Life Processes

The governing concept is the role of chlorophyll as the main light-absorbing pigment in green plants. Photosynthesis requires light energy to drive the formation of carbohydrates from carbon dioxide and water. If chlorophyll is absent or greatly reduced, less light energy is absorbed and the rate of food formation generally decreases, though other conditions also affect the rate. Hence A is correct; B, C, and D assign unrelated animal or digestive functions to chlorophyll.

Stomata are small pores, usually in the epidermis of leaves, that regulate exchange with the atmosphere. Carbon dioxide enters through them and is required for photosynthesis; oxygen produced during photosynthesis can also leave. Water evaporates from internal leaf surfaces and exits mainly through these pores, producing transpiration. Therefore A correctly describes both roles. The other options refer to storage or animal functions unrelated to stomata.

Guard cells surround each stomatal pore and regulate its opening. When they take up water, they become more turgid and their shape pulls the pore open; when they lose water, turgor falls and the pore tends to close. This regulation balances carbon-dioxide entry with water loss through transpiration. Thus A is correct. The other options describe invented or animal-specific functions and have no role in stomatal movement.

Photosynthesis requires carbon dioxide as a raw material for producing carbohydrates. Stomata provide the main pathway by which atmospheric carbon dioxide enters the leaf. If they remain closed, carbon-dioxide diffusion into the leaf decreases; after the available internal supply is used, photosynthetic rate and food formation may fall. Therefore A is correct. Oxygen does not become food, xylem transports water, and villi belong to the intestine.

Leaves are the main sites of photosynthesis, so they produce sugars such as sucrose. These dissolved organic substances must be distributed to roots, stems, growing buds, fruits, and storage organs. Phloem sieve tubes and associated cells transport this food from source tissues to sink tissues, and movement can occur in different directions according to demand. Hence A is correct. Xylem carries water, stomata exchange gases, and urine formation is an animal function.

The governing concept is holozoic nutrition in a unicellular organism. Amoeba has no specialised mouth, so its flexible cell membrane extends outward to form temporary projections called pseudopodia. These projections surround and engulf a food particle, forming a food vacuole where digestion occurs. Therefore, option A is correct; stomata belong to plants, villi line the small intestine, and alveoli are lung structures, so the other options are unrelated.

The governing concept is the alimentary canal, a continuous digestive tube open at both ends. Food enters through the mouth, then moves by swallowing and peristaltic contractions through the oesophagus, stomach, small intestine and large intestine. Undigested material finally leaves through the anus. Thus option A correctly describes its tube-like continuity. Blood is carried by vessels, air by the respiratory tract, and urine is formed in the kidneys, so B, C and D are incorrect.

The governing concept is the protective and digestive role of gastric hydrochloric acid. Food may carry microbes into the stomach, and the strongly acidic medium destroys or inhibits many of them. The acid also provides the conditions needed for pepsin to digest proteins. Thus option A is correct. Oxygen binding is performed by haemoglobin, light capture by chlorophyll, and urine storage by the urinary bladder, not by stomach acid.

The governing concept is emulsification of fats. Fat does not mix readily with the watery digestive contents, so bile salts divide large fat globules into many tiny droplets. This greatly increases the total surface area available to lipase, allowing the enzyme to digest fat more effectively. Therefore option A is correct. Bile does not change protein into acid, convert glucose into oxygen, or transport blood; those are biologically incorrect functions.

The governing concept is completion of digestion followed by absorption in the small intestine. It receives bile, pancreatic juice and intestinal juice, which help break carbohydrates, proteins and fats into simpler, absorbable substances. Its inner lining contains numerous villi with thin walls and blood capillaries, so digested nutrients can pass efficiently into the circulation. Thus option A is correct; water storage, lung circulation and urine formation are not its primary functions.

The governing concept is adaptation of structure for efficient absorption. Villi are numerous finger-like projections on the inner lining of the small intestine. Together they greatly increase the available surface area, allowing more digested nutrients to contact the absorptive lining at the same time. Their thin epithelium and nearby blood capillaries further support transfer into the blood. Therefore option A is correct; villi do not make acid, pump blood, or fill lungs with air.

The governing concept is water reabsorption in the large intestine. As undigested material passes through it, the large intestine normally removes part of the remaining water and helps form relatively solid faeces. If this absorption is greatly reduced, excess water stays in the faecal matter, making it loose or watery; prolonged loss can contribute to dehydration. Hence option A is correct. The other options concern oxygen production, heart anatomy and plant stomata, not intestinal water balance.

The governing concept is surface area and diffusion. Each alveolus has a thin moist wall, and millions of alveoli together create a very large exchange surface. Oxygen can therefore diffuse efficiently into surrounding capillaries, while carbon dioxide diffuses out. Option A is correct; digestion, urine storage and transport to leaves are not functions of lung alveoli.

The governing concept is rapid diffusion across a thin respiratory surface. Alveoli contain air, while the surrounding capillaries carry deoxygenated and oxygenated blood. Their dense network keeps blood close to a large alveolar surface, maintaining a short diffusion distance and concentration gradients. Thus option A is correct; the other options refer to digestion, plant transport or excretion.

The governing concept is haemoglobin-mediated oxygen transport. Haemoglobin in red blood cells binds oxygen in the lungs and carries it to tissues. If haemoglobin is low, the blood may deliver less oxygen, so aerobic cellular respiration can produce less energy for normal activities; this may cause tiredness. Option A is correct, while B, C and D are unrelated.

The governing concept is complete double circulation. The right side of the four-chambered heart receives deoxygenated blood and sends it to the lungs, while the left side receives oxygenated blood and pumps it to the body. Septa prevent major mixing, supporting efficient oxygen delivery. Option A is correct; B, C and D assign digestive or excretory functions incorrectly.

The governing concept is pressure-resistant blood transport. The ventricles pump blood into arteries with strong pressure, so arterial walls need thick muscular layers to withstand that force. Their elasticity allows them to expand during a heartbeat and recoil between beats, helping maintain smoother flow. Option A is correct; B, C and D describe functions of other systems or organisms.

The governing concept is one-way movement of blood under relatively low pressure. Veins return blood toward the heart, and skeletal-muscle movement can help push that blood forward. Because venous pressure is low, blood could fall backward, especially in limbs; valves close to stop reverse flow. Therefore A is correct, while B, C and D describe unrelated processes.

The governing concept is double circulation in the human circulatory system. In one complete cycle, deoxygenated blood travels from the heart to the lungs for oxygenation, and oxygenated blood returns to the heart before being pumped to the whole body. This separation prevents excessive mixing and supports efficient oxygen delivery at suitable pressure. Thus option A is correct; the other options concern digestion, plants, or an incorrect route for urine.

The governing concept is the role of the lymphatic system in maintaining tissue-fluid balance. Some plasma leaves blood capillaries and bathes cells; most returns directly, but excess tissue fluid enters lymph vessels. Lymph is eventually returned to the bloodstream and also transports certain absorbed fats and supports immunity. Therefore option A is correct, while the other choices describe gastric, plant, or kidney functions.

The governing concept is transpiration pull, supported by cohesion between water molecules and adhesion to xylem walls. When water vapour escapes through stomata, the water level in leaf tissues falls and tension develops in the continuous xylem column. This tension pulls water upward from the roots, helping replace the lost water. Hence option A is correct; phloem transports food, and the other choices are biologically unrelated.

The governing concept is selective urine formation in a nephron. Glomerular filtration allows small molecules, water, salts, glucose, and urea to leave the blood, so wastes can be removed but useful substances may also enter the filtrate. During reabsorption, needed water, glucose, and suitable ions return to the blood according to the body’s requirements. Therefore option A is correct; the other choices confuse excretion with photosynthesis, circulation, or respiration.

The governing concept is kidney function in excretion and maintenance of the internal environment. Metabolism continuously produces wastes such as urea, and healthy kidneys filter these substances from the blood and remove them in urine while regulating water and salts. If filtration is seriously impaired, wastes and excess substances remain in the bloodstream, causing harmful imbalance and illness. Thus option A is correct; the other options concern impossible or unrelated events.

The governing concept is excretion: healthy kidneys filter the blood, remove nitrogenous wastes and excess water, and form urine. If kidney function becomes severely reduced, urea and other wastes can accumulate in the blood. Dialysis uses a semipermeable membrane and special fluid to remove these substances artificially. Therefore option A is correct; the other options describe unrelated normal or plant processes.

The governing concept is plant excretion. Plants do not possess animal-like kidneys or lungs, so they use several alternative methods. Some wastes are stored in vacuoles, deposited in leaves or bark, or released as leaves and bark are shed. Gases may also diffuse out through stomata. Thus option A is correct, while B, C and D refer to animal organs or an impossible process.