Priority 1: Balanced diet and nutrients
Seven components: carbohydrates, proteins, fats, vitamins (C and D), minerals (iron and calcium), fibre (roughage), and water. Know the function, source, and deficiency disease for each. Vitamin D deficiency → rickets. Iron deficiency → anaemia. Vitamin C deficiency → scurvy.
Priority 2: Digestive enzymes
Three main enzyme groups:
Amylase: starch → maltose (mouth and small intestine, optimum pH ~7).
Protease (pepsin): proteins → amino acids (stomach, optimum pH ~2).
Lipase: fats → fatty acids + glycerol (small intestine, optimum pH ~8).
Bile is not an enzyme: it emulsifies fats (increases surface area for lipase) and neutralises stomach acid.
Priority 3: Absorption through villi
Villi in the small intestine are adapted for absorption: large surface area (many villi with microvilli), thin walls (one cell thick, short diffusion distance), rich blood supply (maintains concentration gradient), lacteals (absorb fatty acids and glycerol).