Life Processes

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.

The urinary system uses two different tubes with different routes. Each ureter is a muscular tube that carries urine produced by a kidney to the urinary bladder, where urine is temporarily stored. The urethra is the passage through which urine leaves the bladder and exits the body during urination. Thus option A correctly identifies both directions and endpoints. The remaining options confuse these tubes with airways, food passages, blood vessels, or bile-producing organs.

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.

The trachea is an air passage leading toward the bronchi and lungs. Its lining helps trap dust and other particles in mucus. A cough is a protective reflex that produces a forceful outward flow of air, helping dislodge and expel the irritant so breathing remains easier. Thus option A is correct; the other options refer to digestion, excretion, or plant transpiration.

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.

Excretion removes metabolic wastes produced by normal cellular activity. The kidneys filter blood and eliminate nitrogenous wastes, especially urea, in urine. The lungs remove carbon dioxide and some water vapour produced during respiration. Thus both organs contribute to waste removal but handle different wastes, making option A correct; the other options incorrectly assign digestive, pumping, or bile-producing roles.

The governing concept is excretion in plants. Plants carry out metabolism, so they produce wastes even though they lack specialised excretory organs such as kidneys. Gases may diffuse out through stomata, while substances such as resins, gums and some wastes can be stored in vacuoles, leaves, bark or old tissues and removed when these parts are shed. Therefore, option A is correct; the other choices incorrectly apply animal organs or deny plant metabolism.

The governing concept is the interdependence of life processes. Nutrition supplies raw materials, respiration releases usable energy from food, transportation carries materials and gases to appropriate cells, and excretion removes metabolic wastes while helping maintain internal balance. These processes support one another rather than functioning independently. Option A includes all four correct relationships. Options B, C and D either give false definitions, wrongly restrict processes, or deny their integration.

The governing concept is gas exchange during photosynthesis. Carbon dioxide is a necessary raw material and normally enters the leaf mainly through stomata. A thick petroleum-jelly layer can cover or block these pores, reducing carbon-dioxide diffusion. Even if light and water remain available, less carbon dioxide limits glucose formation and therefore lowers the photosynthetic rate. Option A states this cause; the other options describe processes that are unrelated or biologically impossible.

The governing concept is the iodine test for starch and the role of light in photosynthesis. Iodine turns blue-black when starch is present. A plant kept in darkness cannot receive the light energy required to drive photosynthesis, so the leaf does not produce enough stored starch for the test. Thus option A is correct. Excess water, absence of xylem and the number of guard cells do not explain the missing iodine colour in this experiment.

The governing concept is the need for chlorophyll in photosynthesis. A non-green region generally lacks chlorophyll or contains too little of it to absorb light effectively. Without this pigment, the light-dependent energy capture needed for food formation is greatly reduced, so starch is not detected there by iodine. Option A is therefore correct. Leaf thickness, roots and blood are not the required factors stated by this controlled observation.