Nutrition, Digestion and Metabolism
Nutrition, Digestion and Metabolism tests nutrients, balanced diets, deficiency diseases, digestive enzymes and the sites where food is broken down and absorbed. Expect matching questions and short explanations of enzyme action.
Nutrients and balanced diet
Carbohydrates give energy; proteins build and repair tissues; fats give concentrated energy and carry fat-soluble vitamins. Water and roughage are also essential. Vitamins and minerals are micronutrients. A balanced diet includes cereals, pulses, milk, vegetables, fruits and some fat in suitable proportions.
Digestion
In the mouth, salivary amylase begins starch digestion, turning starch into maltose. The stomach secretes hydrochloric acid, which kills microbes and activates pepsin; pepsin begins protein digestion. In the small intestine, pancreatic amylase, trypsin and lipase act, while bile emulsifies fats. Intestinal enzymes complete digestion, and villi absorb glucose, amino acids, fatty acids and glycerol. The large intestine absorbs water and forms faeces.
Metabolism and deficiency
Anabolism builds complex molecules; catabolism breaks them down to release energy. Vitamin A deficiency causes night blindness, B1 deficiency beriberi, C deficiency scurvy, and D deficiency rickets. Iron deficiency causes anaemia; iodine deficiency causes goitre.
Worked example
Question: Why is bile needed for fat digestion when it is not an enzyme? Reasoning: fats are hydrophobic and form large droplets; bile salts emulsify them into smaller droplets, increasing surface area for lipase. Without bile, fat digestion is slow and incomplete.
Traps
Starch digestion begins in the mouth but is completed in the small intestine; protein digestion begins in the stomach; bile is not an enzyme; vitamins are micronutrients, not energy foods.