Theory question 102
Food Substances and Enzymes(a) What is a balanced diet?
(b) Name the classes of food stating the importance of any two to the human diet.
(c) In a tabular form, state the source, substrate and end products of the following enzymes:
(i) ptyalin; (ii) pepsin; (iii) lipase.
Show the model answer
(a) A balanced diet is one that contains all the classes of food in the right amounts and proportions for the body's needs.
(b) Classes: carbohydrates, proteins, fats and oils, vitamins, mineral salts, water (and roughage).
Any two: carbohydrates – main source of energy; proteins – growth and repair of tissues, making enzymes and hormones; fats – energy store, insulation; vitamins – prevent deficiency diseases, help body processes; minerals – build bones and teeth (calcium), make haemoglobin (iron); water – solvent, transport, temperature control; roughage – prevents constipation.
(c) Ptyalin: source – salivary glands (saliva); substrate – starch; product – maltose.
Pepsin: source – gastric glands of stomach; substrate – proteins; product – peptones/polypeptides.
Lipase: source – pancreas (pancreatic juice) and intestinal glands; substrate – fats and oils; product – fatty acids and glycerol.
Use a table with source, substrate, product columns.