Respiration

The governing concept is coordination between gas exchange and transport. In the alveoli of the lungs, oxygen from inhaled air diffuses into the blood, while carbon dioxide diffuses out. The circulatory system then carries oxygen, mainly bound to haemoglobin, to body cells. Cells use it to release energy from food during aerobic respiration, and the blood carries carbon dioxide back toward the lungs. Therefore option A is correct.

The governing concept is the completeness of glucose oxidation. In anaerobic respiration, oxygen is unavailable or insufficient, so glucose is only partially broken down into products such as lactic acid in muscles or alcohol and carbon dioxide in yeast. Much of the chemical energy remains in these products, so less ATP is obtained than in aerobic respiration. Therefore A is correct; excess oxygen and light production are false, and carbon dioxide entry is not the cause.

The governing concept is anaerobic respiration in muscle cells. During intense or rapid running, the demand for oxygen and ATP can temporarily exceed the oxygen supply. Muscle cells then obtain some energy by partially breaking down glucose, producing lactic acid. Its accumulation is associated with fatigue, pain, or cramps after strenuous activity. Thus A is correct; muscles do not form starch, haemoglobin does not become bile, and digestion does not occur in lungs.

The governing concept is oxygen transport by haemoglobin. Haemoglobin in red blood cells binds oxygen in the lungs and carries it to tissues. Cellular aerobic respiration uses that oxygen to release energy from glucose. If haemoglobin levels fall greatly, the oxygen-carrying capacity of blood decreases, so cells may receive less oxygen and produce less energy aerobically. Therefore A is correct; the remaining choices involve starch, bile, or plant transport and are unrelated.