100+ Free BGCSE Human & Social Biology Practice Questions

Explanation: Mitochondria are the organelles responsible for aerobic respiration, releasing ATP energy from glucose. Ribosomes synthesize proteins, while the nucleus controls cellular activities. The Golgi apparatus modifies and packages proteins for transport.

Explanation: Osmosis is the net movement of water molecules from a high water potential (dilute solution) to a lower water potential (concentrated solution) through a selectively permeable membrane. Diffusion applies to solute particles down a concentration gradient. Active transport requires ATP to move substances against a gradient.

Explanation: Red blood cells (erythrocytes) contain hemoglobin, an iron-rich protein that reversibly binds oxygen to form oxyhemoglobin for transport to body tissues. White blood cells defend against pathogens, and platelets assist in blood clotting. Plasma carries dissolved nutrients, wastes, and hormones.

Explanation: The left atrium receives oxygenated blood coming back from the lungs through the pulmonary veins. It then contracts to pump this blood into the left ventricle. The right atrium receives deoxygenated blood from the vena cava.

Explanation: Arteries carry blood away from the heart under high pressure, so they possess thick, muscular walls with elastic tissue to withstand and maintain blood pressure. Veins have thinner walls, wider lumens, and valves to prevent backflow under low pressure. Capillaries are single-celled vessels that facilitate material exchange.

Explanation: During inhalation, the diaphragm contracts and flattens while the external intercostal muscles contract to pull the ribcage upward and outward. This expands the thoracic cavity, decreasing pressure inside the lungs below atmospheric pressure so air rushes in.

Explanation: The alveoli are tiny air sacs in the lungs surrounded by dense capillary networks, providing a large surface area and thin barrier for rapid diffusion of oxygen into the blood and carbon dioxide out. The trachea, bronchi, and larynx are conducting airways.

Explanation: Peristalsis is the rhythmic, wave-like contraction of smooth muscles in the walls of the digestive tract that pushes food forward. Mastication is chewing, deglutition is swallowing, and emulsification is the breakdown of fat globules by bile.

Explanation: The liver produces bile (which emulsifies fats) and converts excess blood glucose into stored glycogen. The gallbladder stores and concentrates bile produced by the liver. The pancreas secretes digestive enzymes and hormones like insulin.

Explanation: The nephron is the microscopic functional unit of the kidney, containing a glomerulus, Bowman's capsule, and renal tubules that filter blood and form urine. Neurons are nerve cells. The ureter carries urine from kidney to bladder, and the glomerulus is just the capillary tuft within a nephron.