Describe the digestion of food in human beings. Draw a labelled diagram of the human alimentary canal.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. Digestion is the breaking down of complex food into simple, soluble substances that the body can absorb, with the help of enzymes.
2 · Mouth and oesophagus. Salivary amylase breaks starch into sugar; peristalsis pushes food down the oesophagus.
3 · Stomach. HCl turns pepsinogen into pepsin and kills germs; pepsin breaks proteins into peptones.
4 · Small intestine.
Bile from the liver emulsifies fat and makes the medium alkaline.
Pancreatic juice: trypsin for proteins, amylase for starch, lipase for fats.
End products: glucose, amino acids, fatty acids and glycerol, absorbed by the villi.
5 · Large intestine. Water is absorbed; the faeces pass to the rectum and leave through the anus.
6 · Draw the alimentary canal. [Diagram: mouth, salivary glands, oesophagus, stomach, liver, gall bladder, pancreas, small intestine, large intestine, rectum, anus]
7 · Link to daily life. Chewing food well and eating raw vegetables for roughage keep digestion smooth.
8 · Close in one line. Thus food is digested step by step and absorbed mainly in the small intestine.
Scoring tip: Name the enzyme and its product at each part; examiners give marks for amylase, pepsin, bile, trypsin and lipase.
