Life Processes

Life processes are the essential activities that keep an organism alive and functioning. They include nutrition for obtaining materials and energy, respiration for releasing usable energy, transportation for distributing substances, and excretion for removing wastes. Therefore option A gives the broad and correct meaning. Changing colour, moving outside, or sleeping may occur in some situations, but none of these alone defines life processes.

Organisms that manufacture their own organic food from simple inorganic substances are called autotrophs. Green plants are the standard example: they use chlorophyll, sunlight, carbon dioxide, and water to perform photosynthesis. Therefore option A is correct. Heterotrophs obtain food from other organisms, parasites depend on hosts, and saprophytes absorb nutrients from dead or decaying matter, so these alternatives do not fit.

Heterotrophs are organisms that cannot synthesize their own food from simple inorganic substances and therefore obtain nutrients from other organisms or organic matter. Animals, fungi, and many microorganisms are examples. Hence option B is correct. Autotrophs make their own food, stomata are leaf pores involved in gas exchange, and chlorophyll is a pigment, not an organism. These distinctions eliminate the other options.

During photosynthesis, green plants convert light energy into chemical energy stored in glucose. Chlorophyll absorbs mainly the useful wavelengths of sunlight, while carbon dioxide and water supply the materials for food formation. Therefore option A is correct. Sound, magnetic, and muscle energy are not the energy source used by green leaves to synthesize food, so options B, C, and D are unsuitable.

Photosynthesis uses carbon dioxide from the atmosphere and water from the soil to produce glucose, with light energy captured by chlorophyll. Thus carbon dioxide is the principal gas taken in for carbon fixation, making option B correct. Oxygen is mainly released as a product, nitrogen is not the chief gaseous raw material in this equation, and free hydrogen is not normally taken in by green plants for photosynthesis.

In photosynthesis, green plants use carbon dioxide and water to form glucose with the help of light energy. Oxygen is produced during the light-dependent reactions and is released to the surroundings, so option A is correct. Carbon dioxide is mainly taken in as a raw material. Chlorine and ammonia are not normal gaseous products of photosynthesis, which rules out options C and D.

Chlorophyll is the green pigment located in chloroplasts of plant cells. It absorbs light energy and enables the light reactions that support photosynthesis, so option A is correct. Haemoglobin is the oxygen-carrying pigment in blood, pepsin is a digestive enzyme in the stomach, and insulin is a hormone that helps regulate blood glucose. None of these performs chlorophyll’s role in leaves.

The governing concept is gaseous exchange in plants. Leaves need carbon dioxide for photosynthesis and release oxygen; they also exchange water vapour during transpiration. These gases move through microscopic openings in the leaf epidermis. Such openings are called stomata, so option A is correct. Root hairs absorb water and minerals, veins transport materials, and pollen grains are involved in reproduction, not leaf gas exchange.

The governing concept is regulation of stomatal movement in plants. Each stoma is surrounded by a pair of specialised guard cells. When their water content and turgidity change, the cells change shape, causing the pore to open or close. Therefore option A, guard cells, is correct. Red blood cells transport oxygen, neurons conduct nerve impulses, and bone cells form or maintain bone; none controls stomata.

The governing concept is the sequence of human digestion. Food first enters the mouth, where the teeth mechanically break it into smaller pieces and the tongue mixes it with saliva. Salivary amylase begins the chemical digestion of starch there. Thus option A, the mouth, is correct. The stomach and small intestine continue major stages of digestion, while the large intestine mainly absorbs water and forms faeces.

The governing concept is enzyme-specific digestion. Salivary glands release saliva, which contains amylase. In the mouth, this enzyme begins breaking complex starch into simpler sugars, such as maltose, under suitable conditions. Therefore option A is correct. Pepsin digests proteins mainly in the stomach, lipase acts on fats, and trypsin digests proteins in the small intestine, so these distractors do not match starch digestion by saliva.

The governing concept is the chemical environment of the stomach. Gastric glands release hydrochloric acid, which makes the stomach contents strongly acidic. This acidic medium helps activate pepsin and supports protein digestion; it also helps destroy many microbes entering with food. Therefore option A is correct. Sulphuric and nitric acids are not normal stomach secretions, while citric acid is associated with citrus fruits rather than gastric juice.

The governing concept is digestion of different nutrients by specific enzymes. In the stomach, hydrochloric acid provides an acidic medium that activates pepsin. Pepsin begins breaking large protein molecules into smaller peptides, so option A is correct. Amylase acts mainly on starch in the mouth and small intestine, lactase digests lactose in the small intestine, and chlorophyll is a photosynthetic pigment rather than a digestive enzyme.

The governing concept is the role of accessory organs in digestion. Bile is synthesised by the liver and then stored and concentrated in the gallbladder before being released into the small intestine. It does not contain a digestive enzyme, but it emulsifies fats and helps provide an alkaline medium. Therefore option A, liver, is correct. The lungs exchange gases, kidneys form urine, and the heart pumps blood.

The governing concept is the emulsification of fats during digestion. Fat does not mix readily with watery digestive juices, so bile salts break large fat globules into many tiny droplets. This increases the surface area available to lipase and makes fat digestion more efficient. Therefore option A, fats, is correct. Water, mineral salts, and oxygen are not nutrients that require bile-mediated emulsification for digestion.

The governing concept is absorption in the human digestive system. Digestion is largely completed in the small intestine with the help of pancreatic and intestinal juices. Its inner lining has numerous villi, which greatly increase surface area. Soluble nutrients then pass through the villi into blood or lymph. Therefore option A is correct. The heart pumps blood, green plants release oxygen during photosynthesis, and kidneys form urine.

The governing concept is structural adaptation for absorption. The inner lining of the small intestine contains numerous tiny finger-like projections called villi. Each villus has a thin wall and a network of blood capillaries, allowing digested nutrients to pass efficiently into the circulation; lacteals also help absorb fats. Therefore option A is correct. Stomata are leaf pores, alveoli are lung air sacs, and nephrons are kidney units.

The large intestine receives undigested material after most nutrients have already been absorbed in the small intestine. Its major function is to absorb water and some salts from this material, helping form semi-solid faeces. Therefore, option A is correct. Photosynthesis occurs mainly in green plants, oxygen production is not its function, and blood formation is associated mainly with bone marrow, not the large intestine.

In aerobic respiration, glucose is oxidised in the presence of oxygen. The overall breakdown produces carbon dioxide and water, while the chemical energy stored in glucose is released and captured largely as ATP for cellular work. Therefore option A is correct. Lactic acid is associated with anaerobic respiration in muscles, oxygen is a reactant, and starch is not an end product.

Human lungs contain millions of tiny air sacs called alveoli. Each alveolus has a moist, very thin wall and is surrounded by a network of blood capillaries. Oxygen diffuses from the inhaled air into the blood, while carbon dioxide diffuses in the opposite direction. Thus option A is correct; the stomach and small intestine digest or absorb food, and the kidney filters blood.

The thin walls of alveoli reduce the distance across which respiratory gases must diffuse. Because the alveoli are also moist and closely associated with blood capillaries, oxygen can enter the blood and carbon dioxide can leave it rapidly. Therefore option A is correct. Digestion occurs in the alimentary canal, blood cells are formed mainly in bone marrow, and urine is produced by the kidneys.

The heart is a muscular organ that contracts rhythmically to pump blood through the pulmonary and systemic circulations. The right side sends deoxygenated blood to the lungs, while the left side pumps oxygenated blood to the body. Therefore option A is correct. Lungs exchange gases, the stomach digests food and the liver performs metabolic and processing functions; none acts as the main blood pump.

The governing concept is the structure of the human circulatory system. The human heart is divided into two upper chambers, called atria, and two lower chambers, called ventricles. Adding them gives 2 + 2 = 4 chambers. Therefore, option C is correct. Two and three are incomplete counts, while five is more than the actual number of chambers in the normal human heart.

The governing concept is the direction of blood flow through blood vessels. Arteries generally carry blood away from the heart to body tissues; this definition is based on direction, not on whether the blood is oxygen-rich. Thus option A is correct. Veins usually return blood toward the heart, whereas the stomach, kidney, and lungs are not the general destinations described by the term artery.

The governing concept is the direction of circulation in veins. Veins generally carry blood from body tissues back toward the heart, so option B is correct. This directional rule applies even though pulmonary veins carry oxygenated blood; they still move it toward the heart. Option A describes the usual direction of arteries, while options C and D are not definitions of venous transport.