Life Processes

Bile is important even though it contains no digestive enzyme. 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. Bile does not convert fat into oxygen; starch and urine are unrelated to this function, and it cannot change blood colour.

Villi are finger-like projections that greatly enlarge the inner surface of the small intestine. Digested nutrients pass through their thin lining, and the network of blood capillaries carries absorbed sugars, amino acids, minerals, and other soluble substances away. Therefore option A correctly combines absorption with transport. Urine formation, lung gas entry, and stomatal movement occur in different organs or structures.

The wave-like muscular movement is called peristalsis. Alternating contraction and relaxation of circular and longitudinal muscles in the alimentary canal produces a pressure wave that pushes food forward, even when a person changes posture. This maintains one-way movement from the oesophagus through the intestine. Therefore option A is correct; peristalsis does not make blood, produce bile, or open alveoli.

During intense running, the oxygen supply may not meet the muscles’ immediate energy demand. Muscle cells then partially break down glucose anaerobically, producing a small amount of ATP and lactic acid rather than completing oxidation to carbon dioxide and water. Lactic acid accumulation is associated with fatigue or cramps. Therefore option A is correct; photosynthesis, bile, and nephrons do not provide this pathway.

Alveoli are adapted for rapid diffusion because they have very thin walls, a moist surface, and a rich capillary supply. Thickening the alveolar wall increases the distance that oxygen and carbon dioxide must cross, so diffusion becomes slower and less efficient. Consequently, less oxygen may enter the blood in a given time. Therefore option A is correct; the other effects do not follow from wall thickening.

The governing concept is efficient gaseous exchange in the lungs. Alveoli have very thin walls and are surrounded by a dense network of capillaries. Oxygen diffuses from the alveolar air into the blood, while carbon dioxide diffuses from the blood into the alveoli to be exhaled. Their close contact shortens the diffusion distance, so option A is correct. The other options describe functions of digestion or excretion, not alveolar capillaries.

The governing concept is the role of haemoglobin in transport and aerobic respiration. Haemoglobin in red blood cells binds oxygen in the lungs and carries it to body tissues. If its amount is low, less oxygen reaches cells, so aerobic respiration may produce less usable energy for muscles. This explains tiredness and makes option A correct. The other choices incorrectly assign digestive, urinary or plant functions to human organs.

The governing concept is complete separation of oxygenated and deoxygenated blood in double circulation. The right side of the human heart sends deoxygenated blood to the lungs, while the left side sends oxygen-rich blood to the body. The septum and four chambers prevent significant mixing, allowing tissues to receive blood with a high oxygen concentration for efficient respiration and energy release. Thus option A is correct; the other choices are not heart functions.

The governing concept is adaptation of blood-vessel structure to pressure. Arteries receive blood directly from the ventricles, so blood flows through them at relatively high and pulsating pressure; their walls are therefore thick, muscular and elastic. Veins return blood at lower pressure and have thinner walls, wider lumens and valves to prevent backflow. Hence option A gives the main reason. Blood colour is not a permanent artery–vein distinction, and the other options are irrelevant.

The governing concept is one-way movement of blood in veins. Venous blood returns to the heart at relatively low pressure, and body movements help push it upward, especially from the legs. Valves open toward the heart and close when blood tends to move backward. Without these valves, gravity and low pressure could permit backflow and pooling of blood. Therefore option A is correct; the other choices involve unrelated organs or plant tissue.

The governing concept is diffusion across exchange surfaces. Capillaries form a fine network beside body cells and have walls only about one cell thick. This short distance allows oxygen and dissolved nutrients to move from blood to tissues, while carbon dioxide and other wastes move into the blood. Their thin walls are therefore best suited for exchange, making option A correct. Pumping is done by the heart, urine is stored in the bladder, and fat emulsification involves bile.

The governing concept is clot formation during blood clotting. When a blood vessel is damaged, platelets collect at the wound and help form a temporary plug; clotting proteins then strengthen it, limiting blood loss. If platelet numbers are very low, this initial plug forms poorly or slowly, so bleeding may continue even after a small injury. Therefore option A is correct. The remaining options do not describe platelet function or consequences of low platelet count.

The governing concept is transport of raw materials for photosynthesis. Xylem carries water and dissolved minerals upward from roots to stems and leaves. Water is a reactant in photosynthesis, and mineral ions support chlorophyll formation and enzyme activity. If xylem is blocked, the leaf receives less water and minerals, so photosynthetic food production may fall. Thus option A is correct; phloem transports food, while the other choices concern unrelated animal functions.

The governing concept is translocation through phloem. Leaves prepare sugars by photosynthesis, and phloem distributes these food substances to growing and storage organs, including roots. A damaged region can interrupt or reduce movement of sugars beyond that point, so roots may receive less food for respiration, growth and storage over time. Therefore option A is correct. Xylem carries water, and the other options incorrectly apply animal functions to roots.

The governing concept is the transpiration pull in the xylem stream. Water evaporating from leaf surfaces creates tension that helps draw water and dissolved minerals upward from the roots. This supports transport and cooling, but a hot, dry day can greatly increase evaporation. If water loss becomes faster than absorption, the plant may wilt and its stomata may close, reducing gas exchange. Hence option A correctly states both effects.

A nephron first filters blood under pressure, producing a filtrate that contains wastes but may also contain useful substances such as glucose, salts, and water. Selective reabsorption returns the required amount of these substances to the blood, while unwanted materials remain in the tubule and form urine. Therefore filtration removes materials from blood and reabsorption prevents excessive loss of useful substances, making option A correct. The other options describe unrelated processes.

The governing concept is selective reabsorption during urine formation. Filtration moves small substances from blood into the nephron tubule, and the filtrate can include water, glucose, amino acids, and needed ions as well as wastes. Reabsorption normally returns useful materials and much of the required water to the blood. If it stopped, these substances would remain in the filtrate and be lost in urine, causing dehydration and serious imbalance. Hence option A is correct.

Healthy kidneys filter blood and remove nitrogenous wastes, excess salts, and extra water while helping maintain the internal balance of the body. In kidney failure, these wastes can accumulate to harmful levels. During dialysis, blood passes along a selectively permeable membrane against dialysis fluid, allowing some dissolved wastes and excess substances to diffuse out before the cleaned blood is returned. Thus dialysis partly substitutes for the kidneys’ excretory function, so option A is correct.

Plants do not possess specialized excretory organs comparable to animal kidneys, so they use several ways to handle wastes. Some waste products can be stored in vacuoles or deposited in older tissues such as leaves, bark, and heartwood. When these parts are shed, fall, or are removed, the stored wastes leave the plant with them. Therefore option A explains the advantage. The other choices refer to animal structures and are unrelated to plant waste management.

Diffusion is effective over short distances when a cell has a large surface area relative to its volume and is directly exposed to the surroundings. A unicellular organism can exchange gases, water, and dissolved substances across its cell membrane in this way. Humans are large, multicellular organisms; many internal cells lie far from the external environment, and diffusion alone would be too slow to meet their oxygen and nutrient demands. Therefore option A is correct, while the other statements are false.

The governing concept is the interdependence of life processes. Digestion breaks complex food into soluble nutrients such as glucose, while breathing supplies oxygen. The circulatory transport system carries absorbed glucose and oxygen in the blood to body cells, where aerobic respiration releases energy. Thus option A correctly combines the roles; the other options assign digestion or transport functions that belong to neither process.

Aerobic respiration in cells uses oxygen to oxidise glucose and release a large amount of usable energy. If oxygenated blood mixes with deoxygenated blood, the resulting blood has a lower oxygen concentration than fully oxygenated blood. Less oxygen reaches tissues, so aerobic energy production can fall. Hence option A is correct; the other choices concern unrelated digestive or plant functions.

Arteries carry blood away from the heart, and this blood is generally under high pressure. Elastic arterial walls expand when the heart pumps and recoil between beats, helping maintain smoother flow and pressure. Loss of elasticity makes this pressure regulation less effective and may disturb blood flow. Therefore option A is correct; the other options describe unrelated digestive, plant, or kidney functions.

The governing concept is coordination among life processes. Nutrition supplies raw materials such as glucose, respiration releases energy from them, transport carries nutrients and gases to cells, and excretion removes harmful wastes. Each process supports the others, so failure of one can affect the whole organism. Option A gives this complete relationship; the remaining choices deny or misstate their functions.

Alveoli are tiny air sacs where oxygen diffuses into blood and carbon dioxide diffuses out. Their large number and clustered arrangement provide a very extensive, thin exchange surface. If alveoli are lost, the total surface area available for diffusion decreases, so gas exchange and oxygen uptake may become less efficient. Therefore option A is correct; the other choices are unrelated effects.