Excretion

The governing concept is excretion and internal balance, or homeostasis. Metabolic reactions produce wastes such as carbon dioxide, urea and excess salts. If these substances accumulate, they can alter pH and water balance, damage cells, and interfere with enzyme activity and organ function. Consequently, essential life processes are disturbed. Option A is correct; the other options incorrectly describe wastes as useful food, oxygen or plant regulators.

Excretion is the removal of metabolic wastes produced inside cells, such as urea, excess salts, carbon dioxide, and extra water. The removal of undigested food from the alimentary canal is called egestion, not excretion. Kidneys filter blood and form urine containing nitrogenous wastes, while lungs remove carbon dioxide. Therefore option A gives the correct definition; the other options confuse processes or deny the kidney’s role.

The governing concept is excretion and maintenance of the internal environment. Healthy kidneys filter the blood, remove nitrogenous wastes and excess water or salts, and form urine. When kidneys fail, these substances can accumulate and disturb body function. Dialysis uses a special membrane and dialysis fluid to remove some wastes and excess water from blood. Thus option A is correct; the other options concern unrelated organs or plant functions.

Metabolic reactions help cells obtain energy, but they also produce wastes such as carbon dioxide and nitrogenous compounds. If these substances accumulate, they can alter the internal chemical conditions and interfere with enzyme activity and cell function. Excretion removes or detoxifies such wastes and helps maintain a stable internal environment. Therefore option A is correct; wastes are not food, oxygen carriers, or a necessary product for energy formation itself.

The transport system carries nutrients and oxygen to cells, but it also collects carbon dioxide and other metabolic wastes from them. Excretion is required to remove these wastes through organs such as the kidneys and lungs. If excretion stops, wastes will remain in body fluids and blood, disturbing pH, water balance, and normal cell activity, eventually causing serious harm. Therefore option A is correct; the other choices are biologically unrelated.

Excretion and egestion differ in both the material removed and the process involved. Excretion eliminates metabolic wastes produced by chemical reactions in cells, such as carbon dioxide, urea, and excess water or salts. Egestion is the removal of undigested and unabsorbed food from the alimentary canal; it is not a cellular metabolic waste-removal process. Therefore option A gives the correct distinction, while the other options describe unrelated functions or processes.