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Confusion about resting membrane potential and the Na/K pump
To this day, very few people and sources have been able to clear up my confusion about resting membrane potential and how it is maintained. It seems like this is one of those topics that few people are able to explain very well...
Here is what I do understand:
Chemical Gradients:

at rest, the inside of a neuron is negative and comprised mostly of Potassium (+) and negatively charged proteins (-)
at rest, the outside of a neuron is positive and comprised mostly of Sodium (+) and Chloride (-)

Electrical Gradients:

at rest, the sodium ions are attracted to the negative charge on the inside of the cell and tend to move inwards
at rest, the Potassium ions on the inside of the cell are attracted to the negatively charged chloride ions on the outside of the cell and thus move outwards

So overall, there is a net inflow of Sodium and a net outflow of Potassium. Got it, pretty simple.
However, the sodium/potassium pump is where I get lost. Why does it reverse all that just happened, and why doesn't it cancel out the resting potential if it moves K+ back inside and Na+ back outside? Isn't the voltage fluctuating because of this back and forth movement of K+ out, K+ back in, Na+ in, Na+ back out, etc.? I would imagine this would completely negate the positive/negative charge distribution, but it doesn't. Why?
Clarification: there is a net outflow of Potassium and a net inflow of Sodium. Why does the Sodium/Potassium pump intentionally reverse this by pumping out Sodium and pumping in Potassium? How does that contribute to resting potential?

would you mind clarifying your question a bit?

Sure, just did that

And see http://biology.stackexchange.com/questions/17840/resting-and-action-membrane-potential?rq=1

And this one has a clear illustrated answer to it: http://biology.stackexchange.com/questions/36123/if-the-average-resting-potential-of-a-neuron-is-70-mv-why-is-there-such-a-high

I suggest to skim through these links and search across the site for your answer first. If you are left with a more specific question feel more than free to post.

@Christiaan Thank you. I looked through the first two links before posting and they didn't quite clear up my confusion. Thank you for the 3rd link with the illustration, that picture is a little helpful

The Sodium/Potassium pump maintains the overall concentrations of ions on either side of the membrane. In other words it keeps the neuron's battery charged.

Imagine the neuron like a circuit. We can imagine that the electro-chemical gradient for each ion species (Potassium, Sodium, and so on) as batteries. So When the ions flow according to their electrochemical gradient, the potassium current flows outward and sodium  current flows inward as dictated by these batteries reversal potentials [negative for potassium, positive for sodium].
However, note that this will discharge those batteries, i.e. the concentration of sodium on the outside of the cell will drop (slightly) as sodium flows inward the cell, and potassium flows outward the concentration on the inside will drop slightly. Thus the magnitude of the reversal potential of the Sodium and Potassium drops (they move closer to zero).
To counteract this discharge the Sodium/Potassium pumps expends energy in the form of ATP in order to recharge the batteries. The amount of current that the pumps moves is very small relative to the larger currents of sodium rushing in and the potassium rushing out during an Action Potential. Thus when a neuron fires there is very little overall current contribution from the pumps.
When the neuron is at rest (not firing) then the Sodium/Potassium pump is able to recharge the membrane and the current becomes important. Still this is a very slow process, relative to action potentials.
Another thing to note, even though the cell is at rest the batteries are discharging slightly. Their is a leakiness to the membrane, sodium leaks in and potassium leaks out. Thus the pump's current will counteract these leaky currents at rest, keeping the batteries charged and thus the overall net current  across the membrane at rest will be zero.
Remember though, these currents are very small currents.
EDIT: Based on Discussion with @Christiaan, I decided to post a update to clarify.
At rest potential Sodium Ion influx is much smaller than potassium ion efflux and thus can be ignored. Whether or not Sodium is ignored the above still holds true. The neuron's membrane is at rest which means the net current is equal to zero. This means that the outward potassium current is counterbalanced by the pump's current thus keeping the relative concentrations of Potassium and Sodium constant while at rest and maintaining a steady rest potential.
EDIT 2: Clarifying as per OP comment:
So during an action potential Sodium and Potassium ions move in large currents and this current flow discharges the batteries. At rest there is still current flowing (thus smaller discharging of the battery) but there is no Net current flow thus no change in voltage(thus the neuron is at rest). It is exactly counterbalanced by the sodium/potassium pumps. The reasons the pump doesn't overcharge the batteries is the constant but smaller discharge at rest. When the recharging current is equal and opposite to the discharge via the leak current, a equilibrium is reached.
However when lots of action potentials fire, the resting potential will be altered from the larger discharge rate, thus when the neuron returns to its new resting potential the leak current and pump current will not be balanced, thus the recharging pump current will be larger in magnitude and will bring resting potential back to its normal value.  (Note what constitutes large is relative between species and even neurons.)
Edit 3: Rates of Leakiness and Pump activity.
If only you could say one is stronger than the other. It depends on the conditions of the cell.
Lets focus in on potassium. The leak current for potassium is dependent on two (really three) things. The permeability (or conductance) to the membrane to potassium, and the reversal potential of potassium (which is dependant on the internal and external Concentration of Potassium. Thus varying these things will strengthen/weaken the power of the leak current.
The Sodium Potassium Pump is dependent on three things. The External Concentration of Potassium, The internal concentration of Sodium and the availability of energy (in the form of ATP).
The point where these two strengths are about the same is when there is more Potassium on the inside of the cell. That is to say pump is capable of keeping up with the leakiness of the membrane until the internal concentration of potassium reaches about $140$ $mM$ (again that just a ballpark number). If their is less Potassium in the cell then $140$ $mM$ the pump is stronger, if there is more than $140$ $mM$ the leak of potassium is stronger.

Isn't it so that the K channels leak, but the N channels don't, or at least negibly so?

Yes, at rest there is more K leakage, but there is a Na leakage as well. As for its relative magnitude I cannot say off the top of my head, but over long periods of time this small leak of both Ions must be rectified. At anyrate, the main influx of Sodium is durning the AP by far the major source. I will clarify my post after lunch :)

@Christiaan I ran a quick simulation using the Hodgkin-Huxley model to measure the K and Na currents at rest (~$-65$ $mV$) and it showed that the K current is ~4 times stronger. I would caution that this is just a simple simulation however, but it predicts that the sodium channels don't fully close at rest state, and in fact allow small amounts of Na Ions to leak across the membrane.  Still looking at primary literature however, and not sure this level of detail is necessary to answer the question. Thus a comment.

Question is on resting membrane potential and K+ is the main player in this due to leakiness afaik.

@Christiaan not sure what afaik is? At any rate, I looked more into it and I see your point, Ignoring the small contributions of sodium gives a good description. Furthermore, your answer in from (http://biology.stackexchange.com/questions/21394/what-keeps-the-resting-potential-of-neurons-constant-at-70-mv)  you are completely right the pump counterbalances the leak current. Guess however, my answer didn't make that too clear, updating now to reflect this.

Okay, so I seemed to understand everything until this bit: "This means that the outward potassium current is counterbalanced by the pump's current thus keeping the relative concentrations of Potassium and Sodium constant while at rest and maintaining a steady rest potential". But in your 2nd paragraph, you state that "The amount of current that the pumps moves is very small relative to the larger currents of sodium rushing in and the potassium rushing out during an Action Potential." I'm a little confused there. Could you please explain that part?

So to summarize my confusion: (1) does the NA/K ATPase work at the same rate as the ion leak channels or does it lag behind? (2) Why do so many sources state that the interior concentration of K+ ions is greater than the concentration on the outside if K+ ions are always leaking out into the extracellular fluid?

I apologize that I'm struggling to understand this so much. I appreciate your effort and have accepted your answer. I still don't understand, but that's fine.

@AleksandrH Not a problem, Sorry I can't be clear enough. Always happy to help and I can try to help more if need be. Another way to word an answer to your question is the potassium pump grabs the ions that escape to the extracellular space . However it can only grab so much. thus the two forces eventually come to equilibrium with most of the potassium on the inside.

@AleksandrH May I ask what is your background. I find knowing student's background helps when explaining difficult concepts. I personally come from a math background and sometimes my awnsers can get a little divorced from the biology.

Sure, I'm in my last year of high school and I'm taking AP Biology. We're using Campbell's Biology, but it does a very poor job of explaining this particular concept.

Let us continue this discussion in chat.

I'll try to add some clarity beyond the good efforts xelo747 has made. I will refer to sodium as "Na+" and potassium as "K+", following the standard convention.

Chemical Gradients:
at rest, the inside of a neuron is negative and comprised mostly of Potassium (+) and negatively charged proteins (-)

at rest, the outside of a neuron is positive and comprised mostly of Sodium (+) and Chloride (-)

The main point of the chemical gradient is that the concentration of the various ions is what matters. Concentration gradients drive diffusion, because these ions are at body temperature and therefore slamming into each other constantly, thereby driving each other to areas of lower concentration. For the purposes of talking about the chemical gradient, the charges of the ions can be completely ignored.

[at rest] So overall, there is a net inflow of Sodium and a net outflow of Potassium. Got it, pretty simple.

At rest, there is actually not very much inflow of Na+, because most of the Na+ channels are closed. There is some small outflow of K+, called the leak current. There may also be a very small Cl- (chloride) flow (probably into the cell).

Electrical Gradients:
at rest, the sodium ions are attracted to the negative charge on the inside of the cell and tend to move inwards

at rest, the Potassium ions on the inside of the cell are attracted to the negatively charged chloride ions on the outside of

the cell and thus move outwards

Keep in mind, movements of ions are not only due to the electrical forces of attraction/repulsion. They are also due to the diffusional (chemical gradient) force above. The way you are phrasing things here suggests you are seeing their movements due only to the electrical forces.

So overall, there is a net inflow of Sodium and a net outflow of
  Potassium. Got it, pretty simple.

A very small net inflow of Na+ during rest. During an action potential--which, keep in mind, can happen up to ~200 times a second (!) and is the neuron's main job, there is a big inflow of Na+.

However, the sodium/potassium pump is where I get lost. Why does it
  reverse all that just happened,

Why do you "reverse all that just happened" with the workings of a mousetrap when you want to catch the next mouse? You're resetting it. In the same way, the pumps are there to (continually) reset the imbalance of ions--that is, to make sure there is an imbalance (instead of an equal amount of all types of ions on both sides of the membrane). The neuron needs to have this imbalance of ions so that it is like a set mousetrap, ready to fire an action potential when the Na+ channels are "sprung".

and why doesn't it cancel out the resting potential if it moves K+
  back inside and Na+ back outside?

The potential is due to the difference in number of charges on the inside edge of the neuron's membrane relative to the outside edge of the neuron's membrane, and not due to the small movements of the K+ leak current and the much smaller Na+ leak current. That difference is set up by the pumps, so the order of events is:

The pumps set up (and maintain) the ionic concentration differences.
That causes a voltage difference (think of it as "electrical pressure").
That voltage drives the leak current, mostly through open K+ channels.
The pumps run continually reset the small K+ concentration rundown due to the leak current as well as the small Na+ buildup after action potentials.
This always-on nature of the pumps uses up a good amount of ATP, thus the brain has a blood glucose demand to manufacture more ATP for these pumps (among other needs).

Please see this page, and click on #9, "Na-K Exchange pump".
Note, when I say "small", I mean it. Even in a "dramatic" action potential, the % gain in Na+ concentration inside the cell is only about 0.06%. This is because, when it comes to voltage change, only a small amount of ions can result in a big change in voltage.

Isn't the voltage fluctuating because of this back and forth movement
  of K+ out, K+ back in, Na+ in, Na+ back out, etc.?

At rest, the voltage is not fluctuating: it holds steady. And the movement of ions, in net, is not a back-and-forth movement during rest; it's a steady stream. To illustrate this...
Imagine an office building with many doors. Some are regular doors (K+ leak channels) that say "RED SHIRTED PEOPLE ONLY!", some are gasoline (ATP) powered revolving doors (the pumps). There are also locked doors that say "BLUE SHIRTED PEOPLE ONLY!".
The scene you should picture is the building filled mostly with people wearing red t-shirts (K+), with a small percentage wearing blue t-shirts (Na+). Outside the building, the situation is reversed (many more blue shirts). On both sides, all people are more gathered against the walls of the building (membrane) than elsewhere. Some very small amount of red-shirted people are leaving through dozens of regular red-only doors, in a continual flow. Another very small amount of both red and blue shirted people are going through the revolving doors: two red shirts go in (K+)) while three blue shirts go out (Na+). And there are dozens of these revolving doors in the building. The net effect is that the overall proportion of red to blue shirted people in an outside the building remains the same.
And of course, every now and then, suddenly lots of blue shirt only doors unlock from some magic command from the building computer, and a noticeable amount of blue shirted people enter the building (an action potential)...but not nearly close to enough of them to change the proportions of blue:red in any significant way. They are soon pumped right back out by the revolving doors. (I'm leaving out some other details, but you get the point).
If this scene makes sense, that's a reasonable metaphor for what is happening in the cell with respect to K+ and Na+.

I would imagine this would completely negate the positive/negative charge
  distribution, but it doesn't. Why?

I'm not sure what you mean by "completely negate the positive/negative charge distribution". This is the crux of your whole question and confusion. The pumps are there to set up and maintain the charge distribution, not negate it. In fact, they require ATP as a source of energy to pump ions where they "do not want to go" if it were only up to diffusion and electrostatic forces. They are constantly opposing rundown of the distribution of charges.
Please let me know if this clears it up, and if not, I can try to amend what I've written.

Sorry for the late response. What I don't understand is why the gradients would dissipate in the absence of the Na/K ATPase pump. From what I understand, Potassium leaks out along its concentration gradient from high to low, but this creates an opposing electrical attraction that drives some Potassium back inside. Eventually, the inward movement is equal to the outward movement and there is no "net" movement of Potassium. However, if there is no net movement of Potassium, I don't really understand why the charge isn't neutral but instead is negative. Could you explain that particular bit?

I'll answer you in two comments. 1. The eventual point you refer to for potassium is the equilibrium potential for potassium (about -80 mV in mammals), and yes, at that potential there IS no net movement of potassium. BUT, neurons are NOT sitting at -80 mV when at rest; resting membrane potential is about -65 mV. Therefore, there IS a net movement of potassium outward--the leak current.

"I don't really understand why the charge isn't neutral but instead is negative." Just to clarify terms: we want to talk about the VOLTAGE (aka POTENTIAL), not charge (which is something related but different). Voltage is essentially a difference in the clustering of charges between two locations. It's considered an electrical "potential" because it has potential energy, in that if you dropped an ion from a helicopter in between the two locations, it would feel a push and would be moved by the electrical field of that clustered-charge differential. The point is, the neuron winds up with..

...a difference in charge clustering on either side of the membrane, such that the voltage is negative on the inside with respect to the outside.


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What causes anorexia nervorsa?
I've heard of anorexia nervosa being a severe loss of appetite. I'm wondering what causes such disease in humans?

People with anorexia usually tend to have high levels of cortisol, the brain hormone most related to stress, and decreased levels of serotonin and norepinephrine, which are associated with feelings of well-being. But you may want to ask this question on the Cognitive Sciences Stack exchange

Definitely a good target for CogSci, but dependent on the answer also here. If @gone.'s comment holds, it's definitely ontopic here too. One way or another, nice question +1

"Is there a physiological underpinning for anorexia?" would be on topic here. "Why do people become anorexic?" might be more cogsci. It's semantics though and I like the question. +1

What is anorexia nervosa?
Generally, it is an eating disorder which is characterised by a tremendous fear of food as well as an extreme weight loss.
Patients with anorexia nervosa do not necessarily lose their appetite but rather obsessively control and restrict their food intake.

Anorexia Nervosa as an inherited disease/genetic factors
There has been a lot of research proposing that eating disorders are often biologically inherited and tend to run in families.

Recent research suggests that inherited biological and genetic factors contribute approximately 56% of the risk for developing an eating disorder. Individuals who have a mother or a sister with anorexia nervosa are approximately twelve times more likely to develop anorexia and four times more likely to develop bulimia than other individuals without a family history of these disorders. Studies of twins have shown a higher rate of eating disorders when they are identical (compared to fraternal twins or other siblings).

The hormone serotonin
There has been found that anorexics have an overproduction of serotonin, which can cause a continual state of acute stress and anxiety.

Researchers are still puzzled as to why, if anorexics already have high levels of serotonin, then SSRIs (medications like Prozac which raise serotonin levels) are successful treatments for some individuals. These scientists speculate that that there may be different subtypes of this disease, and that different groups of anorexics may have different neurochemical characteristics.
Researchers have also noted that abnormal eating behaviours and the resulting changes in the body can actually cause a disruption in serotonin levels, thus contributing to an already existing problem. Abnormalities in serotonin levels can lead to depression and anxiety. Studies also suggest that there are genetic predispositions to serotonin disruptions that appear to run in some families.

The hormone dopamine

Research suggests that women who develop anorexia nervosa may have altered levels of dopamine in their brains. Dopamine disturbances can cause hyperactivity, repetition of behaviour (such as food restriction), and anhedonia (a decreased sense of pleasure). This neurotransmitter also affects reward-motivated behaviour.

The hormone cortisol/hydrocortisone

Numerous other hormones in the brain have also been linked to eating disorders. Stress triggers the production and release of a hormone called cortisol; chronically elevated cortisol levels have been observed in patients with anorexia. Cortisol can inhibit appetite.

The hormone leptin

Leptin is a protein hormone produced by the body's adipose tissue. Leptin is regarded as a hormone which can regulate fact storage and appetite. If individuals with anorexia nervosa lose extreme amounts of body fat, their levels of leptin drop which is known as hypoleptinaemia. The side effects of hypoleptinaemia can include amenorrhea, impaired metabolism, and bone loss.

Also, if people receive treatment, their leptin levels do not immediately return to normal. Initially during the treatment, leptin levels rise through the sky, which is also the reason why most patients are most susceptible of relapsing back into an eating order, since very high levels of leptin may cause a weight gain.

Sources:

ENGEL, BRIDGET, NATALIE STAATS REISS, and MARK DOMBECK. "Causes Of Eating Disorders - Biological Factors Continued." Mental Help Causes of Eating Disorders Biological Factors Continued Comments. 2 Feb. 2007
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3010958/
http://www.apa.org/monitor/mar02/genetic.aspx

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How long does it take for blood to travel from the lungs to the fingertips?
I've noticed that a pulse oximeter at my fingertip lags my breathing effort by a noticable amount.  I conclude that it takes some time for freshly oxygenated blood to travel from the lungs to the fingertips.
What lag time should I expect? Is there a chart or study which provides an estimate based on heart rate?
Is the lag greater for fingers, or toes? Presumably toes, being further from the heart and lungs, but perhaps the circulatory system has a larger carrying capacity and evens it out for the legs and feet.

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Resting membrane potential: K+ concentrations and charges on inside and outside of the neuron
According to this site, there is a greater concentration of K+ ions inside the cell than outside. The following screenshot, taken from this website, supports this statement.

However, I don't understand how the inside of the cell can have a net negative charge if there is a greater concentration of K+ inside the cell. This seems like a contradictory statement to me. (1) Why is the interior negative despite the fact that there are more K+ ions inside than outside, and (2) What exactly causes the net negative charge?

Why is the interior negative despite the fact that there are more K+ ions inside than outside, and (2) What exactly causes the net negative charge?

It's because K+ isn't the only player in the game. Yes, there is a bigger concentration of K+ inside of the cell, however, there is also a higher concentration of Na+ outside of the cell, and also, there are other charged ions, such as Cl- or proteins.
One of the main reasons for the gradient is Na+/K+ ATPase, which transports 2 K+ ions to the inside of the cell, while 3 Na+ ions are pumped to the exterior of the cell. This generally yields in a higher concentration of + charge on the outside of the cell.
The final membrane potential depends on the permeability of the membrane to these ions. Higher the permeability for an ion, the closer is the actual potential to the equilibrium potential of this ion. (you can read about its calculation here.). Since the membrane in a normal state is not permeable to Na+ to a big extent, but is permeable to K+, the resting potential is similar to the equilibrium potential for K+, which is negative (the actual value depends on the specific cell type, generally we can say -70mV in neurons). (The K+ is driven to exit the cell because of the chemical and electrical gradient, which results in negative charge inside of the cell). The approximation of final potential can be calculated by using Goldman equation.
The principle is therefore in selective opening and closing of specific ion channels and functioning of transmembrane pumps.

Thanks for the response. I'm still having trouble understanding how the membrane potential can be negative, since the Na/K ATPase is constantly pumping K+ ions back into the cell.

Because Na/K ATPase throws out 3 Na+ for taking 2 K+ inside i.e. +3 outside and +2 inside. Also K+ can move in and out easily i.e. concentration of K+ outside is still more. Adding it with Cl- and other anions (inside), there becomes more +ve charge outside i.e. more -ve charge inside (relatively, if thats what you couldn't get).

Sorry that I'm struggling so much with this. @aayushsrivastav You said that "concentration of K+ outside is still more", but the sources I mentioned say the opposite--that the concentration of K+ inside is higher. Could you please clarify?

K+ is pumped in by ATPase, exchanging it with Na+. But K+ can still move out easily as membrane is permeable to it. Sorry I didnt mean "more outside" I just meant that "as soon as K+ is pumped in, its concentration increases inside. So it moves out creating concentration balance on both sides. So charge inside is (K+ - Na+) and that outside is (K+ +Na+)

Another quick thing to point out is that voltage is a relative measure. Recall that the outside is the "ground" or point where voltage is consider zero. Thus all measures of voltage are relative to this. Excuse my math but lets consider the Nernst equation
$$\frac{RT}{Fz}\ln(\frac{[Ion]_{out}}{[Ion]_{in}})$$
Where $R$ is the gas constant, $T$ is temperature in kelvin, $F$ is Farady's constant and $z$ is the charge of the ion.
Now because we have (arbitrarily) decided that outside is the reference point the outside Ion Concentration is on top. Thus In potassium's case $z= +1$ it is $\frac{[Ion]_{out}}{[Ion_{in}}=\frac{smaller}{larger}$ is a number less than 1. Recall the natural log of a number less then 1 is negative thus Potassium presence on the inside means the driving potential is negative on the inside.
Now take into account what Matej Pribis said, Potassium is more permeable at rest, thus its driving potential is more contributory to the rest state than say sodium which has a lower permeability at rest.
This means at rest the potassium Ions negative driving potential is more contributory at the neurons resting state.

I'd actually like to answer my own question for any future viewers, as I found this exceptional website that thoroughly and clearly explains how membrane potential is established. Then, this page in particular, belonging to the same site, goes into more detail as to how the membrane potential for a neuron is maintained via the Na/K Pump. Thank you to everyone who posted a response!


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Are chilies technically peppers?
Nando's chain of restaurants (UK) refers to chili peppers as just "chilies". My friend and I had a discussion with regard to whether chilies can be called "peppers" or if they do not belong to the pepper family at all. In fact, my friend added that there are 2 types of this specimen - "chilies" and "chili peppers."
To what extent is this all true, and what exactly are chilies?

Chili is a common reference to chili peppers in an abundance of countries, but they fall within the same designation as other so-called "peppers" such as bell pepper, cayenne, jalapeno, etc. because they are all of the same genus Capsicum. They differ, however, from traditional real peppers (black pepper for example) of the Piperaceae family. Capsicum actually belongs to the nightshade family (Solanaceae), but so do potatoes.
The word pepper originates from a south Indian term for the long pepper plant which was used as spice at the time and is a member of the Piperaceae family. I think that people have generalized chili as a pepper in this case due to the heat component, but this section of the answer is also off topic for this site.

All the bell peppers and chilli peppers and jalapeno's and cayenne peppers are the same species, Capsicum annuum. The bell pepper was developed in the 1920's from a hotter variety. Here are photos of the wild varieties: https://www.fataliiseeds.net/product-category/wild_chiles/ They are berries. All the american plants like tomatos and potatoes are all from the american nightshade family, Solanaceae, which evolved after America and Africa devided 180 million years ago. they are New World plants.
CKM gives you the information for paprika, a different type of plant from i.e. Sri-Lanka https://twitter.com/srilankanflora/status/773690156385644545. Black peppercorns were found stuffed in the nostrils of Ramesses II, placed there as part of the mummification rituals shortly after his death in 1213 BCE.
The only ambiguous nightshade plant which arrived before the conquest of the Americas is the datura plant, also a cousin of the pepper family, for which illustrations in indian books exist from 800 years ago, although that is a mystery and yet to be proven by DNA. If it did arrive in the old world in ancient times, then it may have arrived as seed through the Bering straights or through natural dissemination.

Chilis are from the New World, and as CMosychuk has answered, belong in the Capsicum genus. Their name derives from the Aztec Nahuatl word for the plant chilli, and this name has been used by the Aztecs to refer to the plant prior to Spanish contact and spread of the plant to the Old World.
The pepper, however, belongs to the completely unrelated Piper genus, and the plant originated in the Old World. Its etymology derives from the Sanskrit word pippali, also referring to the plant. As the Etymonline entry suggests, the word "pepper" was also used to refer to the Capsicum plants when they were first introduced to the Old World, perhaps due to their similar spicy taste.
Therefore, it is not the case that chilis are peppers, since the Capsicum genus has no recent genetic relation to the Piper genus.

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Origin of the double membrane of mitochondria and chloroplasts
Most websites and textbooks say that the double membrane of mitochondria and chloroplasts are a result of the endocytosis of ancient prokaryotes (the outer membrane is from the vesicle containing the prokaryote, the inner membrane is from the prokaryote itself).
However, some sources say that this is not the case. The precursor to the mitochondrion (alphaproteobacteria) was a gram-negative bacteria, which has a double membrane. This site says that the reasoning for the double membrane that is often taught is a lie, and that the mitochondrial precursor had a double membrane already to generate ATP through the ETC.
So, if this is the case, why do mitochondria now have two membranes, and not three (two from the prokaryote and one from the vesicle)?

This is a genuine question about your question; why would the Gram negative bacteria need to have a vesicle? Perhaps it the case of Gram positive and vesicle versus Gram negative only.

@James How would the Gram negative bacteria (or any bacteria) be endocytosed or enter the cytoplasm of the proto-eukaryotic cell if it's not surrounded by a vesicle?

From the link you shared "It's simply not true that the double membranes of bacteria and chloroplasts were the result of endocytosis." After a brief bit of googling and reading some comments by internet folk I am convinced that the third membrane could be lost. I still can't answer the question though. Very interesting!

The answer lies in the protein composition of mitochondrial membranes, which undoubtedly prove that the outer membrane (OM) is of alphaproteobacterial origin, and the phagosomal membrane (if there was any) is lost. Though the endosymbiotic origin is without question, bear in mind that the phagocytotic origin is still debated (cf. López-García & Moreira 2015). And if the symbiont has entered the host some other ways than phagocytosis (cf. papers of Tom Cavalier-Smith) or syntrophic engulfment (cf. papers by Bill Martin; Searcy; López-García & Moreira) (e.g. puncturing the plasma membrane as a pathogen), then there never was a third membrane.
From Symbiogenesis Wikipedia:

Porins (transport proteins) are found in the OM of mitochondria and
  chloroplasts, are also found in bacterial cell membrane (Fischer et
  al. 1994Zeth & Thein 2010Fairman et al. 2011). The
  membrane lipid cardiolipin is exclusively found in the inner membrane
  of mitochondria and bacterial cell membrane Mleykovskaya & Dowhan
  2009.

According to many (Cavalier-Smith 2002, Cavalier-Smith 2006, Zeth 2010), the presence of β-barrel transport proteins proves that the OM evolved from the bacterial OM, not from the host food vacuole membrane. Both mitochondria and plastids contain in their OM β-barrel proteins (e.g. Tom40, Sam50 and porins in mitochondria, Toc75 homologue of Sam50 and their joint negibacterial ancestor Omp85 in chloroplasts) and these are only present in the OMs of gram-negative bacteria (cf. Schleiff & Soll 2005). All Alphaproteobacteria are gram-negative, hence the ancestor of mitochondria originating from the Rickettsiales or very close was also.
Note, that many secondary and tertiary plastids still retain their third, outermoest phagosomal membrane originating from the host's plasma membrane (cf. Keeling 2010).


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Question about DNP derivatives of amino acids (specifically epsilon-DNP-lysine)
I have a pretty basic biochemistry question but am having trouble finding the answer to it:
Normally, 1-Fluoro-2,4-dinitrobenzene (DNFB) reacts with just the amino terminus of amino acids. However, with lysine, DNFB can react in two places (at the amino terminus and to the epsilon amino group). The DNP derivative of lysine is referred to as "epsilon-DNP-lysine".
Does "epsilon-DNP-lysine" refer to a product where the DNP is bound only to the epsilon amino group (but not to the amino terminus), or does it refer to a product where DNP is bound simultaneously to the epsilon amino group and to the amino terminus?
Also, can the same thing happen with other amino acids that have an amino group in the side chain? i.e. can there be epsilon-DNP-arginine, for instance, or is this behavior unique to lysine?

Cross posted on chemistry: http://chemistry.stackexchange.com/questions/46359/question-about-dnp-derivatives-of-amino-acids-specifically-epsilon-dnp-lysine


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Is there some research paper which focus on the influence of using cancer cell as experimental materials on experimental result?
Cancer cell is unstable cell and high variation, but there are many experiment use cancer cell as experimental materials. I always wonder how much influence can using cancer cell as experimental materials exert over experimental result?
Is there any study about this? If any, please give me the study paper.
Thanks for any help.

Depends on what is the objective of the experiment. In some cases the cancer cells are decent models while they are poor for others. You need to specify what kind of experimental objectives you are interested in. You should also remember that no model is perfect. They are useful and good approximations for certain conditions and you need to know these conditions beforehand.

Sorry, I didn't make it clear. What interests me is evaluating existing result which have been published. Not the experiment design.

That is just too broad. We cannot evaluate all the published literature for problems in the experimental design. Do you mean to ask if there are studies that have done this kind of survey? Again there are many articles on this topic. Did you try a google search?

I have tried scholar. I didn't get satisfied answer, can you give some paper  that focus on this topic?

There are several articles on this. You may look at these for a start:

Masters, John RW. "Human cancer cell lines: fact and fantasy." Nature reviews Molecular cell biology 1.3 (2000): 233-236.
Masters, John R. “False Cell Lines: The Problem and a Solution.” Cytotechnology 39.2 (2002): 69–74.
Masters, John R. "HeLa cells 50 years on: the good, the bad and the ugly." Nature Reviews Cancer 2.4 (2002): 315-319.
Holliday, Deborah L., and Valerie Speirs. "Choosing the right cell line for breast cancer research." Breast Cancer Res 13.4 (2011): 215.
Lacroix, Marc. "Persistent use of “false” cell lines." International journal of cancer 122.1 (2008): 1-4.


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Why does hemoglobin electrophoresis in sickle cell trait gives two bands but not three?
Electrophoresis of hemoglobin from a patient with sickle cell trait (carrier for sickle cell anemia) shows two bands. Why not three?  Since there are two beta chains in each hemoglobin, it seems to me they should have three types of hemoglobin: HBB/HBB, HBBs/HBBs, and HBB/HBBs. Does the HBB not form hybrids with HBBs? Aren't both polypeptides produced in the cell?
*HBBs signifying mutated beta chain

"Shows" as in from your experiment or as a general question on an ideal result (like ones asked in exams)?

It appears to be "shows" as in real results used for diagnosis, either with alkaline cellulose acetate or other forms of electrophoresis that separate by charge. Just do a google search for images using the term "electrophoresis of sickle-cell haemoglobin".

This is a really interesting question and again reminds of how ignorant we are about things as subtle as this which otherwise should have been an obvious question.
First of all, although there seems to be no confusion, I'd like to clarify that we are talking of the protein being separated on electrophoresis. Hemoglobin electrophoresis classically refers to the cellulose acetate/citrate agar electrophoresis where the RBC hemolysate is used as the sample. This method uses the fact that, hemoglobinopathies generally have mutated Hb which differ in charge from the original HbA. Charge is a property of separation in cellulose acetate electrophoresis unlike SDS-PAGE where separation is on the basis of mol. wt.
We can also do a DNA electrophoresis (digressing) to identify a Hbpathy after digesting with restriction enzymes which would give a different results, depending on the restriction enzyme that has been used to differentiate the mutation from the original. Here is an example using MstII for RFLPs. This isn't the topic of discussion here. Our sample is the protein, and not the DNA.
So it is important that the electrophoresis we are going to talk of, is of a protein electrophoresis based on charge.
Considering the sickle cell trait, let us clarify the terminology now. HbA is normal hemoglobin tetramer which composes of $\ \alpha_2\beta_2^A $. HbS on the other hand is $\ \alpha_2\beta_2^S $. The terminology you have used not only isn't standard but also is conveying a different meaning. Now logicaly, in a person with sickle cell trait, one should be expecting a hemoglobin with both different beta chains. And it does happen! Literature calls it the assymetric hybrid. Let us indicate it with AH which is $\ \alpha_2\beta^A\beta^S $. Let's sum this up a bit.
HbA = $\ \alpha_2\beta_2^A $
HbS = $\ \alpha_2\beta_2^S $
AH = $\ \alpha_2\beta^A\beta^S $
The assymetric hybrid that has been mentioned here is only for the sickle cell trait. There are many other hemoglobinopathies and in their heterozygous states one can obtain other assymetric hybrids with a different beta chain.
Now that we know that assymetric hybrids are formed, why do they not show up on the Hb electrophoresis?
It is generally believed that under physiological conditions, at equilibrium, hemoglobin is a mixture of tetramers ($\ \alpha_2\beta_2$) and dimers ($\ \alpha\beta $) as $$\ \alpha_2\beta_2 ⇌ 2\alpha\beta $$ The dissociation equilibrium constant for oxyhemoglobin is approximately $\ 2x10^{-6} M $ (heme) and is much less for deoxyhemoglobin. The asymmetric hybrid is generally not isolated by conventional techniques, since the tetramer-dimer dissociation constant is much lower in-vitro than in-vivo . Thus the asymmetric hybrid dissociates into dimers $\ \alpha\beta^A:\alpha\beta^S$ and reassociates into more symmetric forms during the separation process.
There are slightly modified methods to isolate the assymetric hybrids under deoxygenated conditions such as isoelectric gel focussing, cross linking the chains, etc. The amount of AH formed in proportion to HbA and HbS can be measured in these kind of experiments and has been found to be comparable to the expected binomial distribution of $\ a^2 + 2ab + b^2 $. This implies that the stability of the AH is comparable to HbA and HbS.
Hope it helped.
To delve further, here are a couple of reference that should be of use.

HF Bunn and M McDonough (1974), Assymetrical Hemoglobin Hybrids.
  An Approach to the Study of Subunit Interactions, Biochemistry,
  13(5)989-93.
MK. McCormack, TG. Westbrook, RM. Paull & S Berman (1981),
  Identification of the Asymmetric Hybrid of Human Oxy Hemoglobins A
  and S (α2βAβS) at 4° C by Cellulose Acetate Electrophoresis,
  Hemoglobin, 5(3)251-56.

Could someone help me with the reversible arrow up there?

Glad you've solved the mystery at last. When I've digested your answer I'll, no doubt, upvote it and remove my own. In the meantime I've inserted the reversible arrows from the Mac OS Character Viewer (under arrows). If you are not on Mac OS, there is an excellent online Unicode site for this sort of thing, especially for web or computer use (although for the current case a generally query is a better way to find this.)

@David A very beautiful question. My biochem proff was also intrigued and after a little search mailed me the article. Hats off to the OP for such a thought! Anyway, thanks!


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Sodium hydroxide grade in library denaturation for NGS
If the NaOH, 1N which I bought does not have the label of molecular biology grade can it be used safely for library denaturation in NGS? Thank you!

The "molecular biology grade" is just a gimmick in many situations. The reagent grade NaOH is quite pure (≥98%). The usual impurities (major being Na2CO3; ~1%) are also chemically insignificant (See the Sigma-Aldrich products 1 and 2). For the product that you have, read the label for details. It should be more or less the same.
Just prepare your solution in MilliQ water and pass it through a 0.2µm filter.


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A molecular marker for global protein synthesis
I know that protein synthesis is governed by a lot of factors (I'm mostly studying the mTOR pathway), but I'm looking for some kind of marker that will indicate the global protein synthesis rates.
I know there are tissue-specific markers (like actin/myosin in muscle) but I'd like something more that is ubiquitous and is proportional to global protein production (maybe a muscle can make more or less myosin depending on whether there are some factors).
I assume protein synthesis factors (like mTOR, S6K1 etc.) are quickly regulated, so they cannot be used as markers.
So, what would serve as the best molecular marker?

Witness is a wrong term. "Marker" is a right term for what you mean. I edited the question. See if this matches with what you intend to ask.

You could measure the fractional synthesis rate in vivo in humans if that's what you're after, e.g. http://ajpendo.physiology.org/content/273/1/E99.short describes it extensively.

The answer will not satisfy you. The truth is no protein marker will do.
On one hand you seem to be looking at some individual, representative protein, which you could measure by immunoblot. But most proteins are in scant concentrations, just as many as required for their job, and go up and down depending on their specific roles, rather than on general metabolic trends. Even if some general control mechanism increases protein synthesis across the board, in a cell proteins are 20% actin, 20% tubulin, 0.0001% 4E-BP and 0.0001% p70-S6K (made-up numbers for the sake of example), any 1% total protein increase you'd like to measure would be 200,000 easier to detect in tubulin than in p70-R6K. In order to be a marker of general control of protein synthesis, the marker protein you'd want to measure should be a plentiful protein, with little to no specific control.
On the other hand, those are the characteristics of a house-keeping gene. So you won't be able to normalize such a "representative" blot! Normalizing house-keeping by house-keeping, you will have pretty much no change.
Embrace labeling experiments. Even there, the right normalization is debatable. If anything, the fact that everyone does those, rather than looking at protein X, should be an indication of how much you will struggle to prove points about protein synthesis rate using anything else.

That's a really interesting answer, and you make points. You are right about labeling experiments, but I cannot do that in my current project.


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How to quantify quality of vegetables and fruits?
I am interested in knowing if there have been studies in quantifying the quality of vegetables and fruits. By simple examination, it is possible for us to identify if a particular vegetable is 'spoilt'. But does this transitioning from 'edible' to 'spoilt' happen instantaneously? Or is it possible to model this transformation by a random process?
When producers and retailers determine shelf life, is it only based on anecdotal knowledge? Is there a systematic process by which quality can be determined and quantified?
I shall be glad if you could point me to studies that look at time to expiry and hazard rates of vegetables under variously controlled environments. I am happy to have the data for one or more common vegetables or fruits.

What exactly do you mean by "quality"? Do you only mean edible vs spoilt?

@terdon: Spoilt is an extreme case. I am more interested in the 'curve' from edible to spoilt, over time. Is it a step function, where suddenly on a day, it becomes spoilt? Or is it more gradual? Again, is this curve deterministic or random? Such type of questions.

OK, in that case, please [edit] your question and make it more specific. "Quality" can refer to any number of things.

At which level do you want to detect spoilage? By spoilage do you mean decay or just infected by some microbe? Some fruits/vegetables may lose their quality i.e. start degrading by themseleves and this may have not result from exogenous infection. Can you clarify on this. In any case, the assay may vary for different fruits and vegetables.

@WYSIWYG: I am specifically interested in the case when there is no exogenous infection, that is, the natural decay process.

In that case I would suggest that you focus on a specific kind of fruit/vegetable because each one of them can yield different degradation products. Or else, you frame your question like a [tag:reference-request] which means you should mention what all details you are expecting. (Optional but recommended: add some results from your own search [such as this], and indicate what kind of topics you are/aren't expecting)


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Minimum size for a peptide/protein to be immunogenic in human?
What is the minimum size for an (injected) peptide/protein to cause immunogenic response in human?
A reference is very helpful, as well.
Thanks in advance

Possible duplicate of http://biology.stackexchange.com/q/7905/3340

@WYSIWYG Looks a bit like, but I think this question goes further, especially since the other question and the answer focus more on metal conjugates.

There's a few limiting factors including how proteins are presented that constrains the actual size needed to get peptide presentation. These depend largely on the MHC molecules (HLA in humans). The binding groove in MHC-I actually limits the size of peptides it can load to 8-10 amino acids, 9 being the most common. This is because "pockets" at either end of the binding groove are said to actually grasp the peptide, and it doesn't allow for much longer sequences. MHC-II lacks these grasping pockets, and so it can bind much longer sequences (Figure 1). MHC-II typically binds sequences of 13-25 amino acids.

Figure 1. Difference between the MHC-I and II binding groove.
There are also a given number of requisite anchor residues that complement the binding pocket of the MHC binding groove that mostly display a particular character at the given position (normally polar at a given position, etc.) (Figure 2).

Figure 2. Just a sampling of possibilities across HLA isoforms.
All information and figures courtesy of Parham "The Immune System," 4th ED.
If the presented peptide has met the prerequisities and has been identified by a leukocyte, in theory it should produce an immune response. I think these are some good considerations to make when you're thinking about how small can a peptide be. I'm assuming here that MHC-II would be handling your injected protein through an extracellular pathway (I can't know for sure), and so the smallest literature MHC-II peptide range I've ever seen is 11 amino acids on the low side. There are a number of computational studies out there that attempt to predict MHC affinity, but it's problematic due to the range of sizes MHC-II may bind and there is variability among the binding cores that contain the anchor amino acids.

Can small peptides can act like haptens? Can you add some details on this, if you know? MHC peptide length may not really mean the smallest immunogenic size. In fact, very recently I heard someone talk about an antibody against a tripeptide for doing immunoprecipitation. I asked the speaker if he really meant an antibody against a general tripeptide epitope and he confirmed so. I forgot which tripeptide it was but it was supposedly generated after a tryptic digest of the ubiquitin tag (so possibly the RGG tripeptide). Even the well known FLAG-tag (DYKDDDDK) is an octapeptide.

I will attempt to find the resources, but from what I understood about tripeptide antigens is they're considered non-immunogenic as they typically can't elicit a primary immune response, whereas they're perfectly capable of somehow activating a DTH reaction. So in that sense they would act more like a nucleic acid or lipid in that they're largely non-immunogenic haptens. I'm unsure if that would end up out-of-scope for OPs question about immunogenic peptides.


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Is this a saltwater millipede?
I spotted this millipede-like creature in Hervey Bay, Australia at low tide, just kind of hanging out at the bottom of a small saltwater tidepool.

It's several inches long, composed of a large number of segments, each of which appears to sport a pair of legs.
Hard to tell from the photos, but the creature is aquatic and in both instances was observed moving around under about an inch or so of water.  No specimens, alive or dead, were observed outside of the water.
They leave obvious trails behind them in the sand at the bottom of the tidepool as they move across it, and I assume they have some ability to burrow into the sand as I saw far more trails than I did creatures.
What are these things?

Could be a Eunicid Polychaete worm. From the species present in Australia (from this site), this seems like Marphysa

I agree, it looks like a polychaete worm. These have a pair of legs on each body segment (which explains one of their common names, bristle worm) and can be found in shallow waters and soft sediments.

This is indeed a polychaete worm, and likely a member of the beachworm family Onuphidae.
From the Marine Education Society of Australasia  :

Polychaetes are particularly common on and in muddy and sandy shores. Their most obvious feature are the pairs of parapodia appendages. One pair comes from each body segment. These parapodia are used for crawling and swimming. "Para" means "like", and "podia", "pod" or "ped" means "legs". These parapodia are often tipped with hardened spine-like setae or dorsal cirri.

You can find some good informaiton on beach worms here, and information on the distribution, abundance and
population dynamics of various species here.
I'm sure a quick message to Dr. Pat Hutchings, the Austrtalian Museum's polychate expert, would prove to be be your best chance to get a species identification.
For those interested in additional polychaete identification, you can download a digital ID key.


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In molecular docking, what is the difference between ligand and cofactor?
In molecular docking aspect, what is the difference between the Ligand and Cofactor? Can a Cofactor be used like a ligand for docking with the target?

Ligand is an umbrella term for non-covalently bound anything. A cofactor, substrate, or allosteric regulator could be a ligand. This is a biochemical definition ligand, don't confuse it with a formal chemistry definition of ligand.
What's generally important about cofactors is they're not protein, but they're essential to the protein's biological activity. They could be a metal ion, organic complex, a vitamin, etc. Organic complexes that act as cofactors are also known as coenzymes. Cofactors that bind tightly or become covalently bound are called prosthetic groups. The protein without the required cofactors is called an apoenzyme, and with it's cofactors is called the holoenzyme.
Keep in mind to be on-topic for this site you need to do some research ahead of time and produce a focused, studied question. Wikipedia regularly provides the same answer verbatim!

@Kendall  I read this article before, but I expect answer in 'Molecular Docking' aspect. I mean, whether the cofactor can also be considered as ligand for docking? Does removing the cofactor affects nature of the docking?

Apoenzymes largely don't attain their catalytic effect due to conformational changes or active site changes that cofactors induce upon binding in forming a holoenzyme. This means that sometimes there will be two docking states: one for the cofactor/coenyme, and if there is a conformational change another docking state for the substrate. In short though, it depends.

Kendall So, In molecular docking of ligands... Should the cofactors must also be included?

You need to know what you're modeling. If you're modeling the docking of a cofactor to an apoenzyme, that's a different study than the binding of a substrate to a holoenzyme. Since apoenzymes lack catalytic activity, you wouldn't want to model binding of a substrate to an apoenzyme, however, so you would probably be modeling the interactions with a holoenzyme (which has cofactors bound). The design of your study and what your goals are will dramatically affect that question.


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Are these birch or aspen trees?
I was just wondering if anybody could help me identify the trees in this image? I am confused as to whether they are aspen or birch, a mix of the two, or whether the brown/reddish trees are some other species I don't know about? Thanks!

pretty sure they're aspen trees (https://upload.wikimedia.org/wikipedia/commons/a/a8/Fall_Colors_at_Kebler_Pass,_Colorado_USA.JPG) rather than birchs. The leave colour of birches is normally a darkish green. To make the identification easier, a geographical description would be helpful, and some close-up photos of leaves, branches and the main stem.

From the growth pattern, I'd say aspens, since they're clonal organisms that grow in groves like that.

Thanks for the quick answers! It's just picture from a google image search, so I have no idea about the geographic location etc. as this information was not provided. So they are probably aspens then! How about the reddish trees? Do some aspen trees get like that?

Jes, some aspens can be somewhat orange to red, even in a stand where most are golden yellow.  In fact, I've never seen a grove that's all orange, and aspens are common in the mountains here, wherever there is sufficient water.

I don't have the vocabulary, but my experience working in forestry alongside professional foresters STRONGLY leans toward aspen. I know that isn't a substantial external justification, but consider it a warning to be sceptical.

The bark texture appears more consistent with aspen than birch, even at this distance it is usually evident.

I think they are birch trees (Betula), based on the white bark with black horizontal patterns (Lenticels). The bark patterns at the base of the trees are also very similar to birch. Either way (relating to one of the comments), it's an autumn picture, where both birch and aspen have yellow leafs (aspen leaves can also be red or reddish, especially at the end of branches).
This page also agrees with me (which doesn't necessarily have to mean that much though), which labels the exact same picture as "birch-tree-wallpaper-3.jpg".
I'm not sure about the exact species, but I know that there are North American species where the bark can shift between white, pink or reddish. One possibe suggestion/pure guess is Betula neoalaskana, but as you can see from the wikipedia page this species can also hybridize with Betula pendula and other species. To me, it doesn't look exactly like the Eurasian Betula pendula or Betula pubescens, which I'm most familiar with (those are the two species found in Sweden).

The name of the .jpg is actually what started my confusion. To me, the bark and the way the leaves are concentrated at the top of the tree makes it look like quaking aspens. However, I don't think I've ever seen the brown/reddish types of aspen before, which makes me think it's birch. Do aspen and birch often grow in the same area? Could it be a mix of the two?

Aspen and birch can definitely grow together. I also think that the distribution of leafs is a bit off compared to what I'm used to in Birch, but I'm not familiar with N. American birch species, or hybrids. The sturdier, shorter tree to the right is extremely similar to a birch though.

The tree with a thicker trunk to the right seems like birch to me too, as well as the other reddish trees. I didn't know that they grow in the same area, so I think I'll conclude that it's a mix of the two. Thank you for all the helpful information!

Taking another look, I'm really unsure though. The overall look of the stand is very aspen-ish. Also, the thinner branches of birch trees are often relatively dark, while aspen branches are usually ligher and more similar to the trunk, which is more similar to the trees in the picture. Both  Populus tremuloides and Populus grandidentata can also be were white with horizontal black stripes.

I also think they look very much like aspen, and the color of the branches is also a good point!

@fileunderwater If you're unsure, you should modify or delete your answer. And I think you're right being unsure, the stand does look very aspen-ish. And btw: Sweden has one more betula: Dvärgbjörk ;-)

Look like aspen to me.

Turns out this is harder than it seems from just the picture...
The three candidates I think one could most argue for are:

Quaking Aspen (Populus tremuloides)
Paper Birch (Betula papyrifera)
Grey Birch (Betula populifolia)

Here is a picture of Populus tremuloides from the USDA:

Notice the smoothness of the above Aspen bark (identical to that of the picture in the OP's question). Now compare it to the peely nature of typical birch bark (here pictured B. papyrifera or paper birch):

Though not all birch species have peely bark: (my emphasis below)

Grey birch (Betula populifolia) typically remains fairly smooth. From Viginia Tech's tree guide:

Bark: Reddish brown with numerous lighter lenticels on very young stems, later turning gray to white and very chalky; remains smooth and generally does not peel.

B. pendula (European white birch) bark is also described as being smooth and only somewhat peely. From Virginia Tech:

Bark: Reddish brown with light lenticels when very young, later turning white, generally smooth but does peel a bit; the base of the tree develops thick bark which splits into narrow, vertical furrows which are nearly black.

However, the branches in the OP's picture are not drooping as is also common for B. pendula (AKA the European weeping birch). So this is not our tree!

Also, some sources describe paper birch as simply being smooth (vs. emphasizing the peeliness). See here for an example.

Here are images of European white birch (left) and gray birch (right) :

But Gray birch remains smooth, even at the base of the tree (though see here)...
Pay attention to the bottom of the trees in the OP's picture. The bark at the base of the trees is becoming furrowed:
Zoomed in OP picture:

This base furrowing is a characteristic of P. tremuloides:

According to the Virginia Tech Tree Guide (my emphasis):

Bark: At first smooth, creamy yellowish-white to very light green; later developing thick furrows and becoming dark, especially near the base.

And according to The Sibley Guide to Trees  (my emphasis):

Bark color from white to greenish, grayish, or bronze. Bark smooth, pale with dark scars that persist for many years; base of trunk becomes coarsely ridged grey on old trunks.

And from the NDSU Agriculture webpage (my emphasis):

Bark Color - Varies from chalky white to olive-gray, and becomes rough furrowed on the lower trunk of mature trees.

[Note: I give all 3 sources to demonstrate the inconsistency in description of P. tremuloides bark color].

Here is a close-up of furrowed aspen bark from the USDA website (yes, this is still aspen):

However, this furrowing can also occur in paper birch.

From V tech (my emphasis):

Bark: Reddish brown with light lenticels on very young stems; later turning chalky to creamy white, peeling in horizontal papery strips; brown to black and may be furrowed at base; orange inner bark.

From Field Guide to Trees of North America (my emphasis):

Bark white papery; older trees have rough black bark near base.

I will comment that I have never seen paper birch with furrowed bark at the base. Further, I was unable to find visual evidence from any reputable sources by searching on Google.

So what about tree shape and form?
Again, according to The Sibley Guide to Trees:

[P. tremuloides has a] single main trunk with relatively stout , jagged twigs (unlike more slender and graceful twigs of birches).
[B. papyrifera] branches begin lower on trunk than in aspens; more graceful, ascending, and regular with slender straight twigs. Mature tree has oval habit, few strong branches, clumps of fine twigs in the crown.
[B. populifolia has] typically multiple leaning, crooked trunks and narrow crowns. Bark of mature trunks grayish white, nonpeeling.

Citing a different source (Field Guide to Trees of North America) to address different language to differentiate the species:

[P. tremuloides:] Small to medium-sized tree. slender trunk; pyrimidal to round crown of spreading branches with sparse foliage.
[B. papyrifera:] Medium-sized tree. One to several slender, straight trunks; narrow to broad crown; branches upraised in youth, often becoming horizontal or drooping in age
[B. populifolia:] Small tree. sometimes shrubby; One to several trunks; narrow, conical crown.

The smaller trees in the front left of the OP's picture demonstrate a more birch-like architecture and have branches growing along the stem as the description for B. papyrifera describes. These qualities are reduced or eliminated in the larger trees in the OP's picture.
For visual clarification, the typical pyrimidal crown shape of P. tremuloides is shown below (from Oregon State Department of Horticulture). The trees in this image appear more slender (pyrimidal) than the trees in the OP's image, but aspen trees can also have "round" crowns as stated above.

The following photo from Michigan State University Extension's Tree ID Key attempts to demonstrate a difference between paper birch and aspen crown coloration:

The crown branches/twigs visible in the OP's picture seem to be lighter colored, and so this line of evidence points to aspen.

Ok, so what about size? According to Field Guide to Trees of North America the typical sizes of the species under question are fairly similar, but with gray birch being smaller than the other two species:

Quaking Aspen (Populus tremuloides) = 30-70' tall, 1-1.5' diameter
Paper Birch (Betula papyrifera) = 50-70' tall, 1-2' diameter
Grey Birch (Betula populifolia) = 20-30' tall, 0.5-1' diameter

The relative sizes of the trees in the OP's picture don't seem to preclude any of these species.
Both birches and aspens develop yellow leaves in autumn, so this characteristic additionally is not useful for differentiating the two genera (or 3 species).

Though @fileunderwater is correct in stating that birches have horizontal lenticels that are helpful in identifying birch trees, the OP's image is far too zoomed out to make out any lenticels (even when zooming into the OP's picture). Those black spots are not lenticels; they are scars (generally from lost limbs). Regardless, other species (including some aspen species) also develop lenticels.
Here is a close-up of lenticels. The little slits are birch lenticels (here from B. papyrifera):

Names on files and webpages are notoriously incorrect so using that as a line of evidence is dangerous. I saw a number of misidentified species in pictures while I was searching myself.

So thus far it seems as though aspen is a pretty good choice, but paper birch could also be potentially correct. The distance of the picture makes this distinction difficult, but I will point to the two lines of evidence that have convinced me that some of the trees are in fact paper birches.

The girth and shape of the larger trees are more consistent with the growth form of birches vs. the usually slender, single-stemmed aspen.
In the OP's picture, you cannot see peeling or lenticels, but this might be due simply to the distance from the trees. However, you can see a brownish/orangish coloration on a number of the trees, which is consistent with numerous descriptions of paper birch trees that have already started peeling revealing brown/orange bark.

Conclusion = Hard to tell, and likely actually a mix of Paper Birch (Betula papyrifera) and Quaking Aspen (Populus tremuloides). I think you're looking at taller aspen and mostly wider paper birch.

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


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What are mouse LS cells?
I have seen the term "mouse LS cell" used in several papers now, but I haven't found an explanation for the origin of these cells (for example, this paper).
What are mouse LS cells? What is their origin (besides coming from mouse!)?

Not an easy question, but I got some references about it.
Mouse LS cells are Fibroblasts growing in suspension culture, the paper in reference 1 has this paragraph in its Materials and Methods section:

This cell line seems to be in culture since the 1940s, as the reference to Sanford, Earle and Likely, 1948 suggests. Digging up this reference (number 2 below) tells a bit more about the isolation:

The cells of this study were from Earle's strain
  L (6), which originated from normal, subcutaneous,
  connective tissue of an adult C311 strain
  mouse.

Reference 6 in the Sanford et al. paper is:

EARLE, W. R.: Production of malignancy in vitro.
  IV. The mouse fibroblast cultures and changes
  seen in the living cells. J. Nat. Cancer Inst, 4:
  165-212 (1943).

which gives no further details. It is a methodic paper which analyzes the conditions necessary for cell culture - interesting on a historical point of view, since the techniques where developed at that time. The full PDF is linked in reference 3.
About the name I need to speculate a bit, but since the original cells where named "Strain L", and LS cells where derived from there to grow in suspension, it might translate into Strain L Suspension cells.
References:

The Uptake of Amino Acids by Mouse Cells (Strain LS) During Growth
In Batch Culture and Chemostat Culture: The Influence Of Cell Growth
Rate
The Growth in Vitro of Single Isolated Tissue Cells
Production of Malignancy in Vitro.


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Negative feedback loop and oscillations
According to the textbook Alberts Molecular Biology of the Cell (5th ed., p. 902), negative feedback loops cause oscillations when they are long delayed. I just can't figure out why.
Except for that, in case of short delayed feedback, the inhibition doesn't seem to be full and to go down only mid-way, according to the attached plot. Why?

It is nice to see that MOBTC has included some stuff on systems biology. The edition that I read did not have these.

Heyyy look at almost similar another http://electronics.stackexchange.com/questions/243977/what-will-happen-if-the-output-from-a-not-gate-injected-back-to-its-own-input and wikipedia article https://en.wikipedia.org/wiki/Ring_oscillator

For that you would need to understand the dynamical systems theory behind the loop. The point at which the oscillation starts is called the Hopf-bifurcation. I shall explain this in simple intuitive terms. Lets assume that Protein-X activates the production of Protein-Y which in-turn causes inhibition of Protein-X production. This is a negative feedback loop.
X → Y
Y ⊣ X
Situation-1: No/little delay
You switch on the production of X. This leads to rapid production of Y which will in-turn quickly repress the formation of X. This would happen so quickly and all that would be observed is a reduction in the steady-state level of X (compared to an unregulated system). Mathematically, the eigenvalues of the system (jacobian matrix- denotes the slope of the function) evaluated at the steady state would be negative and real.
Situation-2: Some delay
In this case, it will take some time for Y to accumulate. This will cause X to shoot up above its final steady state level. This, in-turn, will cause higher production of Y. Because of higher production of Y, X will start getting repressed strongly when Y gets accumulated and starts acting. This will cause X to shoot down below the steady-state but the magnitude of this shoot-"down", will be less than the first shoot-"up". Finally, the system will settle to the steady state. This phenomenon is called damped oscillation. In this case, the eigenvalues of the jacobian are complex with negative real parts.
Situation 3: long delay
In this case the delay between production of Y and its action is so high that the system does not damp but sustains its oscillations. The eigenvalues of the jacobian are imaginary. These kind of oscillations are generally sensitive to different factors.
More robust forms of oscillations exist, called limit cycles. The network structures responsible for this are more complex than a delayed negative feedback loop. Typically it has a coupled positive and negative feedback. Understanding limit cycles is little bit more complicated and I shall not discuss them here.

Also, check out these reviews:
Tyson, John J., and Béla Novák. "Functional motifs in biochemical reaction networks." Annual Review of Physical Chemistry 61 (2010): 219.
Tyson, John J., Katherine C. Chen, and Béla Novák. "Sniffers, buzzers, toggles and blinkers: dynamics of regulatory and signaling pathways in the cell." Current Opinion in Cell Biology 15.2 (2003): 221-231.
and this book:
Alon, Uri. An introduction to systems biology: design principles of biological circuits. CRC press, 2006. ISBN 9781584886426

This was our causal loop.

Fig-1 Our situation
Oscillation is simply an up and down of something, occurring in repeat with time. Now let's see why it causing an oscillation.

Fig 2.  Analogy with toilet siphon. C = Cause. E = Effect. E(min)= minimum value of effect . E(max)= maximum value of effect (as much allowed by time delay).
I've compared here this process with a toilet siphon.
Here I've considered the constantly adding up water from tap; is cause. As in your case, Enzyme-E is always present at the left side.
In my case (siphon), the water-level is the effect (In your case it is phosphorylated enzyme (EP), that may present at right side, or may not, if inhibition is high.)
Step-1: starting point: cause is applied
Step-2 : Since inhibition take-place a while latter, your EP adds up (my water level goes up). The dotted inhibition sign on fig2 indicates it yet not reached to the target.
Step-3: When a certain time passed, no-more EP accumulates in your system-of interest. Because inhibition starts. In my case, siphon-effect starts, and water level decrease.
Step 4: Ongoing inhibition decrease the result (in your given-case it is phosphorylation product EP, in my case water siphon it is water level. The siphon start pump out some water.)
Step 5: At next stage, your product EP become so low-concentration, that feedback became feeble, and once stops. In my case, the water level come down below siphon input. so siphon-effect stops.
And Step 6 (Similar to step-1)the process repeats once again.

See also:
what will happen if the output from a not gate injected back to its own input
Ring Oscillator

Any Feedbacks are welcome.

One of the conditions for oscillations in a negative feedback system are delays. The question is how much of a delay and what do we even mean by a delay? Imagine a sine wave signal being transmitted along the pathway:
-> x1 -> x2 -> x3 -> x4 -> etc
As the signal moves from one species to the next it will get delayed because it takes time for species to accumulate and empty. Using a sine wave is useful because the delay will be related to shifts in the sine wave itself. It is possible to show that the maximum delay a sine wave can experience at each species is 90 degrees.  See figure below. The blue wave is the wave we see at x1 and the red wave is approxiamtely the one we see at x2. Notice it has been pushed to the right 90 degrees.

For the linear pathway above, the delay at x2 will be up to 90 degrees, at x3 another 90 degrees (180 relative to x1) and another 90 degrees at x4 (total of 270 relative to x1). The actual amount of delay will depend on the frequency of the wave, the higher the frequency the more likely it will experience the maximum delay.
Now consider a system where x4 negatively feedbacks to the reaction x1 -> x2.
In a real system we won't be injecting a sine wave but there will be noise and that noise will contain many frequencies including one where the phase shift at x4 will be exactly 180. Note we can't get exactly 180 at x3 because we can only approach 180. Consider now that a noisy signal has been shifted exactly 180 degrees at x4, this signal is transmitted back via the negative feedback to the reaction x1->x2. Guess what the negative feedback does, it shifts the signal by another 180 degrees (eg a 0 turns into a 1 and a 1 turns into a 0, it inverts the signal), therefore the full phase shift is now 360 degrees. This means instead of the dampening down disturbances the negative fedback will actually  start to amplify them. The negative feedback has turned into a positive feedback. At this point, the system becomes unstable. The instability doesn't cause things to go to infinity however because of physical contraints and nonlinearities in the system. This explains why it is impossible to get sustained oscillations in a negative fedback with only one step or two steps, oscillations only occurs when you have three steps inside the signal loop because that is the only time you can actually get a 180 phase shift.
The other thing to note is that one other thing needs to be present for oscillations to occur, even if you get a positive feedback. That is the instability has to be amplified, if the instbility is dampend as it goes round the loop nothing will happen. Therefore the other condition, the so-called loop gain, has to be at least one. This can be achieved is there is cooperativity of the signal molecule on the inhibition site.


text:
Do we vaccinate sick people?
As I understand, vaccination helps the human body to create antibodies and stimulate immune system to react against specific antigens. If someone gets sick, do vaccines help to stimulate immune system? If so, do we vaccine sick people for some specific disease?

This at the moment could be construed as being quite broad. An example of a post exposure vaccine would be rabies. Source from WHO. There are likely many more examples.

@James Your comment is quite good and may be developped and promoted to an answer. It provides keywords ("post exposure vaccine") and example to answer the question.

Yes. Sick people are occasionally administered vaccines. But you need to keep in mind the mechanism of action of vaccines.
Broadly speaking, there are two types of vaccines.
Active immunization works by exposing the immune system of an individual with a pathogen (be it organism or derived proteins, etc). This type of immunization results in development of adaptive immunity in the individual, with long lasting effect; but it can days or weeks to fully develop.
On the contrary, passive immunization works by directly administering protective agents (antibody, etc). This will provide the individual with almost immediate protection; but will not lead to development of adaptive immunity, and thus will be short-lived.
You may find this wikipedia article informative.

Hi at welcome to Bio.SE! This is a good answer and overviews vaccines neatly, however you've glossed over the core of your answer to the question. Could you provide some examples of situations where sick people have been administered vaccines?

HI James. Thank you. A common example is a tetanus vaccine. I believe if people are thought to have a potential exposure, as in an accident, etc and do not remember whether they are up-to-date with their vaccination, they will get passive immunization for immediate but temporary protection. Other examples are small-pox, chicken-pox, hepatitis A & B. There is a more comprehensive list under "FDA licensed immunoglobulins" on this wiki page.

Are you sure passive immunization is vaccination?

The only case I can think about is postexposure vaccination against rabies.
As rabies virus proliferates unnoticed by the immune system, immediate vaccination after exposure is one of possible treatments (and the first one successfuly used).


text:
What is the function of the kidney in terms of osmoregulation and excretion
Also include the role that ADH plays
I am fully aware that ADH has a role in osmoregulation  but does it also play a role in exretion?

This seems like a homework question. Per the community guidelines, homework questions are off topic unless you've shown an attempt at answering the question or doing research. I suggest looking around online for information regarding ADH. Wikipedia is a pretty good start for information regarding the hormone's role in osmoregulation/excretion.


text:
Average Beginning of Action Potential in ECG by t-f HRV
I have some ECG data where I am estimating the average beginning of the action potential.
I am interested in the discrete Fourier analysis of joint t-f HRV when input data is ECG.
Frequency domain method here - a simplification of the joint t-f HRV.
However, I am uncertain how this method works because I see several limitations and mistakes in designs of several systems. There are also several publications about the topic, but little has been peer-reviewed. Also little data and research systems are publicly available for reviews.  According to @Christiaan (see comments), ECG shows compound action potential which is most likely detected by detecting R peaks.
In HRV analysis, they do currently
Estimate R-R interval in time and frequency domains:
Consider an estimate of R peaks.
It is not always the maxima.
There can be two peaks of equal length at maximum.

I think, in including two R peaks, they think they cancel the error of estimating the start of R peak, although the uncertainty actually increases. I think this is wrong in ignoring the uncertainty about the estimate of the start of R-R or simplifically the start of AP.
I think we should be able to estimate the precise location of action potential better.
They are using commonly exclusion principles which lose much original signal and decrease sensitivity

by excluding small time, frequency $|x|, |\eta| \in \mathbf R$ by choosing the window $w$ such that $w(t) \approx 0 \approx \hat{w}(\eta)$.
by excluding one beat normal beat before and after each ectopic beat.
system fails if more than 20% of ectopic beats.
system fails in 24h recordings because of computational issues of longer segments - so limiting to 5 minutes and averaging.

My Exclusions and Hypothesis
To detect the exact beginning of the action potential $s$ value $s(x) \in \mathbf R$ at exact instance $x \in \mathbf R$ is unpractical.
Instead, I measure some averages of the signal: $A_{\sigma} s(x) := \int_{\mathbf R} x(y) \varphi_{0,\sigma}(y-x) dy$ where $\varphi_{0,\sigma}$ is 0-average-valued $\sigma$-variance of normal density function.

$A_{\sigma} s(x) := \int_{\mathbf R} x(y) \varphi{0,\sigma}(y-x) dy$.
No windowing function so including also small time, frequency $|x|, |\eta| \in \mathbf R$.

Processes limiting to detect the beginning of action potential

Technical processes (fine with these)
HR Saturation process.
HR Recovery process.

I am very interested in how you can characterize HR saturation process and the HR recovery process.
I think they are using individual signals measure in three circumstances: Paced, Exercise and Recovery, here.
How can you characterise differences between such circumstances?
Views
Labview (most likely LabVIEW Biomedical Toolkit) or Matlab (which should be fine!)

ECG,
R-wave detection,
IBI signal (Inter-Beat Interval),
Expanded ECG,
HRV spectrum.

I do not understand the reason which component is requiring to use Labview here and most likely its Biomedical Toolkit in the analysis like in 4. I sent a message to the developer about the thing but waiting for an answer. Why? I would like to use Matlab, but I need to know if there can be some electronics that limits you and is only suitable for Labview. I have built my own ECG boards and systems with mostly Analog Devices' electronics.
How is the R-wave detection done? I think this can describe the challenge better about the beginning of the action potential.
Which channel(s) is/are used precisely in the view ECG? How can the electrical activity view be created? Summation of all channels in steady intervals? I think we should not exclude things now but it can be later done if some some anatomical/physiological reason is found.
What is precisely the Expanded ECG?
How does the expanded ECG allow you to evaluate the mean electrical axis?

I think another problem with such views is that they are not fixing the mean electrical axis. However, I may be wrong, since I do not understand the definition of ECG view and expanded ECG view. How are you considering ECG channels here?
Joint time-frequency domain HRV
I am interested in how you associate frequencies (high, mid, low) with different intrinsic, autonomically-modulated periodic rhythms.
I only see in slides the following link without an association
High Frequency = 0.25 Hz (15 cycles/min
Low Frequency = 0.1 Hz (6 cycles/min)
Very Low Frequency = 0.016 Hz
(1 cycle/min)

Adapted from the presentation here and here but changed for t-f
N-N - normal-to-normal
To calculate a standard deviation of a series of numbers:
[0. missing step about location of action potential]
1. Find the average in R-R intervals [4]
2. Calculate the differences between each number and the average
3. Square each difference (so they don’t cancel out)
4. Sum
5. Divide by number of datapoints
6. Take square root
...
n. no interpolation because FFT

How can you estimate the average beginning of the action potential in the joint t-f domain?
I think you measure the distance between two peaks and count the variance.
Sources

https://www.heartmath.org/research/, organisation about the field.
Pruneti, C. A, and McCraty, R. Very interesting presentations about the topic.
www2.unipr.it/~cprunet9/files/Heart-Rate-Variability.ppt, one example of HRV presentation.
BME 333 Biomedical Signals and Systems, J. Schesser. https://web.njit.edu/~joelsd/signals/classwork/BME314signalscw12a.pdf About R-R intervals in time and frequency domains

The question is unclear; 1) ECGs don't show action potentials, but compound action potentials. 2) an image of a waveform would help 3) what is some analysis of channels' function? and 4) with sensitivity - sensitivity is dependent on the hardware, you might be talking about accuracy? And that is a subjective term, what is accurate? And for that matter, what is sensitive? Explain please.

A start of something in the frequency domain is impossible. That's why it is called frequency domain.

There is no time interval in the frequency domain.

@Christiaan Yes, you are right. There is a time interval in the joint t-f.


text:
How to cut out a specific named gene from plant DNA
Suppose one has extracted RNA from a plant, converted it to the corresponding cDNA & amplified it but now wants to cut out a particular, already-sequenced gene out from it, how does one proceed?
i.e. How does one cut out that particular segment of the whole DNA which one wants? Does one always find restriction sites (or rather cleavage sites)  at both ends of the desired gene segment & then one treats the cDNA sample with those specific restriction enzymes?
To get the gene shown below I'd find an enzyme that cuts at the GGCCAC site and another to cut at AAAAAA?

You could also PCR amplify the gene using primers with fitting restriction enzyme recognition sites (+ some extra bases) on the ends.

PCR, as Chris suggested. Also, when you made the cDNA library, you don't really have "whole DNA" as you suggested, but many pieces of DNA corresponding to the mRNAs you extracted. Some of those should be the gene of interest and can be amplified.

@user137 Thanks! Must one go through the mRNA & cDNA  stages? Or is there an easier way to get the gene? e.g. Can't one extract the DNA itself from the plant cell nucleus. Why start from mRNA? Sorry if some of my questions are naive.

mRNAs are generally used because they tend to have a much higher copy number than genomic DNA and because the introns are already removed, so you are left with the coding sequence. You can isolate genomic DNA and do PCR directly off that, but the introns will be there, potentially making for a much much much larger gene. If you just want the exons, use the mRNA -> cDNA approach. It should be pointed out that if you want to express protein in bacteria, the introns will probably not be removed properly on transcription, so the protein won't be right.

@user137 Makes a lot of sense now the way you described it! Thank you.


text:
Problem with phosphorylated and total forms of antibodies
Antibodies are available that can detect both phosphorylated and total endogeneous levels of the given protein. I have a question here, why is it necessary to have equal amounts of total protein? This is a common assumption that variations come in phosphorylation status but since total detects levels of both phosphorylated and non-phosphorylated forms, it is supposed to be equal. Not necessarily! Depending on the requirement of cells, phosphorylation status may change. And so does the expression of the total protein itself specially if the non-phosphorylated form is acting as a transcription factor.This is what I find in my studies as well. But the literature suggests the opposite. Why?


text:
Are there examples of selection on males influencing female phenotypes?
I've been studying selection on female body color in a sexually dimorphic species and am intrigued by the possibility that selection on males, whether it be through sexual or natural selection, may influence the color of females. I think pleiotropic interactions may lead to this, or maybe some sort of genetic linkage.
A hypothetical example may be that selection for red dewlap color in anoles results in more melanic females.
I'm having trouble finding examples of this but I think it's a real phenomenon. Does anybody know examples of this occurring in a sexually dimorphic species?

Selection in one sex can produce a correlated response in the other when there is pleiotropy (or linkage disequilibrium) (see Lynch & Walsh 1998, and Lande 1979 & 1980).
Genes can be considered pleiotropic when they affect more than one trait, for example; the male and female forms of equivalent traits, and this can be seen as covariance between the sexes. Cross-sex covariance is common (see Bonduriansky & Rowe 2005, Poissant et al. 2010, Lewis et al. 2011, Griffin et al. 2013, and Blows et al. 2015 for good examples). This means that selection in one sex will often lead to a response in the other.
The correlated response to selection is captured within Lande's multivariate breeders equation, where the change in a vector of traits ($\Delta \bar{z}$) is a result of the genetic variance-covariance matrix ("G-matrix", $G$) multiplied by a vector of selection on the traits ($\beta$).
$\Delta \bar{z} = G \times \beta$
If covariance is zero (i.e. genes have independent male and female effects) then selection does not produce a correlated response in the unselected sex. However, cross-sex covariance is generally present, so correlated responses to selection should impose constraint on the evolution of sexual dimorphism under sexually antagonistic selection. Note that the within-trait cross-sex covariance is in the diagonal elements of the B-submatrix.
One good example of selection on one sex producing a response in the other is this paper. The authors selected on male mandible size in replicate populations of broad horned flour beetles. The mandible is a male limited secondary sexual trait, but selection on the mandible in males produced changes in female fitness and female traits. Selection for larger (smaller) male mandibles resulted in significantly decreased (increased) female abdomen size, and reduced lifetime reproductive success.

"We find that females from populations selected for larger male
  mandibles have lower fitness, whereas females in small-mandible
  populations have highest fitness, even though females never develop
  exaggerated mandibles."

One thing that is really quite cool about that experiment is that the response came in a non-equivalent trait, i.e. it was not female mandibles but other traits that evolved. There is generally less prior probability that there will be a cross-sex cross-trait covariance unless the traits have clear links.

Thank you very much for the detailed answer! I will definitely check out the papers you suggested. I can't upvote your answer until I gain more reputation, but will when I can.

@Connor I ignored genetic linkage in my answer, generally that is transient (recombination will breakdown the genetic correlation relatively quickly compared to pleiotropic genetic correlations), so is of lesser consequence to evolution in the bigger picture (see Lynch & Walsh).


text:
Blood clumping in mosquitos
Will a mosquito die due to blood clumping if it sucks blood from two people who have different blood groups? What will happen in its gut? Is there any mechanism to avoid clumping? Or do mosquitoes know what group it should suck?

Mosquitoes are not affected by blood clumping as they have to digest blood (cells, proteins, etc.) to assimilate them.

Female mosquitoes need blood for laying their eggs. This actually means that they need a source of rich protein and iron for their kids and hence, prey on us.
It is worthwhile for us to pause here and ponder over the difference between clumping and clotting before proceeding to the actual answer.
Agglutination tests as you may have come across are essentially antigen antibody reactions visible to the naked eye. Antibodies and antigens (on the RBCs) bind leading to the clumping that you talk of.
Clotting on the other hand is a complex set of reactions involving the thrombins and the platelets.
When a person is transfused of a wrong blood type, as in blood of another group is injected into his blood, something very bad is ought to happen. The clumping is extensive (an immune reaction) which leads to a clotting reaction, leading to a condition called DIC (Disseminated Intravascular Coagulation). This is an emergency situation since there can even be Acute Kidney failure.
Coming to the mosquito,

In the human case, we injected into the blood. Here it gets into the gut. The gut has enzymes which breaks down the proteins. Theres no antibody no antigen left out there!! Proteolytic enzymes start right from the very beginning.
Even if some clumping occurs, it doesn't actually matter. It mattered in the human case since it was a transfusion and the sequelae mattered.
Another important thing to keep in mind is we are talking only of clumping and not clotting. The mosquito takes care of clotting by secreting anticoagulants into the blood stream right when it is ready to have it meal. Clumping on the other hand, per se, doesn't turn the blood into a clot. If you have seen blood clumping in agglutination test, its not such a dramatic thing to occur. The blood still stays in liquidy. So clumping wouldn't pose much of a problem.

Hope this helps! Sorry but the climax wasn't that dramatic :)

interesting answer... do you have some citations/preferred sources so users can read more?

Maybe I could add that mosquitoes digest the blood before biting again, assuming they got all they needed in the first place


text:
To what group does coconut plant belong?
I've tried looking it up but I couldn't find an answer. Could someone please tell me to what group of plants do coconuts belong depending upon the natural availability of water?

what do you mean by "group" (https://en.wikipedia.org/wiki/Taxonomic_rank) and what relevance is the availability of water?

I mean it's neither in halophytes nor in hydrophytes. Does it have a separate classification on the basis of availability of water in its natural habitat?

In terms of taxonomy and morphology:

Although coconut trees display considerable morphological diversity,
  they are considered taxonomically a single species (and the only
  species) within the genus Cocos. Based on stature and breeding,
  coconut cultivars can be divided into two groups: tall and dwarf.
  The former typically grows up to 35 to 40 meters and is mainly
  outcrossing, whereas the latter can only grow up to 25 to 30 meters
  and usually is selfing. Dwarf coconuts, which are less common than the
  tall variety, are usually found growing close to humans and have
  traits that likely result from human selection.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0074736
I've found little information about whether or not they are halophytes, hydrophytes, xerophytes,or mesophytes - but according to a Google Book, a number of crops are widely cultivated in non-saline soils, including Cocos nucifera (coconuts). Another Google book with a lot of information about coconuts states this: Some experiments show that a small quantity of salt added to the tree roots is beneficial.
Cocos nucifera also love sunlight, so they can be considered heliophytes.


text:
Can soap kill cockroaches and/or ants? If so, how?
Is it possible to use dishwashing soap as an alternative insecticide? How would that and what are the components of the dishwashing soap that would kill the insect?

please read the help pages before posting questions

I'm not completely confident that the aforementioned post is a duplicate, because the question explicitly asks "Why do cockroaches burst from soapy water?" While this question explicitly asks "Can soap kill cockroaches and/or ants?"
The short answer to your question is yes.
According to this website:

The soapy water kills [cockroaches] by forming a thin film over the
  roach's breathing pores that stays in place due to surface tension,
  causing the roach to suffocate.

Ants are killed in a similar manner (see this archived Reddit post).
For a more scientific read, check out this paper: Behavioral Responses and Mortality in German Cockroaches (Blattodea: Blattellidae) After Exposure to Dishwashing Liquid.