text:
How can you stabilize enzymes in pellets made from microcrystalline cellulose?
I want to make pellets consisting of mainly the following:

microcrystalline cellulose
saccharose
rice starch
ascorbic acid
glycerin

and an enzyme as active component.
Is it furthermore necessary to add protease inhibitors or other stabilizers to remain the activity of the enzymes for a periode of at least one year OR is the dry environment conservation enough?
The enzyme is called histaminase and is extracted from kidney cortex through a series of centrifugation, filtration and dialysation. To be more precise, it is a liquid protein extract containing small amounts of this enzyme. No buffer etc. is added to the protein extract so far. The whole purification process is done at 4°C. I don't know how long the enzyme is stable without further preparation. Probably not that long because some proteases should remain in the natural homogenate from porcine kidney cortex. The other components of the pellets are of pharmaceutical quality. The aim of this experiment is to feed the pellets to dogs with digestive complaints. For this purpose the pellets will get a enteric coating to survive acid environment of the stomach.

So you're trying to make pills?

Other questions: what is the enzyme? How is it purified, and how pure is it? Has it been lyophilized? What storage condition requirements do you have - room temp? +4? -20? -80? What is the stability of your prepared enzyme, without putting it into pill form? Does it have BSA or other carrier proteins with it? If so, at what concentration? Are your other materials sterile? Have they been tested for protein content? As you can see, a lot of factors go into determining the stability of a protein. Please use the [edit] link to add all of the requested information into your question.

@MattDMo hope the added informations help

As you can probably guess from my comment, there are a lot of factors to take into account when thinking about protein stability. Here's what I would recommend you do.
First, make sure your extract is in a neutral buffer, like PBS, HEPES, or something similar. This is a fairly standard procedure when working with proteins. Next, since this is a kidney extract, there are likely to be gobs of proteases around, so I would strongly recommend adding broad-spectrum protease inhibitors, and keeping the extract as cold as possible to inhibit any enzyme activity. I would also add BSA at 10 mg/ml, both to stabilize the proteins and keep them from precipitating while in solution, and to lessen the chances that any proteases present will attack your enzyme of interest.
Once you have your solution stabilized, I would aliquot it and lyophilize it. Proteases are most active in solution, so once dried you'll reduce their activity even more. You can now add the inert ingredients (microcrystalline cellulose, etc.), mix thoroughly, press your tablets, and add the enteric coating. Finally, once everything is prepared, I would store the final product at as cold a temperature as is convenient. Again, this will inhibit any enzyme activity and prevent degradation.
I don't know if you have a functional assay to determine activity of the enzyme of interest, but if you don't I'd highly recommend developing one if at all possible. This way, you can test the activity of the fresh preparation of extract and compare it to various stages of processing into tablets, especially the finished goods, to ensure that you haven't lost much activity. I would also test random tablets throughout the year to make sure they haven't lost activity in storage, otherwise you won't be able to compare your experimental results.

I don't want to press tablets. I plan to use pellets like those ones. So I don't have to lyophilize the extract because the process works with a moist compound. But I asked myself if the dogs could get in troubles because of bacteria etc. I centrifugalize at max. 50000g. So cells shouldn't remain in the liquid but what's with viruses?!

Furthermore I read that most of the proteases like PMSF or AEBSF are toxic for cells. So is there a solution for the case of feeding dogs with the pellets?

@Luke I apologize, I misunderstood the type of pill you were making. The reason I suggested lyophilization was not to just dry out your extract, but to preserve it and help protect it against proteases and other degradation, so even through you're making capsules, I'd try to keep everything as dry as possible. As far as the bacteria/virus question, you'll have to decide that for yourself. We (and dogs) don't eat sterile food, everything has various microorganisms in it. Dogs are able to tolerate a wide variety of them, what with the anal licking and eating food off the ground and whatnot.

@Luke as with all potential toxins, the dose makes the poison. Figure out how much of those inhibitors you'd like to add, as well as compounds like leupeptin and aprotinin, look up their LD50 or toxic dose, then calculate out milligrams of inhibitor (or micrograms, whatever) per kilogram of canine, and consult with a toxicologist if necessary. Search around, you may be able to find safer inhibitors. However, throughout all of this, an enzymatic functional assay is vitally important for making decisions about dose and stability - it may turn out you need few or no inhibitors at all.

I know this question was some while ago, but maybe you could help me out again ;-) After the centrifugation I want to make a ammoniumsulfate precipitation with the supernant. Do you think that I have to do a dialysis to remove the ammoniumsulfate OR  could I use the homogenate direct without any further preparation in my pellets?


text:
How to measure heat loss in Tardigrades
I want to measure metabolism in tardigrades (a jar of 30 tardigrades). I know that an easy way to measure metabolism is heat loss; I can just measure the temperature of the water before and after a certain period of time and take the difference. I have a few questions:
1) Is this a viable way?
2) Do I need to put the tardigrades in a controlled system (or is the outside environment a constant)?
3) Will the measurements be really really small (so I would need a very precise thermometer?)
4) How long should I wait between the two measurements?

1 and 2) You need to build/use a calorimeter : http://en.wikipedia.org/wiki/Calorimeter
Different types exist, depending on your constraints.
3 and 4) It will depend on the size of your system.
If you decide to use an adiabatic calorimeter: First have an estimate of their metabolism (see e.g. [1]), then divide the energy spent over the duration you think you'll use by the heat capacity of the water volume you have, you get the temperature elevation.
If you use a flux calorimeter, then you don't multiply by the duration but check that the calorimeter will be sensitive enough.

Do these cold-blooded critters emit heat at all you think? +1 for your calorimeter idea. Nice one.

@ChrisStronks: they cannot live and emit no heat at all. Any process will generate some heat, be it only by molecular friction in flows. "Cold-blooded" is misleading, as it rather means that they have no thermal homeostasis target that they'd maintain by internal metabolic processes.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


text:
True or false & fill in the blanks

A ribosome is where amino acids are linked together by peptide bonds.
A virus is NOT considered prokaryotic because it does not have a membrane.
The nucleotide ATP is one of the most used energy molecules of a cell.
Sugar phosphates are the type of lipid moved through the blood.
A compound that lowers the pH is called an acid.
The cell wall is a carbohydrate covering of all cells.
The term cytosol is only applied to (blank) cells?
An A-U base pair is part of the (blank) found in RNA.
The major form of usable energy in animals is (what)?
A polypeptide is a subunit of a what?

This is what I said
1. True
2.True
3. True
4. False (cholesterol)
5. True less than 7 acidic
6. False
7. Don't know
8.complementary
9. ATP
10. Protein or amino acid? Don't know

Welcome! Homework questions are accepted, but the PO should show signs of effort. We are not here to do it for you :) We are here to help. Please see the help center: http://biology.stackexchange.com/help/homework

1-6: OK;

prokaryotes. Cytosol is the portion of cytoplasm which is devoid of any organelles, i.e., cytoplasm = cytosol + organelles. As prokaryotes don't have any organelles in their cytoplasm, they have only cytosol. So the answer would be prokaryotes (their cytoplasm consist of cytosol only). For a special case in eukaryotes see Crags answer below.
Double strand;
Glucose? (but not ATP, fat would also be a suitable alternative specially in animal living in cold regions thanks to @CRags);
protein

You are very sweet. I can say that and get away with it because I'm an old lady. ')

@anongoodnurse - I am flattered, thank you (also for the lonely upvote :-)

Glucose and fat (lipid) too for 9

@CRags - yes, but if you have to pick one it would be glucose guess? I think some of the questions are quite vague :)

I think some questions have more than one answer! Lol, yes some are vague

Chris, I think you misunderstood. Prokaryotes have cytoplasm devoid of organelles which means they have cytosol only. The rbcs are similar because they also don't have organelles.

Eukaryotes have cytosol and organelles so not pure cytosol

@ChrisStronks I am editing your answer to correct it. Please feel free to undo it.

Please check it now

@CRags - Great! If I could upvote your edited answer I would :)

I'm not sure if the glucose or fat answer is correct, though. It completely depends on how the "usable" is defined. Does it have to be immediately usable, or does it have to be oxidised first?

A ribosome is where amino acids are linked together by peptide bonds.

True.

A virus is NOT considered prokaryotic because it does not have a membrane.

Some have capsules or envelopes, the latter of which are composed of the host cell's membrane. A virus would not be considered a prokaryote because it is not strictly alive -- prokaryotes do not have membrane-bound organelles, but they still produce the cellular machinery necessary to process nutrients and create proteins de novo without hijacking another cell. I would say False on this one, because the presence of a membrane doesn't define either viruses or prokaryotes, ergo the lack of one wouldn't either.

The nucleotide ATP is one of the most used energy molecules of a cell.

True. The other extremely common one is GTP, an ATP analogue.

Sugar phosphates are the type of lipid moved through the blood.

False. Sugars are phosphorylated to make sure they stay inside the cell and don't enter the blood (first thing that happens to glucose and fructose is phosphorylation in energy metabolism). They are also not lipids; they are not composed of long carbon chains of varying saturation.

A compound that lowers the pH is called an acid.

True. Since pH is a measurement of the available H+ ions in solution and acids contribute available H+ ions to the solution, the more acidic the compound the lower the pH will be.

The cell wall is a carbohydrate covering of all cells.

Generally speaking, True -- of plant, some bacteria, and some archae cells. Eukaryotes do not have cell walls. The cell walls of plants are composed of a carbohydrate (sugar) polymer called cellulose (aka - dietary fiber).

The term cytosol is only applied to (blank) cells?

Prokaryotic -- for reasons listed by others.

An A-U base pair is part of the (blank) found in RNA.

I'm a bit confused on this one. RNA is generally single-stranded, not double-stranded. It should not be base-pairing with itself unless specifically designed to. However, the Uracil is the RNA complement (my best guess) to Adenosine and replaces Thymine found in regular DNA.

The major form of usable energy in animals is (what)?

Either ATP or sugars/carbohydrates. Sugars are eventually used to regenerate ATP, and fats are broken down into sugars or further down-stream metabolic components of sugars.

A polypeptide is a subunit of a what?

A protein. Proteins are composed of many polypeptide strands which usually come together to compose discrete formations (alpha-helices or beta-sheets) that then eventually form proteins.

All monomeric proteins are composed of a single polypeptide.

@canadianer -- Yeah, but the nomenclature conventions make "polypeptides" to usually 3-5 peptides chained together. Before is "dipeptide" and after can get up to "oligilopeptide" IIRC.

Nomenclature certainly varies; I generally go for a polypeptide being anything >20 whereas an oligopeptide is 2-20. 20 is entirely arbitrary, I just see it a lot in texts. Regardless of nomenclature, the point is that a monomeric protein is a single "strand" of amino acids. I'm not trying to nit-pick, it just seems misleading that you said many polypeptide strands come together to form alpha helices and beta sheets.

Well explained +1 :)

@canadianer -- I agree, the nomenclature is pretty arbitrary and can be misleading. Thanks for bringing it up. :-)

Cytosol is the fluid portion of cytoplasm.  All organelles are suspended in the cytosol but they do not form a part of cytosol. See here for a detailed explanation.
As Chris Stronks mentioned all cells have cytosol, but the red blood cells specifically do not have any organelles. The cytoplasm of RBC has only cytosol in which hemoglobin is suspended.
So even though all cells have cytosol, RBCs are a special case. That may be the answer to your question.

"Cytosol is the fluid portion of cell which does not have any organelles": do you mean "cytosol is the fluid portion of the cell containing the organelles"? And cytosol and cytoplasm are synonyms right? So I don't understand the second paragraph?

Cytosol is the soluble part of cytoplasm where minerals are dissolved. It excludes the cell organelles. Cytoplasm = cytosol + cell organelles. The cell organelles are suspended in cytosol, but the space occupied by them is not cytosol. https://www.google.co.in/url?sa=t&source=web&rct=j&ei=dvvAVIneDaalmQWgmoCQCw&url=http://www.saylor.org/site/wp-content/uploads/2010/11/BIO101-Difference-Between-Cytosol-and-Cytoplasm.pdf&ved=0CCcQFjAC&usg=AFQjCNGoxSNppwoKdETuuQe1WNKc-Qx3ZQ

@ChrisStronks when do you sleep? Lol, you always seem to be online giving great answers!!!

Aha! You may want to edit your answer :) One way or another  +1

Thanks :)  !! I sleep now and then though :)

Have to say, this community is much more friendly compared to meta, thanks for all your support people!

Meta is a minefield...

Great thought, add to your answer. I will leave this as such, as an addition to your answer, which is great Btw... If it's ok, add lipid also to 9th question. I'll leave mine as special case in eukaryotes

Sorry, I misread your comment in a hurry

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can a hydra get cancer?
Because hydras have immune systems, telomerase activity, and Piwi-piRNA like cancer cells I wonder if they can get cancer?

Yes.

Research in cnidarians shows that even pre‐bilaterian animals can develop neoplasia (Domazet‐Lošo et al., 2014). Two different species of Hydra have presented with tumour‐bearing polyps. The cells in these tumours were invasive, which suggests that metastatic capacity has ancient roots. Additionally, the tumours had several orthologues to tumour‐related genes in mammals and displayed parallels to the hallmarks of cancer in vertebrates. The proposed mechanism for tumourigenesis in Hydra is the accumulation of stem cells if they are not appropriately removed by programmed cell death (Domazet‐Lošo et al., 2014). Scientists have also identified several cancer‐like lesions in corals (Aktipis et al., 2015).

--From humans to hydra: patterns of cancer across the tree of life

Yes. May I suggest a mention that this is a significant finding in understanding the evolutionary origin of cancer (i.e., it supports the prediction that cancer originated with the earliest animals).

@DeNovo : I'm not really sure that the (rather obvious) observation that as soon as the very first DNA (etc.) existed there was (by the very definition of what it is) then a potential for copying errors really qualifies as a "prediction"? just my (not entirely) latent pedant gene kicking in, sorry about that :)

Cancer is intrinsic to any multicellular organism with the same master genome in multiple  cells. For an organism to have a coherent structure, there must be coordination and control between the cells.  If there is genetically based control, those genes can mutate to be dysfunctional, and some versions of dysfunction will release control of the genes causing cellular replication, which will form a neoplasm if not suppressed by other cells of the organism (which may be dysfunctional).

@Pelinore the prediction is that cancer originated with the first animals, not the first DNA (and not single celled organisms, see: the bit where I address that in this answer). The current species who's lineage diverged from other animals at the earliest point (but remain animals) are basal metazoans, like the hydra. Cancer, as we understand it, is not observed, nor is it predicted to exist in single celled organisms. I can't seem to find my reference to the computational model that makes this prediction. If i can find it, i'll add it later.

@DeNovo fair enough, so it needs multi cell organisms before you can call any copy errors cancer, not really anything to do to do with what I said though, I still say "prediction" isn't really the right word.

@Pelinore cancer is more than copy errors. You might find this seminal paper interesting, if you'd like to learn more about how cancer biologists define cancer.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why is it harder to sequence plant genomes than animal genomes?
Plants seem to be less complex organisms than animals, but despite that there are less plant genomes sequenced. Is that because plant genomes are more complex, for example in terms of regulatory regions and transposons that make sequencing more difficult, or are there other reasons why the number of sequenced plant genomes is smaller than animals?

I edited the question to improve clarity. If the current question does not reflect your original question anymore feel free to roll back.

I know the genomes tend to be much larger, and often have many more copies of the genome than animal cells.

There are multiple problems. One already mentioned is polyploidy, another is the fact that plant cells have cell walls and it can be tricky to extract DNA without fragmenting it too much. Also, some plants have quite a lot of repetitive sequence which makes it harder to assemble. But as with every other organism it also depends on the plant, the variety, the technical possibilities one has and much more.

The authors of this 2012 review article summarize the problem well in their introduction:

In contrast to the tremendous advances in throughput, assembling sequencing reads remains a substantial endeavor, much greater than the sequencing efforts alone would suggest [22-24]. Large complex plant genomes remain a particularly difficult challenge for de novo assembly for a variety of biological, computational and biomolecular reasons. Plant genomes can be nearly 100 times larger [25] than the currently sequenced bird [26], fish [27] or mammalian genomes [28]. In addition they can have much higher ploidy, which is estimated to occur in up to 80% of all plant species [29], and higher rates of heterozygosity and repeats [30] than their counterparts in other kingdoms. Furthermore, the gene content in plants can be very complex, as shown by the presence of large gene families and abundant pseudogenes with nearly identical sequences derived from recent whole genome duplication events and transposon activity [13]. Plants tend to have high copy chloroplasts and mitochondria organelles, which complicate assembly of their remnants in the nuclear genome and skew coverage levels [12]. Finally, it is often very difficult to extract large quantities of high-quality DNA from plant material, making it difficult to prepare proper libraries for sequencing.

From: Schatz, Witkowski and McCombie. "Current challenges in de novo plant genome sequencing and assembly". Genome Biology (2012). 13:243
As you can see, all of the key reasons have been touched on by the various people who have commented below your question.


text:
Why didn't the polar bear change its color from white to black during evolution to absorb heat?
Polar bears are white in color and white color is not a good absorbant of heat. Why then didn't they evolve a black color to absorb more heat?

This is thought to be why they have black skin, and they have white fur because it is camouflage in the snow where they hunt, a black bear wouldn't be much good at sneaking up on a seal in the snow!

The white ones survived better and developed fur that would channel sunlight to the dark skin.

This question seems to assume that living beings have reached a pinnacle of evolution and that a pinnacle of evolution entails perfect adaptation, neither of which are true.

Additional nit:  "white...not a good absorber of heat" is untrue.  "White" implies uniform reflectivity in the visible spectrum (more or less), and there's plenty of energy to be had in other portions of the solar irradiance.

No seals ever surfaced near the ones with dark fur waiting for them at their air holes, so those bears died out, and only the “white” bears survived, since they were harder to see.

Polar bears do not have white fur - they don't have pigments in their fur hairs which makes them clear and translucent. The outer fur consists of hollow fibres, which shatter a part of the incoming light (the visible part) which makes them look white. This gives a very good camouflage in a white environment.
It was initially thought (see reference 1) that the hollow fibers work in the same way as fiber optic cables and direct the UV part of the light (the visible was thought to be shattered) towards the black skin of the bears where it generates heat, but this hypothesis has been disproved. The UV part of the light is simply absorbed by the bears outer fur and doesn't reach the skin (see reference 2 for details).
The hollow hair helps with the insulation of the skin and can change the color due to environmental influences. The tend to get yellow after feeding on seals due to the fatty substances from the animals. There have also been reports from zoos that algae lived inside the hollow part of the fur making the animals more grey and sometimes even green (see reference 3).
Reference:

Light collection and solar sensing through the polar bear pelt
Is polar bear hair fiber optic?
The greening of polar bears in zoos

Wouldn't IR, rather than UV, be the relevant part of the spectrum for being warmed?

UV has more energy. And how much IR is present in the arctis?

@Chris - The amount of energy in UV is utterly negligible compared to the bear's metabolism.  See for instance http://en.wikipedia.org/wiki/Ultraviolet_index (where you get numbers of under a watt per square meter even at noon in the tropics).  It might be useful for vitamin D production (if bears need it), but not for warmth.

@RexKerr That's probably why it plays no role.

Bears initially were dark. But in snow it is really poor camouflage, their victims will see them to early. So they evolved to white color.
They have a lot of fat and good fur to keep the temperature, they don't really need more sun energy. They need more food.
In the same way - in the forest all bears are dark - for camouflage.
Read here
http://www.polarbearsinternational.org/about-polar-bears/essentials/fur-and-skin

"in the forest all bears are dark" - What about panda bears?

Panda bears are the perfect color for sneaking up on bamboo.

How much energy could an Arctic-dwelling creature be expected to capture from sunlight?  I think not very much.  How much can it gain from having coloration that allows it to capture prey more easily?  Quite a bit.  Also, given the size of the polar bear, they will probably be generating more than enough waste heat from metabolic activity.  Indeed, if you do a little research, you might discover that the polar bear's problem is, indeed, getting rid of heat:

In bears, the basal metabolic rate varies with climate and season;
  Polar Bear has highest BMR.  Overheat easily when running; can't
  travel any great distance at speeds more than a walk.  Low
  surface-area to volume ratio favors heat retention. Tendency to
  overheat enhanced by layer of fat 11 cm (4.5in) thick.  Young cubs up
  to 6 months old, with little body fat, are susceptible to cold.   Use
  more than twice the predicted energy for moving at a given speed,
  perhaps due to bulky body.   Fat and fur both insulate.   As long as
  bear isn't exposed to wind, body temperature and metabolic rate remain
  normal at -37 degrees C (-35 degrees F).

From http://library.sandiegozoo.org/factsheets/polar_bear/polar.htm
Of course, even if the polar bear was a perfect absorber, it could get at most ~1kW/m^2 of energy from the sun, and that only on a clear day in the summer.  And that heat would be on the outside of its insulating fur & fat.
So there's the answer: a strong selective pressure towards white, little or none towards black.
Re waste heat: What is meant here is that when the polar bear (or any animal) consumes food, part of it goes to producing heat as an unavoidable byproduct of metabolism.  Larger animals usually have to get rid of excess heat, thanks to the surface/volume relationship mentioned in the comments.
For a reference, try thinking about this: http://en.wikipedia.org/wiki/Thermoregulation  And remember that not all answers are written down in a book (or web site, these days).  Sometimes you have to actually think and reason out your own answers :-)

Added: I think the problem with this question is the assumption that polar bears (or indeed, any boreal mammal) need to absorb heat.  Maybe that's down to anthropocentrism, since humans evolved from ancestors that lived in tropical climes, and so have adaptations (like sweating & nearly hairless skin) for cooling.  But if you read the links, you discover that more often the problem is getting rid of excess metabolic heat, and most boreal mammals seem quite comfortable in what we primates consider cold.  (I write this after coming in from playing with my two dogs, who love to run around in the fresh snow.)
You might also think about why almost all (non-domesticated) mammals have evolved protective or camouflaging coloration.  (The only exception I can think of offhand is the skunk.)  Indeed, a number of boreal mammals have evolved seasonal color changes (e.g. http://srel.uga.edu/outreach/ecoviews/ecoview130106.htm ), having darker summer colors (like their more southerly relatives), but turning white in winter.  That suggests that the benefits of camouflage strongly outweigh any possible benefit from solar heat gain.

The point of energy waste isn't true. Bigger animals have a smaller surface in relationship to their volume.

Oh, and can you please add references to you answer?

This is a false answer.

False how, exactly?

In addition to camouflage, consider that during the colder parts of the year, when they need the heat the most, the nights are longer than the day.
Darker fur would radiate more heat away from the body than the lighter fur.
So it's possible that they did evolve the white fur for heat - but in their environment, the coldest part of the year heat retention is more critical than heat gathering, and this would bias towards white fur, not black.

Why should darker fur radiate more heat? This is a question of the insulation through the deeper fur layers and the fat.

@Chris, this is basic physics: dark colors radiate heat more efficiently than light colors.

@Mark Only when there is heat to radiate. When the bear is insulated good enough (which they are) there is nothing which radiates of. In fact it is practically impossible to spot polar bears with a thermal camera. Additionally, dark fur would absorp light more easily than light fur.

@Chris I'm suggesting that one of the reasons there is so little emissions is due, in part, to the fur not being dark. It sounds like you are arguing that even if their fur were dark they would still not have heat emissions. Of course the fur only plays a part of the role in insulating the bear, but it still plays a part.

Although black is a better absorber of (heat) radiation, it is also a better emitter too. As Polar bears live in a cold environment, having black hair would cause them to radiate their body heat away more quickly. Their colour helps them to retain heat better - dark objects equilibrate to the temperature of their surrounding faster, lighter objects more slowly. If they were darker, they would require more food to survive.
Their black skin is irrelevant as the light has already been scattered/reflected away by the white/colourless hairs - as they look white, it's the reflected light that you are seeing.

It would be great if you could add some references to support your response!

interesting answer! Please add references and get some well-deserved credits here

Why then didn't they evolve a black color to absorb more heat?

This assumes that evolution is an active process, working by organisms' will or need.
Do not forget that the theory of evolution works from generation to generation, by random (imperfect and chaotic) mutations, most of which are unfavorable.
The polar bears did not evolve a black color because they can't decide that. If you believe in evolution, and you believe that a black color would draw more heat, increasing the animal's chances of survival over its white peers (so much that the white peers would eventually die off), then we are simply waiting for the black color to come around. Evolution is never finished.

This is a brief expansion on DrAlchemist's response; one that I intended to make myself, but saw that s/he had already covered the basics.
To see that black is a better emitter of heat we have to leave biology and go to physics, specifically quantum mechanics, even more specifically black body radiation. Like most things, absorption and radiation are equally balanced when it comes to a given material/color. A white object is slow to absorb heat and a black object is quick to absorb heat, as we have likely all seen demonstrated in elementary school. What my teacher (and likely yours) did not mention is that the white object cools slowly when taken out of the sun, but the black object will cool much more quickly. Black heats up quickly, and radiates just as quickly when the temperature differential inverts.
As a mental exercise, consider an idealized object that absorbs electromagnetic energy perfectly, called a black body. Turn a heat lamp on it, and it will absorb all the heat it receives. Turn the lamp off and, as in the argument above, it will become a perfect emitter of the radiation it absorbed.

This does not provide an answer to the question.

@Chris I think it does provide an answer by hypothesizing that because polar bears are white, they lose less heat due to radiation. However, this is probably not true: First of all polar bears lose heat by convection, not radiation, since they do not live in a vacuum. Second, if this was true you would expect the fur to be black and the skin to be white, since it is the skin that is warm and not the hairs.

Minor quibble: radiation occurs whether in a vacuum or not. And all we care about is which color is on the outside; a white metal ball painted black is the same as a black metal ball. But I do agree that convection is by far the primary engine for heat loss in the bears' environment and absorption/radiation is negligible. Ultimately I think their color doesn't matter one bit when it comes to heat retention, particularity since they spend a fair amount of time swimming in the Arctic ocean, a far better conductor of heat than even the frigid arctic wind. And yet they do not die of hypothermia.

I think an important point hasn't been mentioned yet.

Why then didn't they evolve a black color

The changes introduced by evolution initially are random.  Only the persistence of those changes over generations can be thought of in a "smart" way.
Technically, evolution can lead to some things getting worse!  For example, if mutations improve a creatures eye-sight but at the same time worsen it's hearing, both traits may end up surviving assuming the improved eye-sight makes more of a difference than the worsened hearing.

Well, Polar bears do have black skin; But, living in the harsh arctic conditions they've adapted several traits such as thick layer of blubber, wide paws etc. But their most peculiar trait is having a white fur coat; unlike other bears, polar bears have evolved to have white fur with hollow hairs which easily allows their black skin to absorb the radiations from the sun. So there's no problem with the heat intake.
Now, the reason behind their white fur lies in their quest to food. The white fur enables them to easily hide/blanket in their surrounding (the white masses of snow) i.e. it helps them in camouflage.
And, I guess that's it! Thanks!

Welcome to bioSE. Can you add some references to your answer?

The claim with the light absorption has eben dismissed. See the reference in my answer.


text:
Where do I purchase this Trypsin?
I am currently on the lookout for Trypsin, but I have some trouble finding something that is fairly cheap, ships to Europe and is equivalent to this Trypsin:

http://www.emsdiasum.com/microscopy/products/chemicals/tannic.aspx#22200
Trypsin powder 1:100 from Porcine Pancreas, 25g
Activity >100 NF units/mg
Used for whole cell preparation

I've found Trypsin on Sigma:

http://www.sigmaaldrich.com/catalog/product/sigma/t4799
Trypsin powder from Porcine Pancreas
Activity 1,000-2,000 BAEE units/mg
Suitable for cell culture

However I am not sure how to compare the activity between the two types and ultimately which concentration I should then use in my experiment if I go with the Sigma one (the protocol I am following uses the EMS Trypsin in a 1g:100ml fashion).
Can anyone shed some light on this? Or perhaps show me the way to some affordable Trypsin that can be shipped to Scandinavia?
Cheers!
/Patricia
*The trypsin will be used for diaphonization (see comment)

Could you update your question to explicitly state what you will use the trypsin for. Trypsin has a number of uses and the use alters which trypsin is appropriate.

Hi Michael. Sure! I will use the trypsin for diaphonization (aka. clearing and staining), which is basically a way of dyeing a whole specimen. Trypsins role is to digest the specimen enough so it becomes transparent, but not so much that it falls apart... If that makes no sense there is a nice video about it here: https://www.youtube.com/watch?v=haopSRCuPdo... I have experience with use of Trypsin with cells - but diaphonization is completely new to me, and the protocols I have give no clue to what type of trypsin they are using.

According to Sigma-Aldrich,

1 USP Unit = 3.0 BAEE Units
  1 NF Unit = 1.1 USP Units

So 1 NF unit is roughly equal to 3.3 BAEE units. You can then directly compare the two trypsin powders, since they are preparations of the same enzyme.

Yeah, I did see that, but the thing that bothered me is then that I need to compare unspecific units like >100 NF and 1,000-2,000 BAEE, and so I am left with questions like "How much is >100 NF? 101 NF? 500 NF?" and "Do I calculate with 1.000 or 2.000 BAEE?"

But I guess the best solution is to note that 100 NF ~ 330 BAEE and so if I end up buying the Sigma one, I can start out with trying a 1:300 solution and see how that goes :)


text:
what would be the scientific name of this variety of dove
recently i came across a small dove who had its feathers tied by a rubber band so that it $would'nt$ fly. it looks some what like this

i was stunned by seeing it as i have never seen a dove in brown colour. and after staring it for some time i noticed that it's feathers or hairs near the neck region were made into a cluster that makes it look like $spike$ $hair$ $style$
so in short what would be the scientific name of this dove ??

This look like a Indian Pigeon(Rock Dove).

@DevashishDas i know you live in bangalore so have you seen these birds around your locality as these birds are'nt seen very often in hyderabad

It's a rock pigeons (Columba livia).

The Color coding of Pigeon
There are three genes responsible for pigmentation in pigeons.

– Tyrp1 gene produces a protein that helps make the pigment eumelanin.
  Pigeons with blue-black feathers have normal Tyrp1. Ash-red and brown
  birds pigeons contain different mutations in the Tyrp1 gene, which
  leads to less or different pigmentation.
– Mutations that affect the Sox10 gene override colors determined by
  various versions of the Tyrp1 gene. Regardless of whether the Tyrp1
  version makes pigeons blue-black, ash-red or brown, mutations that
  regulate the Sox10 gene result in red pigeons.
– Mutation of the Slc45a2 gene decreases the intensity of colors
  determined by Tyrp1, Sox10 and their mutants. Depending on the version
  of the Tyrp1 gene – blue-black, ash-red, and brown − pigeons harboring
  the mutant Slc45a2 gene still display the same colors, but in
  watered-down or diluted versions, less intense than those with normal
  Slc45a2. For example, a pigeon with both the ash-red version of Tyrp1
  and the mutant Slc45a2 gene has ash-yellow feathers. Pigeons with
  Sox10 and Slc45a2 mutations are yellow, which is the dilute form of
  red.

Source: http://unews.utah.edu/news_releases/birds-of-a-different-color/
Source: University of Utah

but what about the arrangement of birds hairs on its neck ???

@agharehanabbas: I pretty sure this a pigeon because of the beak. PS: can you post the picture of the neck if you are in doubt?

surely i will edit my question with that pic

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
what is the margarine metabolism in our body?
margarine is commonly used food ingredients that contribute to both inflammation and
obesity , but actually I want to know the margarine metabolism in the human body
I can find some resources talk about its impact on health but I can't get the idea of its metabolism.

You probably need to look at the components of the margarine, then research the metabolism of each component.

What are its components  ?

Mostly plant oils. Have a look into Wikipedia about it.

As pointed to by @Chris the Wikipedia link for margarine explains that these are formulated upon vegetable oil-based fats. Their melting points and other properties are adjusted by industrial hydrogenation of the unsaturated fatty acids in the vegetable oil.
Most unsaturated fatty acids present in nature are in the cis conformation at the double bonds. The hydrogenation process, if it is not carried to completion, produces the trans isomers of fatty acids. These so-called trans-fats are blamed for the undesirable side effects of consuming margarine, or other foods containing hydrogenated oils.
Most of the fatty acids present in margarine (i.e. cis unsaturated and saturated fatty acids) are metabolised by the normal route (β oxidation).


text:
Why are we carbon-based?
Is that because of evolution?
Does it have something to do with its amount in the universe?
Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy produced by the Sun and other stars as I know.

related post

We are carbon-based because carbon is the only molecule that is able to form the long, long chains of hundreds of molecules that are required to from proteins, DNA, etc. Absolutely no other molecule will do it. (Whatever you may have heard on Star Trek about Silicon-based life, Silicon doesn't form chains anywhere near as long.) Plus it's very handy in that its oxide is carbon dioxide, which is a gas, so using it and oxygen (another gas) as the end-points of respiration is very handy, you can get rid of a lot of gas very quickly. Silicon's oxide is, well, glass.
If you want to know why only carbon forms long chains, it's because of its size (not too large like silicon), its medium electronegativity (it's in a middle column of the periodic table, so it forms what are called "covalent bonds" very easily, especially with hydrogen, the #1 element in the universe by far; covalent bonds are easy to form and easy to break) and its valence (again, because of its position on the periodic table -- it forms four bonds, the maximum for a smallish molecule, giving it the geometry to form long chains).
For life to be based on anything but carbon, it would have to be made only of smaller molecules, which to our knowledge isn't very likely. Our DNA molecule is made up of billions of atoms; it's difficult to conceive how heredity could work on a small scale.

would be nice if you bothered to give references to your answers by which people interested to get more info could read full articles.

Another factor is relative abundances of different elements in the universe.

@The Last Word, all of that stuff is pretty easy to find via google (once you know what terms to look for), I'm sorry, I don't have the references handy, it's all pretty basic background knowledge to people who are familiar with these things. I took time out of my life to answer a question, I'm sorry if you feel I didn't do enough.

@WYSIWYG, you are absolutely correct in that if carbon were not so abundant, there would be no life as we know it!

I just pointed out something that you do on stackexchange to validate answers. Everyone does it and Iam in no way belittling your effort. I noticed that you do most of ur answers without references and if u feel Iam being overbearing I take it back

That's okay, it's just the word 'bothered' that took me aback a bit, but I'm over it. AFAIK, in general you don't put references to basic and easily verifiable information. (This is not an insult to the question, what's basic to someone is not to someone else, and you have to know enough to know how to phrase the question). If I were putting things that were only found in a handful of sources, definitely I'd put a reference. I'm new to StackExchange, so maybe the bar is set lower than I'm used to? What do you think in my response most needs a reference?

Too long for a comment. Just extending the answer from @prooffreader slightly.
It's true that long carbon chains are present in lipids, but in proteins and nucleic acids there are chains of carbon atoms interspersed with other atoms:
nucleic acids: -C[3']-O-P-O-C[5']-C-C[3']-

protein:       -C[alpha]-C-N-C(alpha)-

So the ability of C to form stable bonds with N and O (and S) is also important. It is also important that these bonds with heteroatoms are not too stable, thus allowing for making and breaking bonds at physiological temperatures. Then add to this the fact that most carbon atoms in biomolecules are tetravalent so that even when they are part of a chain they can be linked to other functional groups 'hanging off' the chain (such as amino acid side chains).
This combination of properties is unique to carbon.

Thanks for pointing that out, I wasn't clear in my resonse, I didn't mean carbons form long chains just with each other, but every long biomolecule chain involves carbon, there's no other element that's in every biomolecule chain bond).


text:
How does the Cuttlefish camouflage itself accurately despite being color-blind?
I have seen/read that the Cuttlefish is able to camouflage itself extremely accurately. I have also seen/read that they are completely color-blind, though see with very high contrast. How does the Cuttlefish manage to blend itself so well to its changing surroundings if it is not able to perceive the colors it is changing itself to?

Plants have evolved coloured flowers which they cannot see. Insect mimics have evolved patterns of colour which they cannot see. If the phenotype offers an advantage it can be selected for. Presumably cuttlefish can use other sensory cues to determine the nature of their surroundings and this information can be used as an input into the chromatophores and iridophores.

@AlanBoyd indeed but since the cuttlefish changes as a function of its environment, it must have some sort of sensory apparatus that can "see" the colors. Whether this happens at the cellular or the organismal level is another matter and what I hope this question might answer.

@terdon I'm suggesting that there is no need to see the colours. If other (strictly non-visual) sensory inputs are an indicator of lying on a sandy surface then these could be used to promote the "correct" choice of colours.

The reason why the cuttlefish is colour blind is because

it just has one type of cone cell. Humans have three different types,
  each sensitive to a different color of light. With only one cone type,
  you couldn’t differentiate between different colors (reference).

A study was conducted in the lab of Dr Lydia M. Mäthger where two different checkerboards were used to test their colorblindness.

1) Gray – Green. One green shade, matched to the maximum absorption
  wavelength of cuttlefish, was combined with 16 different shades of
  gray. As supposed some shades of gray couldn’t be distinguished from
  the green by the cuttlefish, which didn’t adapt the body pattern.
  Experiment one was successful.
2) Blue – Yellow. A checkerboard of blue and yellow matching in
  intensity was used for the second experiment. The skin color of the
  test species didn’t change either and therefore experiment two was
  also successful (reference).

These experiments concluded that it was indeed colourblind.
To confirm the effectiveness of the camouflage, HyperSpectral Imaging (HSI) was used to measure the colour match between the cuttlefish and its background. Using this technology it was perceived as to how a predator would view a camouflaged cuttlefish. It was found that

Cuttlefish can produce color-coordinated camouflage on natural
  substrates despite lacking color vision, and that the color aspect of
  cuttlefish camouflage is highly effective against fish predators. Much
  of the contrast information (which allows a predator to "pick out" a
  cuttlefish from the background environment) resides in the brightness
  (luminance) rather than in the color (chromatic) aspect of the
  reflected light. What this means is that cuttlefish camouflage
  strategies take away a tool from predators in their ability to pick
  out their prey from the background and instead leave them with only
  brightness as a method for prey identification (reference 1 and reference 2).

And now we get to the main question as to how they do it. Cuttlefish are apparently able to detect the intensity of light reflected from objects in its surroundings. It is able to perceive even a 15% change in contrast. In an experiment, it was found that

The animals did not respond to the checkerboard pattern when placed on
  substrates whose color intensities were matched to the Sepia visual
  system, suggesting that these checkerboards appeared to their eyes as
  uniform backgrounds (reference).

In another bit of interesting research done on the ability to copy the patterns on checkerboards (reference), three inferences were drawn

The first find was that the range (relative to the size of the
  cuttlefish ‘white square’) for the animal to exhibit disruptive skin
  patterning had to be withing a certain  narrow range. Secondly, given
  the appropriate size of checker, cuttlefish regulated their disruptive
  skin patterns according to the contrast between white and black
  squares. Third, by manipulating the number of white squares on a board to just  4
  among 316 black squares (or 1.25 %) produced disruptive patterning,
  yet increasing the number of white squares to 20, 40 or 80 did not
  increase the frequency of appearance of the cuttlefish ‘white square’,
  but only its clarity of expression.

This study shows that the number of white objects in the background significantly influence cuttlefish skin patterns further putting stress on its ability to view the polarization of light (reference).

Some cuttlefish camouflage examples

This is a standard answer from @TheLastWord; A very good answer showing an impressive amount of work with many references! Good job +1


text:
Does documentation exist that shows the evolutionary connection between common horses and the okapi?
I'm trying to put together some documentation on the relation between the common (modern) horse and the okapi. I've found a tree that shows that connection but it has no references. I'm hoping that someone has documented this connection somehow.

Can you add a link to the tree?

Okapi is like a giraffe right... so you have to go back to a pretty basal ungulate.

I have started to recreate the tree image that I found in Google Docs as a Drawing. Here is the link: https://docs.google.com/drawings/d/19NuQ0BgnUKuYqhabovdEI-UG6Tj3OfcEOb8h23UThIk/edit?usp=sharing

tolweb.org is your friend!
Because the okapi and the horse are not so closely related you will probably find several articles on the subject. Okapi belongs to the order of artiodactyla while the horse belongs to the order of perissodactyla. They are both mammals, eutheria, ungalata (superorder).
Here is the tree of the eutheria (within the mammals) from tolweb. You have approximatively 150 references. You can click on perissodactyla and artiodactyla and you will find 100 more references.
These two references may help you (I only read the titles)

Graur, D., M. Gouy, and L. Duret. 1997. Evolutionary affinities of the order Perissodactyla and the phylogenetic status of the superordinal taxa Ungulata and Altungulata. Molecular Phylogenetics and Evolution 7:195-200
Xu, X. F., A. Janke, and U. Arnason. 1996. The complete mitochondrial DNA sequence of the greater Indian rhinoceros, Rhinoceros unicornis, and the phylogenetic relationship among Carnivora, Perissodactyla, and Artiodactyla (plus Cetacea). Molecular Biology and Evolution 13:1167-1173


text:
Ribosomes and DNA in chloroplast
Are there multiple copies of circular DNA and membrane bound ribosomes IN CHLOROPLAST ?
Are polysomes found in them ?

Wikipedia says the number of chloroplast DNA copies (nucleoids) drops from 100 to 15-20 as the chloroplast ages (https://en.wikipedia.org/wiki/Chloroplast_DNA#Nucleoids). No luck looking up membrane-bound ribo-/polysomes. I found lots on protein import into chloroplasts, but no export. My guess is that with many chloroplast genes migrating into the plant genome, protein flux is in rather than out (why would something the whole cell needs be made in just the chloroplast?). If you look at a list of chloroplast DNA genes, it's pretty self-contained; no proteins that would need to be exported.

ribosomes are never membrane bound.. they are adsorbed on ER (in case of RER)

The chloroplast, having multiple circular copies of its chromosome and its own tRNA and ribosome genes more resembles the bacterial systems it is descended from.  See @A.Kennard comment
Polysomes being found in bacteria frequently are single mRNA to which are attached multiple ribosomes.  This paper shows that chloroplast polysomes were observed in the mid 1960s by centrifugal sedimentation.


text:
Calculating photosynthetic efficiency
While calculating photosynthetic efficiency, do we take into account the Gross Primary Production or the Net Primary Production ?

We can actually use either depending on the specified convention, but a more convenient way to characterise the photosynthetic efficiency is:-

Considering the total incident solar radiation instead of that part which is absorbed (so that the calculated efficiency takes into account the total available solar energy on earth)
Using Net Primary Productivity instead of Gross PP.(so that the efficiency is characterised by the useful output (product) of photosynthesis by removing the non-useful respiratory losses of plant.)

I should also mention that using GPP instead of NPP was the practice followed in a large number of texts I read. But I think using NPP is not only the modern view, but also scientifically more convenient.
Here is the wikipedia page on photosynthetic efficiency and here is the book which houses the technicalities of these definitions along with several values of the various efficiencies.


text:
Transmission of disease from mother to fetus
Can  parasite, microbes be passed from mother to fetus through the placenta ?
I know some like HIV can be.

HIV rarely crosses the placenta and almost exclusively where it has been left untreated leading to vary high viral load - a greater risk is in delivery itself leading to many HIV+ve mothers chose to undergo elective Caesarean sections

Pregnant mothers can indeed pass on various microbes to their fetuses but it is not always directly through the placenta, as the placenta can be protective.  Although the blood of the mother and fetus do not mix directly, the two can interact.  Maternal proteins can flow across to the fetus, as maternal antibodies are actually the source of a newborn's immune system for a few months, and maternal immune cells have even been found in fetuses, which of course means other cells or viruses can get across.
HIV is a good example for your question, actually.  HIV can infect newborns through the placenta, but the majority of infections occur during birth, not in utero.  Birth is a pretty bloody process, and the rupturing of the amniotic sac exposes the infant to anything in the mother's blood, which is when most infections occur.  For HIV specifically, physicians can all but prevent mother-to-infant transmission by administering anti-HIV drugs just before birth.
Here is a list from the CDC of some STDs which details how infections may be passed on to newborns; most clarify that it mainly happens during the birthing process.  That being said, plenty of diseases will cause transplacental infections.  Usually they are viruses, as viruses are simply smaller, but there are definitely bacterial and parasitic examples, such as Borrelia duttonii, Trypanosoma cruzi, and Toxoplasma gondii.  Here's a list of bacterial ones and here's a list of viral ones.

Parasite are organisms, and they can pass through mother to her child while its in hers womb. Toxoplasma gondii is an example, it passed from mother to child as it moves through her body, and since child is present inside her, of course it will get into the child.
You can diagnose for the parasites, or can even get them treated well just like getting your self treated, but measurements should be taken while treating as the their might be a danger of miscarriage.
So the answer is Yes, parasites can pass through the body of mother to her baby. Since the baby is inside her being a part of her body.
There is an infection called toxoplasmosis which doesnot passed from person to person, yet it can pass while in pregnancy.
Chagas disease is a disease that can get transferred from Mother to her child, during pregnancy. Which is called by a Parasite called Trypanosoma cruzi.
Reference:
http://voices.yahoo.com/can-parasite-passed-unborn-children-via-their-4839156.html?cat=70
http://kidshealth.org/parent/infections/parasitic/toxoplasmosis.html
http://www.livescience.com/21432-chagas-disease-mother-child-pregnancy.html


text:
How is bacterial plasma membrane made?
Eukaryotes have ER which manufactures plasma membrane of cells. How is prokaryotic plasma membrane made ? What is the pathway and which enzymes are involved ?

The processes that occur at the ER membrane in eukaryotic cells take place directly at the bacterial plasma membrane. Phospholipids are synthesised and inserted at the plasma membrane, and there is a protein translocation apparatus for translocation of proteins into the periplasmic space and insertion of transmembrane proteins into the plasma membrane.

Thank you Alan. It would be nice if you could add some more detail.


text:
What magnification do I need to see blood cells?
If I want to buy a microscope for my kids to be able to view single celled creatures and blood cells, about what magnification is required?  A Celestron Pentaview digital scope claims up to 600×. Is that going to be sufficient? I somehow get the impression that I'd need 2000× or better, but I'm having trouble verifying any information about magnifications via my good friend Google.

If you know what to look for, 400x is sufficient. Anything higher is usually a marketing claim and not possible with cheap consumer microscopes.

@Chris, That's part of my question actually, as well. If I want to get a good 400× magnified image, then how much higher should the scope be rated for?

I suggest doing a google image search for an idea of what detail you can see at a given magnification.

@canadianer, Oh I've tried that. people are not very clear about magnification at all. sometimes, if you're lucky, they will put the power of the eyepiece, but that is not total magnification.

Resolution is significantly more important than magnification.  You will see more with a good 50X than an inexpensive 500 X.

Depending on how much detail you want to see, 400X (as Chris commented) is definitely sufficient. Remember, the lens(es) under/over the stage are labeled 10X, 20X, 40X, etc., while the eyepiece is generally 10X or perhaps 20X (multiplying the two together gives the final magnification). If your target magnification is 400X, then get a 400X scope - it doesn't need to be rated any higher than the highest magnification you want. 600X sounds nice, it's actually higher than the (non-digital) scopes I routinely use for examining mammalian cell cultures. 400-600X should give a very clear detail of both red and white blood cells.

Quick question. For prepared slides it should be no problem, but if the OP is planning on having their kids prepare their own slides, won't they need Hematoxylin & Eosin stain to really see anything interesting?

@AMR of course, there's a whole bunch of supplies they can/should get to create nice slides, stain various structures, preserve things, etc. That wasn't part of the question, though, so I didn't address it. However, you don't need H&E to see cells - you can see their outlines and occasionally internal structures just with bright phase. I use it to examine growing cells in culture all the time - just take the flask out of the incubator, turn on the microscope light, take a peek, focus, and you're all set.

Same here. I wondered why they would ask what mag they needed to see blood cells, and I thought, Okay, they are going to prick their finger and make a slide, and if they are looking at Google images (or @AliceD addendum) and think that that is what they will see right out of their finger, then they may want to know that they will need to stain the cells to see more than just the outline of the cells. Though I could still look a pond water sample and be fascinated for hours, nothing fancy required. Must have been amazing to have been Leeuwenhoek and not have taken any of this for granted.

As so often in science; it depends. In this case the magnification needed to visualize RBCs depends on the amount of detail you wish to see. Below I have added my 2-cents worth as visual add-on to @MattDMo's answer below:

Blood smear showing red blood cells and two white blood cells at 400x. Source: Microscope Master

Human red blood cells 1000x. Source: Wikipedia

Human white blood cells 2000x. The small dots (red arrow) are Diplococcus gonorrhea bacteria (Neisseria gonorrhoeae), each ~0.5 micrometers in diameter. Some of the neutrophils have phagocytosed bacteria. Source: Waynes World

Red blood cells visualized by scanning electron miscroscopy. Source: Pinterest.
Note: for illustrative and comparative purposes only; electron microscopy is not the most advisable method for home use.

C'mon Mate! They said for their Kids.... Hey mom! Joey is hogging all the SEM time again... Joey, let Sheila have her time to scan for HepB. ;-)

@AMR bwahaha, LOL, I should have pointed out the SEM was added for illustrative purposes only.

BTW the 2kx; do you know if that is degranulation, platelets, or a bad mycoplasma contamination? It is a pretty cool image.

@AMR - It is actually closer to HepB :-) edited. Thanks again for your keen eye.

Helpful.  I was critically reading a "journal" "article" - https://ijvtpr.com/index.php/IJVTPR/article/view/47/123 and noticed that the "40x" images of RBCs seemed way off.  Sadly/amusingly, I noticed other problems with the images, such as a lot of redundancy/near duplication. (And those are just the problems I noticed with the images...)

@WHO'sNoToOldRx4CovidIsMurder ijvtpr seems to be a bogus journal.

Did you not notice the quotation marks I put around journal and article?  SMH.


text:
How can space-time affect ageing?
I recently watched the movie -"interstellar" and I came through the question that how can ageing be affected by space-time? Wherever I look, I get it as a fact that it's kind of ageing slows down in space, but I don't understand why.
How can space-time affect internal cellular metabolism? And if it is related to our biological clock, then can it be a sufficient explanation for this kind of drastic ageing changes?

This is a physics question related to the time dilation explained by the special theory of relativity, and is therefore off-topic in [biology.se].

See this

@WYSIWYG- I was just trying to get some kind of biological explanation on the slowing down of the chemical processes occurring in our cells. I had earlier read on wiki about time dialation and there was just this that wrt earth ageing slows down. I wasn't able to get the feeling of it ... that's why I asked it here...in biology... but as "Christiaan" explained that even the rates of reactions can slow down ....even though I don't get the feeling ....I am trying to grasp this idea....

There is no change in mechanics as you can note in the linked Physics post and wikipedia. This is just a property of the spacetime itself. As noted by someone in the [physics.se] post, the theory of relativity is not very intuitive.

According to Einstein's Special Theory of Relativity, moving objects measure shorter in their direction of motion as their velocity increases until, at the speed of light, they disappear. It also tells us that moving clocks run more slowly as their velocity increases until, at the speed of light, they stop running altogether.
Hence,  astronauts traveling at great speeds for long periods of time return to earth younger than had they stayed on earth.
Technology, however, limits the velocities of astronauts, the differences are hence minuscule: after 6 months on the International Space Station (ISS), the astronaut crew had indeed aged less than those on Earth, but only by about 0.005 seconds. Hence, your notion that there are drastic changes do not find solid ground in the light of current technology. The effects would be greater if the astronauts were traveling nearer to the speed of light (299,792,458 m/s).
It is the mere physics behind it. Everything slows down relative to a slower moving observer. Not just metabolism, but time itself.

@Christiaan- so you mean everything slows down ... like  rate of any chemical reaction occurring in our cells?

@anamikaSingh - everything slows down


text:
Double use of ATP in relaxing myosin & active transportation of calcium?
Is the ATP molecule which is bound to the myosin head for relaxation of the muscle (i.e., to break the cross bridge) also utilized for active transport of calcium to the sarcoplasmic reticulum during muscle relaxation?

ATP is used for ion pumps as well as movement of molecular motors. It is of course not the same molecule that does both simultaneously. How can it!!

Thanks. ..I just read in a book , I got confused. ..thanks for clearing up the matter

@WYSIWYG: you have my deepest respect for understanding this question! I edited accordingly, thanks! Convert to an answer and you will get a much deserved +1

Yeah I somewhat guessed the meaning. Tried some edits but I left it to the OP to explain the rest.

ATP is used (hydrolyzed) by ion pumps to transport ions such as calcium against their concentration gradient.
Molecular motors (such as myosin and kinesin) also couple ATP hydrolysis with movement.
However both these processes are separate and just because calcium flux changes happen during muscle contraction doesn't mean that it is the same ATP that drives some kind of a bifuntional enzyme to perform both tasks.
Moreover calcium is released during the contraction phase from the sarcoplasmic reticulum (SR); pumping back the calcium to the SR happens during the repolarization (there is no myosin movement at this stage).


text:
Why can't we see in low light if staring long enough?
For me it seems reasonable that if I kept my gaze on a fixed point in a room with low light, a progressively brighter and better picture would appear before my eyes, just like a camera can see in the dark if the shutter speed is really slow, e.g. 4 seconds exposure. Why can't our brain do this trick as well (accumulate visual information over time)? Or is it a limitation of the eyes?
edit:
To further clarify what I'm after; I will show a concrete example from the world of photography (images taken from this website).
Here is an example where we have a series of underexposed images - this would be what the brain receives:

Now, combining all of them with a simple add-operation reveals one image that has normal exposure.

This seems like a simple trick for our powerful brain - surely it can add incoming signals?

Calling it a simple trick that the brain should be able to do is really kind of missing the entire point of the answer.

Maybe it would be a simple trick, but what would be the evolutionary benefit to such a trick?  The visual system works quite differently, detecting change/movement (which probably equals threat) far more easily than static scenery.  The human eye has built-in motion - saccades - that allow it to see more clearly.  IIRC (though I can't quickly find a reference) if you electronically compensate for the saccades, so the visual field stays fixed, everything washes out and you're effectively blind.

@jamesqf - Thank you. I guess my answer was too vague, that "not be[ing] able to detect change rapidly [is] something that would be most inconvenient." Your comment adds a lot to the answer.

Also think in terms of evolution.  Say you're a species evolving towards being nocturnal, and "need" to improve your low-light vision.  The easiest route is simply to increase the size of the eye.  You could also add a reflective layer, e.g. the " tapetum lucidum".

out of curiosity - have you tried to add your 8-bit, noisy, underexposed pictures to obtain the exact final image? I bet you can't :)

A point that I missed the first time around: evolution has not had much time to work in dark rooms.  Even though humans are not primarily nocturnal, our low-light vision is perfectly adequate to cope with most natural low-light settings, where there is still light from moon & stars.

For simplicity's sake, let's really reduce this to something like photography.
A camera's aperture can stay open indefinitely, allowing the plate (or whatever is receiving and recording light) to "collect and save the effect of photons" over time, if you want to phrase it that way. That allows a camera to make images that our eyes never can, for example, of "star trails".

The retina isn't like a photographic plate or a digital sensor's photosites (or pixels). It can't "collect and save" like a camera can. There is a "refresh rate", if you will, that disallows a collection and saving of light that doesn't apply to cameras, because cameras don't care if something in their vicinity is sneaking up on them and presenting a danger to their lives. Not being able to detect change rapidly is something that would be most inconvenient to survival.

It is the time sampling with long exposures that really makes the magic of digital astrophotography possible. A digital sensor's true power comes from its ability to integrate, or collect, photons over much longer time periods than the eye. This is why we can record details in long exposures that are invisible to the eye, even through a large telescope.

How Digital Cameras Work

Good answer - I have added an additional example in my question to handle this as well by not relying on a single long exposure.

And for an extreme example of this, consider the Hubble Ultra-Feep Field (https://en.wikipedia.org/wiki/Hubble_Ultra-Deep_Field ), with an exposure time of about a million seconds, or over 11 days (if I did my math right).

I don't feel that this is the answer: it assumes that it would be the retina's job to record data, but that's not necessarily true. The question should be answered with this and why it's not feasible for the brain to record the light as well. A combination of this and some of the answers below that actually address that would be perfect.

@Numeri - I did say it was a simplification.

@anongoodnurse Fair enough :), but I do think you should mention why the retina 'refreshes': our eyes move themselves every so often in order to keep alert (still a simplification, but I feel like it would be more informative). But thank you for your well written answer!

The differences at the photoreceptor level have been addressed by others. The mechanical restrictions of the visual system were shortly hinted at by @gilhad et al., but deserve more attention in my opinion.
First off, in darkness we cannot focus on an object and our eyes will move. And even when we focus on a specific point there is always movement of the eyes due to due to tremor, drift and microsaccades. Microsaccades are involuntary small movements of the eye (Fig. 1) that have received quite some attention lately. It is estimated they occur 1 - 2 times per second and they can reach amplitudes of up to 1 degrees of field of view (Martinez-Conde et al., 2013) and last for about 15 ms (Cui et al., 2009). It is thought that these movements prevent adaptation at the retinal level, and prevent image fading. Hence, images on the retina are constantly mechanically refreshed. The brain in turn stabilizes the image by correcting the image at the perceptual level through oculomotor feedback (Martinez-Conde et al., 2013).

Fig. 1. Microsaccades recorded by an eye tracker. Source: Martinez-Conde et al. (2013)
While a camera must be fixated on a tripod stand to allow for overexposure,  our eyes cannot be fixated to the same extent, even when we try. Hence, combining exposures as indicated in the question is impossible and results in image blur. Instead, retinal images are constantly refreshed and when lighting conditions are too dim we cannot integrate photon input in the temporal domain.
Note, however, that photoreceptors do integrate photon input to some extent, given that higher luminance results in brighter perceptions.  However, this operates only in the order of milliseconds and doesn't allow for long-term exposures as necessary to obtain images like the one shown in the great answer from @anongoodnurse.
References
- Cui et al., Vis Res (2009); 49(2): 228–36
- Martinez-Conde et al., Nature Reviews Neurosci (2013); 14: 83-96

I'd like to think, if we just focused on something for even half a second, that our brain could take in half a seconds light, process the directions we were moving in and adjust the images before threading then through to remove blur and then we could see in low light. I just wonder, from a purely technical point of view. Could our brains do this. As of course, half a second, or however long, would have impacts on survival. So again, just technically

The simple answer is, that eye is not constructed such way.
The eye have much more "pixels" than "links" to the brain and sends in "preprocessed" image. Moreover the the eye is constantly moving and scanning the "area of vision" and the body and head are supposedly also moving (willingly or not - nobody can freeze totally) so longer accumulation of data would lead to big blur.
And the main purpose of eye is to spot danger - something changing, or moving victim - as we human are not nocturnal animals, we are constructed/optimized to work in mode active on light, passive and sleeping in dark. As there is real need for sleep anyway, there is not good reason to develope secondary system for night vision - meaning duplicate the main vision system completely with totally different mode of work (long time collecting data) which would be used only in very little split of time - when predator find us in night sleeping and we survive the first attack.
So only the main system was slightly modified with other kind of pixels more sensitive to light, but less to color, which allows us work to relatively last night and from really early morning when only split of light is accessible. At the price of color and details. But it is much cheaper, then mainly unused secondary system. And covers more time, than we usually use to move in.

There's probably a theoretical capacity to do so.  The brain is amazingly good at signal processing, and could probably pull off such a summation.  However, there is a limit.  You have to hold very very still for it to work.
Go take one of the time lapse pictures, like anongoodnurse's answer posted.  The shutter is open for quite some time (her picture looks like a 30 minute or 1 hour exposure to me).  During that exposure, the camera holds perfectly still. All motion you see is motion due to the objects in the scene moving (or,  if you prefer the technicality, the stars are holding still, and the camera is rotating... really really really smoothly).
The body does not have such an ability to lock itself down.  Try taking one of those pictures while holding the camera in your hands, and you'll see its particularly difficult.  Now consider that your eyes are even more twitchy than the rest of your body, capable of darting this way and that.  We have good control over our eyes, but nothing close to what you need to create an effect similar to that of a tripod.
Thus, if you were to try to use your eyes in this way, almost all of what you would see is your own motion.  Presumably a very well controlled individual might be able to sense that movement and account for it, but there's little reason for the brain to have that ability in "hardware."
Of course we can lock our eyes on to see with incredible accuracy, right?  We can read words on an eye chart at 20 paces.  Those activities are being done in a scene which permits visual feedback.  If its too dark, we don't get enough visual feedback to see where our eyes are pointing and compensate.

What I believe you are referring to, is the phenomenon by which the camera adjusts light exposure by adjusting aperture. We can also do this, but it happens very fast. Go from a dark room to a brighter room and you will be blinded, but that effect soon subsides, and vice-versa.
The pupil opens up in a dark room and production of visual purple or Rhodopsin takes place in the Retina, a pigment responsible for visibility in low light. When you enter a bright area, the pupil contracts and Rhodopsin is photobleached, with production of Iodopsin taking place.
https://en.wikipedia.org/wiki/Adaptation_(eye)
^
Check out the Dark adaptaion and Light adaptation sections
(Sorry I don't have more sources, I had done this from my highschool bio textbook, and I can't find it)

Thanks for your input, but unfortunately that's not what I'm after. You did however send me on the right track to find the correct term I'm looking for: shutter speed.

I think the question's actually referring to a camera adjusting exposure by increasing shutter speed. Increasing aperture would be, as you say, (literally) equivalent to opening the pupils of your eyes, but the question's talking about staring at a scene for a long time, "collecting" lots of light and summing (rather than averaging) that into an image.

Oh alright, got it. Glad I could help!

"adjusting exposure by increasing shutter speed" Er, I mean decreasing shutter speed but you probably all figured that out.

I wish my computer as capable of sending an illustration of the arrangement of the human eye, versus the hypothetical "camera lens" idea, as organic eyes and camera optics are in NO WAY SIMILAR! Most of you have been in gross error by doing such, in your discussions.
The eye uses a combination of organic optical cells called "rods," and "cones," in order to manifest an image. In addition, there is a "dead spot" on the image perceived by an eye, owing to the insertion-point of the optical nerve. Any discussion of organic vision has to take these facts into account.
Organic eyes MUST go through a variable period of "dark-adaptation" in order to be able to perceive an image,as well. The minimum period is between 50-120 minutes; and even then, even an instant's exposure to "brighter" light will erase all of this adaptation, necessitating "restarting the clock" to dark-adapt the eye, again.
There's an anecdotal tale purporting that pirates had worn eye patches so that they achieved and kept dark-adaptation in one eye. There are many advantages to keeping one eye dark-adapted--- one is going from a brightly-lit deck, down into the very dim below-decks areas of a victim's ship. This is a case where being able to pull off the patch and being able to immediately see the enemy crewman coming in with a cutlass would be very valuable!
Another factor is that the distribution of rods and cones is not uniform, across the eye. Cones deal with colour-perception, and are concentrated at the centre of of the visual field. The concentration of cones rapidly declines, going outward.
Densities of rods in the same eye rapidly increases, going out from about five degrees from dead centre to a maximum of approximately 25 degrees from dead centre. Rods are responsible for our peripheral vision, our "sensitivity" to even seemingly-microscopic motion, AND OUR NIGHT VISION.
Because of the lack of rod-cells at the centre of our eyes' visual field, we are unable to see anything dead-ahead of us, under low-light conditions!
In order to be able to bring the maximum number of rod-cells to bear on an "item of interest" in our visual field, we have to use our peripheral vision and "cheat" off to one side of our visual field by about 25 degrees. This is like watching the front door in the centre of a building by looking "straight" at the middle of the left or right facade.
One would also be able to detect motion far easier than exact shape by looking in such a way. By continually "looking to one side," and by altering our location so as to change the background, it is entirely possible for an astute woodsman (a Native American or a Hillbilly, for example!) to be able to not only spot a raccoon in the top of an oak tree, but also to make out the form of the opossum looking up at him, from a lower limb!
Many animals far better able to operate at night have eyes that are not only better-equipped with rod-cells, but are in fact, much larger than ours! We would see as well as any owl, had only we been born with eyes the diameters of "jumbo" grapefruit!
Plus, watching and closely emulating the owl, with the head-bobbing, the weaving from side to side, and the peering-ahead, we would naturally improve the peripheral-sensitivity and the "looking to one side" conjuring of sharper images of those objects of interest to us!
I am sorry to be critical, as many comments showed great understanding of non-organic optics, as well as great imagination, but it is simply not possible to be able to blythly interchange the principles of non-organic optics and organic optics.

Pretty much all answers which focus on movement of the eye causing blur (something a digital camera does not have to deal with) are wrong. The brain has absolutely no problem processing images in low-light at speed.
The answer is all to do with the fact that the eye is not a camera. Much of the old-school theories which where based on the fact that the eye works like a camera, such as persistence of vision, etc, have been proven demonstrably wrong. The eye does not have a shutter speed - information is constantly being sent back to the brain with no interval delay.
(https://en.wikipedia.org/wiki/Persistence_of_vision)
This means that resolving blur/etc is done in the brain, not by the eye. Think of digital image stabilization that actually works, and works in real-time.
However, the brain does appear to work on chunks of eye-input, at roughly 16-24 chunks a second. Why this speed? Well, liking the brain to a computer, it probably has something to do with the amount of memory the brain can store for unprocessed eye-data. Long-exposure photos require a lot of RAM to store the raw data, then a lot of time to compile it into a single image. The brain could do no doubt do the compilation from raw data to image, but it very likely cannot store more than 1/24th of a second's worth of data in "memory" before it has to compile.
More importantly, doing so would reduce our reaction time significantly. This is important because you do not want an organism that can see a branch clearly at night, but when they try to grab it, miss by 5-10 seconds.

This is more like the kind of answer I was expecting to this question. Makes me wonder if slow moving nocturnal animals already uses this kind of temporal accumulation of visual information to improve their vision.

The brain has absolutely no problem processing images in low-light at speed is true, as rods are built for speed. However, because of eye movements the brain cannot integrate signals barred each frame would be re-positioned over the previous one. That doesn't happen.  Hence, calling out that ...all answers which focus on movement of the eye causing blur are wrong is off, especially because the arguments you pose are based on a lot of 'probablies' and 'likelies'. Show us the references that prove the other answers incorrect, or otherwise you might want to tone down your answer.

I should tone it down because that would just be better - however i cant do much about the references because all the articles I read for this post state that the field itself is unsure how the brain does it. All we really know is that it doesnt work like a camera, which is all I stated. Would be great to get some more info though - I find this really fascinating :D


text:
Names of nerves in hands, shins and face
I am looking for the names of the nerves in 3 specific locations of the human body:

The nerve running along the "top" (opposite side of the palm) portion of the thumb, from knuckle to fingernail (see 1st picture below); and
The nerve running along the anterior tibia (also see 1st picture below); and
The nerve(s) of the face running along the eyebrows and outer edges of the eye sockets (see 2nd picture below)

After looking here, here and here, the best I could muster was:

The median nerve is the nerve that carries sensory signals from the top of my thumb; and
The superficial peroneal nerve is the nerve that carries sensory signals from my anterior tibia

But in every diagram of the face's nerves, there are simply too many for the article/blog/diagram to enumerate, and I can't discern which specific nerve or nerves runs outside of the eyes and across the brows.
Any ideas? Here are the pics to solidify the specific areas I'm looking for:

Please note: this is not homework! And although it may be considered by some to be a rudimentary question, I have actively tried to research this myself and have come up short. Below, I explain all the failed methods I attempted to figure this out on my own. So all this to say: if you do down/closevote this, please don't do it because you think it's homework or because you think it shows a lack of research!

I have made some structural edits by placing the this-is-not-homework comment below the question. Hope that's fine. You can roll back easily if you don't like it. I edited the tags. This is definitely unrelated to the central nervous system.

http://classes.kumc.edu/sah/resources/handkines/nerves/nerve.htm

https://home.comcast.net/~wnor/antlegdorsalfoot.htm

You are looking for the Trigeminal nerve, the largest nerve in the face. Here it is with its branches.

It is both afferent and efferent.

Afferent and efferent components of the facial nerve in the bullfrog (Rana catesbeiana)
Cranial Nerves Illustrated: Figure V-4 General sensory component of the trigeminal nerve, ophthalmic (V1) division.
General sensory afferent (blue-green)


text:
Mechanics of Peregrine Falcon Dive Pull Up
There are loads of information on how fast the Peregrine Falcon dives, but aside from having specialized lungs, eyes, etc... to survive the dive.
What mechanics does it use to pull out of such a dive, specifically after it has hit it's prey.
My take is that it uses its momentum to loop back in a U-shape, understand that by changing the angle of attack, this generates the necessary drag & lift to pull out of the dive saftely.
My question is how effective is this & can a larger bird pull this off assuming it has all of said mechanics?


text:
How long does it take for dopamine to reach normal levels after a significant drop?
The building block sequence for is: Phenylalanine << Tyrosine << L-Dopa << Dopamine. It’s produced in only a few, very specific regions: Substantia Nigra and the Ventral Tegmental Area. Although, on average does this take minutes, hours, days, weeks? And does releasing it between synapses or something else for normal activity affect the time?
Ultimately, I am trying to find a graph of the average anergia level after sex. Or similarly, dopamine levels after orgasm. Most of the research I have come across is about disorders or is too general. Also, there are informal articles and graphs of dopamine levels, but they very widely and are not sourced.

dupe from same user. http://biology.stackexchange.com/questions/51445/how-is-dopamine-produced-in-the-brain You know you can edit previous questions right? You should look at the comments, expand your answer and ask questions if you don't know what to do.

That's the whole point of SE way of doing things. You get new information and you expand the same question not create another one a bit more in detail. Or would you like someone to just answer vaguely to the other question and more in detail to this one? You should improve the previous questions instead of re-writing the same question it just gets confusing otherwise not to say completely redundant.

200 milliseconds as the half life of dopamine provides no meaningful (to me at least) connection to the question at hand. The Study of dopamine turnover uses a very obfuscated argot to laymen. Is there significance to this study in relation to the question? As for the question itself, is it too complicated to answer to a non-chemist?

Nice that you put everything together, that was my only point.

I transformed the chat into an answer...

I can see a couple of problems in the question:
First problem, you assume that anergia (not sure that's how you call being tired) after sex is caused by dopamine depletion, I'm not sure this is the case or that lack of dopamine has been related to anergia at all. We know from Parkinson patients that Dopamine is related with action initiation (http://www.nature.com/nature/journal/v466/n7305/abs/nature09263.html) not necessarily with lack of energy or motivation.
Second problem, depletion (the term you originally used) means no more dopamine is system, either because you block it somehow (antagonist), you block its receptors (receptor antagonist) or you block one of the precusors involved in synthesizing it eventually depleting your reserves. "Significant drop" needs to be quantified.
Dopamine (DA) synthesis is an ongoing process, and DA is an essential neurotransmitter / neuromodulator in the brain just like Serotonin (more on that later). This means that it probably has different roles. One phasic referring to its neurotransmitter properties and one tonic referring to its global levels in the brain and how it modulates ongoing synaptic activity.
Normal activity does not deplete DA, and yes, no matter how crazy you think you are, sex is considered normal activity. You can obviously have variations of basal levels of DA depending on your activity but they are way removed from the depletion criteria.
Furthermore, the brain is very parsimonious in its synthesis efforts, it has specialized molecules that recover neurotransmitters that where unused from the synaptic cleft, these molecules are appropriately called reuptakers.
Now to attempt to answer your question considering the problems:
I don't know about DA but I do have some experience with serotonin depletion.
Serotonin (5-hydroxytryptamine, 5-HT) is synthesized from tryptophan that you cannot produce endogenously. Lucky for us that tryptophan is in almost every food we eat which means that there is no lack of it.
You can, in experimental conditions, ask people to drink a glass of a very disgusting liquid that will bind to your tryptophan preventing it from being used in new 5-HT synthesis. It takes approximately 4-6 hours for it to work (e.g. http://web.stanford.edu/~knutson/ans/bjork99.pdf methods section), which means that in 5 hours you used up all your reserves of 5-HT. This meansthat your "refilling" process would be about the same time  in order to get to pre-depletion levels (you might be able to be in a functional regime before that if you ignore the reserves part).
So from this 5-HT example I would say that unless something is very different in the case of DA to recover from depletion it would have to be in the hours time frame.
Another way of looking at it can be looking at the half-life of the molecule which gives you an idea of how much time it lives. This can be used to calculate how much production there has to be to maintain a level of X. The turnover is the amount of time that it takes to, well, turn over, so replace DA in the system that should be in the same order of magnitude as coming back from a depletion experiment.

I may have been trying to be pretentious before by having "depletion." I was about to put this question on Cog Psych SE.  (It should not be asked on Cog Psych SE, correct?)

I wouldn't in its current form, but maybe people there can have some insight, you are not convinced with my answer?

Assuming sex reduces tonic levels of dopamine, you want to know how long it takes to go back up? I would say, as stated in the answer, that if it would take hours to go to basal levels after depletion it could take minutes to recover from a small dip because of sex. or do you have a specific question in mind?


text:
Identifying internal structure of dissected prawn
Note: Some of the images might be disturbing.
I have dissected prawn for the first time. Would like your help in identifying some structures
.

This is the dissection of the posterior part of the prawn. What is this blackish structure in the middle ? This structure becomes whitish farther down. Then, it forms a small sac like structure and then becomes thin again. This whole structure appeared just after I cut the exoskeleton. It is directly above the muscles.

I think that this is it's alimentary canal and the black area has digested food in it. The sac like structure might be the rectum.

It is, indeed, the alimentary canal. It is actually this canal that it's important for one to remove when "de-veining" shrimp, rather than the vein itself, which lies immediately dorsal to the digestive tract.

In the future, I might suggest doing a little more research prior to asking the stack exchange, as frequent users of the site do like to see evidence of effort on the part of the user to find their own answers. A quick search for "alimentary canal prawn" or "arthropod anatomy" would likely have turned up your answer.


text:
What do the qualifiers used in botanical species names mean?
These are all the qualifiers I've come across so far. The first 3 were quite easy to google, but the other 4 have me stumped.
I also can't say I'm completely clear on the nuances of s.s. vs. s.l..

agg.
s.s.
s.l.
cf.
cv.
auct.
ined.

agg. means aggregate and is used when species have been grouped together.
s.s. stands for sensu stricto and is used for a strict or narrow usage of definition.
s.l. stands for sensu lato and is used for a wide or broad usage of definition. these two pop up a lot in paleontology since species definition can be vague.
cf. stands for "conferre" and is used for provisional names when an organism is not completely known, such as when a variant is found and they are not sure which species to place it in.
cv. stands for cultivar and is usually followed by the unitalicized name of the cultivar.
auct. means "of author" and means the name is used in a different way than it is currently or in a different way than the paper using it does, such as quoting a incorrect name from another author or a debate between two possible usages. (used a lot with overturned or contested names) it is often followed by a qualifier giving more information about usage.
ined. means undescribed, and is used for a new proposed species before it has been formally described (common in paleontology when many papers about the same new specimen may be released at the same conference or where a specimen might not be identified yet still yield useful information in other ways.)
if you put the exact form of the epithet (include the period) followed by the word "species" in google it will usually return the usage, failing that you can search this site.


text:
How does boiling water revive cut flowers?
A classic tip to revive wilted cut flowers is to plunge the stem into boiling water for some period of time, and then back into cold water.
What process is occurring that causes the flower to be "revived"?

@jmusser A cursory google search shows that this is method is commonly described.

A google search also shows, that this is done to "remove air locks". Maybe the hot water is supposed to widen the capillaries and thus water flow can be restored at places where they were blocked by air bubbles.

I do not know about "reviving" but the process you just described is called "hardening". I do not know how or why it works, but the idea is that after this process the plant will take up more water than before.

I could not find any scientific papers that have done research into this phenomenon but the general reason given for wilted flowers to being resuscitated is given as the hot water being absorbed faster and I quote

Florists use warm water only for resuscitating wilted flowers, because
  warm water is absorbed quickly. For restoring wilted stems, hot water
  (110 degrees Fahrenheit) is recommended. For woody or badly wilted
  stems, very hot water (180 to 200 degrees) is better. Florists then
  move them into a refrigerator (reference).

The reason for absorbtion faster is given as
luke warm water in a vase arrangement because warm water is “thinner” (has fewer air
bubbles) and moves up the stem faster than cold water (reference) and Warm water molecules move faster than cold water molecules and so can be absorbed by flowers with greater ease (reference).

as a physicist I can confirm there is no such thing. Warm water is not "thinner", the temperature of the water (if in normal human range) is in no way tied to the amount of air bubbles in it. After reviewing the "ramsey" reference I am sorry to say that person has no idea what he is talking about, because in addition he states that warm water has more oxygen in it. Uh, no, tiny temperature changes do not alter chemical compositions, thank you very much! Finally warm water molecules move slightly faster than cold water molecules, which, in any event, has no effect on water uptake by plants.

@mathgenius Thank you for your valuable information.


text:
How much fat can the body absorb? Implications for daily fat distribution
This question is named analogous to this research: How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution http://ncbi.nlm.nih.gov/pmc/articles/PMC5828430
How many grams of lipids can the body absorb in one sitting? (I ask because a strict vegetarian or vegan diet is characteristically low in fat. Therefore, I consume extra virgin olive oil and nuts.)

Most of the research on pubmed.gov is about oral lipid drug administration/absorption. This work that seemed to come close is over my head and just doesn't seem to specify:
Intestinal Lipid Absorption and Transport by C T Phan 1 and P Tso
PMID: 11229876 DOI: 10.2741/phan
https://www.bioscience.org/2001/v6/af/A612/fulltext.htm

Image sources: Cronometer.com and Jackedonplants.co.uk

just a piece of advice, "nuts" covers a lot of things many common nuts are very low in saturated fat, and so its olive oil.

Indeed, lipid fecal loss remains below 5% (w/w) even in situation of
  high fat supply in healthy humans, [30].

All about those guts and bowls folks!

Niot, I., Poirier, H., Tran, T. T. T., & Besnard, P. (2009). Intestinal absorption of long-chain fatty acids: Evidence and uncertainties. Progress in Lipid Research, 48(2), 101–115. doi:10.1016/j.plipres.2009.01.001
https://sci-hub.tw/10.1016/j.plipres.2009.01.001
[30] Ross AC. Overview of retinoid metabolism. J Nutr 1993;123:346–50

The issue remaining is how Ross' work doesn't seem to say anything about lipids. Yet, it appears from the mice studies nearly all fat is absorbed (except for ones with special conditions).
Ross, A. C. (1993). Overview of Retinoid Metabolism. The Journal of Nutrition, 123(suppl_2), 346–350. doi:10.1093/jn/123.suppl_2.346
https://sci-hub.tw/https://doi.org/10.1093/jn/123.suppl_2.346

Your first sentence answers the question. Or practically: If the amount of fat you consume does not make your stools fatty (steathorrhea), it means you are absorbing most of it.

Maybe the amount of bile liver is able to produce and gall to secrete is some super natural limit.

@Jan or gut bacteria is breaking it all down inot something else.


text:
A book about the palmaceae
I hope this isn't inappropriate for the forum - I'm trying to find a book that I read several decades ago, possibly 40 years or so. As I recall, it was a systematic treatment of the whole of the palmaceae. The title was fairly brief, possible just the word 'Palms'; however, I don't think it was this one Martius: The Book of Palms. (I could be wrong, though.) Any ideas?