Excretion

The governing concept is removal of metabolic waste. Cellular reactions produce substances such as carbon dioxide, nitrogenous wastes, and excess water or salts; if they accumulate, they can harm the body. Their removal is called excretion, making option A correct. Taking in food is ingestion, pumping blood is circulation, and making oxygen is not the meaning of excretion.

The governing concept is the human excretory system. Kidneys continuously filter the blood, remove nitrogenous wastes such as urea, regulate water and salts, and form urine. Therefore option A is correct and the kidneys are considered the main excretory organs. The heart pumps blood, the stomach digests food, and a hair is not an excretory organ, although skin can remove small amounts of sweat.

The governing concept is excretion, the removal of metabolic waste products from an organism. Cellular activities produce substances such as carbon dioxide, excess water and nitrogenous wastes, which can disturb the internal balance if they accumulate. The body therefore removes them through organs such as kidneys, lungs and skin. Option A is correct. Nutrition supplies materials, transport moves substances, and respiration releases energy; none of these terms specifically means waste removal.

Excretion is the biological process by which metabolic waste products are removed from an organism. Cellular activities produce substances such as carbon dioxide, excess water, and nitrogenous wastes; their accumulation can be harmful. Therefore, option A gives the correct meaning. Taking in food is ingestion, whereas the other choices are not definitions of excretion.

Plants remove much of their excess water by transpiration. Water reaches the leaves through xylem, evaporates from moist leaf cells, and then diffuses out mainly through stomata as water vapour. This process also supports cooling and helps maintain the upward movement of water. Therefore option A is correct; digestion, blood circulation, and breathing are not the appropriate plant process here.

The governing concept is the distinction between nutrition and waste removal. Digestion is a nutritional process that mechanically and chemically breaks complex food into simpler, absorbable substances such as glucose and amino acids. Excretion removes wastes produced by metabolism, including nitrogenous wastes, excess salts, water, and carbon dioxide through appropriate organs. Therefore option A is correct; digestion does not itself mean urine formation, and the other choices confuse separate processes.

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.

A nephron is the structural and functional unit of the kidney. It filters blood, reabsorbs useful substances, and secretes certain wastes to form urine. A neuron conducts nerve impulses, so it is not involved in urine formation. Exam tip: Associate the kidney and urine formation with the nephron.