Life Processes

Gas exchange in human lungs takes place mainly in the alveoli, millions of tiny balloon-like air sacs at the ends of bronchioles. Their walls are only one cell thick and are closely surrounded by blood capillaries, giving oxygen a short diffusion path into blood and carbon dioxide a path out. The stomach and small intestine digest food, while the heart pumps blood, so option A is correct.

The heart is a muscular organ that functions as the central pump of the circulatory system. Its rhythmic contractions push blood through pulmonary circulation to the lungs and systemic circulation to the rest of the body, delivering oxygen and nutrients and carrying away wastes. The kidneys filter blood, the liver processes substances, and the lungs exchange gases; therefore option A is correct.

The human heart has four chambers: the right atrium and right ventricle receive and pump deoxygenated blood toward the lungs, while the left atrium and left ventricle receive and pump oxygenated blood to the body. Septa help prevent mixing of oxygenated and deoxygenated blood. The stomach, kidney and liver do not have this four-chambered pumping arrangement, so option A is correct.

The defining function of an artery is to carry blood away from the heart under relatively high pressure. Arteries usually have thick, elastic and muscular walls to withstand and regulate this pressure. Most arteries carry oxygenated blood, although the pulmonary artery carries deoxygenated blood to the lungs, so direction—not oxygen content—is the rule. Veins return blood, while urine formation and digestion are unrelated; hence A is correct.

Veins are blood vessels whose main function is to return blood from body tissues to the heart. They generally carry deoxygenated blood, except for pulmonary veins, which bring oxygenated blood from the lungs to the left atrium. Veins usually have thinner walls and valves that help prevent backflow, especially in the limbs. Arteries carry blood away, while oxygen production and food breakdown are different processes; therefore A is correct.

The governing concept is blood clotting, or coagulation, which prevents excessive blood loss after an injury. When a blood vessel is damaged, platelets gather at the site and help form a temporary plug. They also release substances that support the clotting reaction and formation of fibrin threads. Therefore, option A is correct. Red blood cells carry oxygen, white blood cells defend against pathogens, and plasma is the liquid part of blood; these are not the main clot-forming particles.

The governing concept is transport in plants. Roots absorb water and dissolved mineral salts from the soil, and these materials must move upward to the stem and leaves. Xylem vessels and tracheids conduct water and minerals mainly from roots toward aerial parts, supported by root pressure, cohesion and transpiration pull. Thus option A, xylem, is correct. Phloem transports organic food, stomata regulate gas exchange and water loss, while villi occur in the small intestine of animals.

The governing concept is translocation of food in plants. Leaves prepare sugars by photosynthesis, but growing roots, stems, flowers, fruits and storage organs may not produce enough food themselves. Phloem tissue transports dissolved sugars and other organic nutrients from source regions, usually leaves, to sink regions where they are used or stored. Therefore option A is correct. Xylem carries water and minerals, guard cells control stomatal openings, and an alveolus is a gas-exchange structure in lungs.

The governing concept is transpiration, the loss of water vapour from the aerial parts of a plant, especially leaves, through stomata. Water absorbed by roots reaches the leaves, and some of it evaporates from moist leaf surfaces before diffusing out through open stomata. Hence option A gives the correct definition. The other choices describe impossible or unrelated processes: roots do not normally make food, flowers do not drink oxygen, and seeds do not form blood.

The governing concept is the human excretory system and maintenance of internal balance. The kidneys receive blood, filter it through millions of nephrons, selectively reabsorb useful substances and remove excess water, salts and nitrogenous wastes in urine. Thus option A is the best answer because kidneys are the principal excretory organs. Lungs also remove carbon dioxide and water vapour, and skin can release sweat, but eyes and ears are not the main organs of excretion.

The governing concept is the microscopic organization of the kidney. Each kidney contains a very large number of nephrons, and each nephron performs the essential steps of urine formation: filtration of blood, selective reabsorption of useful substances and secretion of certain wastes. Therefore option A, nephron, is correct. An alveolus exchanges gases in the lungs, a villus absorbs nutrients in the small intestine, and a stoma is a pore in a plant epidermis.

The governing concept is urine formation in the human excretory system. Blood enters the kidneys, where nephrons filter small molecules and then selectively reabsorb much of the water and useful solutes. The remaining fluid, containing wastes and excess substances, becomes urine and passes into collecting ducts. Thus option A is correct. The heart pumps blood, the liver performs metabolic and detoxification functions, and the mouth begins digestion; none of these is the primary site of urine formation.

The governing concept is the pathway of urine in the human excretory system. Urine formed in each kidney collects in the renal pelvis and travels to the urinary bladder through a narrow muscular tube called the ureter. The bladder stores urine until it leaves the body through the urethra. Therefore option A is correct. The trachea carries air, the oesophagus carries swallowed food, and an artery carries blood away from the heart.

The urinary system performs excretion by filtering wastes from the blood. The kidneys form urine, and the ureters carry it to the urinary bladder. The bladder is a muscular storage sac that temporarily holds urine until it is released through the urethra. Therefore, option A is correct; the kidney forms urine, while the heart and lungs have different functions.

Excretion maintains the internal balance of the body by removing metabolic wastes. When the kidneys cannot adequately filter wastes and excess water from the blood, a dialysis machine performs this function through a semipermeable membrane. Thus, option A, dialysis, is correct. Photosynthesis occurs in plants, transpiration is water loss from leaves, and digestion breaks down food.

Plants do not have specialized excretory organs like animal kidneys. They may store certain waste products in vacuoles or in old tissues, and substances such as resins and gums can accumulate in stems or other parts. Wastes may also leave when leaves, bark, or fruits are shed. Hence option A is correct; plants do not make blood or always store wastes as urine.

The food pipe, or oesophagus, is a muscular tube in the digestive tract. Its main role is transport: after swallowing, it carries the bolus from the mouth and throat to the stomach by coordinated muscular contractions. Therefore option A is correct. The heart pumps blood, the kidneys form urine, and oxygen is not produced by the food pipe.

Peristalsis is the governing concept in this question. It consists of rhythmic, wave-like contractions and relaxations of the muscles in the oesophageal wall. These contractions push the swallowed food toward the stomach, even when a person is not upright. Therefore option A is correct; blood flow, transpiration, and filtration are unrelated processes.

Protein digestion mainly begins in the stomach. Gastric glands release hydrochloric acid, creating an acidic medium that activates pepsin, an enzyme that starts breaking proteins into smaller molecules. Therefore option A is correct. Salivary digestion begins mainly for starch, while the large intestine and rectum are not the principal sites where protein digestion starts.

The pancreas contributes to digestion by secreting pancreatic juice into the small intestine. This juice contains enzymes such as amylase, trypsin-related proteases, and lipase, which help digest carbohydrates, proteins, and fats. Thus option A is correct. Bile is produced by the liver, saliva by salivary glands, and urine by the kidneys, so those are not pancreatic secretions.

After most digestion and nutrient absorption occur in the small intestine, the remaining material enters the large intestine. Its important function is to absorb much of the remaining water and some salts, helping form and consolidate faeces for elimination. Therefore option A is correct. It does not make oxygen, pump blood, or absorb light.

The respiratory system provides a passage for air and enables gas exchange. Air entering through the nose or mouth passes into the trachea, which divides into bronchi leading to the lungs. Hence option A is correct. The food pipe carries swallowed food, the ureter carries urine from a kidney, and an artery carries blood, not air.

During cellular respiration, carbon dioxide is produced as a waste product. Most of it enters red blood cells, reacts with water, and is converted into bicarbonate ions, which are transported in the blood plasma. At the lungs, the reaction reverses and carbon dioxide is released for exhalation. Therefore option A is correct; oxygen and glucose are different transported substances, not forms of carbon dioxide.

The governing concept is holozoic nutrition in animals, which occurs through a sequence of ingestion, digestion, absorption, assimilation and egestion. Ingestion means taking food into the body and is therefore the first step. Absorption happens later when digested nutrients enter the blood, while excretion removes metabolic wastes and circulation transports materials. Hence option A is correct.

Life processes are the essential activities that maintain an organism’s living state. Nutrition supplies materials and energy, respiration releases usable energy, transportation distributes substances, and excretion removes wastes. These functions work together to maintain the body. The alternatives describe isolated or incorrect effects, so option A correctly states their main importance.