Life Processes

The governing concept is maintenance of life. Every organism needs energy, nutrients, transport of materials and removal of harmful metabolic wastes. Nutrition, respiration, transportation and excretion perform these functions and keep cells working. Growth may result from life activities, but it is not their only purpose; colour change and stopping movement are unrelated. Thus option A is correct.

Photosynthesis requires carbon dioxide as the carbon source for making carbohydrate. In green leaves, carbon dioxide enters mainly through stomata, while water is supplied by the roots and light energy is captured by chlorophyll. Oxygen is released as a product rather than being the required carbon source. Nitrogen is important for plant proteins but is not the gas directly used to form glucose. Hence option A is correct.

The governing concept is the synthesis of carbohydrate during photosynthesis. Chlorophyll captures light energy, and the plant uses carbon dioxide and water to form glucose, a simple sugar. Glucose may be used immediately in respiration or converted and stored as starch. Proteins, fats and vitamins require different synthesis pathways, so they are not the primary direct product asked for. Therefore option A is correct.

Gas exchange in leaves is mainly controlled by stomata, which are tiny pores usually found in the epidermis. Carbon dioxide diffuses inward for photosynthesis, while oxygen and water vapour can diffuse outward. Root hairs absorb water and minerals, veins transport materials, and flowers are reproductive structures. Therefore the structure responsible for the principal leaf gas exchange is stomata, making option A correct.

Each stoma is surrounded by a pair of specialized guard cells. Changes in their water content alter turgor pressure: when they become turgid, the pore generally opens, and when they lose water, it closes. This regulates carbon dioxide entry and reduces excessive water loss. Root, blood and nerve cells do not directly control stomatal movement. Hence option A is correct.

Chlorophyll is the green pigment located in chloroplasts. Its main function is to absorb and trap light energy, especially the wavelengths useful for photosynthesis. This captured energy drives the formation of glucose from carbon dioxide and water. Chlorophyll may give leaves their green appearance, but water removal, digestion and blood formation are not its functions. Thus option A is correct.

Amoeba shows holozoic nutrition but has no permanent mouth. When it encounters a food particle, temporary projections called pseudopodia extend around it and fuse, enclosing the particle in a food vacuole. Digestion then occurs inside that vacuole. Chewing requires a mouth, lungs are respiratory organs, and roots belong to plants, so option A is the only correct answer.

Digestion is the process of breaking complex food into simpler, soluble substances that the body can absorb. It begins in the mouth because chewing breaks food into smaller pieces and saliva mixes with it. Salivary amylase starts the digestion of starch. The stomach and small intestine continue digestion, while the large intestine mainly absorbs water; therefore, option A is correct.

Salivary amylase is the enzyme present in saliva that begins carbohydrate digestion in the mouth. It acts on starch and changes it into simpler sugars, such as maltose. Pepsin digests proteins in the stomach, lipase acts mainly on fats, and trypsin helps digest proteins in the small intestine. Thus, option A correctly identifies the salivary enzyme.

The stomach secretes hydrochloric acid, usually written as HCl. It creates the strongly acidic medium needed for the action of pepsin, which begins protein digestion, and it helps destroy many harmful microorganisms entering with food. Sulphuric, nitric and acetic acids are not the normal digestive acid of the human stomach. Therefore, option A is correct.

Pepsin is the principal enzyme that begins protein digestion in the stomach. Hydrochloric acid provides the acidic medium that activates pepsin from its inactive form and supports its action on proteins, producing smaller peptide molecules. Amylase digests starch, while maltase and sucrase act on sugars mainly in the small intestine. Hence, option A is correct.

Bile is produced by the liver and stored in the gall bladder. Its bile salts emulsify fats, meaning they divide large fat globules into many small droplets. This does not chemically digest fat, but it increases the surface area available to lipase, making fat digestion more efficient. Bile does not make proteins, transport oxygen or form urine, so option A is correct.

Most chemical digestion and absorption occur in the small intestine. It receives bile, pancreatic juice and intestinal juice, which complete the breakdown of carbohydrates, proteins and fats into simpler substances. Its long, folded lining contains villi that absorb nutrients into blood or lymph. The mouth begins digestion, the oesophagus transports food, and the large intestine mainly absorbs water; therefore, option A is correct.

Villi are numerous finger-like projections on the inner lining of the small intestine. Their central role is to greatly increase the surface area available for absorption of digested nutrients. Each villus contains blood capillaries and a lymph vessel, allowing sugars and amino acids to enter blood and many fatty products to enter lymph. Villi do not move food backward, perform breathing or filter blood; therefore, option A is correct.

The governing concept is respiratory gas exchange. Alveoli are millions of tiny, thin-walled air sacs surrounded by blood capillaries. Oxygen diffuses from the alveolar air into the blood, while carbon dioxide diffuses in the opposite direction. The trachea, nose and larynx mainly conduct or condition air, so option A is correct.

The governing principle is that diffusion becomes more effective when the available surface area is large. Although each alveolus is tiny, millions of alveoli together provide a very extensive, thin exchange surface with a rich capillary supply. This allows oxygen and carbon dioxide to move rapidly, whereas digestion, blood formation and urine production occur in other organs. Thus option A is correct.

The governing concept is transport by blood. Haemoglobin, the iron-containing pigment in red blood cells, combines reversibly with oxygen in the lungs to form oxyhaemoglobin. It then releases oxygen in body tissues where it is needed. Plasma carries a small amount of dissolved oxygen, but it is not the main carrier; bile and saliva have digestive roles. Therefore option A is correct.

The governing concept is the organisation of the human circulatory system. The heart has two upper chambers called atria and two lower chambers called ventricles. The right and left sides are separated, helping keep oxygenated and deoxygenated blood largely apart. Thus the total is 2 + 2 = 4 chambers, making option A correct; the other numbers do not describe the human heart.

The governing concept is circulation. The heart is a muscular pump that contracts rhythmically: its right side sends deoxygenated blood to the lungs, and its left side sends oxygenated blood to the rest of the body. This circulation supplies oxygen and nutrients and carries wastes away. Digestion, urine formation and light detection belong to other organs, so option A is correct.

The governing concept is the direction of blood flow in vessels. Arteries carry blood away from the heart, usually under relatively high pressure because they receive blood from ventricular contractions. Most arteries carry oxygenated blood, but the pulmonary artery is an important exception. Veins generally return blood toward the heart, so option A states the defining rule correctly.

The governing concept is circulation through blood vessels. Veins generally return blood from body tissues toward the heart, where it can be sent to the lungs or pumped onward. Their walls are thinner and pressure is lower than in arteries, so many veins contain valves that help prevent backward flow. The direction away from the heart defines arteries; therefore option A is correct.

The governing concept is transport after digestion. Nutrients produced by digestion are absorbed mainly through the walls of the small intestine into the bloodstream. Blood then circulates through capillaries and delivers glucose, amino acids, fatty acids and other useful substances to cells. Bile and saliva assist digestion, while sweat helps cooling; neither distributes nutrients throughout the body. Hence option A is correct.

The governing concept is translocation in plants. Food made in leaves by photosynthesis, mainly sugars such as sucrose, is transported to growing, storing and respiring regions through phloem tissue. This movement can occur from source to sink in different directions as needed. Xylem carries water and minerals, guard cells control stomata, and alveoli belong to animal lungs; therefore option A is correct.

Transpiration is the loss of water vapour from the aerial parts of a plant, mainly through tiny pores called stomata in the leaves. Water absorbed by roots eventually reaches the leaves, where some of it evaporates and diffuses out. Therefore, option A is correct. The other options describe neither water loss nor a recognised plant life process.

When water evaporates from leaf surfaces during transpiration, it creates a negative pressure or transpiration pull in the continuous water column. Cohesion between water molecules transmits this pull downward through the xylem, helping water rise from roots to leaves. Thus option A is correct; the other choices do not explain upward transport.