Human Anatomy and Physiology
Human physiology questions ask you to trace a substance through a system, match an organ's structure to its function, and explain a homeostatic response in a sequence of steps.
Digestion and absorption
Mechanical breakdown in the mouth and stomach; chemical digestion by enzymes: amylase (starch → maltose), protease (protein → amino acids), lipase (fat → glycerol and fatty acids). Most absorption occurs in the small intestine, whose villi give a large surface, a thin epithelium and a rich blood supply. Water is reabsorbed in the large intestine.
Respiration and circulation
Breathing: intercostal muscles and diaphragm raise the ribcage and flatten the diaphragm, increasing volume and lowering pressure, so air enters. Alveoli are thin, moist, richly supplied with capillaries. The heart has four chambers; the right side pumps deoxygenated blood to the lungs, the left side pumps oxygenated blood to the body - double circulation keeps pressures high. Arteries carry blood away from the heart, veins toward it, capillaries allow exchange.
Excretion and control
The kidneys filter blood in the nephron: filtration in the glomerulus, then selective reabsorption of glucose, some water and salts; the rest becomes urine. Homeostasis uses negative feedback - insulin lowers blood glucose, glucagon raises it; sweating and vasodilation cool the body.
Worked example
A runner stops after a sprint and keeps breathing heavily. Reasoning: during the sprint, muscles respired faster than oxygen could be delivered, so anaerobic respiration produced lactic acid; the extra oxygen after exercise is needed to break the lactic acid down, so ventilation and heart rate stay elevated until the "oxygen debt" is repaid. Each causal step deserves a mark.
Traps
Mixing up the left and right sides of the heart; thinking the pulmonary artery carries oxygenated blood; saying arteries always carry oxygenated blood; forgetting that only the small intestine absorbs nutrients; omitting reabsorption when describing the kidney; giving a homeostatic answer without stating that the change is reversed back to normal.