Life Processes

The governing concept is the relationship between surface area and diffusion. Alveoli are numerous, thin-walled air sacs surrounded by capillaries. Their large combined surface provides more area across which oxygen diffuses into the blood and carbon dioxide diffuses out. This makes gas exchange rapid and efficient, so option A is correct. Digestion, urine formation, and bile storage occur in different organs and are not functions of alveoli.

The governing concept is enzymatic digestion of different food components. Pancreatic juice enters the small intestine and contains amylase for carbohydrates, trypsin-type proteases for proteins, and lipase for fats. These enzymes convert large molecules into smaller substances that can be absorbed. Thus option A is correct. Oxygen transport, urine formation, and clotting are functions of blood, kidneys, and clotting factors rather than pancreatic juice.

The governing concept is the division of digestive functions among accessory organs. The liver produces bile, which emulsifies fats into smaller droplets and helps lipase act more effectively; it is not itself a digestive enzyme. The pancreas releases pancreatic juice containing enzymes that digest carbohydrates, proteins, and fats. Therefore option A is correct, while the other options assign plant or unrelated circulatory and excretory functions.

The governing concept is the dual role of stomata in gas exchange and transpiration. Open stomata allow carbon dioxide to diffuse into the leaf, supporting photosynthesis during daylight. However, the same openings permit water vapour to diffuse out, increasing transpiration and possible water loss, especially in dry conditions. Therefore option A correctly states both effects; the other choices combine unrelated animal organs or unsupported plant changes.

The governing concept is cellular respiration, which supplies usable energy to cells. Glucose acts as the respiratory substrate, while oxygen enables its complete oxidation in aerobic respiration. This process releases energy that is stored mainly as ATP and used for growth, repair, movement and other cellular activities. Therefore, option A is correct; the other options describe unrelated functions.

Life processes work as an integrated system. Digestion breaks complex food into absorbable nutrients such as glucose. Respiration uses these nutrients, especially glucose, to release energy. The transport system carries nutrients and oxygen to cells and moves wastes away. Excretion removes metabolic wastes and helps maintain internal balance. Thus option A correctly describes their connection; the remaining options deny or misassign these functions.

The governing concept is photosynthesis and the role of stomata in gas exchange. Carbon dioxide, a raw material for making glucose, normally enters the leaf through stomatal pores. If the stomata remain closed, carbon-dioxide entry becomes limited, so the rate of photosynthesis and food formation generally decreases. Option A is correct; closure does not increase oxygen entry, instantly stop root absorption, or destroy chlorophyll.

The governing idea is a controlled experiment using starch as evidence of photosynthesis. After destarching a plant, part of a leaf is covered so it receives no light while the remaining part is exposed. After exposure, iodine turns the illuminated region blue-black because starch formed there, whereas the covered region does not. This comparison supports option A and controls the effect of light.

Hydrochloric acid secreted in the stomach creates a strongly acidic medium and also helps activate pepsinogen into pepsin. Pepsin functions effectively in this environment and begins the digestion of proteins into smaller peptide fragments. Salivary amylase is inactivated by the acid, while maltase and lactase act mainly in the small intestine. Hence option A is the only correct answer.

Bile is produced by the liver and stored in the gall bladder. It contains no digestive enzyme, but its bile salts emulsify large fat globules into many tiny droplets. This greatly increases the surface area on which lipase can act, so fat digestion becomes more efficient. Therefore, option A is correct; the other choices describe enzyme-driven digestion or an impossible transformation.

Villi are numerous finger-like projections lining the inner wall of the small intestine. They greatly increase the available surface area and contain a network of blood capillaries and a lacteal. Consequently, digested nutrients can pass efficiently into the blood or lymph. Option A is correct; teeth chew food, the trachea carries air, and guard cells regulate stomatal openings in leaves.

Villi increase the inner surface area of the small intestine and bring absorbed nutrients close to blood capillaries and lymph vessels. If their number or size is reduced, the available area for absorption falls, so fewer digested nutrients enter the circulation. Option A is therefore correct. Chewing occurs in the mouth, air entry belongs to respiration, and clotting is a blood-protection process.

Peristalsis is the rhythmic, wave-like contraction and relaxation of muscles in the wall of the oesophagus. These involuntary waves push the swallowed food bolus downward, even when a person is not upright, until it reaches the stomach. Thus option A is correct. The oesophagus does not add light energy, filter food into blood, or direct food toward the lungs; those suggestions confuse separate body functions.

In aerobic respiration, glucose is broken down in the presence of oxygen through a series of reactions, ultimately producing carbon dioxide and water. Oxygen acts as the final acceptor in the energy-releasing pathway, allowing glucose to be oxidised completely and releasing much more energy than anaerobic respiration. Hence A is correct; light, chlorophyll and closed stomata are not requirements for this process in animal cells.

During strenuous exercise, the oxygen supply to working muscles may become insufficient for aerobic respiration. Muscle cells then obtain some energy by anaerobic breakdown of glucose, producing lactic acid. Its temporary accumulation is associated with fatigue, pain or cramps. Therefore, option A is correct. Glucose is the starting fuel, starch is a storage carbohydrate, and bile is a digestive secretion, so none of those is the substance described.

Yeast can release energy without oxygen by anaerobically breaking down glucose. In this fermentation pathway, one glucose molecule is converted into ethanol and carbon dioxide, with a small amount of energy released. Thus option A is correct. Lactic acid is the typical product in anaerobic muscle respiration, oxygen is a reactant in aerobic respiration, and starch, bile and protein are not the products of yeast fermentation.

Alveoli are numerous tiny air sacs at the ends of bronchioles. Their walls are only one cell thick, they provide a very large combined surface area, and they are surrounded by dense blood capillaries. These features shorten the diffusion distance and maintain efficient exchange: oxygen enters the blood while carbon dioxide leaves it. Therefore A is correct; digestion, urine formation and bile production occur in other organs.

In double circulation, blood passes through the heart twice during one complete journey: once between the heart and lungs, and once between the heart and the rest of the body. The four-chambered human heart keeps oxygenated and deoxygenated blood largely separate and pumps oxygen-rich blood efficiently to tissues. Therefore A is correct; the other options contradict digestion, blood composition or gas exchange.

The governing concept is stomatal regulation. Guard cells surround each stoma and change their turgidity when water enters or leaves them. When they become turgid, the pore generally opens; when they lose water and become flaccid, it closes. This regulates carbon dioxide entry and limits water loss through transpiration. Therefore option A is correct, while root length, flower colour and seed size are not directly controlled by guard-cell movement.

The governing concept is photolysis during the light-dependent reactions of photosynthesis. Light energy absorbed by chlorophyll splits water molecules into components; the released electrons and hydrogen ions support the reactions, while oxygen is liberated as a by-product and diffuses out of the leaf. The oxygen does not come from glucose or starch, and bile is unrelated to plants. Therefore option A is correct.

The governing concept is diffusion across a respiratory surface. In the lungs, the moist lining of the alveoli allows oxygen and carbon dioxide to dissolve before crossing the very thin alveolar-capillary membrane. This supports rapid diffusion down concentration gradients: oxygen enters the blood and carbon dioxide leaves it. A moist surface does not sweeten food, strengthen bones or clot blood. Therefore option A is correct.

The governing concept is efficient gaseous exchange by diffusion. Alveoli provide a large moist surface, and the surrounding capillary network keeps blood in close contact with the air across a very thin barrier. Oxygen therefore diffuses into the blood, while carbon dioxide diffuses from the blood into the alveolar air for exhalation. Close capillaries do not digest food, produce urine or make light. Hence option A is correct.

A nephron is the structural and functional unit of the kidney. Its filtration unit first filters blood, and the renal tubule then selectively reabsorbs useful substances and water while allowing wastes to remain in the forming urine. Therefore, its overall function is to filter blood and help form urine. Digestion occurs in the alimentary canal, oxygen is mainly carried by haemoglobin, and bile is produced by the liver.

The governing concept is excretion and maintenance of the internal environment. Healthy kidneys filter blood, remove nitrogenous wastes and excess water or salts, and form urine. When kidney function fails, wastes can accumulate to dangerous levels. During dialysis, blood passes near a dialysis fluid across a partially permeable membrane, allowing selected wastes and excess substances to diffuse out. It does not add food, fill lungs, or produce stomach acid.

Plants do not possess a specialised excretory system like that of animals, so they use several alternative methods. Some wastes can be stored in cell vacuoles, while others may accumulate in leaves, bark, or old xylem as resins and gums. When leaves or bark are shed, part of the stored waste is removed. Plants have no heart, lungs, or circulating blood system for permanent waste storage, so option A is correct.