Life Processes

The governing concept is cellular respiration. In body cells, glucose is broken down to release energy; during aerobic respiration, carbon dioxide is produced as a waste product. The blood transports this carbon dioxide, mainly in dissolved or chemically combined forms, to the lungs, where it is exhaled. Chewing, blood clotting, and water absorption do not produce carbon dioxide as their main function.

A nephron is the structural and functional unit of the kidney. Its filtration unit first filters blood, and the renal tubule then selectively reabsorbs useful substances and water while allowing wastes to remain in the forming urine. Therefore, its overall function is to filter blood and help form urine. Digestion occurs in the alimentary canal, oxygen is mainly carried by haemoglobin, and bile is produced by the liver.

The governing concept is excretion and maintenance of the internal environment. Healthy kidneys filter blood, remove nitrogenous wastes and excess water or salts, and form urine. When kidney function fails, wastes can accumulate to dangerous levels. During dialysis, blood passes near a dialysis fluid across a partially permeable membrane, allowing selected wastes and excess substances to diffuse out. It does not add food, fill lungs, or produce stomach acid.

The urinary system has separate tubes with different functions. Urine is produced in the kidneys, and each ureter is a muscular tube that carries urine from a kidney to the urinary bladder, where it is temporarily stored. The vessel carrying blood from the heart to the lungs is the pulmonary artery, food travels through the oesophagus, and air travels through the trachea. Thus option A is the only correct description.

Plants do not possess a specialised excretory system like that of animals, so they use several alternative methods. Some wastes can be stored in cell vacuoles, while others may accumulate in leaves, bark, or old xylem as resins and gums. When leaves or bark are shed, part of the stored waste is removed. Plants have no heart, lungs, or circulating blood system for permanent waste storage, so option A is correct.

The governing concept is nitrogenous waste management. Breakdown of amino acids produces ammonia, which is highly toxic, especially to body tissues. In the liver, humans convert ammonia into urea through the urea cycle. Urea is considerably less toxic, can be transported safely in the blood, and is removed by the kidneys in urine. It neither produces oxygen nor digests food or pumps blood, so option A correctly explains the advantage.

The governing concept is selective reabsorption during urine formation. Filtration at the nephron may place water and useful dissolved substances into the filtrate. The renal tubule reabsorbs an appropriate amount of water, depending on the body's needs, and returns it to the blood. This prevents excessive water loss and helps maintain internal water and salt balance. The other options are unrelated to kidney function, so A is correct.

The governing concept is the source of organic food. Autotrophs synthesise their own organic food from inorganic substances such as carbon dioxide and water, usually using light energy in photosynthesis. Heterotrophs cannot generally make food in this way and obtain ready-made organic matter from plants, animals, or other sources. Therefore option A states the basic difference; the remaining options reverse or deny the distinction.

Parasitic nutrition means obtaining nourishment from a living host instead of preparing sufficient food independently. Cuscuta has very little or no chlorophyll, so it cannot carry out adequate photosynthesis. It develops special sucking structures called haustoria that penetrate the host plant and absorb water and nutrients. Therefore, option A is correct; the other options describe impossible or unrelated functions.

The pancreas is an important digestive gland. It releases pancreatic juice into the small intestine, where enzymes act on carbohydrates, proteins, and fats. Thus, it supports the digestion of several major food components rather than performing only one narrow function. Option A is correct. Pumping blood is the work of the heart, air filtration is associated with the respiratory system, and urine is stored in the urinary bladder.

The liver produces bile, an alkaline digestive secretion that is stored temporarily in the gallbladder and released into the small intestine. Bile does not chemically digest fat by itself; it emulsifies fat into smaller droplets, increasing the surface area for lipase to act. Therefore, option A is correct. Saliva is produced by salivary glands, urine by the kidneys, and haemoglobin is a red-cell pigment.

Carbon dioxide produced during cellular respiration diffuses into the blood and is transported in more than one form. Most of it is converted in red blood cells into carbonic acid and then bicarbonate ions, which travel dissolved in plasma. A smaller amount is carried as carbaminohaemoglobin or physically dissolved gas. Hence option A is correct; solid particles and fat droplets are not transport forms, and CO2 is not completely bound to haemoglobin.

Fish obtain oxygen from water rather than breathing atmospheric air directly. Water passes over the thin, moist filaments and lamellae of the gills, where dissolved oxygen diffuses into the blood and carbon dioxide diffuses out. This large, well-supplied surface makes gills suitable for aquatic gas exchange. Therefore, option A is correct. Lungs and alveoli are characteristic of air-breathing organisms, while scales do not perform the main exchange.

Terrestrial organisms obtain oxygen from air, but an exposed moist respiratory surface would allow water to evaporate rapidly. Natural selection and body organization therefore commonly place the respiratory surface inside protected structures, such as lungs or tracheal systems, while still providing a thin area for diffusion. Option A is correct. A completely open and dry surface would hinder diffusion, and the remaining choices are not general features of terrestrial respiration.

Roots absorb water and mineral ions from the soil, and xylem vessels conduct them through the stem to aerial parts. Transpiration from leaves creates a pull that helps maintain this upward movement, assisted by cohesion between water molecules and adhesion to vessel walls. Therefore, the usual direction is from roots to leaves, making option A correct. The other directions do not represent the main xylem pathway.

When a blood vessel is damaged, platelets gather at the injured site and become involved in a chain of reactions that forms a fibrin mesh. This mesh traps blood cells and produces a clot, helping seal the wound and limit blood loss. Therefore, option A is correct. Red blood cells mainly transport respiratory gases, white blood cells defend against pathogens, and water in plasma is a transport medium rather than the main clotting component.

White blood cells are immune cells that protect the body from pathogens such as bacteria, viruses, and other disease-causing agents. They may engulf foreign particles or help coordinate immune responses and antibody production. Hence option A is correct. Red blood cells primarily carry oxygen using haemoglobin, bile is produced by the liver, and starch is synthesized by green plants during photosynthesis, not by white blood cells.

The governing concept is the complementary relationship between two life processes. During photosynthesis, green plants use light energy, carbon dioxide and water to form glucose and release oxygen. During cellular respiration, glucose is broken down, usually with oxygen, to release usable energy as ATP. Therefore, option A is correct; the other options deny or misrepresent this clear exchange of food and energy.

The governing concept is coordination among life processes. Cells continuously produce waste such as carbon dioxide, excess water and nitrogenous compounds. The transport system, especially blood, carries these materials from tissues to organs such as the lungs and kidneys, where they are removed. Thus option A correctly explains the link; the other choices describe impossible functions or deny the relationship.

Photosynthesis requires light energy, carbon dioxide, water, and suitable pigments. Chlorophyll, the main green pigment, absorbs much of the light energy used to drive the reactions that form glucose. If chlorophyll is greatly reduced, light capture becomes inefficient even when water and light are available, so option B is correct. Carbon dioxide entry does not stop immediately, roots can still absorb minerals, and phloem transports food rather than water.