Phosphoanhydride bonds contain lots of stored energy, with a  of . This energy, when released during ATP hydrolysis, can then be used for various anabolic pathways.

Diffusion and facilitated diffusion are methods by which molecules can pass through membranes without the use of ATP. Even though facilitated diffusion does require a channel to function, movement is still controlled by differences in concentration gradients. Primary active transport uses ATP directly to drive molecules against their concentration gradients, and secondary active transport uses the pre-established electrochemical gradient from primary transport to create movement for other molecules - so it still does require ATP to function even though it is indirect.

Fick's law describes the factors that influence diffusion of molecules through a membrane. All of the variables listed as answer choices, if changed, can influence the level of diffusion that can occur through the membrane.

The correct Nernst potential for sodium is  and the correct Nernst potential for potassium is . The resting membrane potential for the cell membrane as a whole is about . 

For this question, we're asked to identify the correct measure that allows us to predict the direction of a chemical reaction. Let's take a look at each answer choice.

The change in enthalpy of a reaction, , represents the amount of heat energy absorbed by or given off in a chemical reaction. Generally, chemical reactions that give off heat tend to go in the forward reaction. However, by itself, enthalpy cannot predict the direction of a chemical reaction.

The change in entropy of a reaction, , represents the change in disorder of a chemical reaction. Generally, chemical reactions that become more disordered as they progress tend to be driven in the forward direction. However, this alone is not enough to predict the direction of a chemical reaction.

The temperature at which a reaction occurs is another important factor to take into account when deciding the direction in which a chemical reaction will take. Reactions tend to be driven forward when they give off heat in low temperature environments. Also, reactions tend to be driven forward when they absorb heat in high temperature environments. But, by itself, temperature is not sufficient to predict the direction of a chemical reaction.

The activation energy of a reaction represents the amount of energy that must be put into a reaction in order for the reactants to reach the high-energy transition state. However, activation energy only affects the rate of a reaction and not its direction. Reactions that have higher activation energies will necessarily have a harder time reaching the transition state, which is necessary in order for the reaction to progress. But activation energy does not affect the change in energy of the reactants and products themselves. In other words, activation energy is not concerned with the thermodynamics of a reaction, but rather with the kinetics. Thus, activation energy will not allow us to predict the direction of a chemical reaction.

Finally, let's take a look at the change in Gibb's free energy, . This measurement takes into account several other variables, including , , and temperature. In doing so, the  term allows us to accurately predict the direction of a chemical reaction, since it takes these other important factors into account. When the value of  is negative, this indicates a reaction that will be driven in the forward direction, because the reactants are losing free energy as they are converted into products. Conversely, a positive  indicates a reaction that is driven in the reverse direction. Put into the form of an equation,  takes the following form.

When  is negative, the reaction will occur spontaneously. So, if the change in enthalpy  and the change in entropy  are both positive,  will only be negative when temperature is high enough to make  greater than .

If the RBC is placed into a hypotonic solution, water will rush into the cell because there is a higher osmotic pressure in the cell than outside of it. The osmotic pressure in the cell will actually decrease as water flows in from the outside. Red blood cells do not have mitochondria.

The stomach: The lower pH will result in the drug being in the neutral form, and this less polar form will be able to pass through the membrane more easily and absorbed into the blood stream.

Remember that negative feedback means the production of a metabolite will prevent the formation of either itself or any other metabolite preceding it. Product D inhibiting the formation of product B is the only choice that satisfies the definition of negative feedback. 

To answer this question, we'll need to take a look at all of the answer choices and see which one of them does not display feedback inhibition.

Generally speaking, negative feedback mechanisms help ensure that a homeostatic set point will be maintained. Thus, negative feedback can be viewed as a process that helps to maintain an equilibrium level. In other words, when things begin to deviate away from a set point, negative feedback helps shift things back to that set point.

When blood pressure is low, one of the consequences of this is that the kidneys begin to decrease the rate at which they filter the blood. Because the vasculature of the kidneys is very sensitive to even tiny changes in its filtration rate, it is well poised to detect and alter blood pressure. Upon sensing a reduced filtration rate, the kidneys increase their production of renin. This enzyme goes on to initiate a chain of events that ultimately result in increased blood pressure. This heightened blood pressure, in turn, reduces the kidneys' release of renin. Thus, this is an example of negative feedback.

Conversely, when blood pressure is too high, this can put increased stress on the walls of the heart. When the walls become slightly more distended and stretched due to increased pressure, the atria can release a compound known as atrial natriuretic peptide (ANP). This peptide then goes on to affect several other physiological events that finally culminate in a decrease in blood pressure. The reduced pressure, in turn, causes the heart to turn down its secretion of ANP. Consequently, this is also an example of negative feedback.

Levels of sugar in the blood also need to be regulated, as having too low or too high of a concentration can have many adverse consequences. As expected after eating a meal, blood sugar levels rise. In order to ensure homeostasis, the pancreas increases its production of insulin, a hormone that enables many cells to take up glucose across their plasma membrane, which cause a reduction in blood sugar levels. Therefore, the secretion of insulin by the pancreas is yet another example of negative feedback.

We can also see negative feedback at the molecular level when considering the interaction of neurotransmitters with their receptors. In this hypothetical example, we're told that elevated levels of dopamine have caused down-regulation in dopamine receptors. What this essentially means is that because there has been so much dopamine hanging out near the post-synaptic membrane, the cell has been constantly affected by the presence of all that dopamine. In response, the cell has decided to turn down its production of dopamine receptors. This is a process that happens inside the cell, where the action of certain genes results in the synthesis of dopamine receptors that are eventually deposited in the cell membrane. By manufacturing less dopamine receptors, the cell will have a reduced capacity for responding to all that dopamine that's been outside of the cell. Thus, this is certainly an example of negative feedback.

Lastly, let's take a look at blood clotting. The blood contains a large variety of clotting factors. However, in the absence of tissue damage, there are regulatory mechanisms that keep these clotting factors inactivated. This is important, because if these clotting factors were able to from clots, unimpeded by any kind of regulation, the blood would end up clotting too much and thus the function of the circulatory system to carry nutrients and wastes throughout the body would be compromised. Under normal physiological conditions (meaning in the absence of any pathology or disease), blood clotting will only happen at sites of cell or tissue damage. Once activated by chemicals and other factors that are associated with injury, clotting factors begin to initiate an extraordinarily complex cascade that culminates in the formation of a clot. One such compound, known as fibrinogen, becomes converted into its active form, fibrin. Multiple fibrin molecules are then able to cross-link to help form the clot. As more and more clotting factors and fibrin molecules are assembled and assimilated, the result is that more and more clotting factors are recruited to the site of injury to help ensure that a clot forms. Although there aren't too many examples of positive feedback in biochemistry, this is one that stands out.