedia.org/wiki/Food_intolerance
The Wikipedia points even directly to salicylate in fruits but I think you cannot exclude allergies against essential oils like limonene and such. Plants are really chemistry factories and not all is well that you can get with them.
The following is multiple choice question (with options) to answer.
What system carries nerve impulses to internal organs, controlling activities that are not under your control, such as sweating and digesting food? | [
"hormonal nervous system",
"limbic nervous system",
"circulatory nervous system",
"autonomic nervous system"
] | D | The autonomic nervous system carries nerve impulses to internal organs. It controls activities that are not under your control, such as sweating and digesting food. The autonomic nervous system has two parts:. |
SciQ | SciQ-5741 | zoology, terminology, nomenclature, invertebrates, etymology
Urochorda
Cephalochorda
Craniata
which is more or less the accepted division today, with Urochorda being called Urochordata now.
In this essay, Lankester says:
The evidence of degeneration is admitted as conclusive in the case of the parasitic Crustacea and Cirrhipedes. It is equally incontestable in that very large and varied group of non-parasitic organisms, the Tunicata (Urochordate Vertebrata).2
(in the above 'Vertebrata' is what we call 'Chordata'). He adds this footnote:
2The whole argument as to the Tunicates of course rests on the view- supported by many arguments, that the larval urochord, which many of
them possess, is not a larval organ acquired by larval adaptation, but is hereditary and transmitted from adult ancestors.
The term 'urochord' seems to be established and used without comment there, and probably is taken as simple neo-Latin for 'tail chord', although that may be somewhat loose, perhaps meaning the notochord is present but does not extend into the head. A 1913 Webster's Dictionary defines urochord as:
(Zool.) The central axis or cord in the tail of larval ascidians and of certain adult tunicates.
In 1882, Lankester futher discussed the anatomy of the tunicates in the context of the division of the chordata in a paper called "The Vertebration of the Tail of Appendiculariæ". This paper includes an illustration of a larval tunicate with the "notochord (urochord)" indicated.
The following is multiple choice question (with options) to answer.
What are invertebrate chordates that retain all four defining chordate traits as adults called? | [
"sporozoans",
"lancelets",
"vertebrates",
"tunicates"
] | B | Lancelets are invertebrate chordates that retain all four defining chordate traits as adults. There are only about 25 species of living lancelets. Lancelets resemble tunicates in several ways. For example:. |
SciQ | SciQ-5742 | newtonian-mechanics, newtonian-gravity, celestial-mechanics
Title: Attraction between two objects in the universe. The resulting number of forces between them Right now I am studying Newton's Law of Universal Gravitation and I already learned his Third Law. It is said that there is an action-reaction pair between the falling apple and the Earth which results in the apple being attracted to the Earth and Earth to the apple at the same time and with the same force. But if we imagine bigger objects like Earth and Mars in the close distance, will it mean that Earth attracts to Mars and Mars is being attracted to the Earth with the gravitational force of Earth and at the same time Mars attracts to Earth and Earth to Mars because of Mars gravitational force. So as a result I counted 4 forces between two objects. Is it correct or not, and please explain why :) There's only the one gravitational interaction. You can describe it however many ways you like, but the physical interaction is only happening once.
If you want to know how two objects will move because of a force between them, relative to a distant inertial observer, calculate the change of their relative velocity by picking whatever frame measures the acceleration due to gravity that you want to integrate over time, then conserve momentum in the distant inertial frame.
For example: Bob and Alice are standing together on some frictionless ice. Bob (mass $m_B$) pushes on Alice (mass $m_A$) such that Alice has a velocity of $v$ relative to Bob. Conserve momentum $P_0$ in the frame in which you want to measure Alice's and Bob's velocity. (If this is the frame in which Alice and Bob were initially standing still, $P_0 = 0$.)
$P_0 = m_A v_a + m_Bv_b$
$v = v_a - v_b$
Solve for $v_a$ and $v_b$ in terms of $v, m_A, m_B, P_0$.
The following is multiple choice question (with options) to answer.
What has traditionally been defined as a force of attraction between two masses? | [
"motion",
"volume",
"mass",
"gravity"
] | D | Gravity has traditionally been defined as a force of attraction between two masses. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. The effect of gravity is that objects exert a pull on other objects. Unlike friction, which acts only between objects that are touching, gravity also acts between objects that are not touching. In fact, gravity can act over very long distances. |
SciQ | SciQ-5743 | biochemistry, food
Title: Who creates first nitrogen compounds in the food supply chain As I understand the food supply chain, organic compounds have to be created from a unlimited source (air, water...).
For instance, I figure that plants transform CO2 from air to organic carbon compounds, mainly carbohydrates, which are then the main source for most other life forms.
But I never heard about a plant turning atmospheric N2 to nitrogen compounds.
Where nitrogen compounds come from, and from which source ? There are nitrogen fixing bacteria who turn N2 into NH3. Some are free-living in soil, others live symbiotically with plants.
https://en.wikipedia.org/wiki/Nitrogen_fixation
The following is multiple choice question (with options) to answer.
What members of an ecosystem food chain take in food by eating producers or other living things? | [
"insectivores",
"decomposers",
"consumers",
"primary producers"
] | C | Consumers take in food by eating producers or other living things. |
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