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.

Roots absorb water from the soil, mainly through root hairs. The xylem is the plant vascular tissue specialized for conducting water and dissolved mineral ions from roots toward stems and leaves. Cohesion, adhesion, root pressure, and especially transpiration pull help support this upward movement. Therefore A is correct. Phloem transports organic food, whereas alveoli and nephrons are structures of animal respiratory and excretory systems.

The governing concept is mechanical digestion and the beginning of chemical digestion. Teeth break food into smaller pieces, increasing the surface area on which digestive enzymes can act. The tongue mixes these pieces with saliva, and salivary amylase begins starch digestion. Therefore option A is correct. Chewing does not convert food directly into urine or blood, and it is not a process of removing oxygen from food, so B, C and D are unsuitable.

The governing concept is enzyme-assisted carbohydrate digestion. Salivary amylase acts on starch, a complex carbohydrate, and begins breaking it into simpler sugars such as maltose while food is still in the mouth. This is why option A is correct and why carbohydrate digestion starts before food reaches the stomach. Amylase does not convert fat into bile, produce oxygen from protein, or filter blood; those claims describe unrelated processes.

The governing concept is protection of the stomach lining during digestion. Gastric glands secrete mucus, which forms a coating over the inner stomach wall. This layer acts as a barrier and reduces direct contact between hydrochloric acid, pepsin and the living epithelial cells. Therefore option A is correct. Chlorophyll is a plant pigment, haemoglobin transports oxygen in blood, and bile salts assist fat digestion in the small intestine; none protects the stomach wall from acid.

The governing concept is efficient exchange between blood and body cells. Capillaries have extremely thin walls, generally only one cell thick, so oxygen and dissolved nutrients can diffuse from the blood into tissues, while carbon dioxide and other wastes can diffuse back into the blood. Their extensive network also provides a large exchange surface. Therefore option A is correct; thick walls would hinder diffusion, and the other choices describe unrelated functions.

The governing concept is diffusion in unicellular organisms. A unicellular organism consists of one small cell, and its cell membrane is directly exposed to the surrounding medium. The distance from the membrane to the cell interior is short, so oxygen, nutrients and wastes can move mainly by diffusion. A complex transport system is unnecessary. Thus option A is correct; the other choices describe organs or tissues absent from such organisms.

The governing concept is that stomata are microscopic pores that permit gas exchange between a leaf and the atmosphere. Carbon dioxide, a raw material for photosynthesis, normally enters through these pores. If a wax-like coating closes them, carbon-dioxide entry decreases first, so the photosynthetic rate may subsequently fall. Option A is correct; oxygen production would not immediately rise, root water uptake does not stop at once, and chlorophyll cannot turn into blood.

Photosynthesis requires light energy, water, carbon dioxide, and chlorophyll. Carbon dioxide supplies the carbon used to build glucose, so it is a direct raw material for the process. If light is available but carbon dioxide is deficient, carbon fixation slows and glucose production decreases sharply. Therefore option B is correct. Nitrogen is important for plant growth but is not the immediate carbon source, oxygen is mainly a product, and urea is a nitrogen fertilizer rather than a photosynthetic raw material.