Life Processes

The governing concept is double circulation in the human circulatory system. In one complete cycle, deoxygenated blood travels from the heart to the lungs for oxygenation, and oxygenated blood returns to the heart before being pumped to the whole body. This separation prevents excessive mixing and supports efficient oxygen delivery at suitable pressure. Thus option A is correct; the other options concern digestion, plants, or an incorrect route for urine.

The governing concept is the role of the lymphatic system in maintaining tissue-fluid balance. Some plasma leaves blood capillaries and bathes cells; most returns directly, but excess tissue fluid enters lymph vessels. Lymph is eventually returned to the bloodstream and also transports certain absorbed fats and supports immunity. Therefore option A is correct, while the other choices describe gastric, plant, or kidney functions.

The governing concept is transpiration pull, supported by cohesion between water molecules and adhesion to xylem walls. When water vapour escapes through stomata, the water level in leaf tissues falls and tension develops in the continuous xylem column. This tension pulls water upward from the roots, helping replace the lost water. Hence option A is correct; phloem transports food, and the other choices are biologically unrelated.

The governing concept is selective urine formation in a nephron. Glomerular filtration allows small molecules, water, salts, glucose, and urea to leave the blood, so wastes can be removed but useful substances may also enter the filtrate. During reabsorption, needed water, glucose, and suitable ions return to the blood according to the body’s requirements. Therefore option A is correct; the other choices confuse excretion with photosynthesis, circulation, or respiration.

The governing concept is kidney function in excretion and maintenance of the internal environment. Metabolism continuously produces wastes such as urea, and healthy kidneys filter these substances from the blood and remove them in urine while regulating water and salts. If filtration is seriously impaired, wastes and excess substances remain in the bloodstream, causing harmful imbalance and illness. Thus option A is correct; the other options concern impossible or unrelated events.

The governing concept is excretion: healthy kidneys filter the blood, remove nitrogenous wastes and excess water, and form urine. If kidney function becomes severely reduced, urea and other wastes can accumulate in the blood. Dialysis uses a semipermeable membrane and special fluid to remove these substances artificially. Therefore option A is correct; the other options describe unrelated normal or plant processes.

The governing concept is plant excretion. Plants do not possess animal-like kidneys or lungs, so they use several alternative methods. Some wastes are stored in vacuoles, deposited in leaves or bark, or released as leaves and bark are shed. Gases may also diffuse out through stomata. Thus option A is correct, while B, C and D refer to animal organs or an impossible process.

The governing concept is energy release in life processes. Nutrition obtains or prepares nutrients such as glucose, which provide the raw material for cellular respiration. During respiration, glucose is oxidised and its stored chemical energy is released for movement, growth, repair and other activities. Therefore option A correctly links the processes; the remaining options confuse them with excretion, filtration or gas exchange.

The governing concept is the sequence of human nutrition. Digestion is the mechanical and chemical breakdown of complex carbohydrates, proteins and fats into smaller soluble molecules. Absorption is the movement of these digested nutrients through the intestinal wall, mainly in the small intestine, into blood or lymph. Hence option A is correct; the other choices assign circulatory, excretory or respiratory functions incorrectly.

The governing concept is the distinction between gas exchange and cellular respiration. Gas exchange is the physical diffusion of oxygen and carbon dioxide across respiratory surfaces such as alveoli or plant stomata. Cellular respiration is a chemical process inside cells in which food molecules are broken down to release usable energy. Therefore A is correct; gas exchange alone does not release all cellular energy, and the other options are biologically incorrect.

The governing concept is transport in multicellular life. Cells deep inside a large organism are far from the external environment, so diffusion alone is too slow to deliver oxygen and nutrients or remove carbon dioxide and other wastes. Circulatory or vascular systems move materials over these distances. Therefore option A is correct; the other choices contradict basic cellular requirements and organism structure.

The governing concept is diffusion in unicellular organisms. A unicellular organism consists of one small cell, and its cell membrane is directly exposed to the surrounding medium. The distance from the membrane to the cell interior is short, so oxygen, nutrients and wastes can move mainly by diffusion. A complex transport system is unnecessary. Thus option A is correct; the other choices describe organs or tissues absent from such organisms.

The governing concept is coordination between respiratory and circulatory systems. The respiratory system exchanges gases between air and blood at the alveoli: oxygen enters the blood and carbon dioxide leaves it. The circulatory system, with haemoglobin in red blood cells, transports oxygen to tissues and carries carbon dioxide back to the lungs for exhalation. Therefore option A is correct; the other pairs do not perform this complete gas-transport function.

The governing concept is that life processes require a continuous supply of usable energy. First, an organism makes or obtains food, which stores chemical energy. During cellular respiration, this energy is released and transferred mainly to ATP. ATP then powers transport, movement, growth, repair and other activities. Therefore, option A gives the correct sequence; the other options incorrectly connect unrelated processes.

Life processes collectively explain how organisms obtain nutrients and oxygen, release usable energy, transport materials, regulate internal conditions and remove wastes. These activities maintain the material and energy balance needed for survival. Thus option A is correct. Size alone cannot sustain life, wastes are produced by metabolism, and multicellular organisms require transport systems.

The governing concept is that stomata are microscopic pores that permit gas exchange between a leaf and the atmosphere. Carbon dioxide, a raw material for photosynthesis, normally enters through these pores. If a wax-like coating closes them, carbon-dioxide entry decreases first, so the photosynthetic rate may subsequently fall. Option A is correct; oxygen production would not immediately rise, root water uptake does not stop at once, and chlorophyll cannot turn into blood.

Photosynthesis requires light energy, water, carbon dioxide, and chlorophyll. Carbon dioxide supplies the carbon used to build glucose, so it is a direct raw material for the process. If light is available but carbon dioxide is deficient, carbon fixation slows and glucose production decreases sharply. Therefore option B is correct. Nitrogen is important for plant growth but is not the immediate carbon source, oxygen is mainly a product, and urea is a nitrogen fertilizer rather than a photosynthetic raw material.

Stomatal opening is controlled by the turgor pressure of the two guard cells. When they contain sufficient water, they become turgid and the pore generally opens; when water content decreases, they lose turgor and become flaccid. The pore can then close, limiting further water loss through transpiration. Thus option B is correct. Wider opening requires increased turgidity, while options C and D incorrectly assign unrelated functions to guard cells.

The governing concept is that green plants synthesize glucose by photosynthesis using light energy, carbon dioxide, and water; excess glucose is commonly stored as starch. When a plant is kept in darkness, the light-dependent stage cannot provide the required energy, so new food and starch formation become very limited or stop. Therefore option A is the best reason. Roots, oxygen uptake, and the absurd claim about blood do not explain the starch test.

The governing concept is the source and method of obtaining food. Autotrophic organisms, such as green plants, manufacture organic food from inorganic raw materials, usually using light energy, carbon dioxide, and water. Heterotrophic organisms cannot synthesize sufficient food from these materials and obtain it from other organisms or their products. Thus option A states the real distinction; blood colour, body size, and movement speed are unrelated characteristics.