Cholesterol is essential for the synthesis of steroid hormones.

A. Diastolic:Diastolic pressure is the lower number in a blood pressure reading. It represents the pressure in the arteries when the heart is relaxed between beats, not the higher value.

B. Repolarization:Repolarization refers to the process of cardiac muscle cells returning to a resting electrical state after contraction. It is not directly measured in a blood pressure reading.

C. Systolic:Systolic pressure is the higher number in a blood pressure reading. In this example, 110 mmHg represents the arterial pressure when the ventricles contract, pushing blood into the arteries.

D. Depolarization:Depolarization is the process by which cardiac cells generate an action potential to initiate contraction. It is an electrical event and does not correspond to the numeric values of blood pressure.

A. Nitrogen:Nitrogen makes up approximately 78% of the air we breathe, making it the most abundant gas in the atmosphere. It is largely inert and does not participate directly in human respiration.

B. Water vapor:Water vapor is present in variable amounts depending on humidity but generally constitutes a very small fraction of air, far less than nitrogen. Its concentration is not sufficient to be the highest component.

C. Carbon dioxide:Carbon dioxide is present at only about 0.04% in the atmosphere. Despite its critical role in respiration and pH regulation, it is not the major constituent of inhaled air.

D. Hydrogen:Hydrogen exists in trace amounts in the atmosphere and plays no significant role in the composition of breathable air. Its concentration is negligible compared to nitrogen or oxygen.

E. Oxygen:Oxygen makes up roughly 21% of atmospheric air, making it the second most abundant gas. While essential for cellular respiration, its concentration is much lower than that of nitrogen.