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.

The answer is "wound healing." In negative feedback systems, the product of the process will inhibit the process when it reaches a certain level. This is true whether that product is the actual product of an enzymatic reaction, or just a change in body temperature, blood sugar levels, or blood pH. This is because all of those processes are working to stay at a fairly precise level to maintain homeostasis. Wound healing, however, involves positive feedback. Platelets attract more platelets and induce other factors in the healing response.

Diabetes mellitus type II is when the cells do not uptake glucose from the blood in the presence of insulin. Exercise allows the activation of GLUT4, which results in glucose uptake from the blood without the need of insulin.

The GLUT1 transporter is a uniport member of the major facilitator superfamily. Glucose flux varies depending on glucose concentration as the transporter approaches maximum saturation. This, along with competitive inhibition, indicates mediated transport in GLUT1.

Hemoglobin exhibits cooperative binding, so each oxygen atom which binds allows the following one to bind with more ease (for a maximum of four). Hemoglobin unbound is initially in the tense (T) state, which contains 8 ionic bonds. These bonds cause the irons atom of the heme groups to be relatively non-planar with their surrounding protoporphyrin rings, which is less stable than them being planar. Each oxygen which binds causes 2 of these ionic bonds to break, allowing the iron atom to become more and more planar upon binding more oxygens. By the time four oxygens are bound, all 8 bonds have been broken and the hemoglobin is in its fully relaxed state, with the iron atoms stably planar with their rings.

A zymogen is a protein which is released as an inactive precursor and then requires some kind of modification (such as cleavage, hydrolysis, etc.) to become activated. An example is pepsinogen, which is released by chief cells in the stomach in an inactive form, which is then activated to become pepsin by hydrochloric acid in the stomach. Pepsin catalyzes breakdown of consumed proteins. All of the other answers are incorrect.

3-hydroxybutyrate is a ketone body, which accumulates as a result of an increase of glucagon. Increased glycogen synthesis, decreased glycogenolysis, and action of hormone-sensitive lipase are all results of an increase in insulin levels. 

In a hypertonic solution, the net flow of water will be from the cell into the environment, the process will cause the cell to lose water and shrink. This will be passive requiring no energy. In plant cells it is called plasmolysis, and in animal cells it is called crenation.