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Alternative to distilled water for pH test
I am looking to test soil pH in a remote location. The test results don't need to be perfectly precise, and a pH test strip should provide sufficient accuracy. However generally this kind of testing uses boiled distilled water - and in this location it will be very difficult to buy distilled water.
The location is off grid, and getting specialized equipment to the location is not an option. (This is for field experimentation with farmers in rural Africa)
The process I have seen used for this is:

Add 1 part boiled distilled water and 1part soil by volume, in a clean container
stir and leave to settle.
Test the water pH with a pH test strip

Would it be possible to use boiled rain water for this process, or would this be likely to contain impurities which would interfere with the test results?
If there are likely to be impurities but there are approaches that can mitigate for them, please explain.

Have you considered getting a portable distiller?  It would require access either to a socket or a car with a transformer, and they can cost a bit, but it would probably do the job.

That is a possibility; however the cost and logistical challenge of getting and running one is quite high (For example there is no grid electricity). If it comes to that it may be worth buying a full soil testing kit with it's required equipment, rather than just using pH strips. I am also considering the possibility of setting up a DIY distiller- suitable parts may be locally available.

@Ben What about commercially available solar distillers? Of course the cost may be more than pH strips but I doubt that is your only source of costs in the first place. I'm not too familiar with soil testing but what sort of size of sample and number of samples are you talking about here?

Have you considered making a single stage distillation unit by placing an inverted bowl above boiling water and capturing the condensate then maybe boil the water once more to kill off any air contaminants?

@GyroGearloose not that it really matters to the question, but I can post a pack of soil test strips to for my friend on location to pick up when he is next in town for about £4. Sending a still along with that is sure to cost >£40, even if you don't take account of the risk of loss and breakage in the post. Asking about an alternative costs nothing (but the 50 rep bounty), and I judged it to be an interesting enough question that it could benefit someone else sometime in the future.

Hi Ben, thanks! you can get global maps of acid rain and for the study zone. You can double check your rain medium by via it's reaction to a fraction of salt and compare it to 5.5 distilled water. if a few moles of salt raise the pH to 7 equally in both waters then the unknown water is similar. You can also take a 100g of citric acid with you, and check the reactivity of the soil (pHBC) very easily, i.e. in quartzy barren soil it would swing a lot. Unreactive sandy soil is poor and easy to amend, it's better than high pH chalk. I studied soil sciences in university, it's a good read.

The h2co3 content of unadulterated rain is 15 micromoles of H+/Kg at room temp. The pHBC of average field soil from a 3000km transect in asia varied from 10 to 188 - mmol-kg-ph unit... from 40 localities. This other research found soil values of 45-1000 pHBC. https://www.science.gov/topicpages/s/spiked+soil+samples.html
That means that H2CO3 would affect arid meadow soil by 0.08 to 1.0 pH points if 1kg of water reacted completely with 1kg soil in a sealed environment. And 0.33 to 0.015 pH points for the referenced research.
However, if you boil the water, the gases expand and leave the water even prior to boiling point, which can be seen as bubbles previous to 100'C, boiled water error becomes 0.2 to 0.003 pH points.
This is the only ref i can find:
https://www.engineeringtoolbox.com/docs/documents/1000/solubility_CO_water.png
ttps://www-engineeringtoolbox-com.cdn.ampproject.org/ii/w1200/s/www.engineeringtoolbox.com/docs/documents/1148/solubility-co2-water.png
That means that if you have unadulterated rainwater at pH 5.5, and you boil it and jar it, you will have water with a pH near 7 after sealing and cooling.
Pure water is not natural or biological and it is aggressive to get to equilibrium. Upon contact with the atmosphere, it will immediately begin absorbing CO2 and the pH will drop and settle in at about 5.5 after about two hours.
Carbonic acidification is a background effect of the athmosphere aerated soil and rain to similar degrees.
Strong acid - pKa < 2
Weak acid - 7 > pKa > 2
Weak base - 10 >pKa > 7
Strong base- pKa > 10
oxalic acid and citric acid have a pKa in the range of 1 to 3, they are fairly strong, whereas CO2 has a pKa of about 6.4.
If your rainwater has a pH below 5.3, something is wrong with it and if the rainwater is around 5.5, it's nearly the same as distilled water.
I micromole of HCl rects completely and gives distilled water a pH of 6, whereas 1 umol of CO2 causes [a pH of 6,997][6], because only 0.3% of it converts to H2CO3.
[6]: https://books.google.fr/books?id=yRMgYc-8mTIC&pg=PA124&lpg=PA124&dq=hcl%20micromole%20co2%20distilled%20water%20concentration&source=bl&ots=OFKb4CB3MI&sig=ACfU3U0a1XQ_GSIZ5E-nj7JgPsaeDv7SbA&hl=en&sa=X&ved=2ahUKEwib-vuMkc_hAhVEThoKHYIcDtQQ6AEwCXoECFAQAQ#v=onepage&q=hcl%20micromole%20co2%20distilled%20water%20concentrationhcl&f=false

I don't think the issue is the reactivity of CO2 with the soil, but rather that the rain water will have a pH below 6 and therefore would impact any pH tests that incorporate use of that water. This impact is significant if the distilled water being used for tests normally would have a pH significantly higher than the rain water. What the OP could do is test the pH of both water sources to see if they differ, and if so, what effect using the two water sources has on the soil analyses. I would think that water pH would have varying degrees of effect depending on the soil makeup.

However, your point about any water source absorbing CO2 to equilibrate with the atmosphere within 2 hours might very well be true and nullify this issue (though presence of N or S acids from air pollution would impact the rain and not the water source held by the OP). Regardless, please provide a source to back up this claim and the various others that you make in your post. I'll be happy to upvote with proper support :).

For agricultural purposes in rural Africa, rain is also part of the agricultural equation. High precipitation does change soil pH and leaches minerals, especially if it acid, and distilled water does too. distilled water is probably more important to test soil where for an arid region where it doesn't rain. For the purposes of the test, the dissolved elements will be present in the sample, and not leached. For agriculture, a good process is to use the tools that the farmers have, the local water and soil amendments and find the best soil mix. references would use pHBC.

https://www.researchgate.net/publication/236878026_Soil_pH_buffering_capacity_A_descriptive_function_and_its_application_to_some_acidic_tropical_soils the pHBC on the following page is measured as 1-2 mol/Kg of H+, versus the H2CO3 content of natural rain which is in micromoles/Kg of H+: https://www.google.com/search?q=soil+phbc&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjWt8S2kcnhAhUGJBoKHUIsB_MQ_AUIDigB&biw=1271&bih=646#imgrc=wmfw9DvqBCAMWM:

So a soil's pHBC (more often, I believe, discussed in terms of CEC - cation exchange capacity) is all about determining just how much buffering capacity a soil has. So unless all soil types being sampled are of the same type (i.e., have the same CEC), then water pH would impact each differently. The impact of the difference could be directly related to the pH of the water solution used in the OP's pH test. Perhaps one soil sample has a pH that is more resistant to neutral but less resistant to acidic sampling methods...

IF the OP truly doesn't care about precision, then perhaps you're right that the pH difference in rainwater might not be significant. But to go into a study with that known potential source of error is not very good science. Again, I recommend that if rainwater is to be used, that the OP at least tests to confirm that it doesn't skew results.

Also, thanks @com.prehensible for including sources in your comment. However, please add the sources to the post directly. You also include graphs and make a number of very specific claims and assumptions without supporting them or citing their source. Your post would be made much stronger if you supported each claim directly and individually. Please provide context and source for your graphic, too. Thanks.

Hi, I have researched the query further, because carbonic acid is so very unreactive, that scientists don't bother with it very much, and so i had difficulty to find sources. I added some extra information, notably the notion that boiling drives of the CO2 in rain, that only 0.03% of CO2 becomes H2CO3 at pH 5.6, and some graphics. yours, apondecologist ;)

I want to accept this answer, and give it the bounty, but clearer references would be good.

A found a graph stating the co2 concentration of boiled water, which reduces the co2 by 5 at sea level, less at altitude, and perhaps 20 minutes of boiling brings the acid to zero, i don't know. Frankly it sounds like it would be worth making substrate analysis available to african farmers like it is here where we can post it to a lab to have CEC and pHBC minerals Calcium and organic content of it

Rainwater might not be the best option.
Rain water is naturally acidic due to the reaction of CO2 forming some weak carbonic acid [see here for explanation].

 Source: Wikipedia
As a result, pH of "pure" rainwater is usually between 5-6; usually around pH 5.6. See here.

Most rainwater has a pH of 5.6 to 5.8, simply due to the pressence of carbonic acid (H2CO3).

Presence of any sulfur or nitrogen oxides in the air (perhaps from burning coal plants or city traffic from 100s of km away) would lead to rain becoming even more acidic. From environment.co.za:

Sulphur dioxide reacts with water vapour and sunlight to form sulphuric acid. Likewise NOX form nitric acid in the air. These reactions takes hours, or even days, during which polluted air may move hundreds of kilometres. Thus acid rain can fall far from the source of pollution.

I had hoped that boiling the water would be sufficient to bring the levels of dissolved CO2 to a consistent low level. I am fairly convinced that this would not work reliably - after looking further into sulfuric and nitric acids as described in your answer, so I think this answer is correct. I think this answer would be even better if it addressed what if any effect boiling would have on the amounts of these impurities.

@Ben, a discussion about the impacts boiling has on water pH is really more appropriate for Chemistry.StackExchange, so I'd advise you to ask that question there.

@Ben: To hypothesize (because I don't know the answer): I would guess any solutes (if any) dissolved in the rain water would increase in relative concentration and as a result the water's pH would shift in relation to the acidity/alkalinity of the solutes. This is totally conjectural, and I'm not really sure there would be enough solutes to make a difference. You can read here for a discussion about the impact of boiling on water pH, though I don't think it quite answers your question.


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Myopia & the Blur Effect
I know myopia is caused by elongation of the eyeball. When the eye is too long, light entering the eye balls falls in front of the retina instead of on it.
However I do not quite understand how this leads to the "blur" we observe. If part of the light entering the eyeball "misses" the retina shouldn't the observed effects simply be a reduction in the brightness of the object - as if I were standing in a less illuminated place? For example, if I take off my glasses in broad daylight my retina is getting a far greater dose of light than when I'm indoors (wearing my glasses) under artificial lighting. Yet the world still looks blurry outside (without glasses) and clear indoors (with glasses).
What causes the blur effect? If less light is hitting the retina it should simply look less illuminated, not blurry.

You have some misconceptions about visual acuity. You need to understand how lenses work to understand why objects up close are blurry in myopia.
Sure, if one elongates the orbit, blurring will occur, but that's not usually the cause unless it's in childhood. As we age, the elasticity of the lens has more to do with it.
Light comes in through the pupil. The amount of light is what determines brightness; too little, and we can't see, too much and we look away. In between we "see". Being able to focus doesn't have any effect on brightness; the size of the aperture does, however (the aperture in this case being the pupil.)
Blurriness is caused by where the light rays striking the object we're looking at come into sharp focus in out eye. Sharpness falls within a very small range, then once the range is exceeded, the image becomes progressively blurrier because the rays scatter again. This is why looking through a pinhole improves our vision: less scatter. If your pupil could constrict down to a pinhole, that would be pretty amazing, but it can't.
The purpose of the lens is to focus the image. It can do so (with the help of ciliary muscles) by changing shape. But it can only change shape within a range. If it cannot change shape enough to focus the image where it needs to be - on the retina itself - you have blurry vision.
That's why additional lenses (or changing the contour of the cornea) help.

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Composition and quality of mushroom spores
Message to moderator(s):
This question was deleted since it looks similar to a question in another SE.
However, the question being asked in this SE is completely different. Would that be a strong enough basis to restore this post?

From this source, it states that:

Living spores have been found and collected in every level of earth’s atmosphere. Mushroom spores are electron-dense and can survive in the vacuum of space. Additionally, their outer layer is actually metallic and of a purple hue, which naturally allows the spore to deflect ultraviolet light. And as if all this wasn’t unique enough, the outer shell of the spore is the hardest organic compound to exist in nature.

With regards to a mushroom spore's electron density, having an outer metallic / purple layer, and the hardness of its outer shell, have these things been confirmed in biological experiments?

Were there any references associated with these claims?  Where have you looked to see whether there is any credible support for these statements?

@tyersome No, there were no references in that article, I also heard similar claims in a podcast that predates that article. I have looked into general websites regarding mushroom spores (don't have access to peer-reviewed biology publications), and they don't seem to have any information with regards to the composition and quality of mushroom spores.

Please don't cross post to multiple SE sites.

This post is not substantially different from the other one. See https://meta.stackexchange.com/questions/64068/is-cross-posting-a-question-on-multiple-stack-exchange-sites-permitted-if-the-qu - answers to both of these questions are going to touch on the same sorts of source, if the source even exists. Generally "is there support for this claim I found on the internet" questions are not acceptable here, either, without some additional research on your part.

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If we introduce any disease or deadly effect to a large group of living things, will such a group be able to develop a resistance?
Like for instance, introducing cancer or radiation,
to a large group of insects/animals that can reproduce very quickly,
would it result in the surviving population of these living things to be more resistant to whatever adverse condition that was subjected upon it?

Or how about conditions that should lead to cancer? I guess having that "pathology" tag wouldn't make sense in this case, I'll remove that.

From your edit, it seems that you are not interested in transmissible disease anymore (and so my answer would be off) but in cancer specifically. It feels like you may not really know what a cancer is (esp. when we consider what you wrote before the edit). You should definitely read a bit about cancers. Is the question "Is there selection to reduce sensitivity to cancer?", the answer is yes but almost by definition of what a cancer is, so I am unsure what you are really asking.

Thanks @Remi.b, Reading some general info about cancer, https://www.medicalnewstoday.com/info/cancer-oncology, I'm not sure how that could by definition imply "selection to reduce sensitivity to cancer". I really have zero background in any biology-related field, but this question had been an ongoing curiosity for some time.

@Remi.b As for what I'm really asking, I just wanted to know if it were possible to over natural selection, gradually evolve some group of living things to be more resistant to any harsh condition, such as extreme heat/cold, intense radiation, any disease, etc. This curiosity might have been inspired by new stories related to "tardigrades" (https://gizmodo.com/genes-hold-the-key-to-the-water-bears-indestructibility-1786814698), that are highly resistant to extreme conditions.

I'm not sure what you mean by to over natural selection?

@Remi.b By "natural selection", I meant, for instance, introduce an extreme condition to a group of ants (i.e.: low temperature that kills most but not all), then after several generations, the surviving ants should be more able to tolerate low temperatures. So if other things were applied the same way (introducing a disease that causes most but not all things to die), we should get similar results? I assume this is what you meant in your response by "selection against".

Yes, your description of the consequences of natural selection is correct. It is more the use of the verb over that I did not understand in the context of your sentence. Did you mean 'to put an end to selection' or something?

Selection against a trait is the same as selection for the opposite trait. For example, for mice living on white sand, there is selection for being white and against being black for increased camouflage (and the opposite is true on darker substrate; Nachman et al. 2002).

@Remi.b, I'm not able to edit the comment, but it should be rephrased as: "I just wanted to know if it were possible to, by the means of natural selection, gradually evolve some group of living things....", sorry for any confusion.

Oh I get what you meant now! No worries. Btw, I made a tiny edit at my answer you might want to have a look at.

Resistance is usually present in a population already and the selective pressure makes it apparent. So organisms don't develop resistance. They have resistance that is selected for. Even in bacteria that can survive ever more antibiotics at higher doses, they do not survive until a mutant arises that when exposed to the environment, survives.

Is there selection against cancer?
What is selection?
Let's start by explaining what selection is. Selection is a differential in fitness among different genotypes. In other words, if you consider a phenotypic trait for which there is some variance in the population. If, in the population, there is a correlation between this trait and fitness and there is a correlation between this trait and genetics, then there is selection.
The three ingredients for selection are

Variance for the phenotypic trait
Correlation between the phenotypic trait and fitness
Correlation between the phenotypic trait and genetics

These three bullet points are known as Lewontin's recipe. The last bullet point could be rephrased into "the phenotypic trait is heritable" and all bullet points put together could be rephrased into "fitness is heritable". Have a look at the post Why is a heritability coefficient not an index of how “genetic” something is? to understand the concept of heritability.
Is there selection on cancer?
Cancer is fundamentally a genetic disease. If this is unclear to you, you might want to read a bit more about cancer.
There is variance in the population in cancer (not everybody has a cancer but some people do) so we satisfied our first bullet point. Cancer is a genetic trait. So we satisfied our second bullet point. Cancer is a disease and therefore affect fitness (cancers kill) so we satisfied our third bullet point. In short, yes there is selection on cancer.
How does increasing the amount of carcinogens in our environment will affect selection on cancer?
From wiki

A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis, the formation of cancer.

If you increase the amount of carcinogens in our environment, you are going to increase the prevalence of the disease, which will increase the variance for the disease (unless the prevalence would become very very very high) and therefore increase selection against cancer.
Does selection work?

I just wanted to know if it were possible [, by the means of] natural selection [to] gradually evolve some group of living things to be more resistant to any harsh condition, such as extreme heat/cold, intense radiation, any disease, etc.

Yes, it is possible. Natural selection does work.
Note that if you are interested in a short intro course to evolutionary biology, then you may enjoy having a look at Evo101 by UC Berkeley.

Thanks for edit to more closely follow updates in the the comments. I'll have a look into that Evo101 link sometime.

I don't think this answer answers the post given the discussion and new edits. I will leave it here nevertheless just in case I still misunderstand the OP's question.

[..] introducing cancer or radiation [..]

A cancer is not a transmissible disease (except very few cancer last the facial tumor in Tasmianian devils). A radiation is not even a pathology, it is a physical phenomenon which include light. Did you rather mean something like a virulent flu for example?

If we introduce any disease or deadly effect to a large group of living things, will such a group be able to develop a resistance?

The population may or may not survive. It depends upon many parameters such as how virulent is the parasite, how large is the population, whether individuals in the population have already encountered the parasite before, whether there is already genetic variants resistant in the population or whether de novo mutations will be needed, etc... There is no way to answer to this question in the general sense.
Note by the way, that an individual may be resistant or tolerant to a certain disease.
Most of the time, the population survive well. The population will likely decrease in size a little bit though.

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Flowers sent by the birds
Birds have sown seeds on my ground and this beautiful flower has sprung.  What's the name of this flower?
I live in Sao Paulo, Brazil

It's a type of begonia. With 1800 species in the genus, it's hard to say which it is, but the leaves which seem palmate would place it in the aconitifolia species. Your leaves don't appear to be variegated, and your flower is deeper pink, but it's the same flower species.

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Why are monotremes so rare?
There are currently only five species of monotremes remaining, and all of them are found in Australia. Additionally, I read a science article claiming that competition from marsupials essentially forced monotremes into the water, where marsupials couldn't follow without drowning their young.
Why are monotremes so rare? Are the traits that define a monotreme (such as egg-laying) inherently less competitive, or is their relative scarcity more of a quirk of fate?

Can you please link to the article you're referring to?

@Remi.b Sure, there you go.

When you stop to think about it there is one big reason live birth has an advantage. Lets assume with habe organism A and organism B, A and B both have offspring of exactly the same size and needing the exact same amount of resources (nutrients, etc.) A lays and egg and B gives live birth. A needs to have all of the nutrients its offspring  will need all together at once because once it forms hte egg it cant add anything while organism B does not need it all, they can keep eating and supplying the nutrients over an extended period of time, as they gain it, so they need less "on hand" as it were. A and B may be putting the same amount of resources into their offspring but A does it all at once but B can spread it out over a long period of time meaning it does not need to build up huge reserves before breeding. As an added benefit if times are bad B can dump the offspring and try again later, saving all that would be wasted material for itself, so it can survive famine and drought better.

Its hard to definitively say "why" some groups are more successful than others. Without replication, answers can simply be "Just-so stories". But there is some replication here. Monotremes have been eliminated everywhere they once existed, except for Australia, and New Guinea. There is a similar replicate of what happened to the marsupials in S. America when the Panama isthmus connected the eutherians of Central America to the marsupials in S. America; extinction of many of the marsupials in S. America. The same thing happened in Australia when eutherians were introduced, but on a lesser scale (so far). These are two examples of eutherians outcompeting marsupials. I know, not the same as monotremes. That monotremes found refuge in Australia may not be a coincidence in that they did not need to compete with eutherians. Marsupials not laying eggs may have been an advantage that allowed them to outcompete monotremes. But there is not similar replication to move beyond "Just so".


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Maternal Effects
Does anyone know of a good review of non-human maternal effects, preferably the most recent? I'm looking for a breakdown of the most well-studied/least studied biotic and abiotic cues. Perhaps something more comprehensive than Bell & Hellmann (2019), with an emphasis on maternal effects as opposed to the more general "transgenerational plasticity".

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.

Maternal effects of what sort? I could suggest some social effects of neglect of children by working mothers, but I doubt that you had that in mind. If you define your problem clearly, An internet search will surely provide answers. Any opinions of what constitutes “good” here would be subjective — you need to make your own judgment.

Also did you tag predation and toxicology for a reason?

@user438383 Predation and toxicology are two possible environmental cues that can promote maternal effects (see linked paper, table 1). Others include temperature extremes, nutrition quality, in eutero hormone cascades.

@David I narrowed my question to non-human maternal effects. Regarding what kinds, I am interested in a contemporary review paper, so all possible kinds.

The word “effects” is meaningless scientifically without saying what is doing the affecting, and what is being affected. Questions here should be self-contained, and I certainly am not going to follow a link to find out what you are talking about. So let’s try again: “Maternal effects of ****** on ****”. You know what you have in mind, but you need to make it clear to us, because we do not.

@David I am unsure about your field as "biology" is extraordinarily broad. In evolutionary biology, the phrase "maternal effects" has a precise meaning. It is a subset of transgenerational phenotypic plasticity, and a considerable body of literature is associated with it.


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Enhancer elements in prokaryotic DNA?
I know that in terms of post-translational modifications of genes, prokaryotes and eukaryotes differ highly because of the lack of introns in prokaryotic DNA.
With this said, do prokaryotic DNA sequences contain enhancer elements other than the UAS(upstream activating sequence)?
In addition, are enhancer elements like promoter-proximal elements and enhancer elements encoded directly within the DNA? Or are they proteins that attach themselves to the strand of DNA in order to enhance transcription?

do prokaryotic DNA sequences contain enhancer elements

Yes: https://www.ncbi.nlm.nih.gov/pubmed/1776167

other than the UAS(upstream activating sequence)

The Gal4/UAS system is borrowed from yeast, a eukaryote https://en.wikipedia.org/wiki/GAL4/UAS_system

In addition, are enhancer elements like promoter-proximal elements and enhancer elements encoded directly within the DNA?

Yes. Enhancers are usually considered to be encoded directly within the DNA; e.g.: see the following recently published historic perspective on the discovery of enhancers by its discoverer, Walter Schaffner : https://www.ncbi.nlm.nih.gov/pubmed/25719310
Sidenote: Enhancers have originally been discovered in a virus, and thus neither in prokaryotes nor eukaryotes

Or are they proteins that attach themselves to the strand of DNA in order to enhance transcription?

Enhances (often / ~always) exert their function though proteins. https://en.wikipedia.org/wiki/Enhancer_(genetics) Note that this doesn't necessarily affect the definition of enhancers.


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A stem cell method for creating artificial wombs?
1) Grow the endometrium using stem cells (It has already been done (Cambridge, 2017))
2) Attach the embryo to it and allow the placenta to grow.
In 2003, there was a
researcher at Columbia  who did something like this, but there was no technology  to create endometrium tissue. She used some donated infertile tissues, but the rat embryos did attach to it and grow, although the growth itself was retarded. That's understandable since the endometrium has some special secretory functions.  So what could be the issues with the method I have suggested?
A lot of the new approaches seem to involve artificial placentas , which are probably not very easy to create. The don't seem to be the most obvious approach either. I think a large part of the issue is that you won't get funding if you say you want to create an artificial womb, because of the ethical issues involved. So you have to show some connection to neonatal stuff and hence the easiest approach is neglected. Am I right in this assessment?

Links to the papers you are referring to would be much appreciated.

@alec_djinn I have included popular science articles.

personally I think that artificial wombs grown by robots are the only way that advanced speciecs such as humans can be reborn on a star system 100 or 1000 light yeaers away. i like the technology.  ... Your question didn't specify In Vivo or Vitro artificial wombs. you need heart/blood/lymph etc.

In the paper you have (indirectly) linked, the authors describe cultures of organoids. Despite their fancy name and the catchy title of some news article about them, organoids are very far from being mini organs. They are a bunch of cells that grow in a 3D structure and they may resemble an organ in term of cell type and some cell-to-cell communication, but that's pretty much all. Mind that an organ is vascularized, organoids are not. The vascularization allows for organ-to-organ communication, like the delivery of brain-made hormones, for example. Such communication is extremely important during the embryo development, it's not only the endometrium missing here. I am not saying that is impossible to make artificial wombs, but organoids alone will not be sufficient.

Well, as far as I understand, the womb requires just one tissue effectively, the endometrium. The other tissues in the womb (smooth muscle, stem cells) are not necessary if you just want gestation. So it doesn't seem like an entire organ with all the signalling is required. The hormonal levels in the blood itself can be mimicked I guess, as long as those hormones can be received and understood by the endometrium.


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Why does breathing increase in higher temperatures?
In my experiment, my group increased the temperature of a fish's water. We noticed the fish took more breaths than the prior normal temperature. Is this because the fish is trying to breathe in the water's oxygen, which is evaporating more quickly than in normal temperature?

As you can see on the diagram below, oxygen solubulity in water drops by increasing temperature, so your fish has to breath more to get the same amount of oxygen.

ref

You can find more info about why gas solubility is temperature dependent here:
Chemistry (Averill & Eldredge) / Effects of Temperature and Pressure on Solubility.

In3mo informed about oxygen content varying with temperature, and another factor is the fish metabolic rate:

Standard Metabolic Rate (SMR) is the metabolic benchmark in fish. It
  is the metabolic rate of a resting fish at a specified temperature in
  the middle of its normal range. Therefore a trout's SMR15 would be the
  resting metabolic rate of a trout at 15'C. There is natural law called
  Q10 = 2: chemical reactions tend to double with every 10'C increase
  in temperature of the reactants. In poikilotherms, this is translated
  into biochemical events and in turn into metabolism. The metabolic
  rates of fish roughly double with every 10'C increase in temperature,
  except at the extreme ends of their temperature tolerance.

The fish become stressed and their physiological rate increases. for example, a fish at 5 degrees, his stomach can take 2 weeks to digest a meal, and at 25 degrees it takes 2 days.

Nice answer! :-)


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Did radial symmetry evolve twice?
In the history of animal evolution, both the Cnidarians and the Echinoderms have radial symmetry, according to this cladogram:

Source: http://www.cpalms.org/Public/PreviewResourceLesson/Preview/45851
Do both groups having this feature mean radial symmetry evolved twice?

Can you please add the source of where you got this image from?

Thank you for mentioning, @Remi.b. The source is in updated post.

Good question! I had never really though about it, so thank you!
Echinodermata have a pentaradial symmetry
Echinodermata actually don't have a radial symmetry like jellyfish do. They have a pentaradial symmetry as they systematically have 5 arms.
Parsimony
Even if Echinodermata were radially symmetric, then it would actually be unlikely that bilateral symmetry evolved, was then lost and evolved again. It is much more parsimonious that bilateral symmetry evolved once and was later lost in the echinodermata lineage.
Developmental and Genetics of pentaradial symmetry
As one would expect modifications of hox genes are involved into the evolution of this peculiar body plan. From Lowe and Wray 1997

Here we report the expression domains in echinoderms of three important developmental regulatory genes ( distal-less, engrailed and orthodenticle ), all of which encode transcription factors that contain a homeodomain. Our findings show that the reorganization of body architecture involved extensive changes in the deployment and roles of homeobox genes. These changes include modifications in the symmetry of expression domains and the evolution of several new developmental roles, as well as the loss of roles conserved between arthropods and chordates. Some of these modifications seem to have evolved very early in the history of echinoderms, whereas others probably evolved during the subsequent diversification of adult and larval morphology.

Here is the whole abstract of Mooi and David 2008

The strangeness of echinoderm pentaradiality results from superposition of radial symmetry onto ancestral deuterostome bilaterality. The Extraxial-Axial Theory shows that echinoderms also have an anterior/posterior (A/P) axis developed independently and ontogenetically before radiality. The A/P axis is first established via coelomic stacking in the extraxial region, with ensuing development of the pentamerous hydrocoel in the axial region. This is strongly correlated with a variety of gene expression patterns. The echinoid Hox cluster is disordered into two different sets of genes. During embryogenesis, members of the posterior class demonstrate temporal, spatial, and genetic colinearity within the extraxial region. We suggest that displacement of genes from the more anterior Hox classes toward the 5′ end of the chromosome leads to control of the later-developing, radially symmetric axial region. Genetic disorder is therefore another way of using colinearity to build the unique echinoderm symmetry.

As insinuated above, note that (in most echinodermata species at least) only adults have a radial symmetry. Larvea have a bilateral symmetry. Here are a bunch of picturesand schema.
Larvea

Adults

It is actually hypothesized that radial symmetry did evolve again, but there are homologies between the echinoderm symmetry and bilateral animals:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2176165/


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Why can fish survive out of water?
Obviously, humans can survive underwater for a short while. I've assumed this is because at some point it benefited us to stop breathing momentarily, and so we evolved a respiratory system that was able to take short breaks.
Similarly, fish can survive outside of water for a short while. However, I can't think of a single instance for most fish where they may have needed to evolve that ability. Even their ancestors originated from aquatic environments, so I don't think it's a residual ability they no longer need.
Why did fish evolve a respiratory system that could take breaks like ours can?

Do not have too a "panselectionist" view of evolution!
You can survive in a bath of mercury for a little while. You can survive naked in the outer space for a while (see here). Yet none of your ancestors where exposed to such conditions. We can be tolerant to certain conditions without having been selected to tolerate it.
Similarly, you managed to survive in your very specific environment. Yet none of your ancestors ever encountered this specific environment.
In other words, evolution is more than just natural selection. Not every phenotype in every environment you can think of is the result of a direct selective pressure acting on it. A classical and easy to read paper on the subject is Gould and Lewontin (1979).
Why fish not die suddenly outside of the water?
The main reason why fish die outside of water is that they cannot intake oxygen from air (see Breathing under water; not considering lungfish). So once fish are exposed to air only, they stop intaking oxygen, consume the oxygen that they have left in their circulatory system and tissues and slowly die of asphyxie but there is no reason for the death to be direct and sudden.

As I understand it, we could survive a mercury bath because we evolved a barrier (skin), and our homeostatic levels for mercury are far lower than instant death. The same goes for space and temperature (I don't die at 98.5 degrees). I'm pretty sure we evolved a resilience to things like that when we left the roughly-constant temperature and alkalinity of the ocean, since we needed to respond to huge environmental fluctuations. Fish do encounter a pretty standard environment though. Is it nutrition perhaps or other factors which led to them needing a response to changes in homeostasis?

Or is your first point that there's not always a reason?

I just mean fish still have oxygen in their tissues and there is no reason for them to die instantly. They were not selected (not that I am aware of) for surviving to this condition, they just happened to be pre-adapted due to various reasons, including the fact that they are big and therefore always keep a certain amount of oxygen in their tissues.

Do you consider lungfishes as fishes? When their pond dries they can survive hybernating in cocoon for up to four years.

A lot of fish (not just lung fish) can breath air quite well they start dehydrating quickly however and no organisms breathing mechanism works onces it dries out. .

Actually there is a huge group of fish that need to breath air, swamp living fish, stagnant water is very low in oxygen that is why many fish gulp air (air contains a lot more available oxygen than stagnant water) even house goldfish will do this is poorly oxygenated bowls (see below). in fact the early ancestors of terrestrial vertebrates show a lot of adaptations for swamp living, legs also work better in swamps than fins (at least above a certain size) that is why so many swamp fish develop leg like fins, such as the snakehead fish. These are not adaptations for land but for shallow stagnant water, air gulping for hypoxic water in particular.
Note most of these fish are not lungfish (or lobe finned fish) they are ray finned fish, they are using their swim bladder to extract oxygen. Aquatic surface respiration is actually a very widespread behavior in fish, and can be triggered in a very large number of ray finned fish. The behavior is quite well studied and has lead to better developed air breathing multiple times.
Fish that cannot do this (like sharks) will die very quickly on land as the suffocate, since gills don't work in the air. The risk for normal fish is dehydration of their breathing tissue, of while they are IN water this has a easy solution.

Correct that they cannot take in "sufficient" amounts, but a bit is all it takes them from asphyxia for an hour or so. The question was not why can't fish live their entire lives out of water, but why they don't die immediately.

The answer is simple. A fishes gills are exposed to air that is oxygen rich. Gills can take oxygen from the air. We do not inhale water, so humans under water must hold their breath. I am assuming the question is not referring to lungfish, who have modified their swim bladders (homologous to our lungs) to take up oxygen.

Gills cannot take up sufficient amounts of oxygen from the air - this is why fish cannot survive out of water for long.

Also, do we know that lungfish modified their swim bladders to take up oxygen? I can't recall offhand if the current consensus says that lungs are ancestral to swim bladders, or that we don't know which is derived from which, but I'm pretty sure it's one of the two.


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Why isn't photosynthesis catabolic reaction?
Here is the chemical equation of photosynthesis
$$CO_2 + H_{2}O \longrightarrow C_{6}H_{12}O_{6} + O_2 $$
We see that the water is in reactant side of the equation. By the way, It ought to be catabolic reaction. However, It seems anabolic reaction on my textbook.

What should we think for this reaction?
How do we get If energy turned out in product side of the equation?
Why isn't photosynthesis catabolic reaction?

How do you define catabolic reactions in the first place? From what I see, the only thing I could say is "water on the reactant side != hydrolysis"

@another'Homosapien' That's my bad.

Possible duplicate of Catabolic and Anabolic Reactions

Catabolic reactions are those that make larger/more complex molecules into those that are smaller/less complex, releasing energy.
Anabolic reactions are those that makes smaller/less complex molecules into those that are larger/more complex, costing energy.
Photosynthesis takes two of the least complex molecules from the perspective of biology, carbon dioxide and water, and forms glucose which is high-energy and complex - this is clearly an anabolic reaction.
The only way I can interpret your question is that you were misunderstanding the definitions of catabolic and anabolic.


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Catabolic and Anabolic Reactions
How do we differenciate between catabolic and anabolic reactions?
According to my researches;
Catabolic Reactions

Catabolic reactions (also called “catabolism”) break down larger, more complex molecules into smaller molecules and release energy in the process. The smaller end products of a catabolic reaction may be released as waste or they may be fed into other reactions. The energy that is released by catabolic reactions can be captured and used in many ways. Some of the energy is released as heat and increases the temperature of the cell. Sometimes the energy is stored in the chemical bonds of another molecule. And sometimes it can be used to do work, such as movement of cellular machinery to power the active transport of materials across cell membranes. Catabolic reactions are central to biological processes such as cellular respiration and the digestion of food molecules.

Anabolic Reactions

Anabolic reactions (also referred to as "anabolism") use energy to build more complex molecules from relatively simple raw materials. “Anabolic” and “catabolic” sound similar but are opposites. To remember the difference, it may help to think about how “anabolic steroids” promote the buildup of muscle mass. All of the complex molecules of life — carbohydrates, lipids, proteins, nucleic acids — are generated by anabolic reactions. Anabolic reactions are central to processes like photosynthesis, protein synthesis, and DNA replication.

Here are my questions

Is there water in every chemical reaction?
Do i just need to look at water ($H_{2}O$)?

Regards


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Do Tardigrades preserve water or replace water?
If you find something funny in my argument, then please pardon me, as I lack knowledge of biology. I was reading an article titled as "Water Bears Can Replace All The Fluid In their Bodies With A Glass Matrix"
Being extremely new to biology, I am a bit confused. Do Tardigrades preserve water through this protein or entirely change their biological structure to flush away all the water present in their body and rely on these proteins? Does this mean that their bodies no longer contain water?
Thanks.

neither they are desiccating, some water remains but too little to sustain normal processes, the matrix just preventing all the normally destructive side effects of desiccation that would destroy the cellular machinery, the cellular processes are still essentially stopped.

Cellular processes are essential for living. You haven't clarified how Tardigrades survive without cellular processing taking place in them.

not really, if the proteins and other molecular structures are not degraded they can be interrupted and restarted, your own article discussed how the tardigrade proteins keep other proteins from degrading during dehydration. and tardigrades have other molecules to protect cellular membranes and nucleotides. Its just for 99% of all life the molecules degrade if   dessicated and wont function if rehydrated. Some single celled organisms and spores can survive suspended processeshttp://onlinelibrary.wiley.com/doi/10.1017/S095283690200078X/abstract;jsessionid=9D9B775F84753DB9AC7B12BCDFDD120D.f02t01


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Quantification of concentration from chromatogram paper
In an experiment, I recently isolated and purified calf thymus DNA, hydrolyzed it with perchloric acid, and then applied the hydrolyzate to a Whatman paper in a polar solvent and let it run overnight.
I must now determine a way to quantify the concentration of each base, now separated based on polarity on the chromatogram. This cannot be the following method: Cutting the paper containing the base and putting it into an acid-containing flask, then measuring the absorbance, followed by Beer-Lambert's Law calculation for the concentration.
I would appreciate any ideas.


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Are earthworms edible?
Just that. It seemed weird for me not to find anything on Google. But I still think that they might be edible.

Strange, for me google returns thousands of good results for edible earthworms.

Asking whether something is edible is tricky business. You can get caloric value out of a lot of things without being poisoned, like grass, or random leaves and flowers. This doesn’t necessarily make them “edible”. It depends on the bar you set, and more logically how desperate you are for food

@mgkrebbs did my search in Spanish, found nothing, did again in English after your comment, found something. Interesting XD

they are notoriously unpalatable, but they are not especially noxious. it's also opinion based, because eating 1 is probably manageable and 5 of them will probably give someone unaccustomed indigestion/dysentery which would leave them less healthy that they were before. just a guess. they are full of earth and fermenting leaf matter.

@com.prehensible I guess that some preparation as with snails must be done in order to be able to actually eat them.

@com.prehensible I guess that some preparation as with snails must be done in order to be able to actually eat them.

Yes, they’re edible and even eaten in some places.
https://culinarylore.com/food-science:are-earthworms-edible/


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Can domestic breeding be considered evolution?
Domestic breeding of animals (and plants) by humans seems to match some of the definitions of evolution I have been able to find:

"a process that results in heritable changes in a population spread over many generations." (the TalkOrigins website)
"cumulative inherited change in a population of organisms through time leading to the appearance of new forms" (Merriam-Webster)
"Changes in the heritable attributes of populations of organisms over time" (this SE's 'evolution' tag info)

But other definitions seem to be less of a fit:

"the way in which living things change and develop over millions of years" (Cambridge)
(domestic breeding does not take millions of years)
"The process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth" (Oxford)
(Does breeding lead to different 'kinds' or organisms?)
"The gradual development of more complex organisms from simpler ones" (Chambers)
(Breeding may not result in more complex organisms)

I've seen people argue that domestic breeding can not be considered evolution, because domestic breeding:

does not involve natural selection
doesn't direct towards 'fitness'
does not lead to new species
decreases, rather than increases, the size of the gene pool (is this actually true?)
does not (or may not) lead to more complex organisms

I was not able to find whether or not there is a general consensus among experts from relevant fields on whether domestic breeding can be considered evolution. Is there?
EDIT: I've made the list of arguments I've heard against calling it evolution a bit clearer, and also added an extra one.
EDIT 2: Added why the second set of definitions seem to exclude domestic breeding as evolution

Humans are a part of nature, therefore selection by humans is perfectly natural.  2) "Fitness" is something of a misnomer: whatever survives to pass on its genes is fit in the evolutionary sense, by definition, even commercial turkeys that have to be artificially inseminated by humans - and how are they different from say an orchid that's pollinated by one species of moth?

@jamesqf The second part of your comment is spot on, but the first bit is spurious. There is a reason evolutionary biologists define human-induced evolution as 'artificial selection' to distinguish it from natural selection, since they are categorically different phenomena. Natural selection is non-teleological, whereas artificial selection is.

@et is: I suppose the distinction between natural and artificial selection might be a good question for philosophy, but I didn't mean it like that.  What I meant is that genes don't care what is applying the selection pressure.

Yes, selective breeding results in evolution.
Definitions of evolution
I don't understand why you say that for 3 of the definitions you found, selective breeding would not be considered as evolution. To me, all of these definitions match with the idea that selective breeding results in evolution. If you think otherwise, can you please explain why?
There are a number of related definition out there, some of them being more clear and straight forward than others. The simplest definition is probably the classical population genetics definition which says

Evolution is a change in allele frequency over time.

See wikipedia > allele. You might want to have a look at How to define evolution? too.
Under this definition, any event of death or birth in a population is evolution as it affects allele frequency. In the human species for example, that means an evolution happens about 254 times per second (computed from these numbers from ecology.com)!
Specific statements
All these statements are stupid and none-sense! The easiest is probably for you to just have a look at an intro course to evolutionary biology (such as Understanding Evolution by UC Berkeley for example) and you will be able to refute those statements yourself.
Let's go through these statements...

There is no natural selection

First, evolution is much more than just natural selection. There is genetic drift, mutations, gene flow and plenty of interacting processes.
Second, it is silly to separate natural selection from artificial selection (aka. selective breeding). The only difference between these two is that in artificial selection someone is willingly affecting the environment of the individual to affect selection pressures. This is really it.
Note, btw, you never totally get rid of natural selection. Under selective breeding you may affect the environment but some things will remain the same. For example, a mutation causing the cell membranes to be extremely unstable will not be selected for whether under an artificial setting or a natural one.

It doesn't direct towards 'fitness'

The claim is unclear. What is "it" and assuming it refers to a population, then what does it mean a population is directing toward "fitness"?
Fitness is a function of survival and fecundity. Each genotype is associated to a particular fitness in a specific environment. Ignoring stochastic processes such as genetic drift, the mean fitness of a population is increasing from one generation to the other by the amount of the additive genetic variance. This is true for (artificial or natural) selection.
The only thing to consider is that the environments under which this happen is different. Under selective breeding, the population evolves to a higher fitness for the specific environmental conditions set by the farmer (or who ever who selectively breed). It is possible (and quite common in fact) that genotypes associated with a high fitness under one environment has a low fitness under another environment.

It does not lead to new species

In short, 1) it does lead to new species 2) the concept of species is often meaningless as poorly defined 3) evolution > speciation. In more details, below..

It does lead to new species. Different lineages of cabbage are considered different species. Cows and ox are different species. Pigs and boars are often considered different species. While wolves and dogs are considered same species, some lineages within this species (such as a Chihuahua and a Great Dane) are, I think, reproductively isolated. You might also want to have a look at the post Have we ever observed two drosophila lineages that evolved reproductive isolation in labs?
The question of whether selective breeding lead to speciation or not does not matter much on the question of whether it leads to evolution. Speciation is one outcome of evolution but is definitely not the same as evolution. Evolution does not need to lead to speciation. For example, evolution of the lactase gene in humans (see this post) did not lead to any speciation. It is still an evolutionary process.
The concept of species is mainly arbitrary. If you want to understand the concept of species, have a look at the post How could humans have interbred with Neanderthals if we're a different species?.

It decreases, rather than increases, the size of the gene pool (is this actually true?)

The term "size of the gene pool" is very undefined. I suppose, it just means genetic diversity, aka. expected heterozygosity.
All act of selection, whether artificial or natural, decreases genetic diversity. This is correct. Mutations is the fundamental process increasing this genetic diversity and selection selects the variants associate with the highest fitness.
Because, the selection pressures imposed under selective breeding are often extreme, the decrease of genetic diversity via selection is often faster in selective breeding than in nature.
Note however, that if we split a lineage in two and select the two populations under different optimas, then the total genetic diversity will increased (the within-population genetic diversity will still decrease). As such, via selective breeding we created a gigantic diversity of dogs and a fantastic diversity of cabbage but each cabbage lineage (e.g. brussel sprouts) and each dog lineage (cocker spaniel) have very low genetic diversity.
What the claim is suggesting is that because selection is often stronger (and therefore change in allele frequencies is faster) under selective breeding than in natural environments, we should not consider artificial selection as resulting in evolution? How silly is that!

The word 'it' in the second argument refers to domestic breeding. I will update my question to be more clear.

Whether or not it leads to separate species has nothing to do with evolution. I know you know this but you should probably emphasize it more; there's a widespread vague belief that speciation and evolution are the same thing, whereas in reality speciation is just one small and specialized aspect of evolution.

@iayork and Gerardo Thanks for your comments. I've edited my post accordingly.

@GerardoFurtado these is a lot of debate about whether wolves and dogs are the same species, and goes back to the problems with defining species. Technically all of Canis may be able to interbreed.

@ Remi  I meant Canis as a genus, All the members of Canis are cross fertile, minus jackals, and may turn out to be polyphyletic . Also not everything from the same species can interbreed, that is one of the problems with defining species that way, ring species are a thing. I just wanted you to understand that referring to them as the same species or not is more opinion than anything else. https://www.ncbi.nlm.nih.gov/pubmed/16341006

sorry thats the link to the paoer about Canis being polyphyletic, this is the one about dogs not being domesticated gray wolves. http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004016

@Gerardo Furtado: If dogs and wolves are the same species, why not dogs and coyotes, or wolves and coyotes?  They interbreed quite successfully where their ranges overlap, and indeed, the eastern North American "coyote" seems to be a hybrid of coyote, wolf, and dog.

@Gerardo Furtado: But genetic studies show North American wolves and coyotes diverging around 6,000–117,000 years ago, with all modern populations being somewhat intermixed: https://en.wikipedia.org/wiki/Evolution_of_the_wolf#Divergence_with_the_coyote  That overlaps the ~16kya wolf-dog divergence.  Which just points up the fact that species are largely a matter of opinion.

The answer is "yes". Evolution is defined as a change in heritable characteristics of a population over generations, and to me, there is no reason not to define domestic animals as populations.
The statements you list can all be refuted:

Part of the selection human-driven, part "natural". You cannot control all genes.
The concept of fitness talks about offspring and contribution to the gene pool. Humans enhancing the fitness of desired individuals should also count as fitness. It is just the "human selection" that partly drives the evolution (i.e. human selection works as an environment).
Dog, chicken, cow are all species created by domestic breeding. They are all considered species by some biologists.
Strong selection pressure sometimes decreases the size of the gene pool, but again if you take dogs as an example: they are likely genetically more diverse than wolves. There are so many factors involved in domestic breeding that you cannot say that it decreases the size of the gene pool. It can go both ways.

But again, evolution is a human-created concept to understand our surroundings. If somebody wants to think that humans should not be a driving factor in evolution, that is fine for me.
Next logical question would be whether gene-manipulation is evolution. I will leave that for someone :)

There is not consensus among scientists, that human sciences of should be equaled to natural sciences.
Scientists don't agree if pets and farm stock are new species, and we all agree, domestic animals are in a different, recent, group to all other and selection processes. It's Yes and No andwer. It shares and conflicts with evolution and seems to deserves a human sciences category of it's own.
"Evolution of the chihuaha specif traits from the wolf", wouldn't qualify for a science journal.
Survival of the funny looking animal, for a dominant species, that has a large brain, that devises breeding methods. Contrary to survival of the fittest. It's a form of evolution that was seen only 50k years from 4 billion, that's 0.00125% of evolutionary history. You can compare it to evolution of captive algea used by coral, and ant-aphid relationships.
Darwin studied the topic for decades, and in the actual title of his book he wrote "Natural" selection, so he clearly made a mental difference between human and wild, natural processes.
The difference of the concepts is similar to human geography and physical geography. They are described by different books.
To make a language's semantics clear, it's best not to group different groups of processes with the same word, when new semantics be invented where a discussion is required to differentiate the two.
It's the only form of evolution that uses artificial foods, artificial walls and fences, artificial mating, to make funny looking animals for amusement, and social animals companionship and work.
The result is generally low fitness, stamina, immune system, fainting goats, deaf dogs, dogs that can't breathe well due to snout length, dogs which are tremendously unfit. and animals that are fit for human amusement.


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Saving lives by "conjoining" people
There are many deaths which occur as a result of a cascade of organ failures triggered by a single event, for example traumatic injuries, severe burns, infections and so on.
Since blood transfusion is a well-tested and established procedure which is safe and helps millions of people every year, would it be possible to treat people by "artificially conjoining" them by merging their circulatory systems with a small group of healthy volunteers? This would of course require them to have compatible blood groups and probably also immune systems to some degree, but it should be possible, at the very least for identical siblings.
Examples of use:

A patient has severe burns on >95% of their body, with severe inhalation burns as well. Their lungs are barely working and doctors give them very low chances of survival. Luckily, there are ten volunteers who are wiling to participate in an effort to save this person. Their circulatory systems are merged, so the injured person does not have to rely on their lungs working properly. They do not have to eat, drink or breathe now. The blood from volunteers helps keep the blood of the patient oxygenated and in optimal composition, their immune systems help the patient's body deal with the possible infections and since they are eating well, the blood supplies the injured body with all the nutrients needed for recovery.
A patient is senescent and suffers from all sorts of aging-associated diseases. They are a very important and rich person, so they pay some people to help them fight old age. This has already been tested to some extent.
A patient is suffering from a nasty case of MRSA. The prognosis is bad, but luckily there are many people from the same group of infectees who have already recovered fully. Their immune systems are still on the lookout for any stray bacteria they could kill. So they are connected, the various blood cells and antibodies find the infection in the patient's body and quickly deal with it.

Could this work? Are there any recorded cases where this has been tried? I am looking for an answer which will address the potential biological challenges this could pose. Let's leave the potential ethical problems aside, they are off topic here.
P.S.: I know what you are thinking. Yes, I know about the movie. My question is serious though.
Edit: I talked to a doctor at the transfusion center and she told me that this approach is very similar to how transfusions were performed in the past. It was problematic because they had no way of knowing just how much blood was transferred between the patient and the donor. She thinks that what I suggest would probably not cause any immediate issues if done properly. However, I think there could be some immunological problems down the line if the people's circulatory systems were joined for a prolonged period of time. I would like to see some information about that.

I voted to close because we don't deal with these sorts of speculative questions here, you could possibly try Worldbuilding.SE. There are massive ethical issues with what you propose that will prevent any real world testing of these ideas, but you may want to learn a bit about organ transplant and how difficult of a problem rejection is for just a single organ from one individual to another.

@BryanKrause I'm sorry you feel this way. I have edited the question to clarify that this is not speculative, I want to find out whether my suggestion has some insurmountable problems. The ethical issues are not universal to all societies (as any libertarians will happily confirm) or countries, and even then it all boils down to the question of whether a small health impact on several volunteers adds up to more than the cost of a single human life. If this is the case, shouldn't blood transfusions be illegal? So let's leave the ethical questions aside and focus on biology.

Pretty sure that one person won't be able to supply enough nutrients for another person from his/her blood though, as they will be used up by the healthier one. And if they are used by the diseased person, the healthy volunteer can suffer from the same if not more disorders leading to more problems.

The problems and possible applications may be close to those of corresponding animal experiments. For an overview see: https://en.m.wikipedia.org/wiki/Parabiosis

As mentioned in other answers, the problems with accomplishing this are manifold but primarily relate to the immune systems of the donors and recipient. While it may seem like anastomatizing the circulatory systems of ten donors to one recipient splits the load, in effect you're creating 2048 different donor-recipient relationships. This is a case where more is definitely not better.
Direct transfusion was first documented December 22nd, 1818. Initial problems with transfusion were primarily related to the treatment of all blood as the same, until in 1901 Karl Landsteiner described the first few blood groups. [1]
These groups classify blood by the antibodies present and, when the matching antigen is encountered by this blood, the antibodies attach to them causing hemolysis and signalling to the potential recipient that there is foreign material in their body. The most significant group is known in the US by its antigens A, B, and Rh (the +/- sign at the end). There are, however, at least 340 different documented antigens, 38 of which are unassigned to blood group systems. [2]
While basically matching blood types may work for a little while, the risk of  sensitization and subsequent hemolytic reaction grows the more foreign antigen containing blood a body is exposed to. Sensitization occurs when the body begins to recognize an antigen in the blood and begin creating antigens for it. This is perhaps best known in pregnancy, technically changing the mother's blood group to include Rh+. [3]
Additionally, graft-versus-host disease occurs when leukocytes encounter tissue that exposes non-self antigens. Thus, blood products are typically irradiated to neutralize the immune cells responsible. [4] The complexity of exposing just one immune system to another for an extended period quickly becomes exponential, as can be seen with multiple organ transplantation. Each organ is reactive in its own way, and thus for each type we know how to transplant there are different criteria to match. [5]
The answer to these problems, it would seem, would be to

Match donor and recipient blood groups.
Suppress the recipient and donor immune systems.
Possibly, irradiate the blood as it passes between them.

Matching immune components is already a difficult problem. Partly due to the number of variables, and partly because the number of willing donors is very limited.
In the case of severe burn trauma, victims of which are already immunosuppressed, this would be a terrible idea as the most prominent risk to survival is the ease with which pathogens can enter through wounds. [6]
The very reason to transfuse for, say, MRSA antibodies is hindered with the array of transfusions occuring. In order to prevent donors from hurting recipients and vice versa, their immune systems must be suppressed.
References

Direct blood transfusions
International society of blood transfusion working party on red cell immunogenetics and terminology: report of the Seoul and London meetings
Significance of Rh-sensitization during Pregnancy: Its Relation to a Preventive Programme
A systematic review of transfusion-associated graft-versus-host disease.
A Review of Organ Transplantation: Heart, Lung, Kidney, Liver, and Simultaneous Liver-Kidney.
Burn Wound Infections

Thanks for the effort, despite the question being rather hated by people.


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Do chilli peppers change in composition after they change color?
I grow some chilli peppers and was wondering when the time is right to harvest them. Of course gardening-focused sources say that they are ripe when they change color. This usually happens very quickly (1-2 days) after a long period when they remain green (1-2 months), which would suggest that the gardening advice might be right.
However, I would like to know the full story, so I tried to find some relevant research. Here's what I found so far (mostly paywalled, sadly, so I cannot read the details)
Development of pepper (Capsicum annuum) seed quality
Quite unrelated, but suggests that the end of the ripening process is not simply the end of it all
Variations in germination and longevity of pepper (Capsicum annuum L.) seeds harvested at different stages of maturation
Similar to the above, seeds still continue to change while the pepper changes color
Changes in Carotenoid Esterification during the Fruit Ripening of Capsicum annuum Cv. Bola
New carotenoids are produced during ripening
Formation and transformation of pigments during the fruit ripening of Capsicum annuum Cv. Bola and Agridulce
More information on the above
Carotenoid Biosynthesis Changes in Five Red Pepper (Capsicum annuum L.) Cultivars during Ripening. Cultivar Selection for Breeding
Carotenoid Composition in the Fruits of Capsicum annuum Cv. Szentesi Kosszarvú during Ripening
Researchers were apparently really interested in carotenoids in the 90s...
Variation in phenolic compounds, ascorbic acid and antioxidant activity of five coloured bell pepper (Capsicum annum) fruits at two different harvest times
This one suggests that there are still some changes happening after ripening: With advanced maturation, total antioxidant activity increased, however some antioxidant components such as ascorbic acid, total phenols decreased.
The influence of fruit ripening on the phytochemical content and biological activity of Capsicum chinense Jacq. cv Habanero
This one, while apparently full of interesting data, only deals with two stages of ripening(immature and mature).
Ripening of pepper (Capsicum annuum) fruit is characterized by an enhancement of protein tyrosine nitration
Very promising, but once again, research ends at the color change.
Evolution of total and individual capsaicinoids in peppers during ripening of the Cayenne pepper plant (Capsicum annuum L.)
The only article which actually deals with peppers which were left to ripen a bit more. Capsaicin content decreases as the pepper ripens, followed by an increase when it's over-ripe. Weird, but at least I was able to legally obtain this article. Unfortunately it deals with capsaicinoids only.
Is there more information about what happens to the chillies after they are ripe? I'm not really interested in heat, but rather in other chemicals which affect flavor and nutritional properties of chilli peppers.
Edit: Based on what I observe at home, the peppers do indeed seem to be changing for at least a week or so after the change in color. I left some red chillies on the tree and their color is now noticeably darker than those which have just ripened a few days ago.

I welcome answers here, but this might be a case where it's best to do your own research a bit: you have an experiment already in place, so harvest at different points and see what you think.

@BryanKrause Of course I'm trying in the absence of reliable outside information, but my sample size is very small and this could take a long time, so I'd rather trust a scientific source than my own crappy research. The chillies I keep on the plant seem to not change very much anymore. I also read that keeping them on slows down the development of other fruit, which would support the hypothesis that there are still some resources being used by the ripe fruit.

When ripe the seeds become viable too.


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What does substrate mean?
I have been reading some literature on measurements related to biofilms.
In some articles the word "substrate" seems to stand for the material on which a biofilm is growing. In other articles, it seems to stand for the nutrients that are freely floating in (say water) where the biofilm is growing, and which then diffuse into the biofilm and which it uses to grow.
Have I misunderstood something or are both of these meanings in active use? Is there a disciplinary or some other difference that determines who uses which term?

The review article [1] uses substrate to mean freely floating nutrietnts. Also, searching for "substrate loading" or "substrate loading rate" or such (on Google scholar) gives examples of substrate as something that is fed to the biofilm.
For example Wikipedia uses the other meaning of substrate: https://en.wikipedia.org/wiki/Substrate . Scientific literature with this meaning can be related to how easily biofilms detach from a given material in the presence of shear forces.

[1] Harald Horn and Susanne Lackner. Modeling of biofilm systems: A review. In Kai Muffler and Roland Ulber, editors, Productive Biofilms, pages 53–76. Springer International Publishing, Cham, 2014.

Latin: sub- underneath and stratum = layer... The under-layer literally, the base layer.

A substrate is an underlying substance or layer, or less strictly, the medium within or upon which an organism grows. For instance, you can have a filamentous fungus grow on a solid medium (e.g. on an agar plate) or in liquid medium (e.g. in a shaken flask containing a solution) and its substrate would be the contents of the agar or solution. It's nothing more fancy than that.
For instance, you could design 4 growth conditions for a strain of fungus.
Case in point, a hypothetical table could look like this:
                        *Substrate*

                Wheat straw     Sugar beet pulp
                             |
          Liquid         1   |   2
                             |
*Medium*             -----------------
                             |
           Agar          3   |   4

Simple!

What is the interpretation of all the "substrate loading rate"s, then? Are they simply misusing the terminology?

@TommiBrander, no they are not misusing "substrate". Notice there are more words in the phrase "substrate loading rate".  The phrase is referring to the the rate at which nutrients are loaded into the substrate.

I edited in an explicit reference to a review article where "substrate" explicitly means diffusing nutrients, rather than the meaning mentioned here.

The nutrient can be the substrate. Leaves are a substrate for leaf-eating caterpillars. The skin of an orange is a substrate for mold. In these examples you'd use the word substrate rather than medium. As with all language, it doesn't help to be too pedantic about dictionary definition. The word 'nutrient' is also fuzzy but I would advise against opening a thread about the meaning of nutrient. Happy sciencing!


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Why there is no fluorescent light from my DAPI-stained Hibiscus Rosa Sinensis Pollen?
I currently work with fluorescence microscope to observe generative and vegetative cells within hibiscus rosa sinensis pollen. I used DAPI to stain pollens but there is no light that indicate the existence of both generative and vegetative cells. I simply stained the pollens with 50 ppb DAPI without other procedure. I have referred this steps from Sexual Plant Reproduction textbook from Cresti and Tiezzi, here is the link : le.ac.uk/bl/phh4/openpubs/SPR_HH_pollen_stigma_crestiLR.pdf. From the book, it simply states "For DAPI staining, fresh or fixed pollen is stained on a slide in a drop of 0.005% DAPI (diamidinophenylindole), and the nuclei observed under a fluorescent microscope after 5-30 min (UV excitation, blue DAPI fluorescence).
The result is make me confused because there was no fluorescent light but only reflected light by pollen itself.
I will be very glad if anyone can suggests me what should i do or highlights an error in my steps.

What do you see after the staining? No light at all? How DAPI staining should allow you to distinguish between generative and vegetative cells?

I saw light, certainly. But the light is light that was reflected by an object, not from the fluorescence phenomenon. I am not sure that DAPI can distinguish or make a different look for generative and vegetative cells because DAPI is only a compound that bind the A-T rich region and make the objects that were bounded by it able to emit a light due to fluorescence, not react specifically with generative or vegetative cells and make some different features (or another) between them. cmiiw.

So apparently the problem is that the staining itself didn't work at all. Probably the DAPI didn't penetrate in the cells. Did you solubilized the cell wall somehow? Can you detail all the procedure you followed prior to DAPI staining?

Yes sure, I did it very simple (according to my reference (the textbook that i mentioned before) and suggestion from my lecturer). I just poured the pollens from the Hibiscus r. anther above the aquabidest at specimen glass,  then dropped 50 ppb of DAPI above it and cover it with coverglass. And i think i miss the step of solubilizing the cell wall. Would you mind telling me how the protocol that should I do to solubilizing the cell wall of Hibiscus pollen? Or there is any reference that i can refer to do that?

Actually, this is only a step that my lecturer suggests to check whether or not my DAPI still viable to emit a fluorescence light. The core of my research is to staining a chromosomes with DAPI and observe its image under the microscope using a photonics jet phenomenon.

Could you add the protocol you followed in your question? It gives useful insight on what you did. Also, the textbook reference as it is now is not that useful; can you find a link redirecting to the part you're citing?

I got the ebook for book that i mentioned from here : https://www.le.ac.uk/bl/phh4/openpubs/SPR_HH_pollen_stigma_crestiLR.pdf, it simply says, "For DAPI staining, fresh or fixed pollen is stained on a slide in a
drop of 0.005% DAPI (diamidinophenylindole), and the nuclei observed
under a fluorescent microscope after 5-30 min (UV excitation, blue
DAPI fluorescence)."

Ok, edit your question with all the new information you provided in the comments.

@LinuxBlanket ok i have edited it. Would you mind to telling me the procedure to solubilize pollen wall so the DAPI can penetrate and stain both generative and vegetative cells? Thanks


text:
Is it possible to artificially induce a 40°C fever in a controlled and safe manner?
In search for any possible new treatments for COVID-19, I am of the understanding that the SARS-nCoV-2 virus may suffer deterioration at high temperatures and high humidity, to perhaps weaken it sufficiently for your immune system to be able to handle it.
Is there any research done on artificially inducing a (let's say) 40°C fever, in a controlled manner, such that brain function will not be endangered?
(Are there any fundamental biological functions that would prevent this possibility?)

Possibly Related Questions:

Should we induce fever to assist healing?
How does fever physically work?
Paper shows 2 hours of high humidity and hot temperatures kills corona virus, does this stop the spread of the virus?
What are the environmental conditions for 2019-nCoV to survive?

References:
[1] https://www.cancer.gov/about-cancer/treatment/types/surgery/hyperthermia-fact-sheet
[2] https://en.wikipedia.org/wiki/Hyperthermia_therapy
[3] https://en.wikipedia.org/wiki/Thermoregulation
[4] Janeways Immunobiology (book)

SE Biology is concerned with the mechanisms of biological processes, and questions are generally answered by people with biological rather than medical or epidemiological expertise. It is possible, therefore, that some questions about coronaviruses relating to the recent 2019-nCoV outbreak may not receive a satisfactory answer. You may therefore wish to consult this list of reputable external sources of such information.

In my opinion this question is off-topic. Ostensibly it is asking for information on physiological or medical research, and in this respect it is not asking for an answer to a biological question. However the reality is that it is a question asking for discussion on a proposal for a treatment for an infectious disease. As such it falls in the category of questions of the type "I have this great idea, do you think it's right?", which can only have subjective answers. As the "great idea" it propounds is a medical treatment, it is particularly inappropriate on this list and at this time.

@David Ok, so what do you propose I should do? Close the question?

Yes I think that would be best.

In search for any possible new treatments for COVID-19, I am of the understanding that the SARS-nCoV-2 virus may suffer deterioration at high temperatures and high humidity

If you are referring to the linked question, that is for virus in air on a dry surface.  It is a test of how long the virus can survive outside of a host before it is desiccated and destroyed by the environment.  It is not relevant to viral particles inside of an organism.

Are there any fundamental biological functions that would prevent this possibility?

There is little evidence that elevated body temperature has much effect on duration of infection with most common viral diseases. This is why antipyretic drugs are commonly recommended for people with viral infections.


text:
What antibody targets are being tested for in the publicly offered UK antibody test?
In late August 2021 the NHS (UK) offered people who test positive for COVID what is referred to in this BBC report as a “new antibody test”.
However, I have been unable to find out what exactly is new about this test. I was hoping to find what antibody targets are being tested for, including the virus strains used for them.
From what I understand there are many paths to immunity depending on the antibodies targeting one or more of the viral proteins.

image source: Murphy K, Weaver C. Janeway’s Immunobiology. 9th ed. Boca Raton, FL: CRC Press; 2016. Table 10.27
Q: What exact antibody targets are being tested for?
(What is "new" about this?)

Possibly related questions:

How long after taking a vaccine shot (Oxford–AstraZeneca) could an individual test negative for antibody (IgM)?
Why do antibody tests target different antibodies?

I'm afraid this requires a bit of digging to find what you are actually referring to. The digging itself is not what people do here, so hopefully you'll find a lead to point us to. Otherwise you have to cross your fingers someone knows what exactly you are referring to. Good luck!

It could simply be semantics - the "new" part being that it is now offered, when it wasn't previously.

Yeah, the only thing I find as being "new" here, is that it is being offered for free. But still no clarity what exactly is being offered.

Antibody tests have only been used on people involved in studies or surveys. This is the first time the tests are widely offered to the UK public for the purpose of collecting information about “vaccine effectiveness and the immune response of the broader population”.
This action is what they are referring to as “new” here, not the antibody test itself.

That is indeed unfortunate as T-cells cover a very important part of the overall immunity that is otherwise missed by the currently available tests.


text:
What are the environmental conditions for SARS-CoV-2 to survive?
What do we know about the environmental limits for nCoV to survive outside the body? For example, in:

In open air
On surfaces
In water

What are the limits for temperature, humidity and air pressure, where the virus, can or cannot survive?

Because "any" Coronavirus is so dangerous, much research have been done on viruses with similar properties. They are called "surrogates". Because nCoV is new, we don't have any studies, so we need to estimate it's behavior from previously studied similar viruses.
Here:
RH   = Relative Humidity.
Tr   = Room Temperature
TGEV = Transmissible Gastroenteritis (surrogate)
MHV  = Mouse Hepatitis (surrogate)

Viral survival for the TGEV/MHV surrogate:

on stainless steel:      4°C @ 20% RH:  28 days
in water/sewage (TGEV):  25°C: 22 days
in water/sewage (MHV):   25°C: 17 days
contaminated water is a potential vehicle for exposure if aerosols are generated

For airborne Human Coronavirus 229E (HCV/229E):

Optimal survival:  6°C @ 50% RH:
Poor* survival:     20°C @ "High" relative humidity (RH)
(* "poor" in terms of 20°C but varying RH.)

For SARS CoV-P9:

Serum: 96 h = 4 days
Sputum & Feces: 96 h = 4 days
Urine: 72 h = 3 days

For SARS-CoV (GVU6109):

in diarrheal stool (at low pH): 4 days
in respiratory/air droplets:  >7  days @ 20°C (Tr)
in respiratory/air droplets:  >20 days @ 4°C

"The main route of transmission of SARS CoV infection is presumed to be respiratory droplets. However the virus is also detectable in other body fluids and excreta. The stability of the virus at different temperatures and relative humidity on smooth surfaces were studied. The dried virus on smooth surfaces retained its viability for over 5 days at temperatures of 22–25°C and relative humidity of 40–50%, that is, typical air-conditioned environments. However, virus viability was rapidly lost (>3 log10) at higher temperatures and higher relative humidity (e.g., 38°C, and relative humidity of >95%)."
"We and others have reported that infectivity of SARS CoV (SARS coronavirus) was lost after heating at 56°C for 15 minutes but that it was stable for at least 2 days following drying on plastic."

UPDATE: 2020-03-13
From [7]:

"We found that viable virus could be detected in aerosols up to 3 hours
  post aerosolization, up to 4 hours on copper, up to 24 hours on
  cardboard and up to 2-3 days on plastic and stainless steel. HCoV-19 and
  SARS-CoV-1 exhibited similar half-lives in aerosols, with median
  estimates around 2.7 hours. Both viruses show relatively long viability
  on stainless steel and polypropylene compared to copper or cardboard:
  the median half-life estimate for HCoV-19 is around 13 hours on steel
  and around 16 hours on polypropylene. Our results indicate that aerosol
  and fomite transmission of HCoV-19 is plausible, as the virus can remain
  viable in aerosols for multiple hours and on surfaces up to days."

For SARS-CoV-2:
Experiments were performed @ 40% RH and 21-23°C.

Copper (Cu):      4 hours
Stainless (Fe):   48 hours (2 days)
Cardboard:        24 hours
Plastic:          72 hours (3 days)
SARS-CoV-2 is most stable on plastic and stainless steel.

References:

[1] 20xx https://aem.asm.org/content/76/9/2712.short
[2] 1985 https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-66-12-2743
[3] 2005 https://academic.oup.com/cid/article/41/7/e67/310340
[4] 2009 https://www.sciencedirect.com/science/article/abs/pii/S0043135409000785
[5] 2010 https://www.hindawi.com/journals/av/2011/734690/
[6] 2003 https://www.ncbi.nlm.nih.gov/pubmed/14631830
[7] 2020 Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1


text:
Can I use commercial DNA loading dye for my RNA samples without degrading them?
I was wondering if I have to use special RNA loading dye or can I run RNA samples with regular loading dye that is used for DNA?

What are you running?

I did electrophoresis of my RNA probes for in situ hybridization several times, and every time they were degraded. I am trying to figure out what was wrong, so I realized I used DNA loading dye every time. I just wanted to check if that could be the problem.

Handling of RNA requires extra care, especially using RNase-free pipette tips, tubes and reagents, to prevent RNase contamination. Common labware and reagents usually indicate whether they are RNase-free certified. If there is no such mention written on the box or label, then you should assume it is not RNase-free and you should not use it to handle your RNA.
Check whether your loading dye is certified RNase-free (this should be written on the tube, or easy to find out on the manufacturer's website using the product reference number). If it is, and you exclusively used RNase-free certified tools and reagents all the way, then maybe the loading dye tube or something else got contaminated by one of your co-workers.


text:
What insect could this be?

There is a bush in my garden that I love to observe, as it often has large rain spiders building nests in its leaves, but I occasionally notice large groups of an orange-headed insect on the leaves, and I can only assume that they are the primary prey item of the spiders, but I can't seem to identify them, and I only managed to get a picture of one this morning, as they usually run and hide if I get close enough for a picture.
It has a very similar morphology to a cockroach, in my opinion, but after looking over common species in the area, I still have no matches, it is around 2 - 2.5 cm. I have never seen them anywhere but this bush. I live in Johannesburg, South Africa.
I would really appreciate any help in identifying the species.

please add your location and approximate size of the specimen. Thanks

@theforestecologist Thanks for the feedback, I have added the requested information.

They usually come out during a large rain to prevent drowning

It looks like two insects there, with the one in the background (top) impossible to see. But the one in the front, with its head down looks very much like the American cockroach, Periplaneta americana (Blattodea, Blattidae)

Thanks for the answer, I have considered that, but it looks too dark in my opinion? Although I suppose it could be their diet or some other factor...

The exoskeletal plates on the legs don't really match that cockroach. But yes, looks like something related to that...

The darkness of the American cockroach is affected by its habitat and when it last molted. For example American cockroach found in the forest grasses is usually solid black, where as the pictures you find online are of indoor cockroaches which are more light brown. You can have variations of darkness when they interbreed. The cockroach in this image is hands down an American variety.


text:
Reading an amino acid physicochemical properties diagram
I want to know if I am reading the venn diagram correctly and why there are discrepancies in the diagrams.
I'm trying to determine which amino acids are considered hydrophobic and I am using this diagram suggested by my teacher from Amino acid properties and consequences of subsitutions.

From the diagram I've determined that A, G, C, T, V, I, L, F, W, Y, H, K, M are hydrophobic.
My problem is when I visit other sources I do not get the same results. Using Amino Acid Table I determines that A, G, I, L, M, F, P, W, Y, V were hydrophobic:

Furthermore, there is even another different venn diagram from Decoding the Building Blocks of Life from the Perspective of Quantum Information

Polarity and hydrophobicity are not discrete phenomena and, therefore, categorizing amino acids as such has some measure of arbitrariness, especially at edge cases. It all depends on one’s definition.
Other properties have similar problems. Charge depends on pH. And what is the cut-off between “large” and “medium” sides chains?
What is, in my opinion, more important than memorizing charts/diagrams/etc (unless you have an exam) is understanding why different amino acids have these properties. For example, why can threonine or tyrosine be classified as both hydrophobic and polar? Why can cysteine or serine, which are classified as uncharged, act as strong nucleophiles in enzymatic reactions?

What search terms should I use to research which amino acids can be classified into multiple properties?

@JohnnyJohnston — You don't seem to understand the remark in the answer about "understanding why different amino acids have these properties". You need to look at the structures, look at the classifications, and then use your knowledge of chemistry to see how they apply. If your chemistry is inadequate for this, you need to remedy that deficiency before you can proceed further. Let us know and we can recommend some reading.

@David Thanks for the reply. My knowledge in chemistry is very limited and close to zero.

@JohnnyJohnston — You might try The Biochemical Society's "Essential Chemistry for Biochemists" or The Royal Society of Chemistry's "Chemistry for Biologists".


text:
How do fishes "breathe" while eating?
First of all, a fish opens its mouth and water enters which passes through its gills. This helps in oxygenating its blood. So, if any food particle is in its mouth, how can it "breathe" i.e. how does exchange of gases occur? Shouldn't the pathway where water flows from mouth to gills be clogged like a drain full of sludge?

Food particles don't just sit around in the mouth; they go from the mouth to the stomach. I would expect most animals can survive a lack of oxygen intake for the mere seconds it takes for the food to move on. In any case, according to the Florida Museum of Natural History, fish generally do not chew their food, so the pathways should not be "clogged like a drain full of sludge".

They can pump water over their gills with their opercular flaps (i.e., the structure that covers and protects the gills). This is assisted by the branchiostegal rays. Food would generally not interfere with this process. Additionally, gill rakers assist in keeping food in the mouth.
Some great references for questions like this:
Barton, M., & Bond, C. E. (2007). Bond's biology of fishes. Thomson.
Moyle, P. B., & Cech, J. J. (2004). Fishes: an introduction to ichthyology (Vol. 726). Upper Saddle River, NJ: Pearson Prentice Hall.

Please update your answer by citing and/or summarizing supporting evidence from reputable sources. Thanks.

regardless of your own legitimacy, the internet doesn't know that about you (nor should users passing through necessarily believe that about you -- there are plenty of "fake" experts out there). Having a more formal source of info allows users to check in on the legitimacy of something more completely & objectively. It also enables them to use your source as a doorway to learning more about the topic. Take a look through Yahoo answers or Quora and see how many "legitimate" answers from "experts" are wrong -- without regular citing practices, users will never know one way or the other

I have added 2 sources, besides my own personal expertise as a fisheries research biologist

@theforestecologist You made a good point, thus, I have added to my response

Thanks very much. We're here to educate, so doing our best and most thorough job is worth that extra effort! :D.  +1.

Fish that are filter feeders generally have Gill Rakers which prevent food from actually damaging and clogging the gills.