Life Processes

The kidneys are the main excretory organs in humans because they filter the blood and remove nitrogenous wastes, especially urea, along with excess salts and water. These substances are processed into urine. The lungs remove carbon dioxide and some water vapour, but their primary function is gas exchange; the heart and stomach do not perform the main excretory role. Hence option A is correct.

A nephron is the structural and functional unit of the kidney. Each nephron contains a glomerulus and a tubular system that filter blood, reabsorb useful substances and water, and help form urine. Therefore, option A is correct. An alveolus belongs to the lungs, a villus lines the small intestine, and a stoma is a pore in a plant leaf.

Urine is mainly formed in the kidneys, specifically inside the nephrons. Blood is filtered there, useful substances are selectively reabsorbed, and additional wastes and ions are secreted into the tubule. The remaining fluid becomes urine and passes to the ureters. The heart pumps blood, the lungs exchange gases, and the stomach digests food, so option A is correct.

Heterotrophic organisms cannot synthesise their own food from simple inorganic substances in the way autotrophic green plants do. They obtain ready-made organic food from plants, animals, fungi, or other organisms, either directly or indirectly. Therefore option A is correct. Sunlight may provide energy for plants, but it is not food for heterotrophs; soil and stones alone cannot nourish them.

Fungi generally show saprophytic nutrition. They grow on dead or decaying organic matter, release digestive enzymes outside their bodies, break complex substances into simpler soluble molecules, and absorb those molecules. Therefore option A is correct. Fungi are not generally autotrophs because they do not make food by photosynthesis; “light nutrition” and “blood nutrition” are not standard categories here.

Parasitic nutrition is a mode in which one organism obtains food or nutrients from another living organism, usually called the host, and may harm it. Cuscuta lacks sufficient chlorophyll and develops special structures that draw prepared food from a host plant. Therefore, option A is correct. A green plant making its own food shows autotrophic nutrition, a cow shows holozoic nutrition, and merely living in water is not a nutrition mode.

The oesophagus, or food pipe, is a muscular tube connecting the pharynx to the stomach. After swallowing, its circular and longitudinal muscles contract in a coordinated wave called peristalsis. This movement pushes the food bolus toward the stomach, so option A is correct. Digestion and absorption occur mainly in other organs; the oesophagus does not make oxygen or control urine.

Peristalsis is the coordinated, wave-like contraction and relaxation of muscles in the wall of the alimentary canal. Behind the food bolus, muscles contract, while muscles ahead relax, producing forward movement through the oesophagus and intestine. Thus option A is correct. Transpiration is water loss from plants, respiration releases energy from food, and excretion removes metabolic wastes, so none of these describes food propulsion.

The large intestine receives the undigested and unabsorbed residue from the small intestine. Its important function is to absorb water and some salts, helping convert the remaining material into a more solid faecal mass for elimination. Therefore, option A is correct. Oxygen production is associated with photosynthesis, blood pumping is the heart’s function, and protein synthesis occurs in cells rather than being the main role of the large intestine.

Air enters through the nose or mouth, passes through the pharynx and larynx, and then travels down the trachea, also called the windpipe, before reaching the bronchi and lungs. Hence option A is correct. The oesophagus carries swallowed food to the stomach, the ureter carries urine from a kidney to the urinary bladder, and an artery transports blood away from the heart.

Breathing is the physical process of inhaling air containing oxygen and exhaling carbon dioxide. Respiration is a chemical process occurring inside cells, in which food molecules such as glucose are broken down to release usable energy, with or without oxygen depending on the pathway. Therefore, option A correctly distinguishes them. They are related because breathing supplies gases, but breathing itself is not digestion or cellular energy release.

Human circulation consists of two linked circuits. In pulmonary circulation, deoxygenated blood travels from the right side of the heart to the lungs and returns oxygenated. In systemic circulation, oxygenated blood leaves the left side for the body and returns to the heart. Thus blood passes through the heart twice in one complete cycle, making option A correct. The other options contradict the actual route and chamber functions.

The four-chambered human heart keeps oxygen-rich blood returning from the lungs separate from oxygen-poor blood returning from the body. This prevents significant mixing and allows the left ventricle to pump highly oxygenated blood to tissues at suitable pressure. Consequently, cellular respiration receives oxygen efficiently, so option A is correct. The other options concern unrelated digestive, excretory, or plant processes.

Capillaries are microscopic blood vessels that connect arterioles and venules. Their walls are only about one cell thick, so oxygen and nutrients can diffuse from blood into tissues, while carbon dioxide and other wastes move into the blood. This makes option A correct. Bones are formed by bone tissue, chewing is performed by the mouth and teeth, and filtering inhaled air is mainly associated with nasal structures.

The governing concept is excretion: healthy kidneys filter the blood and remove nitrogenous wastes, excess salts, and water to form urine. If the kidneys fail to perform this function adequately, harmful wastes accumulate in the body. During dialysis, a machine passes the patient’s blood through a selectively permeable membrane, removes wastes and excess fluid, and returns the cleaned blood. Therefore, option A is correct; the other options describe digestion, breathing, or plant nutrition, not kidney failure.

Life processes maintain the conditions needed for an organism to remain alive. Nutrition supplies materials, respiration releases usable energy, transportation distributes substances, and excretion removes harmful metabolic wastes. Together these processes support growth, repair, regulation, and continuous cellular activity. Therefore A is correct. Changes in body size, colour, or sleep may occur in organisms, but none of these alone represents the essential set of life processes.

Autotrophic nutrition means that an organism produces its own organic food rather than obtaining ready-made food from another organism. In photosynthesis, green plants use light energy captured by chlorophyll to combine carbon dioxide and water and form carbohydrates, releasing oxygen as a by-product. Thus A states the central role. Options B, C, and D describe animal digestion, circulation, and excretion, not photosynthesis.

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.