Correct Answer: Option 3 Guard cells change the size of leaf openings, regulating the exchange of gases.

The guard cells regulate the stomata, which are microscopic holes in a plant leaf which allows gases to enter and leave and water vapor to leave as well. The ability of the guard cell to close during periods of limited water availability for the plant allows the plant to maintain water homeostasis. This is an example of feedback mechanism in plants. A feedback mechanism occurs when the level of one substance influences the level of another substance or activity of another organ.   Option 4 states about respiration, which is not a feedback mechanism of plants.

Option 2 is incorrect. Oxygen is a product of photosynthesis. Therefore, if there is decreased rate of oxygen, less oxygen will be also produced by the chloroplast. Carbon dioxide, not nitrogen, is used up by the chloroplast during photosynthesis. Thus, option 1 is incorrect.

Correct Answer: Option 3 low concentration→ high concentration (ATP used)

Active transport is the mediated process of moving particles across a biological membrane against a concentration gradient. Active transport uses energy, unlike passive transport, which does not use any energy. ATP, a form or chemical energy, is needed for this process to take place. Indeed, this setup is an active transport. Since it uses chemical energy, it is termed as primary active transport. If electrochemical gradient was used in the process, it is called secondary active transport.

Option 1 is incorrect because no energy is needed to move particles from high concentration to low concentration. Since there is no energy or ATP (adenosine triphosphate) needed for the process to happen, it is a passive transport.

Option 2 is incorrect. Just like option 1, no energy or ATP was used in the process therefore it is a passive transport.

Option 4 is incorrect. ATP is needed in order to transport particles from low to high concentration.

Correct Answer: Option 1 More oxygen is delivered to muscle cells

Various exercises require a predominance of certain muscle fiber utilization over another. Aerobic exercise involves long, low levels of exertion in which the muscles are used at well below their maximal contraction strength for long periods of time. Aerobic exercise, which rely primarily on the aerobic (with oxygen) system, use a higher percentage of Type I (or slow-twitch) muscle fibers, consume a mixture of fat, protein and carbohydrates for energy, consume large amounts of oxygen and produce little lactic acid.

Exercise has no direct effect on the rate of blood cell excretion, rate of digestion, and hormone production.

Correct Answer: Option 2 a feedback mechanism

It is a negative feedback mechanism. This is the special mechanism for turning the hormones off after they have done their job. When the blood sugar level drops, the amount of insulin produced also falls, and when blood sugar level has risen back to normal, the amount of adrenalin and glucocorticoids falls.

If you are going to be exercising for more than a couple of minutes, your body needs to get oxygen to the muscles or the muscles will stop working. Just how much oxygen your muscles will use depends on two processes: getting blood to the muscles and extracting oxygen from the blood into the muscle tissue. Your working muscles can take oxygen out of the blood three times as well as your resting muscles.

Correct Answer: Option 1

Correct Answer: The blood sugar level is the other indicator of decrease in the secretion of insulin.

When the blood sugar level increases beyond a standard count, it indicates that the insulin secretion has reduced.

Correct Answer: When a virus infects humans, the relationship that exists between virus and humans is that of parasite and host.

The virus uses the human body cells to dwell and grow; and eventually infect the other cells.