Life Processes

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.

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.

Nutrition describes how an organism obtains and uses food. Autotrophs synthesize organic food from inorganic raw materials, commonly carbon dioxide and water, using light or chemical energy. Heterotrophs cannot generally make their own food from these simple substances and obtain ready-made organic matter from other organisms or sources. Thus option A states the defining difference; the body-part and blood-colour choices are unrelated.

Amoeba is unicellular, so it has no separate organs or a tubular digestive tract. It surrounds food using pseudopodia and encloses it in a food vacuole. Digestive enzymes act inside this vacuole, nutrients pass into the cytoplasm, and undigested residue is expelled from the cell. Therefore option A is correct. The other choices incorrectly assign multicellular organs, blood circulation, or photosynthesis to Amoeba.

Different digestive organs provide different enzymes and chemical conditions. In the mouth, salivary amylase begins the digestion of starch in a nearly neutral medium. In the stomach, hydrochloric acid creates an acidic environment and activates pepsin, which begins protein digestion. Therefore option A correctly matches the two roles. The other options confuse digestion with excretion, respiration, circulation, or absorption.

The liver produces bile, and bile salts help emulsify fats in the small intestine. Emulsification does not chemically digest fat, but it divides large droplets into smaller ones so lipase can work over a larger surface. Without bile, fat digestion and subsequent absorption are most affected. Thus option B is correct; vitamins and minerals generally do not require enzymatic digestion, while starch uses amylase.

The large intestine absorbs a substantial amount of water and electrolytes from the undigested residue. This process helps convert the residue into more solid faeces. If water absorption is insufficient, excess water remains in the intestinal contents, so the faeces stay loose or watery and may lead to diarrhoea. Thus option A is correct; the other choices describe unrelated processes or plant transport.

The urinary system uses two different tubes with different routes. Each ureter is a muscular tube that carries urine produced by a kidney to the urinary bladder, where urine is temporarily stored. The urethra is the passage through which urine leaves the bladder and exits the body during urination. Thus option A correctly identifies both directions and endpoints. The remaining options confuse these tubes with airways, food passages, blood vessels, or bile-producing organs.

The trachea is an air passage leading toward the bronchi and lungs. Its lining helps trap dust and other particles in mucus. A cough is a protective reflex that produces a forceful outward flow of air, helping dislodge and expel the irritant so breathing remains easier. Thus option A is correct; the other options refer to digestion, excretion, or plant transpiration.

The brain and spinal cord together form the central nervous system. The brain processes information and coordinates activities, while the spinal cord transmits messages between the brain and body and mediates many reflex actions. The other systems are different in function: the digestive system processes food, the respiratory system handles gas exchange, and the excretory system removes wastes — none are composed of brain and spinal cord. Exam tip: Memorize that the CNS = brain + spinal cord and list one primary function of each in answers.