text:
Drug and antibiotic resistance in organism
Out of gram positive or gram negative or both which one is having a higher resistance to drug or antibiotics? How the organism gains that gene for drug or antibiotics resistance.? Kindly explain it in detail.

This is basically a homework question (simple question without any effort to solve it yourself), you are lucky that this slipped through. It is also kind of broad. Please do some research yourself in the future and state what your problems are.

@Chris it can still be downvoted and closed as homework, even if it was answered. These kinds of "do all my work for me" questions are unacceptable on this site.

@MattDMo Correct point. It will not disappear, though.

Sorry people.. !!  I'll not do it again..!!

The major effect of drugs or antibiotics on bacterium is on its cell wall.
Gram positive bacteria have a thick outer layer of a polymer called peptidoglycan (formed by repeated units of a disaccharide: NAG-NAM) which has many cross-linkages. Beta-lactam antibiotics such as penicillin, cephalosporin etc. competitively inhibit an enzyme called transpeptidase (also penicillin binding protein); which forms the cross-linkages in peptidoglycan; and thus weakening the cell wall. As a result of which osmotic pressure now becomes enough to cause lysis of cell wall and hence the bacterium dies. Also drugs such as Vancomycin inhibit the formation of peptidoglycan polymer.
On the other hand, gram negative bacteria have an outer layer of lipopolysaccharide (endotoxin) beneath which lies a thin cell wall of peptidoglycan. Hence beta-lactam antibiotics do not have much of an effect on the gram negative bacteria.

To conclude, gram positive bacteria are much more sensitive to beta-lactam antibiotics and lysozyme than gram negative bacteria. Also it is worth mentioning that gram negative bacteria are more sensitive to the lytic action of anti-bodies because lipopolysaccharide in their outer membrane produces a high immune response (read about Sepsis for more details on endotoxin).
Hope this is helpful.

Yea thank you.. simple and good explanation...!!

Is there any drug or antibiotics which can be effective for gram negative organisms?

Yes. Gram negative bacteria are sensitive towards detergent like antibiotics which dissolve the outer membrane. Example- Polymyxin disrupts the integrity of the outer membrane (but it has some toxic effect too).

Hey, remember there are many other ways to inhibit the bacterial infection which do not involve degradation of bacterial cell coat.


text:
Can you force human body to mass produce specific proteins?
I've had difficulty finding an answer to this question on Google.
From what I've been taught, DNA is used as a "naive blueprint" to synthesize proteins.
If we can manipulate DNA (Which I hear we can) does this not mean we can force cells to produce specific proteins we want? Purely hypothetically, ethics aside.
I also can't quite understand "what" uses that DNA to create proteins, or does it magically just "replicate itself" and turn into a new cell with the same proteins...
Sorry for the vague last question, but these questions were bothering me for a while now and I wanted to have some more references to read or answers.
Thanks ahead of time.

Welcome to Biology.SE. Currently there are two questions in your post, one of which is way too broad. You should edit your post to restrict it to one question only. In the meantime I am voting to close.

Yes, using recombinant DNA technology, one can take engineered DNA which has been put in an expression vector, induce it by one of various mechanisms to enter cells grown in culture (they can be from human, mouse, monkey, plant, bacteria, yeast, you name it), and the cells machinery will take over, transcribing and then translating it into protein.

does this not mean we can force cells to produce specific proteins we want? Purely hypothetically, ethics aside.

Absolutely, and this is done on a regular basis - sometimes at industrial scales, as a matter of fact. Examples of well-known recombinant proteins include insulin, the blood clotting factor VIII, and therapeutic monoclonal antibodies.

I also can't quite understand "what" uses that DNA to create proteins

This is an extremely broad question, but Wikipedia's Introduction to Genetics may help explain some of these ideas using less technical terms.The quick answer is that it is the cell's transcription and translation machinery mentioned above that do the heavy lifting. Very briefly, DNA is transcribed into messenger RNA or mRNA, which is then targeted to the ribosome for translation in protein. Think of the DNA as the main instructions for the shop, the mRNA as the working templates distributed to many workers, the ribosome as the machinery which takes the template and produces the finished goods, the protein.

I think the OP is asking can this be done in vivo, based on the title of the question. Also wouldn't use hGH and steroids such as testosterone and estradiol cause up regulation of some, but not all proteins? Not as specific as targeted, inducible expression, but would likely affect some but not other proteins.

Thanks this helps a lot! It's a vague quesiton I just wanted a direction to increase my understanding of the subject. I'll do more reading on ribosomes then.

source: Stack Exchange

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

sort: votes


text:
what frequency is the mosquito's whine?
I read on Wikipedia that mosquitoes make the sound they make by beating their wings-- when they are flying, and that the average frequency of the wing beats are about 600 hz.   I went and listened to a 600 hz tone and that is way too low.  Not even close to the sound a mosquito makes.  So I went and found this, which shows the average number of wing beats per second for 29 different species of mosquites:  https://www.researchgate.net/figure/Wingbeat-frequencies-for-29-mosquito-species-Bars-mean-wingbeat-frequency-are_fig1_351489590
and they showed frequencies that were on average EVEN LOWER than 600 hz.  Only one of the 29 species had a frequency higher than 600 hz and that one was only about 750 hz.
But when I listen to pitches of sounds, like from here:https://muted.io/note-frequencies/  the sounds that are even close to what a mosquito sounds like, are more like 2000 hz or 3000 hz.
What am I doing wrong?

Look for a spectrogram of a mosquito buzz, and read about harmonics.

yeah look at waveform as well. try spectrograph too. https://www.google.com/search?q=mosquito+waveform&tbm=isch here's a frequency spectrum:  peak is indeed at 1000 https://www.researchgate.net/publication/8521026/figure/fig1/AS:280254565371909@1443829303583/Waveforms-produced-by-a-female-An-gambiae-in-ssight-top-The-waveform-signal-was.png

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


text:
Do viruses linger/passively transport or attack the body at once?
Do viruses generally attack as soon as they can or do they lie dormant until they reach a cozy spot in the body?
Like is it improbable I have inhaled a virus if I do not feel pain in my lungs?

Different viruses have different "modes of attack". Also, it depends on what you mean with "attack".
As a really short introduction to what viruses are, they are very unlike your body cells or bacteria. They are literally (usually) just genetic information with a kind of shell. The shell allows them to penetrate cells, where they then use the cell itself to produce more viruses. That's all they do, reproduce.
So, what do I mean with different "modes of attack" - well, different viruses lead to different things. For example, infections with Herpes simplex are often asymptotic and many people have no idea that they are infected. If you get the flu, however, you will notice.
Every virus that can infect humans will try to spread as soon as it enters the body. It won't linger around and wait - HIV directly targets immune cells, herpes directly targets nerve cells. The reproduction does takes time, but if they start reproducing and the immune system can't destroy them immediately symptoms can follow soon (think influenza) or late (HIV/AIDS). With most viral infections, the immune system at one point catches up and destroys the virus.

Like is it improbable I have inhaled a virus if I do not feel pain in my lungs?

I'm going to assume you mean either the virus responsible for colds (rhinovirus) or the flu (influenza) here. No, it's perfectly normal to be exposed to either of these viruses without noticing anything. Many people come into contact with infected people without ever showing any symptoms, because their immune system takes care of the infection before any symptoms show up. If it does show up, it will be within a matter of days, though. The flu virus won't stay in your lungs for weeks waiting, it has no way of doing that (viruses are... very simple in that regard).

Like your answer but I am still wondering something: Say you know you are infected. Say you remember the times and the places where you felt pain. Is this a reliable time log/trace of how the virus entered/spread throughout your body? Maybe for some sorts of viruses?

@Emil It takes a certain so-called infectious dose of a given causative agent to become symptomatic of it's disease. The paradigm is that you normally get infected long before you experience symptoms, and by then the virus has rather nicely spread itself around in advance!

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


text:
How much should one smoke in order to prevent Parkinson's?
There are studies who claim that nicotine has a neuroprotective effect against Parkinson's(such as this: http://www.ncbi.nlm.nih.gov/pubmed/11772120)
What would be the minimum amount of nicotine(cigarettes smoked) and frequency in order to prevent Parkinson's, at the same time not to damage his health by becoming an addicted smoker?

The closest thing to an answer you can find is probably in the paper you linked. Did you read it?

@Remi.b I've read only the abstract, I also tried to obtain the full text(as they described here: http://www.ncbi.nlm.nih.gov/guide/howto/obtain-full-text/) and I didn't manage to find it. Do you know how to obtain it by some other means?

@Flowryn I am not too sure about this claim. Yes, nicotine may effect dopamine release to some extent but there is no clear consensus on this issue. See the newer articles that cite this paper. In fact this J.Neuroscience paper says that nicotine free tobacco and decaffeinated coffee can also have neuroprotective effects.

You will not prevent parkinsons by smoking/nicotine consumption, you may see a slight reduction in risk of parkinsons but the effect will be relatively minor and likely outweighed by the negative side effects of smoking/nicotine

You should probably weigh in the total risk of getting Parkinsons (the German Wikipedia names a prevalence between 1,5 and 2%) compared to the risk of getting lung cancer from smoking which is a lot higher.

@Flowryn perhaps you can edit your question to remove the emphasis on smoking because eventually people will tell you a lot more about how smoking is bad instead of how nicotine may possibly help Parkinson's patients. You can instead add a note that nicotine can be administered as inhalant, patch or some oral formulation like gums.

I'm voting to close this question as off-topic because the one paper cited is from 2001, and there is a body of research that shows that COPD, a risk factor from smoking, can be a risk factor in the development of Parkinsonism.


text:
What would happen if Carbon-14 was in a glucose molecule and decayed into Nitrogen?
This interested me because of Melvin Calvin's experiment with photosynthesis where he used radioactive Carbon-14. If a plant used it as a reactant to make glucose, and that Carbon-14 decayed into nitrogen, what would happen to the molecule?

I don't think this is biochemistry. This is clearly radiochemistry and should be asked here: http://chemistry.stackexchange.com/questions/43616/what-would-happen-if-carbon-14-was-in-a-molecule-and-decayed-into-nitrogen ;-)

I'm voting to close this question as off-topic because it should go to chemistry or physics. It is a very interesting question!! But just offtopic here.

Carbon likes having 4 bonds, nitrogen likes having 3, though 4 is possible when the nitrogen is positively charged. The molecule would most likely break a bond when the C became an N, but going from C to N requires converting a neutron to a proton by beta decay. The energetic electron ejected during beta decay might disrupt other parts of the molecule on its way out, but I don't really know, so this is a comment.

Also, it looks like chemistry won't take this question until it's deleted from here, so pick one.

@user137 I don't really know either, but I posted an educated guess. :D

@user137 I think I found the solution, the decay has far more energy than the chemical bonds can withstand, so the molecule will fall apart.

Carbon 14 has a half life of about 6000 years. the only way to know for sure is to synthesize a bunch of radioactive glucose and leave it a few centuries to see what reaction products are formed. An issue is that regular glucose may decompose on a shorter timescale anyway.

@steveverrill You never heard of atomic force microscopy I assume.

I am not experienced in the topic, and could not find any article related to these kind of reactions, but my guess is the following. During the nuclear transmutation the radiocarbon will lose an electron (beta particle), so the nitrogen product will have positive charge. After that there are 2 possible scenarios.
a.) less plausible scenario
The beta particle carries away the energy of the decay, so the molecule will have low energy and it will be able to rearrange.
The electron shells will collapse a little bit, since the nitrogen has smaller nuclear radius. The part after that depends on which carbon we are talking about in the glucose molecule. I would guess the following rearrangements:

${-CH2OH} \rightarrow {-NHOH} + H^+ $
${=CHOH} \rightarrow {=NH} + H^+ $
${-CHO} \rightarrow {-NO} + H^+ $

It is not easier to break an N-H bond compared to the N-C and N-O bonds according to this table, but I think what really matters here is the stability of the final product, and $H^+$ is way more stable than any $^+O*$, $^+C*$, etc. ion.
b.) what really happens
The beta particle carries away the energy of the decay only partially. So the nitrogen will have a lot of energy, which is more than enough to break all of the bonds. According to wikipedia the decay energy is 0.156476 MeV. Let's compare it with the bond energies:
$ 0.156476 MeV = 2.50702189 \cdot 10^{-17} kJ $
${2.51 \cdot 10^{-17} kJ} \cdot {6 \cdot 10^{23} \cdot 1/mol} = 1.51 \cdot 10^7 kJ/mol$
According to our table the covalent bonds have about a few hundred kJ/mol energy, e.g. a C-N bond has 305 kJ/mol energy. So it is very likely that the chemical bonds will break immediately after the decay and the molecule will fall apart.

My guess is it's hard to study because even the C-14 to N transition is slow on lab scale, so getting enough decay products to do structural analysis is hard.


text:
What is intracellular retention?
On the wiki page for proto-cadherins, they write, "The cytoplasmic domain also mediates intracellular retention, a property which distinguishes the clustered protocadherins from the related classical cadherins." citing the following source.
Unfortunately, I was unable to find much anything to go off. Anyone know off-hand what this terminology is referencing?

Based on this line from the paper you linked, it seems like they are using intracellular retention to refer to proto-cadherins being taken up in to the cell via endocytosis.

It is possible that the effects of deleting the intracellular domain might be a result of loss of an organelle retention signal located in the cytoplasmic domain of the protein and/or a decrease in endocytosis of the protein accumulated in the membrane.

This paper also refers to intracellular retention of cadherins in the context of endocytosis of proto-cadherins: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3216661/
Based on this information, the quote from the Wikipedia page ("The cytoplasmic domain also mediates intracellular retention, a property which distinguishes the clustered protocadherins from the related classical cadherins.") seems to be saying that the cytoplasmic domain regulates proto-cadherins on the cell membrane being taken back up into the cell via endocytosis, hence retaining them intracellularly.

Thanks, man. My understanding of your answer is that for proto-cadherins downregulation is via the endocytosis process. As to what happens after endocytosis? Lysosomal degradation? So how would this compare to the up-and-down regulation of non-proto-cadherins? What benefits arise from one mechanism relative to the other?

I'm not too sure, I'd have to do some reading. It might be worth asking another question about that to get a good answer.

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


text:
Why do we define anaerobic respiration as not requiring oxygen, while utilization of the Krebs cycle and electron transport chain both require oxygen?
We have an electron transport chain with the final e- acceptor as SO4 2-. We say this is an anaerobic process, or specifically a case of anaerobic respiration. Elsewhere, as with fermentation and glycolysis, we have anaerobic processes that do not require oxygen. Would it be more appropriate to call these processes with the final e- acceptor as anything other than oxygen to be pseudo-anaerobic?  I say this as it seems misleading to call a process anaerobic that inherently is composed of aerobic processes.

Does this organism grow in the absense of molecular oxygen in the environment?

Okay, thank you user1136. I was misled by the book I read. "The Krebs cycle and the electron transport chain both require oxygen to produce ATP and are collectively known as aerobic cellular respiration." Which I interpreted as the Krebs cycle and the electron transport chain always require oxygen, whether the end process is dubbed anaerobic or aerobic depending on the final e- acceptor.

Because oxygen is not the majority of the energy.
Krebs cycle relies on sugars. Other processes use oxygen but can do without it or primarily use carbon fuels. So they are called anaerobic.


text:
Why when measuring turbidity do we use the minimum wavelength?

As a preface, I read a few other related posts and was able to gather some knowledge, though without any background in physics I am having some trouble here piecing together a coherent view. I looked up videos of Beer-Lambert law on Khan academy and it gave a relationship between transmittance and absorbance as
$$Transmittance (T)=\frac{I_1}{I_0}$$ $$Absorbance(A)=-log_{10}(T)$$
Further, this post points out that turbidity is absorbance, and describes to be in relation to diffuse-reflected and scattered light?
Taking a step back, we see okay, turbidity is really just a measure of 'murkiness' and the amount of light that is scattered as a consequence. What about this diffuse-reflected light? And then this post says scattering is really just the sum of refraction and reflection. I don't think that is correct though, as this video shows refraction and reflection and scattering are different concepts, in so much as refraction is the bending of light as it passes through one medium to another, reflection occurs when light hits a smooth or shiny surface and bounces off, and scattering happens when the surface is rough sending the light in different directions. Then this post here. appears to detail out what would be a satisfying explanation but I haven't taken physics. Are there any good videos that might help better explain these topics?
Then, thinking about absorption my chemistry textbook talks about radiation and I had this concept in my head about light being absorbed then admitted at different wavelengths and I feel like that is true and perhaps that is where we are getting the relationship between transmittance and absorbance?
Bringing it back to the question that brought all this up, through other questions we were able to determine the answers to be To measure levels of pigment production it would be best to use the light of 450 nm, and to measure it turbidity would be best to use the light of 560 nm. In other words, for pigment production, we use the maximum value of absorbance and for turbidity the minimum value. The question we have is why this is the case? The most we were able to come up with is that the color of the Chlorella bacteria is green and that things are green because that wavelength of light is reflected, and that the wavelength of green light is 560 nm. I guess we can't use green light to measure the amount of green pigment because the light that would be returned would be a combination of reflected light (how much green pigment) + scattered light(not green pigment but returns green light) + (some combination of absorbed and reradiated light??). So we wouldn't be isolating the information we are after? If we want to know how much "green" is present this would be best measured by measuring the wavelength of light that is the least reflected, or the most absorbed, so the green pigment absorbs most of this light and the light that is not absorbed will tell of how much green stuff was there to absorb it. When it comes to the why for turbidity I am a tad stuck and I think it is because we appear to have a mixture of definitions above. Perhaps some more concise definitions will shed light. It appears the answer to "why can't we use green light" may help to give a possible answer, as the scattered light is the measure of turbidity and that would be with some margin of error, what we have isolated?

Usually when measuring materials in a spectrophotometer we want to use the absorption maxima to minimize the signal-to-noise ratio, that's why for pigment measurement you'll use the maximum point. But when you measure two materials you want to take two measurements with as little correlation as possible, that is to avoid one material influencing  your measurements of the other.
Imagine you are trying to breed C. marina for more pigment. Obviously more algae = more pigment so you want to measure how much algae you have and normalize by it. If you'd measure alga density in a wavelength correlated with chlorophyll content you'll get inaccurate results.
I think the question is ill-worded. You should measure at the pigment's absorption minima and not at the alga absorption minima. As the alga can have other peaks unrelated to chlorophyll. When doing this you should remember that chlorophyll and many other pigments are insoluble in water but your measurements of live cells are, usually, in water media.
The best in my opinion and that is the method I'm currently using is to build your own curve by counting cells in some manner (like hemacytometer) and measuring the full spectrum (Your graph stops at 750nm, I got up to 1000nm).


text:
Virus lineage, strain, and relation to spike protein variants
On the CDC website we have virus lineage which appears to be constant for all cases presented, or am I reading that wrong? Then the different names and of those with different names, different spike proteins can be associated. Then in these two papers authors use the word strain and describe as so:
paper a)
SARS-CoV-2/human/Liverpool/REMRQ0001/2020
where they mention that they also test the D614G variant of the spike
paper b)
BetaCov/human/CHN/Beijing_IME-BJ05/2020
BetaCoV/Wuhan/IVDC-HB-01/2020|EPI_ISL_402119
How do I use the species information to determine what spike variants were used in the studies?

You can trace the first one back to the original paper. In general though, if you want to check specific sequences, look for the Genbank numbers, have a look on VIPRBRC and/or get a GISAID login (I think you need affiliation with a recognized organisation for this one). GISAID generally has the most sequences, but I'm too lazy to dig out my login and tell you if these ones are deposited. That being said that last one certainly is as the EPI_ISL # is GISAID format

Thank you, bob1. I am wondering whether the discrepancy in the results between paper a and paper b could be attributed to a variance in the spike protein, that's why I'm looking into this. Also, if this not out to not be the reason for the discrepancy, would the use of the pseudovirus in paper b potentially provide an explanation?

It is possible that it is the variant. For the last part, you should post it  as another question.


text:
Using evolution of bacteria against themselves
We know that mutations happen regularly in bacteria and also that one bacteria might get the mutation and become stronger than the others and thus survive, causing antibiotic resistance as well. Can we deliberately make mutations in bacteria that would harm other bacteria but not humans. This would not only make them stronger and thus let them survive but would reduce the very need of antibiotics as they would be less virulent to humans?

(1) Not all bacteria are harmful (2) Even if you are able to make such strain, in future, that will also exposed to mutations and you will see new strains coming up with new mechanisms. You must read Red Queen Hypothesis !

We would do that only with the bacteria that harm humans in some or the other way. Yes, even those would go under mutation. So I am concluding that this is not a cure but a short sighted experimental idea?

Maybe. It will depend on your aim/objective of experiment/project.

Mutating Bacteria is a very plausible idea. If you mutate a particular strain of 'helpful' bacteria to become extremely positively selected for in the current environment then it is possible that the rest of the bacteria interacting with your new mutated will face heavy competition and eventually die out.
The major hole in the idea however, is that bacteria regularly undergo horizontal gene transfer which makes this idea extremely, extremely dangerous for humans. (If your mutated bacteria accidentally passes on the mutated gene to, say, a bacteria that causes Tuberculosis, it would initiate a pandemic. It is also equally possible that a dangerous bacteria might transfer its genes to your mutated bacteria.) It is generally accepted that mutating bacteria or other pathogens(most of which mutate at high rates) is generally a bad idea, because once released into the environment, the possibilities of the mutation going haywire are high(other mutations might make them dangerous).
Horizontal Gene Transfer: Transfer of genes due to recombination processes like Transduction, Transformation and Conjugation which can occur between bacteria of same or different strains, species, domains. etc

That's a logical thinking. Thank you. I get a clearer picture now.


text:
Organ secretions
If an animal secrets an enzyme from an organ that is entirely dedicated for the same secretion, can one or cannot one just use the gene coding for that protein to obtain the protein in vitro. How much relevance does the organ have for production of a particular enzyme. For example, hippopotamus releases the blood sweat from glands in its fat skin. Can one use just the gene coding for the blood sweat and produce it in vitro, or the organ is necessary for it's production?

That is a complicated question that ends up with the answer of, it depends. Most Eukaryotic proteins require chaperone proteins to fold correctly. Many proteins also undergo post-translational modifications, especially those produced in the ER for secretion of presentation on the cell surface. That being said, pharmaceutical human insulin and growth factors are produced by bacteria. Also it is the cell that is relevant, the organ is just the conglomeration of cells of a certain differentiation type. Those cells will express their genes based on how they differentiated.

Also, blood sweat sounds like it results from two compounds, and are small acidic molecules. If you were to isolate the enzyme(s) that produced them and added them to their substrate, then they should catalyze the reaction to produce the molecules, assuming that there are not other cofactors necessary that you have not added to the reaction.

It's not a product of two compounds.....it is called blood sweat as it is red in colour and is released as sweat from the skin

"The secretion is sometimes referred to as "blood sweat", but is neither blood nor sweat. This secretion is initially colourless and turns red-orange within minutes, eventually becoming brown. Two distinct pigments have been identified in the secretions, one red (hipposudoric acid) and one orange (norhipposudoric acid). The two pigments are highly acidic compounds." https://en.wikipedia.org/wiki/Hippopotamus#Description


text:
Gene silencing in C. elegans
I am trying to silence the tph-1 (tryptophan hydroxylase) gene in C. elegans using the pLT63 plasmid to check if that particular gene has anything to do with the pharyneal pumping or not. Am I using the right plasmid for the purpose?

"pLT63 contains 0.8 kb of the fem-1 gene inserted into the L4440 vector" (1). The gene fem-1 is involved in determining the male sexual trait in C. elegans (you can verify this on uniprot). It may be best, however, to stick to a "normal" plasmid like L4440 that'll just have your tph-1 insert ligated in.

Is there any direct link between tph-1 and pharyngeal pumping in the worms that you know of?

I did read through some literature and while some evidence says tph-1(mg280), a deletion of an allele, alters the ability of the worms to fine-tune the speed of their feeding, i think that was here. But overall, and we see in this study, the worms have relatively normal feeding. I haven't done the experimentation myself, however, so I can't 100% make a claim here.

Check out the WormBase site at www.wormbase.org. Just type tph-1 in the search box on the right hand side at the top of the page.


text:
Why there is no neurovascular drug-eluting stent?
I'm researching on neurovascular stents and I'm wondering why there is not much about drug-eluting neurovascular flow diverters in the literature? I read in an article that it's because of complex shape of cerebral arteries in comparison to cardiovascular system. But it doesn't look satisfactory to me. Any suggestion or idea is appreciated.

Despite some superficial similarities, the design of coronary stents and neurovascular stents are quite different. Coronary stents are hard metal, made out of stainless steel. They are quite solid, and if you crush one, it will remain crushed. They are deployed by expanding a balloon at potentially very high pressures (10-20 atm). Coronary stents are relatively short, and are deployed in vessels that are relatively straight given the length of the stent.
Drug-eluting variants of coronary stents are additionally coated in a polymer (i.e., plastic) matrix that contains the active ingredient and releases ('elutes') it over time. The common commercially available drug-eluting stents release anti-proliferative agents to prevent neointimal growth.
The purpose is also somewhat different: you mention flow diverters, so you are likely thinking about the context of aneurysms, where they may be used alongside coils to seal off the aneurysm from the normal flow. They are not providing structural scaffolding to prevent vessel occlusion from atherosclerosis.
Neurovascular stents, including flow diverters, are often made of self-expanding metals like nitinol. They are more flexible, but try to keep their nominal shape. These stents are deployed by retracting a sheath and then they themselves pop out to their nominal diameter. Because of this different deployment strategy, they can also sometimes be retracted and repositioned. The way these stents deploy is a lot more gentle, and they are also typically longer than the coronary varieties. They also may be placed in vessels that can be accessed superficially, such as in the neck. A stainless steel stent in the neck would be a disaster: if you laid pressure on that part of the neck you could permanently collapse the stent. A self-expanding stent will bounce right back open.
Back to your actual question...
The actual purpose of coronary vs flow-diverting stents are different; the purpose of drug-eluting coronary stents, preventing neointimal hyperplasia, is not as relevant in the neurovascular context. Additionally, there are lots of good reasons to use self-expanding metals in the neurovasculature because of tortuous anatomy and superficial vessels in the case of the carotids. The hard plastics that are coated onto steel stents can't be easily placed onto self-expanding stents, so other techniques would need to be developed.
The article you read talking about the complex shape of cerebral arteries is in large part correct.

I read in an another article (https://www.tandfonline.com/doi/abs/10.1179/016164105X35459) that another concern of using DES in the neurovascular interventions is that it is possible to have a therapeutic drug leakage into cerebrospinal fluid or more disastrously into the brain, which limited the applicability of DES to prevent neointima hyperplasia (i.e. in-stent restensosis) in the intracranial arteries. Any idea or suggestion about this claim?

@MehrdadYousefi It could be an issue of concern, just not one of the first I'd have on my list. I'm not aware of any neurological-specific worries with DES drugs like paclitaxel and rapamycin. Pharmacodynamic models that I am familiar with suggest that concentrations of DES drugs are low even in the media, let alone getting through the adventitia, and would be way less than the exposure when those drugs are taken systemically. The study you linked brings it up as an issue but then shows it did not occur in their study (at least not to an extent that they could detect drug in CSF).

So, I take the last reason that you mentioned in your answer as an interesting argument "The hard plastics that are coated onto steel stents can't be easily placed onto self-expanding stents, so other techniques would need to be developed." As a result, it's pretty much like that coating techniques are not capable to coat self-expanding stents (e.g. Nitinol) with polymeric drug coatings? Am I understanding this correctly? Do you have any reference to support this argument? I really appreciate your help because I need it for my PhD proposal.

My knowledge in the field might be outdated, and maybe it is now possible to do, but for example I do see the "Zilver PTX" stent is apparently a nitinol stent with paclitaxel, but it does not use a polymer. One of my concerns would be with how the flexibility of the material would be maintained when coated in plastic, or what would happen to the plastic during flexing (i.e., it could crack and release drug too fast, or produce a surface that is bad for hemocompatibility, etc). That also means that all of the drug is released within 72 hours, however, so not the same as polymer coated.

Thank you so much for your help! The Zilver PTX gave me a really good keyword to find useful references. Regarding the flexibility of drug coated stents I believe it will not change their flexibility so much because the coating thickness is thin in comparison to other stent's length scales. But for microscopic cracks I think it's possible to develop a polymeric coating with comparable mechanical properties to Nitinol to distribute bending stresses more homogeneously across the stent and its coating to prevent micro-cracks formation.

If I remember correctly, I think the polymer coating on a DES about doubles the thickness of the struts. But again, my memory may be incorrect. I see lots of results on Google Scholar for 'polymer coated nitinol' where you can start in your research. Best of luck.


text:
are more males born than females?
I believe that given what I have heard about war and that up until whenever only men fought in wars then to replace the amount dead so that it would be equal on earth then more male births would occur than females. what is your thought?

Yes, the ratio is around 1.07:1, for males to females. But this is likely due to far more factors than male mortality rates. Also, it would've been quicker to Google your question than to ask Stackexchange.

Your post is mainly constituted of a single large sentence. This sentence is very hard to understand and is full of grammatical issues (you might be an ESL, like I am myself). That makes it hard to understand your question. Also, please capitalize the first letter of your sentences.

Are more males born than females in humans?
According to the CIA (the only reference I could find; see here click on "people and society" and look for "sex ratio"), the world wide sex ratio at birth is 1.03 males for every female. This sex ratio is reversed at old age (women's life expectancy is higher than men's).

at birth: 1.03 male(s)/female
0-14 years: 1.07 male(s)/female
15-24 years: 1.07 male(s)/female
25-54 years: 1.02 male(s)/female
55-64 years: 0.95 male(s)/female
65 years and over: 0.81 male(s)/female
total population: 1.02 male(s)/female (2017 est.)

Note that these statistics somehow ignores the cases of intersex which accounts for a not completely negligible part of the population (see here). In short, yes, more males are born than females.
Why are there more males born than females in humans?
It is unclear from your post whether you are looking for proximal or ultimate causation and your explanation is made unclear by the bad grammar in your post.
Orzack et al. (2015) (thanks @iayork for the reference) investigate the reasons for this unequal sex ratio at birth. From their abstract

Our results indicate that the sex ratio at conception is unbiased, the proportion of males increases during the first trimester, and total female mortality during pregnancy exceeds total male mortality

While I have not read the whole paper, intuitively, I would tend to think that females babies might have a higher miscarriage probability, which cause the observed discrepancy. For example, X chromosome inactivation (dosage compensation) that happen in females only, and the development of female reproductive system (which is arguably more complex than the male's reproductive system) could cause of higher miscarriage probability among females than males. This is all hypothetical though and you should have a look at the link paper.

I don't know of any study that investigate the reasons for this unequal sex ratio at birth. There are many. A recent review (The human sex ratio from conception to birth) concludes that "total female mortality during pregnancy exceeds total male mortality".

This is a big correction of my post and an important add up (you could have made it a new post). Thanks. I edited my post.


text:
What gives researchers a reason to test the Radiation Resistance of organisms?
I was reading about the Thermococcus Gammatolerans and its absurdly high radiation resistance, when something occurred to me.
What reason did anyone have in the first place to subject this thing to this level of radiation?
I'm very curious to find out about the process behind deciding which organisms to test the radiation resistance of. Is there an ongoing effort to test the resistance of every species yet discovered? Or are there other factors in determining which species should be subjected to this kind of testing?

OK. You cite the Wikipedia page on this organism. There is a reference to a paper about it on that page. I suggest you look at that paper (no need to read it all) and find out where this organism is found. That should give you an indication of why they chose it. Why should anyone be interested in (or fund research in) the resistance of living organisms to radiation? This is not Guiness book of records stuff — animal with the longest penis and the like — they are interested in the molecular mechanism. Ask yourself what use that might be. Learn to save your own life.


text:
absorption time of zinc in the body
I would like to know how long it takes for the human body to absorb / digest a 10mg zinc capsule?
Note: It is recommended to take zinc  an empty stomach to gain the maximum effect. Regarding to that I think it's also a disadvantage to eat something right after taking zinc?
greetings

Zinc supplements are usually used to treat zinc deficiency or other chronic conditions, so it is not that important in what time they are absorbed but what percent of them is absorbed.
They are certain nutrients, such as calcium (for example, in milk) that can bind to zinc and partially prevent its absorption. This is why it is usually recommended to take zinc on an empty stomach (Mayo Clinic):

Zinc supplements are most effective if they are taken at least 1 hour
  before or 2 hours after meals. However, if zinc supplements cause
  stomach upset, they may be taken with a meal.

Usually there should be no significant difference between taking a pill with food, 2 minutes before or 2 minutes after the food, because in all cases the pill and the food will mix in the stomach. This is because every pill, even if you take it with water, will probably stay in the stomach for at least few minutes before it will be emptied into the small intestine.


text:
What is this tiny translucent worm I found on my desk?
I found this tiny critter crawling vertically up my speakers. It seems to crawl like a caterpillar, but strangely, every now and then, it stops, rears-up and look/ feel around.
It looks sort of grey/ translucent from a distance with a maybe orange-ish head and tail-tip, however, looking at it from above, it seems to have a black center.
It was kind of hard to take a clear picture, but I hope it helps.
P.S. Got it in a glass before, just because I've never seen anything like it before. My friend said it might be an alien.

That is a lepidopteran, most likely in the family, Geometridae. An "inchworm". https://www.thoughtco.com/geometer-moths-inchworms-and-loopers-1968193


text:
Acidity and Alkalinity of Foods
Some foods leave an acidic effect on the body such as meat and dairy, while others leave an alkaline effect, like vegetables. However, are these effects significant enough to greatly alter the blood pH that seems to be strictly monitored by the kidneys, which keep it around 7.4?

Extracellular acid base homeostasis in human physiology is maintained primarily by the bicarbonate buffer, as regulated by both the kidneys and the lungs (and to a certain extent, the intracellular phosphate buffer). Outside of illness or injury, (arterial) blood pH is kept between 7.35 and 7.45. There is an excellent review of acid base homeostasis in Pubmed central that covers these points. Be aware before diving in, though, acid base homeostasis is one of the most complicated topics in human physiology.
As discussed in the reference above, a healthy pair of kidneys can usually compensate for a dietary acid or alkaline load. In these cases, what changes is not your blood, but your urine. There, is, though, some evidence that high blood pressure, diabetes, and possibly poor bone health may be associated with a chronic dietary acid load. Though an alkaline diet is being investigated as a treatment for chronic kidney disease, it is not currently approved for the prevention or treatment of any disease in the US.


text:
What's the difference between the neuroendocrine system vs endocrine system?
This is what I have understood so far:
Neuroendocrine system involved neuroendocrine cells (also known as neurosecretory cells) that receive nerve impulses by a sensory neuron to release neurohormones into the blood stream. The endocrine system releases hormones by endocrine cells into the blood stream when a receptor protein senses a stimulus.
Here are my questions:

When it comes to the brain, are the neurosecretory cells located in
the hypothalamus or the posterior pituitary gland or both?
Is the hypothalamus and the posterior pituitary gland classified as
    neuroendocrine glands and is the anterior pituitary classified as an
    endocrine gland?
If the posterior pituitary gland is indeed a neuroendocrine gland,
    is ADH and Oxytocin, which are both released by the posterior
    pituitary gland, classified as "neurohormones", not just the classic
    hormones?

I'm pretty sure not all ('neuro')hormones released by neuroendocrine cells actually enter the bloodstream. Some of them are only released inside the brain.

Neuroendocrine systems can be defined as the sets of neurons, glands and non-endocrine tissues, and the neurochemicals, hormones, and humoral signals they produce and receive, that function in an integrated manner to collectively regulate a physiological or behavioral state.
The neuroendocrine system is the mechanism by which the hypothalamus maintains homeostasis, regulating reproduction, metabolism, eating and drinking behaviour, energy utilization, osmolarity and blood pressure. (Source)

The central neuroendocrine systems serve as an interface between the brain and many of the peripheral endocrine systems. This chapter discusses the hypothalamic control of anterior pituitary systems regulating stress, basal metabolism, growth, reproduction, and lactation. Each of these systems involves one or more hypothalamic releasing or inhibiting hormones, released from hypothalamic neurons that terminate in the portal capillary vasculature that projects from the median eminence at the base of the hypothalamus to the anterior pituitary gland. There, the hypothalamic hormones act upon subsets of anterior pituitary cells to regulate pituitary hormone release and downstream physiological functions. Other hypothalamic neuroendocrine cells control water/salt balance, and lactation/parturition, through the release of vasopressin and oxytocin from nerve terminals that arise in hypothalamus and project to the posterior pituitary gland. Together, these hypothalamic neuroendocrine functions enable the central nervous system to respond rapidly to internal or external environmental change, and to maintain a response through endocrine hormonal transducers. (Gore, 2013).

The endocrine system is a group of glands and other structures that release internal secretions called hormones into the circulatory system.

Endocrine organs are richly vascularized ductless organs that produce hormones. The epithelial cells of the organ secrete their hormone product directly into the bloodstream where, upon binding with specific receptors in target organs, cellular functions are affected. The endocrine systemincludes not only the endocrine glands (pineal, pituitary, thyroid, parathyroid, and adrenal) but also single cells and small clusters of cells in the thorax and abdomen known as paraganglia. This chapter addresses the thyroid, parathyroid, adrenal, pituitary and pineal glands, and paraganglia. In addition to size differences, several features of endocrine tissues differ between rodents and humans, and often between rodents. (La Perle & Dintzis, 2018).

Question 1

When it comes to the brain, are the neurosecretory cells located in the hypothalamus or the posterior pituitary gland or both?

Neurosecretory cells are found in the hypothalamus. (Source)

There are two types of neurosecretory cells: magnocellular cells and parvocellular cells. Magnocellular cellsare large cells, having long axons that terminate in the neurohypophysis (also known as the posterior pituitary). Magnocellular cells release the hormones vasopressin and oxytocin to the general circulation; we will talk about the physiology of these hormones in Conjoint 403.  The parvocellular cells are small cells, with shorter axons that terminate at a capillary-rich bulge at the base of the hypothalamus known as the median eminence.

Question 2

Is the hypothalamus and the posterior pituitary gland classified as neuroendocrine glands...

No

...and is the anterior pituitary classified as an endocrine gland?

Yes.
The following is from: https://courses.lumenlearning.com/boundless-ap/chapter/the-pituitary-gland
(emphasis mine)

The posterior pituitary (or neurohypophysis) comprises the posterior lobe of the pituitary gland and is part of the endocrine system. Despite its name, the posterior pituitary gland is not a true gland; rather, it is largely a collection of axonal projections from the hypothalamus that terminate behind the anterior pituitary gland.

The pituitary gland is an endocrine gland, about the size of a pea, that sits in a small, bony cavity at the base of the brain whose secretions control the other endocrine glands and influence growth, metabolism, and maturation.
While the pituitary gland is known as the master endocrine gland, both of its lobes are under the control of the hypothalamus: the anterior pituitary receives its signals from the parvocellular neurons, and the posterior pituitary receives its signals from the magnocellular neurons.
The anterior pituitary, also called the adenohypophysis, is a major organ of the endocrine system, and is the glandular, anterior lobe of the pituitary gland.
The anterior pituitary gland secretes 7 hormones: follicle stimulating hormone, luteinizing horomone, adrenocorticotropic horomone, thyroid stimulating horomone, prolactin, endorphins, and growth hormone.
The posterior pituitary gland does not synthesize any hormones.  Hormones known as posterior pituitary hormones are synthesized by the hypothalamus, and include oxytocin and antidiuretic hormone (ADH), also called arginine vasopressin or vasopressin (Liu, 2007). The hormones are then stored in neurosecretory vesicles (Herring bodies) before being secreted by the posterior pituitary into the bloodstream.
With regard to neurohormones mentioned in question 3, neurohormones are hormones that are produced by neurosecretory cells and released by nerve impulses (e.g., norepinephrine, oxytocin, vasopressin).
This is the part which can be confusing. Whilst ADH and oxytocin are released from the posterior pituitary gland, which is an endocrine gland, the hormones are produced by neurosecretory cells within the hypothalamus and they are stored in and released from neurosecretory vesicles within the posterior pituitary gland. Therefore they are classed as neurohormones.
References
Gore, A. C. (2013). Neuroendocrine systems. In Fundamental Neuroscience (Fourth Edition) (pp. 799-817). doi: 10.1016/B978-0-12-385870-2.00038-X
La Perle, K. M. D., & Dintzis, S. M. (2018). Endocrine system. In Comparative Anatomy and Histology (pp. 251-273). Academic Press. doi: 10.1016/B978-0-12-415759-0.00058-3
Liu, K. D. (2007). Hyponatremia and Hypernatremia. In Critical Care Secrets (Fourth Edition) (pp. 285-290). doi: 10.1016/B978-1-4160-3206-9.10044-8

Not all hormones enter the blood - just as a quick addendum to the thorough reply above, and as per a comment above stating not all hormones from neuroendocrine cells go into circulation - seems to be true: many of the neuroendocrine cells release hormones directly into the organ where those cells appear - as per the gut, heart, lungs - here's a nice visual overview
https://byjus.com/biology/hormones-heart-kidney-git/


text:
Why does affinity of Hemoglobin increases for Oxygen in carbon monoxide poisoning?
I have studied this in almost every physiology book but I just can't understand how carbon monoxide can affect oxygen's affinity to Hemoglobin. I know that there is left shift in oxygen dissociation curve but  why?

Affinity for any ligand to a protein is a function of the shape of the protein which provides some place for the ligand to bind/interact.
Hemoglobin typically exists in tetrameric form: it is a collection of 4 subunits that each bind 1 molecule of oxygen.
The shape of hemoglobin is affected by CO2/pH, which is important for having high affinity for oxygen in the lungs and lower affinity for oxygen in tissues where a lot of CO2 is released (i.e., where there is a high rate of metabolism).
The shape is also affected by binding oxygen itself: binding oxygen to one subunit causes conformational change in the other subunits of the tetramer, increasing their affinity for oxygen. This is called "cooperative binding."
So, how does any of this relate to CO? Well, it turns out that not only does CO bind very tightly to hemoglobin in the place oxygen would normally bind, taking up space and reducing the capacity for oxygen, it also very strongly increases the affinity of the other subunits for oxygen. It increases the affinity enough that even in the low-oxygen high-CO2 environment of the capillaries, carboxyhemoglobin (hemoglobin bound to CO) continues to hang on to rather than release oxygen. This is represented by a shift in the dissociation curve to the left: oxygen stays bound even when the concentration is low.
This means that fewer CO molecules are necessary to cause deficits in oxygen transport than would be needed if it was only taking up space: one CO molecule binding to a hemoglobin tetramer effectively prevents transport of up to 4 molecules of oxygen.
As a quick caveat, I believe some of the biophysics here are still incompletely understood, so please consider this answer to be an approximation and an explanation of experimental findings to a level of precision sufficient to understand the pathophysiology of CO poisoning. More depth is necessary for a biophysical approach.

Roughton, F. J. W., & Darling, R. C. (1944). The effect of carbon monoxide on the oxyhemoglobin dissociation curve. American Journal of Physiology-Legacy Content, 141(1), 17-31.
Eaton, W. A., Henry, E. R., Hofrichter, J., & Mozzarelli, A. (1999). Is cooperative oxygen binding by hemoglobin really understood?. Nature Structural & Molecular Biology, 6(4), 351.

Genuine question, as this is one aspect of Hb I never loved at in my teaching. On the tense/relaxed equilibrium model, can CO be considered as affecting the equilibrium in the opposite direction to hydrogen ions? If so it might be helpful to show that in a diagram.

@David Very generally speaking yes that's accurate, but I'm not sure how the other contributors to the TR equilibrium are affected by CO, or how similar or different the states are in terms of actual structure as opposed to O2 affinity. Not really my area of research but my loose understanding is that the TR model is a good but simplified model, similar to other models I'm more familiar with like the HH gating constants for voltage gated channels.

@David This paper says that CO stabilizes the R-state and thereby increasing oxygen affinity. However, it would be interesting to see if this shift is simply because of less oxygen per Hb i.e. reduced co-operativity or some active mechanism of R-state stabilization by CO. I could not find any structural biology articles on this topic.

@WYSIWYG That makes sense. If CO binds well to the same site as oxygen it would be expected to shift the equilibrium to the R form that binds oxygen (as the poster said, although annoyingly without citation). However the oxygenated Hb is no use to the organism as the effect of CO on the equilibrium prevents or decrease its release. I suppose the point to emphasize is that this occurs where there is a greater concentration of oxygen than CO.

@David I think the Eaton paper would be of interest to you.

It doesn’t. Carbon monoxide has a higher affinity to hemoglobin (as in, binds better to the protein), that’s why it prevents oxygen from binding to hemoglobin.

I would also think this is the case, but could you add sources?

This is part of the toxicity of CO but does not answer the OPs question about oxygen dissociation.

To be precise CO binds to Fe atom. It is almost a very well known fact in co-ordination chemistry that CO (carbonyl) is a very strong ligand. It can therefore "poison" the metalloproteins by binding to the metal. CO can also poison the mitochondrial enzymes but I guess the toxic effects due to Hb poisoning start acting faster.


text:
Black caterpillar

What kind of caterpillar is this please?

https://owlcation.com/stem/Black-Caterpillar-Identification

It would be good if you can give some context to the location of the animal (country/region/city) where it was found.


text:
What insect is this? Found in Russia
Found in Russia in the kitchen. Its about 15 mm long.

As you know Russia is a very large country, it would make sense to mention the exact part of Russia where you have taken this picture. It would also be good if you briefly describe the current climatic/weather conditions of your place.

Common name: Stonefly completely harmless!
(the terrestrial adult does not have mouthparts) and is an indication that the stream nearby is somewhat healthy.
Below is great info from online site. I just now joined Biology Stack so not sure if we can post links but I’ll try it at the end.

Neither a stone nor a fly, the stonefly is in an order of insects called "Plecoptera," which means "braided-wing", due to the prominent network of veins in its wings. The common name “stonefly” refers to the fact that the larvae live among stones in rivers and streams, and the adults fly.
Like most insects, the larvae and adults live radically different lives.
By far the majority of the stonefly’s life, two to four years, is spent as a larvae or naiad (the term for larvae that live in water). The naiads are entirely aquatic, living secretive lives in cool streams where they feed on plants, algae and decaying matter.
Giant stoneflies are the largest stonefly species, with adults reaching nearly two inches long. They emerge from the water in late May to early July and live only a few days — just long enough to mate and lay eggs. To attract a mate, the males drum their abdomen on the substrate or surface on which they're resting. The female feels these vibrations and moves towards it, sometimes drumming a response call. Adults have no mouthparts so they do not eat or bite. As large and imposing-looking as giant stoneflies are, they're completely harmless.
While most people would find the giant stonefly to be an interesting-looking insect, fisherpeople get particularly excited about them because they indicate good water quality — and possibly trout. Like trout, stoneflies need fairly cool, stable water temperatures and a high amount of dissolved oxygen. Stoneflies are also a favorite food of trout, so they can be used as lures. Finding these critters in the Mississippi River is another indicator of how water pollution has greatly improved from historical conditions in the early and mid-1900’s.

https://www.fmr.org/news/2017/12/27/nature-notes-its-sign-giant-stonefly-found-downtown-st-paul

Aaand this is about as good an answer as we'll get given the information we have ... Russia is home to hundreds of species of stoneflies, and the size given and visible cerci (the two threadlike appendages visible at the bottom of the animal as seen in the photo) eliminate perhaps a third of these (cerci in the families Leuctridae, Nemouridae, and Taeniopterygidae would not be visible past the wings in fully-winged species -- which this animal is; members of the families Perlidae, Perlodidae and Pteronarcyidae average MUCH larger than the 15mm given by Matt).


text:
Why can dogs hyperventilate without consequences like humans?
During the heat of summer, dogs usually breathes very fast, like 100 times per minute or more. If humans do so, we will experience an array of negative effects like dizziness, finger tingling or losing consciousness, by the results of blood alkalosis and reduced oxygen level. The question is, why don't our canine buddies seem to experience the same consequences?


text:
After SRS, does the tissue that was previously the penis develop into actual, differentiated vaginal tissue?
I keep being told othereise, that the redulting "neo-vagina" isn't 'proper' vagina. This site is the only one that gave me a definitive explanation but I would like too see if there are more.

What is SRS, for those who don't know?

@kmm, SRS is 'sexual reassignment surgery.'

It's true that the microbiome and microscopic structure of the neovagina are not the same as those of a natal vagina, although explicating this outside of circumstances relating to post-surgical dysfunction or pathology seems unnecessary and a potential source of discrimination. Whether post-surgical outcomes are "proper," as you put it, should be evaluated on the basis of patient satisfaction and nothing else, especially not appraisals of minute features.

The medical care of the neovagina of transgender women: a review, Cornelisse et al. Sexual Health. 2017. Emphasis mine.
Microbiology of the neovagina
When assessing a troublesome discharge or bleeding from a neovagina, it is important to keep in mind that the histology and microflora of the neovagina is different from that found in the natal vagina, and hence the aetiology of vaginal discharge in trans women is different from that of cis women. Premenopausal cis women have a vaginal epithelium constructed of glycogen-rich epithelial cells that support the growth of lactobacilli, these produce lactic acid to maintain an acidic vaginal pH and so help to curb the growth of other commensal bacteria. When this mechanism fails, the resultant bacterial vaginosis is characterised by an overgrowth of Gardnerella vaginalis and other anaerobic vaginal bacteria. Neovaginas are not lined by a glycogen-rich epithelium. The microbiology of neovaginas created by penile infibulation and those created by intestinal grafts are discussed separately below.

These more in-depth discussions of the various microbiomes imparted by different approaches to constructing a neovagina begin on the third page (444) of the linked PDF.

I was talking about tissue differentiation. https://web.archive.org/web/20031125030637/http://www.gendercare.com/library/italiano_paper1.html

“Microscopic structure” and “histology” are synonyms for what you’re referring to as tissue differentiation. The cellular phenotypes in the neovagina are not the same as in a natal vagina — ”Neovaginas are not lined by a glycogen-rich epithelium.”

According to my link "They are only partially correct, since the normal female vaginal tissue is not truly mucosa either. It is called mucosa only because it lines a body passageway. It contains no mucous-secreting glands (Fawcett, et. al., 1995). That is why lubrication is a transudate phenomenon, the source being dilation of the capillaries that surround the barrel and the subsequent squeezing out of fluid through the vaginal walls, which in normal and artificially constructed vaginas have been shown to be a functioning two-way membrane"  Is this true?

You're asking about mucus production, then, and not tissue differentiation. It's true that lubrication is a transudative phenomenon, but the basal fluid in the neovagina is not the same as in a natal vagina: "The basal fluid in the vagina is in fact not produced from a single source but is a mixture of fluids from...the fallopian tubes, the uterus, the cervix and...the vestibular glands (Bartholin's glands)..."


text:
does anyone know what snake is this? found on my other family home
pic might be a little dark because it was on night

thank you very much for your answer

welcome. For species ID we need the geographical location (country, state) where you found it, and possibly also what time of year it was, temperature and what kind of habitat it might have coming from (is there forest around your home, ore are you way up in the mountains etc)

Looks like a constrictor, many of which are kept (and released) as pets. So the location my not be an indicator. In any case, it is not venomous.

It is a Boa constrictor. Like the comment mentioned, the geographic location helps. If you are in southern Central America or South America, it's probably native; elsewhere, it's probably someone's escaped pet. They are non-venomous, but will defend themselves if they are threatened or harassed by hissing and striking. They have many, small, very sharp teeth that could easily lacerate your skin, but not deeply.
These snakes populations are very, very reduced, so please do not harm it since it does not want to interact with you at all. They eat rodents and other pests, so it's good to keep their numbers up. They are also magnificently beautiful and have very interesting biology (for example, they give live birth and have pits on their faces that help them sense infrared!).


text:
What proportion of the people who lived 1000 years ago have genetic descendants alive today?
For context, I've been wondering about this for a paper I'm writing (in philosophy). Really, I want to figure out the chances that someone alive today will end up still having descendants 1000 years in the future. But people from 1000 years ago should be a good approximation.
So, any ideas? And are there any published papers which talk about this?

This related question would be a place to start https://biology.stackexchange.com/questions/36715/what-is-the-percentage-of-people-living-in-england-in-1500-ad-whose-lineage-is-s?rq=1

This is not a full answer, but I post it as one because the reasoning is too long to post it as a comment.
You can make a rough estimation using a few assumptions.
1) Let's say 1 generation = 25 years, so 1000 years are 40 generations.
2) Let's say that half of the population is able to leave offspring, so the probability of one individual having descendants = 0.5
3) Supposing that the average number of siblings is 3.

The probability of not having descendants in the 2nd generation  = 0.5
The probability of not having descendants in the 3rd generation is 0.5*(1-0.5^3) = 0.4375

After the 3rd generation, it becomes a combinatorial problem that is too hard for me. I can tell that the probability of not having offsprings, giving that it already has, is going to 0 because of the number of offspring > 2
If this approach appears useful, I suggest you ask for a more complete solution on https://math.stackexchange.com/

Expanding on @heracho's answer and Wikipedia, assume pi denotes the probability of having (exactly) i children, and that dm denotes the probability of extinction by the mth generation (note that this includes extinctions by all generations n with n < m). Then dm can be expressed as:
$\displaystyle d_m = p_0 + p_1 d_{m-1} + p_2 d_{m-1}^2 + p_3 d_{m-1}^3 + \dots = \sum_{i=0}^\infty p_i d_{m-1}^i$
with d0 = 0.
In other words, the probability of going extinct by the mth generation is equal to the probability of i children going extinct in m – 1 generations, summed over i. (The child lineages are assumed independent.) This recurrence relation allows you to calculate the extinction (and, by extension, survival) probability at any desired number of generations, if the values of pi are known. In simple cases it is also possible to work out the asymptotic value of dm by solving the fixed point equation dm = dm – 1 (see the Wikipedia page for an example).
In relation to your specific application, we can assume roughly 40 generations and use some empirical estimates of pi. The parity distribution of Denmark is given by Frejka (2008) as p0 = 0.127, p1 = 0.179, p2 = 0.443, p3 = 0.251 (where I simplify by assuming that people who have strictly more than 3 children actually have only 3 children). Plugging these parameters into the recurrence relation and iterating for 40 generations (see R code below), we get d40 = 0.17. Thus some 83% of the population can be assumed to have descendants in 1000 years.
I have taken Denmark as an example simply because it is the first country mentioned in Table 2 of Frejka (2008). However, to illustrate the dependence of the asymptotic value of dm on the parity parameters consider the case of Italy. From the same publication, we find p0 = 0.240, p1 = 0.235, p2 = 0.369, p3 = 0.156. With these values, we compute d40 = 0.41, obviously a very different situation.
I am not a mathematician, nor a biologist (nor a demographer), and the above logic obviously employs many ridiculous simplifications. It would be very interesting to know how all this pans out in a more realistic model.
Reference
Frejka, Tomas (2008) Parity distribution and completed family size in Europe: Incipient decline of the two-child family model? Demographic Research, 19(4): 47–72. https://www.demographic-research.org/volumes/vol19/4/19-4.pdf
R code
# get extinction probability (d) in generation m, given extinction
# probability in generation m-1, conditioned on probabilities
# of having 0, 1, 2, ... children (vector p)
extinctionprob <- function(d, p) {
  d <- d^(0:(length(p)-1))
  sum(d*p)
}

# iterate for 'ngen' generations
iterate <- function(ngen, p) {
  d <- 0
  for (i in 1:ngen) d <- extinctionprob(d, p)
  d
}

# usage example:
# iterate(ngen=40, p=c(0.240, 0.235, 0.369, 0.156))


text:
Why do NK cells not destroy bacteria, even though bacteria don't have MHC-I?
Part of the function of NK cells is to destroy cells that are unable to bind their KIR receptors. Or in other words, cells that don't express MHC class I. This is why they can kill MHC supressed infected- or tumor cells, which other immune cells can't.
However bacteria also don't express MHC-I. Yet NK cells are said to have very limited influence one microbial infections. I do not understand why NK cells do not degranulate (kill) bacteria upon finding that they do not have the MHC-I receptor complex.
Could someone elaborate this?

Human cells and bacteria are VERY different. Maybe an analogy would by be a police unit instructed to check in on all houses that don't have letter boxes. If they come across an area with tents, shacks or similar (which obviously don't have letter boxes) they'll still ignore it, just because those aren't houses in the first place.

While you’re correct that NK cells are often activated (in part) by the absence of MHC-I, they require other signaling events to become fully activated:

The Molecular Mechanism of Natural Killer Cells Function and Its Importance in Cancer Immunotherapy. Paul & Lal. Frontiers in Immunology. 2017.
Activating Receptors on NK Cells
Lack of MHC class I on the target cell is not sufficient to trigger NK cell activation. Full NK cell activation also requires recognition of stress-induced molecules by NK cell activating receptors.
Natural cytotoxicity receptors (NCRs) are another immunoglobulin superfamily of activating receptors that utilize extracellular immunoglobulin-like domain for ligand binding. Human NK cells express three distinct types of NCRs... NCRs recognize a wide variety of ligands on target cells ranging from viral, bacterial and parasite proteins to molecules from tumor cells and other host cells.
Role of natural killer cells in antibacterial immunity. Schmidt et al. Expert Review of Hematology. 2016.
6 Bacteria fight back and inhibit NK cell activities
During evolution, many bacteria have developed survival strategies which counteract NK cell activity.
Both Gram-positive bacteria such as Streptococcus pneumoniae and Gram-negative bacteria such as Salmonella spp and Escherichia coli are able to induce prostaglandin E2 (PGE2), which negatively affects NK cell functions at different levels. PGE2 inhibits the cytolytic activities of NK cells by suppressing their responsiveness to cytokines such as IL-12 and IL-15, and suppresses NK cell mediated activation of macrophages by inhibiting the production of IFN-γ. Similarly, PGE2 has a deleterious effect on homing, migration, and survival of NK cells, as it has been shown in Human Herpes Virus 8 (HHV8) infection.
  Thus, bacteria are able to inhibit both cytotoxic and immunoregulatory effects of NK cells in various ways.
8 Conclusions
In conclusion, there is a growing body of evidence that NK cells play an important role in the antibacterial host response. NK cells are able to kill bacteria directly, or to modulate the immune system via cytokines and interferons. Further studies are needed to characterize how NK cells are activated by different bacteria. In addition, the role of NK cells among the other arms of the immune system in the defense against bacteria is poorly understood. Last, bacteria are able to inhibit NK cell activities, and a better understanding of this impairment may be the basis to specifically strengthen the antibacterial host response. Therefore, additional in vitro and in vivo data may open new therapeutic strategies using NK cells to fight bacterial infections.

If you’d like a full-text copy of the Schmidt paper, I can share it with you.


text:
Why does cholesterol need to attach to proteins to travel through the blood?
I guess the deeper question is: what makes it possible for proteins like those part of HDL and LDL to move through the bloodstream?

Ah, got it, thanks! With deeper question I meant: How do the proteins in LDL and HDL know that they have to go to the liver? How does their "GPS" work?

Maybe change the question - It think "Is there so called free cholesterol that travels through the blood?" should be some valid question, too, and sounds the same.

It is not LDL that does the Job. The target cells "know" which lipoproteins (LDL,HDL,VLDL...) they should take up. They express the specific Membrane receptor that binds the Protein part of e.g. LDL and therefore take up specifically LDL rather than e.g. HDL from the blood. Example: cells that express receptors for apolipoprotein B-100 (one of the Protein parts of LDL) specifically "filter" LDL from the blood. The "filtering" occurs via endocytosis. Hope that helps.

Thanks! So I guess LDL and HDL just moves through the whole circulatory system until it randomly hits the target cells.

In respect of "randomly hits..." the target might be at the other ending: how does LDL/HDL find the cholesterol. It does, and this refers to cholesterol being soluble in blood (maybe not soluble enough not to take the taxi..., some idea of mine). From Wikipedia: "ABCA1 mediates the efflux of cholesterol and phospholipids to lipid-poor apolipoproteins (apoA1 and apoE) (reverse cholesterol transport), which then form nascent high-density lipoproteins (HDL)." I do believe cholesterol not even esterfied is being shedded from cell for "random" uptake.


text:
Does the law of independent assortment apply to homologous chromosomes or alleles, or both?
My textbook is giving me two definitions

1st def: "random orientation of homologous chromosomes at the metaphase plate in meiosis 1."
2nd def: "alleles for one gene separate into gametes independently of alleles of any other gene (only if genes are on non-homologs or very far apart on same chromosome)."

It's kind of hard to explain but here are my thoughts on this:
It seems to me that the 1st definition is exclusively taking a look at each pair of homologous chromosomes:  It looks like it is talking about alleles on certain homologs themselves and how there's 50% chance that a gamete will get a paternal and maternal allele of a gene after anaphase I.
And I'm guessing that the 2nd definition is an extension of the first by comparing gene assortment in all the homologous chromosomes:
It looks like it is primarily talking about the genes that are on each pair of homologous chromosome and how they (the genes) separate independently of each other (because they are on different homologs) in addition to the "random orientation of homologous chromosomes".
Can someone please clarify?

Check out these answers to other questions: one two

Possible duplicate of What is 'independent assortment'?


text:
Does recombination slow mutation accumulation in sexual populations? Is there any evidence?
Mullers Ratchet is the process by which asexual organisms would accumulate mutations without bound. It is claimed that sexual organisms would slow this mutation accumulation through recombination. Is there any evidence that recombination achieves this? Preferably experimental evidence.

It's a good question and one without a wholly satisfactory answer.  Here's a nice review from 2012 outlining the theoretical questions regarding Mueller's ratchet and recombination.
There also is "unequivocal evidence that deleterious mutations accumulate in low recombining regions of the genome, due to the reduced efficacy of purifying selection. " So if you accept this correlation between recombination and removal of deleterious mutations, then studies such as these are compelling evidence of what's happening in real populations .
One other thing to keep in mind that in terms of experimental evidence, it is non-trivial to translate theoretical measures of fitness (e.g. "selection coefficients") to something that we can directly measure in real populations.  So even determining if there is an increase/decrease in deleterious alleles is going to dependent on having useful data in the first place. The assignment of "true" measures of selection on individual genotypes is the mainstay of experimental evolution (nice review here) and is very labor intensive. Moreover, the vast majority of this work has been carried out in bacteria (due to their short generation times) so effects of recombination are not addressed. Nevertheless there are some cool comparative studies in yeast showing how recombination can make selection more efficient.

Mutations that are positively selected reduce the ratchet effect in large asexual populations. They spread, eliminating everything else, and so other mutations only matter if they happen in descendants of those mutations. It's as if the average population size is smaller.
Unfavorable mutations can hitch-hike with the selected ones, but only if they are unimportant enough that the combination is still selected.
Sexual reproduction reduces the ratchet effect to single linkage groups. But it allows things like meiotic drive. Mutations that result in the mutant version distributed to more than half the offspring can still be selected even if they reduce survival of the offspring later. And that happens a lot faster than the ratchet.
Experimental evidence -- that's hard. Maybe you could grow haploid yeast that don't do sex over a long period in a particular environment and measure changes in fitness in that environment. (The obvious way to measure changes in fitness is to grow them mixed with the wild-type and see how long it takes one to outcompete the other.)
Grow other yeast that do some recombination in the same environment and see whether they evolve faster. (Again, grow them together and see which one consistently wins.)
Some yeast that look reliably asexual have rare events that turn on sexuality. For example if they are all the same mating type, they can rarely have something that turns an individual into the other mating type. If your asexual populations have that happen while the experiment is running it contaminates your results. So be careful about that.
It looks like a whole lot of work. If the sexual form usually evolves faster then you have done a whole lot of work to show what almost everybody already believed.

There have been a ton of mathematical arguments and computer simulations demonstrating Muller's Ratchet and its relationship to asexual reproduction. However, as far as I know, the experimental evidence is still hotly debated. The debate generally revolves around whether a given biological system fulfills the conditions necessary for the ratchet to operate. Here are a couple of relevant papers:
Quantifying the genomic decay paradox due to Muller's ratchet in human mitochondrial DNA.
Asexual Amoebae Escape Muller's Ratchet through Polyploidy


text:
What color is the hemolymph of the Japanese giant hornet?
This is a random and very specific question that's been nagging me for quite some time. I've tried asking on other websites with no luck, and am hoping that somebody here can either give me an answer or redirect me to somebody/somewhere where I can get my answer. I guess it isn't required but I'd also prefer to know, if you can give me an answer, how you got your knowledge on it. Thank you in advanced!

We may never know. Every scientist brave enough to attempt an answer to this question has died from giant hornet attacks.

Well, if anybody lives in Japan then I kindly ask you to cut open a dead one if you find it...

Would it be different from other insects' hemolymph?

Yeah. Spider (an arachnid, but still a valid example)  hemolymph is blue because of copper, whereas some insects have hemolymph that is yellow or green.

I was able to figure this out for myself by watching videos of the hornets being eaten by other insects. The answer is that the hemolymph is a pale yellow color, like I've heard other wasps and some bees have as well.


text:
Does ATP hydrolysis reaction have a high or low activation energy?
I was recently studying about ATP and how it functions as an energy carrier to all biological processes; however, I came across a confusing and paradoxical statement from two sources:
(at 7:36)
and
(the free response question in the bottom of the page)
Basically, in the video, it says that ATP hydrolysis has a high activation energy which is why all of the ATP isn't randomly used by the cell processes.
And in the free response question, the answer is that ATP hydrolysis has a low activation energy and low free energy making it a spontaneous reaction.
A follow up question is: How then does the ATP of the cell used in a selective way to certain processes only?
Thanks for your help.

High and low are not very descriptive since they are relative. ATP hydrolysis may have a high activation energy compared to some reactions and low when compared to others.  The important point is that the activation energy is sufficiently high enough such that ATP is not rapidly hydrolysed under physiological conditions before it can do useful work. In other words ATP hydrolysis is kinetically unfavourable but thermodynamically favourable. The reaction rate is increased by enzymes (by lowering the activation energy), which couple ATP hydrolysis to other processes to do useful work.
Also, a note on reaction spontaneity: it has nothing to do with activation energy but rather depends on the change in free energy; ATP hydrolysis is spontaneous because it is exergonic.

If we take a look at the Sodium-Potasium pump (action potential), it looks like the ATP activation energy is low for that process. Otherwise it can't support the speed of the signal propogation, can it? Perhaps it's a very integrated complex chain reaction where a receptor actives within the cell, that literally tells, "for this particular work, the ATP activation energy should be pretty low" and so on. I am curious to know how it exactly applies in this scenario.

@bonCodigo I'm not really sure what you're getting at. Enzymes lower the activation energy of reactions.

So the video explanation is more accurate. Yes? And I am also confused in something (I am not sure if it was addressed in the answer or not though ) :How do cells control how ATP is used? Because on a wiki page I read that if ATP and ADP are placed in a water container at equillibrium then all the ATP will be converted to ADP.

@mariam Enzymes control how ATP is used.

The video response is more accurate. In particular, saying that the activation barrier is high enough for the reaction not to occur spontaneously in water means that the activation energy is much higher than the thermal energy, $k_B T$, where $k_B$ is Boltzmann's constant and $T$ is the temperature.
You ask, "How do cells control how ATP is used?". As mentioned in the other answer, this energy barrier is lowered by enzymes, in particular ATPases. These are 'machines', such as for example molecular motors or ion pumps, which have a binding pocket for an ATP. When the ATP comes inside this pocket, the activation barrier is lowered and hydrolysis can happen. And, crucially, these 'machines' then use the released energy to perform some useful task. If hydrolysis happened by itself in water, the released energy would be 'lost' in the form of heat.


text:
Pitch shift in hearing after wisdom teeth removal
Yesterday I had my wisdom teeth removed. This morning, when I heard our phone ringing, it sounded a little lower-pitched than usual (I have perfect pitch). Sure enough, when I opened FL Studio (music-making software) and loaded up one of my projects, I had to adjust the master pitch up by about 20 cents for it to sound "in-tune". What could cause this shift in pitch perception?

The change in blood flow to, or damage to the cochlea by vibrational trauma (drilling) were implicated in a hearing loss case here after some dental surgery. You'll want to consult a physician, however, for any of your worries. If this is a personal case, we cannot provide medical assistance, nor do we have enough information about your or your procedure to begin consideration.

Because it's not really hearing loss, I'm not too concerned about it. I'm mostly just curious as to what could cause a shift in pitch perception.

Temporary swelling or edema from the extraction would be my assumption.

Perfect pitch with respect to what note? (A440?) Also, how broad is the supposed pitch shift? I find it rather hard to believe that swelling can cause a logarithmic pitch shift across the entire audible spectrum.

@MarchHo yes, A440. And as far as I can tell, it affects my entire hearing range, although I haven't thoroughly tested it.

Does it affect pure notes or only chords? I'm not sure what tests you've done or what perfect pitch is like(I don't have it and I can't really imagine how it works), but my very first guess would be that higher pitches are more attenuated by your newly detoothed skull, so higher harmonics sound quieter and the overall sound is lower. That would work on a ringing phone but should work less noticeably on pure tones.

I once had an ear infection that, when done, left that ear's perceived pitch shifted by about a quarter tone, which really messed up listening to music (google ToneTester and you'll see the testing app I wrote afterwards). I recovered after a few months.

I just had my wisdom teeth removed, and I'm experiencing the same thing. What I used to hear as 440 for A is now actually at around 450 - 460. When I hear people talking, I don't notice a difference, but when I was tuning my violin today it felt kind of off. Same with the Discord sounds when people left or joined calls; they sounded lower pitch than I was used to.


text:
Number of DNA strands per chromosome
As I was reading Griffith's Introduction to genetic analysis this evidence was provided for single DNA makes single chromosome.
Eventually geneticists demonstrated directly that certain chromosomes contain single DNA molecules. One strategy was to use pulsed field gel electrophoresis, a specialized electrophoretic technique for separating very long DNA molecules by size. The extracted DNA of an organism with relatively small chromosomes, such as the fungus Neurospora, is subjected to electrophoresis for long periods of time in this apparatus. The number of bands that appear on the gel is equal to the number of chromosomes (seven, for Neurospora).
(Page 86).
This points to the fact that one chromosome has single DNA. What I want to know is that what evidence is there that each chromosome is not made up of multiple similar sized DNA molecules all coiled together to give a single chromosome so that the number of different types of DNA molecules to number of chromosomes have ratio one to one but one type of DNA molecule's multiple copies makes one chromosome.

I don't have a copy of Griffith, so I can't check myself. But are you sure that the experiment he describes is not to demonstrate that each Neurospora chromosome is made of one dsDNA molecule (two strands, incidentally) of length 10 arbitrary units, say, rather than three different dsDNA molecules of length 1 + 3 + 6, say. The question you ask is quite valid, but, I imagine, addressed in earlier in other ways, especially in bacteria.

I think that this and along with some other experiments given in Griffith tries to proves both of these points.

I doubt it. I don’t know the answer for certain, but it seems to me that electron microscopy of bacterial chromosomes (no complications of chromosomal proteins) with size markers might have been a possible approach. Pulse field gel electrophoresis separates chromosomes by size but I don’t think it answers your question. I’d offer to research it for you, but I have other fish to fry at the moment.

What do you mean by "coiled together"? I guess you mean kept together by some non-DNA material, i.e. proteins. Proteins are removed using proteinase k or something similar, so this would break any protein fostered coiling between the molecules and you will see a crazily small chromosome. You can find an example of this kind of experiments ehre (http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132005000100001) and some reading and exercises here: https://www.ncbi.nlm.nih.gov/books/NBK21330/


text:
A theoretical ethical dilemma
For all those who keep in touch with advancements in field of biology iPSCs ought not to be a foreign term. iPSCs are now being used to make organ models to be able to study diseases and how drugs will affect them without needing any living host. I expect this organ modelling to become more and more advanced in future and soon all complete organs to be made using this technology. However should making a complete living brain ever be allowed for studying diseases as we are mostly our brain, so maybe while using such living brains we are making conscious systems on which we are experimenting?

Consciousness and the brain are two different things. In-vitro grown brains would have no memories, no experience and thus no consciousness. It's like a computer without software. Plus, animals we are using now in science like rats, mice and other mammals are conscious already. Where is the dilemma?

Yes you are right in a way. But then when anything that becomes anything comes even close to human consciousness the moral obligations increase many folds. So it becomes difficult for me. Thanks for your answer.

I agree that iPSCs will continue to be developed and will probably be used to make brains at some point in the future. Whilst it's obviously not possible right now, feasibility isn't the issue here. A lot of my answer will be somewhat opinion based as a result of the nature of such an ethical question.
As to the ethics of experimenting on such living brains, It's undeniably a tricky question - and, as with all ethical dilemmas, suffers from the inherent variability of ethics and morals (you will struggle to find two people with exactly identical ideas about right and wrong, and from a purely logical and scientific perspective there's no reason to believe that moral objectives exist at all).
An interesting phrase that you use in your question is "we are mostly our brain". I suppose it depends on what characteristics you're looking at: a brain alone would be incapable of surviving and by mass the brain only accounts for around 2% of the human body. we are mostly water; simple, lifeless and unconscious.
Therefore we are evidently ranging into territory of consciousness, and by "we" you are referring to our seemingly conscious 'mind' as conjured by the complexities of the brain. As for this, I think perhaps the philosophy stack exchange is the place to go...
Ultimately it depends on whether we look at a brain as simply a collection of atoms which form molecules, cells, tissues and then organs or as something more - this is the whole idea of emergence (for example, an individual ant is unconscious and negligible, but many thousands of ants communicating using chemicals and simple commands forms a highly complex and adaptable ant colony - the ant colony is greater than the sum of its parts). if the former is true, then there should be no difference in manufacturing a brain and experimenting on it to making muscle tissue and performing experiments on that (or even creating a crystal from chemicals and using that for experiments). If we look at the brain as something greater than the simple sum of its parts - as a living, conscious being - then I suppose we'd need to go through the proper channels that we have now when dealing with something that's alive.
From here an infinite variety of problems crop up: would the brain be given the full rights of a human, or treated more like animal test subjects? Would consent from the brain be required? Could a brain even be conscious if unattached to the rest of a body? Would killing the brain be murder as it would be with a human?
So far I've just been stating issues: my personal opinion is that we ought to find a balance somewhere between treating the potentially conscious brain as merely an impressively complex collection of lifeless components and giving it the full rights of a human being. where that line should be drawn? I don't really know. Personally, I'd rather test drugs and treatments on a mere brain than on a fully formed and functional human being, but someone else might not agree.
These questions are always difficult, and science can't really give any reasonable answers (scientists can't even agree on what makes something alive, let alone conscious). there is an entire field called bioethics devoted to things like this.
my advice would be to ask this on the philosophy stack exchange as you will get some interesting answers there.

Thanks a lot for such a well considered answer.


text:
If fish gills do not split H2O into H2 and O, and just take the dissolved oxygen what is left leaving the gills?
Could you please explain to me the exact left overs after a fish takes oxygen out of H2O?


text:
How does flow rate of Ion channels depend on the length of the selectivity filter?
The length of the selectivity filter of ion channels such as the potassium channel commonly is only half of the thickness of the membrane. Some book such as MBoC says this can benefit the transfer, so I wonder how will the flow rate of the channel depend on the length of the selectivity filter.
Intuitively, the longer it is, the lower the flow rate will be. But consider the following factor this may not be true:
There is no "resistance" in the selectivity filter. The ions in the channel are basically in thermal balance with the selectivity filter wall and bounce forth and back randomly all the time. The driving force of the flow is not kinetic energy, but the ion density difference at both side just as normal diffusion process. From this point of view, the flow rate should not be depend on the length of the selectivity filter, at least not very much.
If so, then the fact that the length of the selectivity filter is only half of the thickness of the membrane maybe only a coincidence in evolution history and doesn't bring much benefits.
Considering most ion channel have very similar selectivity filter length and synthesis of new ion channel proteins with longer selectivity filter is not possible with today's techs, this can't be decided by experiments. Is there some molecular dynamnics simulation about how the flow rate depend on the length of the selectivity filter?

Would you please include a more specific citation, please? (page numbers / journal article)  Thanks!

@rotaredom Figure 11-24 of MBoC "The pore vestibule facilitates transport by allowing the K + ions to remain hydrated even though they are more than halfway across the membrane"


text:
What are the tests performed by NASA's Mars rovers to establish that life could survive on the planet?
I am particularly interested in the Mars Rovers, which are out there trying to find life. Do they believe that the tests they perform are sufficient to verify the existence of life (Also please mention about the tests). How do they accommodate for the possibility of life forms different from the conventional carbon based as that of Earth?
I am really curious to get these answers, please explain.

You can check on NASAs website, as each mission has a page dedicated to it. If I remember correctly, I do not think that any of the rovers to date have technology to directly test for martian life forms. I think that the current missions are only able to test indirectly for conditions favorable to life and also possibly the evidence of organic molecules.

"How do they accommodate for the possibility of life forms different from the conventional carbon based as that of Earth?" - a very important question, life is just a human concept/definition applied to natural things, just like species. We could end up redefining life.

@rg255 I think that you need to remember that there are two things going for carbon as the basis of all organic life. The first is that it is the first element able to form 4 covalent bonds, which leads to the incredible diversity that we see in carbon-based molecules. Second, the second period elements are more abundant in the universe. There is still a good amount of silicon (The group four element below Carbon) but I would check the bond energies of silicon compounds and compare stability to their carbon counterpart.


text:
How much percentage of substance does liver take in one pass?
The portal vein system is to feed the absorbed nutrition and toxin (defined as "substance" here) to liver first for it to take them up as fast as possible, before they reach other organs which may be harmful.
For this to be effective, liver should take as much substance as possible in one pass. For example, if the liver only take up 10% of the substance in one pass, then the portal vein system won't make much difference, since most of the substance will circulate to other organs anyway and get taken up by liver in the following circulation passes.
On the other hand, it seems to be very difficult for an organ to take up most substance in one pass since this is not a "effective design" (i.e. over designed).
How much percentage of substance does liver take in one pass? And if the percentage is low, why is the portal vein architecture important?

It depends entirely on the substance. Substances that are more hydrophobic or quickly metabolized by the liver are absorbed more completely. I think it's worth considering that it isn't as though all the drug must be absorbed quickly in one place, they are passing through a dense capillary bed with lots of distributed opportunity to take substances up throughout the liver.
https://tmedweb.tulane.edu/pharmwiki/doku.php/bioavailability_the_first_pass_effect has some examples... 75-85% propranolol is metabolized first-pass, 70% of oral morphine.

What about the main daily nutritions and toxins?