Life Processes

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.

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.