Nutrition provides the body with energy and materials for growth. Classes of food: Carbohydrates (energy), Proteins (growth/repair), Fats (insulation/energy), Vitamins, Minerals, Water, and Fibre. Digestion breaks large food molecules into small ones. Organs: Mouth (amylase breaks starch), Stomach (pepsin + HCl breaks proteins), Small intestine (lipase, pancreatic amylase; absorption of nutrients), Large intestine (water absorption). Villi increase surface area for absorption.