How is vitamin D synthesized in animals with fur; how do the cells get enough sunlight? If vitamin-D cannot be synthesized because of limited sunlight reaching the skin, do these animals have to obtain the vitamin from the diet or are there any alternate mechanisms of synthesis?
121507
The human body can synthesize vitamin D in the skin from cholesterol, when sun exposure is adequate. But how can haired mammals do it? Do not they need it?
60737
I've heard somewhere said that :     Stomach cells do not absorb anything larger than single amino acids.   Is that wrong?  How do biological toxins (peptides/proteins) from mushroom or bacteria like Botulinum come to our blood and affect our body after we eat them?   Update: In fact, i want to know if we drink milk, is there anyway IGF-1 protein from milk can pass through the intestine and affect our body. Because I see some arguments/debates about the IGF protein in milk can cause acne.
13405
Regenerating health on "Death March" difficulty can take a while if you have a rather big health pool and no perk to regenerate health (e.g. using Quen).  Apart from potions I use food to regenerate health. However, it can take quite a long time if I have to eat Dried Fruit And Nuts 5 times. I eat one, wait 5 seconds, open the inventory again (or use the quick slot) and wait 5 more seconds.  Therefore I'd like to know if vitality regeneration stacks by eating multiple foods.  For example (numbers not accurate):     I eat 1 "Dried Fruit and Nuts"   100 vitality restored over 5 seconds.  I eat 2 "Dried Fruit and Nuts" then leave the inventory screen. What is the outcome?   Regenerate 100 vitality over 5 seconds. Regenerate 200 vitality over 5 seconds.    Which way does it work? Assuming it works like 1. I would have to keep opening the menu, eating 1 piece of food, opening the menu again and eat the next. I don't like placing food in my two quick slots because I usually save those slots for my most important potions.    Edit 1:  After having a look at the question to which this question is flagged as a duplicate I concluded that there are contradictions on how the stacking works.  Two theories that need proof (proven in Edit 2):   Vitality regeneration does stack, no matter what you eat/drink. Vitality regeneration only stacks if the foods consumed are not of the same type (e.g. 2 x Nuts do not stack, but 1 x cow milk + 1 x nuts will stack).   I will test this when I get home looking at the numbers (vitality information on the inventory screen).  Right now, everything points to theory 2 since theory 1 would make you invincible for a short time if you stuff 20 roasted chickens down Geralt's throat.    Edit 2:  I can confirm theory 2.  Eating one raw meat regenerated 508 hp over 5 seconds.  Eating one raw meat and one cow's milk added two regeneration indicators to the UI and regenerating 1432 hp over 30 seconds. The timer for raw meat ran 5 seconds while the cow's milk timer ran 30 seconds.  This also confirms that different foods have different intensities of regeneration. While raw meat regenerates 508 hp over 5 seconds, cow's milk regenerated 924 hp over 30 seconds.  Oddly, drinking cow's milk without eating at the same time regenerated 931 hp.   Raw meat: 508 hp Cow's milk: 931 hp 1 x raw meat + 1 x cow's milk: 1432 hp (instead of predicted 508 + 931 = 1439 hp)   I did the tests at level 30.
120618
I am wondering why some got a moon and others got a sun as Where in the World hat for the same action:   vs.   And is it possible two collect both e.g. from different sites? I only get moons…  I know that there has already been some spoilering .
113837
I'm aware of the general mechanism of mushroom growing (place some mud and sprinkle mushroom seeds on it). However, I'd like to know a bit more about it before I start building my farm, so I'd appreciate it if anyone could give me the lowdown.  Specifically:   How deep down exactly do I have to go to grow mushroom grass? I've heard "0ft or lower", "when the background changes to dirt with rocks in" and "when the music changes". These all seem to be different points for me, so which is it? Is it maybe different for large/small worlds? Can I place background walls to keep monsters out, or will that stop the grass or the mushrooms from growing? How much vertical space should I give the shrooms? Is it possible for the big tree-like mushrooms to grow, given enough space? Is water required at all?
19875
Why do human women have periods when most animals don't? It is known that the unfertilized egg needs to be shed from the uterus. But why shed the whole endometrium? Why didn't evolution put macrophages to work to simply digest the ovum and only the ovum, instead of the physiologically, energy-draining process of menstruation and accompanying blood loss? Also, are there any other purposes for menstruation, besides wiping out dead ova?      Sites I used for references:  1.  -                       Menstruation seems energy draining, in my perspective, given that 30-40 ml of blood is lost × 3-4 days × 12 months × 15 years on average - that is a lot of blood loss.  2. Also see this .    Related question: .   My question is different from this related question because there the OP is concerned about the survival advantage of the menstruation with respect to the predators. Here I've asked why menstruation and why not phagocytosis as the former to me seems to be highly energy consuming process. Also as the fellow post writer had earlier suggested though the two questions  seem to be one and the same, they are subtly different and aimed for two different audiences as I emphasise more on the physiological aspects of menstruation and the related question's OP needs clarification about survival advantage and other ecological aspects of menstruation.
54658
If humans can live without consuming other animals, then why do we do it? From a biological point of view, why do we eat meat? I would also extend the question to other animals because many animals are carnivorous: why did carnivory evolve and why do animals eat meat?
7451
At school, we've been taught that human infants produce rennin/chymosin (which aids in the digestion of milk). More specifically, it is the peptic cells in the stomach which secrete prorennin, the inactive form of rennin (in addition to pepsinogen, the pepsin proenzyme).  User @another'homosapien's answer  also seems to concur with this (excellent answer by the way, I enjoyed reading it).  However  According to Mod. @AliceD's answer  (yet another excellent answer):     ...in humans there is only a chymosin pseudogene present...   Which (probably?) implies that humans (infant or otherwise) do not produce rennin.  I managed to get my hands on the Textbook of Medical Physiology (Guyton and Hall, South-Asian edition), and according to the book (Chapter Gastric secretions, page 406) peptic cells produce a large quantity of pepsinogen. There is, however, no mention of prorennin. I even flipped over to the Appendix at the back to look up "Rennin", but it turns out there is absolutely no mention of rennin in the book.    My questions,   Some sources claim that rennin is produced in human (infants). Is this true? Other sources claim that rennin is not produced in humans ( we have a pseudogene for it though). Is this correct (I mean the "rennin-is-not-produced" bit, not the "pseudogene" bit)? If rennin is produced in humans only during infancy, what stops it from being produced as we mature? (I'm asking this because every source I've seen that claims that rennin is produced in humans, explicitly states that is done so during infancy...which would suggest that rennin is not produced in adults)
70019
I've been looking around and cannot find a definite answer on what it is that tells trees to change their metabolism and drop leaves. I see that such activity is called .  What interests me are the specific mechanisms by which a tree knows that it's time to drop leaves. Is it photoperiod shortening (day duration?) Is it temperature changing metabolism? Is it build up of some toxic compound?  Thank you for your input!
82529
I'm having an hard time understanding primary cells. There are plenty of videos and explanations about the reactions that happen inside the battery, but you must have a strong background in chemistry to really understand them. Instead, I would love to have a description that abstracts from the chemicals details, and still manages to explain its basic working princeples! I would like it to address the following questions/doubts:     Electrons flow form higher potential to lower potential so, when you buy a  battery, is an electric field already there, before connecting it to a wire? (I presume yes) So,How is this field created? Are the electrons at the top and the protons at  the bottom, or just electrons at the top and the bottom is neutral? How are electrons kept together in the same place before connecting the battery  to the wire? What does prevent them to flow inside the battery? How does the battery pump up the electrons? and at which rate? What makes it burn out? and after many cycles does it burn out?       I know there are a lot of questions but my mind is exploding. I don't expect everything to be abstracted from the chemicals but as long as you can through analogies, or intuitive principles, i'd love that. Anyway the main intent of the answer must be addressing the doubts listed.
119773
I recently fell ill with a cold, and began to take a vitamin C capsule each day to help my immune system. When I noticed no change in my condition, I began to incorporate an abundance of citrus into my diet instead of taking the capsules. When I ate the citrus my condition began to improve markedly.   The ingredients listed by the vitamin manufacturer are:   Ascorbic Cellulose Gel Hydroxypropyl Cellulose Croscarmellose Sodium Stearic Acid Magnesium Stearate Silicon Dioxide   Not excluding the possibility of coincidence, I was was intrigued. Has evidence been published to suggest that nutrients in whole foods like vitamin C in citrus fruits are more readily utilized in the body than nutrients in vitamin capsules?
114913
I live in a country where nutritional yeast is not readily available. I'd like to make it. Anyone know how?  Other forms of yeast, such as baking yeast and brewer's yeast are easily found here. I understand these yeasts are essentially the same organism (Saccharomyces cerevisiae?), so I'm wondering if I can't combine yeast—instant baking yeast for example—with some kind of nutritional base like sugar water, let it ferment, dry it out, and "harvest" it.
5949
What is the advantage gained by the substitution of thymine for uracil in DNA?  I have read previously that it is due to thymine being "better protected" and therefore more suited to the storage role of DNA, which seems fine in theory, but why does the addition of a simple methyl group make the base more well protected?
22331
Given that the sun’s temperature is lower than the temperature needed to fuse two protons. How does the sun provide enough energy for this fusion to happen?  Has it do something with tunneling and $E = mc^2$ ? I just can´t seem to understand the concept. If someone could simplify this for me, I would be grateful.   From this , it says " The fusing of two protons which is the first step of the proton-proton cycle created great problems for early theorists because they recognized that the interior temperature of the sun (some 14 million Kelvins) would not provide nearly enough energy to overcome the coulomb barrier of electric repulsion between two protons. With the development of quantum mechanics, it was realized that on this scale the protons must be considered to have wave properties and that there was the possibility of tunneling through the coulomb barrier.".   I was reading through this and my belief was that the sun actually provided a high enough temperature to fuel fusion, however after reading this I am quite confused.
38162
Just what the title states; and this isn't an original question:  On full-moon, moonlight is almost as bright as mid-dawn; yet there is hardly any colour visible. This is not the case with sunlight.   I'm curious to know why this is the case.
82133
My teacher spoke about atomic spectra today, and he explained that, unlike the spectrum obtained by analyzing the sunlight, the spectra of atoms are not continuous.     I have a question about this - even the sunlight has the radiations emitted by the atoms of the elements which compose the sun, still spectra is continuous, which is in opposition to the statement that atomic spectra is discontinuous. So, spectrum obtained by sunlight is continuous even though it atomic spectra. In order to account for spectrum obtained by the sunlight to be continuous and atomic spectra to be discontinuous, can we confirm that sun consists of all those elements (sodium, helium, neon, mercury, etc) which emit the colors of frequency belonging to visible region?
110992
Pardon me if this has been asked before. I was just thinking about how light from a source like the sun is unpolarized. I have two questions:   Is unpolarized light from the sun 100% random? Meaning all wavelengths in the visible spectrum, polarized in all directions? (please correct me if "polarized" is not the right term here) If that's the case, how do the random waves not cancel each other out, rendering the sun invisible to us when we look at it?   Of course my thinking is flawed, so I'm just wondering what I'm missing. The analogy I could come up with is that waves in the ocean are random (I assume?), yet they still occur. Thanks in advance to anyone who can fix my brain.