Programme 21: Food and Digestion

Answers to Activity Sheet 1

Programme Questions

Food Tests

1. Rice, potatoes, pasta, noodles, yam, cassava, sweet potatoes.
2. Test a measured volume of fruit juice and compare the colour at the end of the test. The colour sequence (green, yellow, orange, red) shows an increasing amount of sugar. The test is reliable for simple comparisons but as the fruit ripens the amount of sugar increases.

The Digestive System

1. Muscle contractions push the water up your oesophagus and into your stomach. The stomach has rings of muscle at the top and the bottom which work like doors.
2. The stomach secretes acid. When the stomach is full some acid may be forced out into the oesophagus. You can cure it by taking medicine which contains a weak base.
3. The intestine is a 6m long, folded tube. Its surface is folded and each fold is covered in thousands of tiny projections called villi.
4. It has a large surface area, a thin wall and a good blood supply.
5. Mouth, oesophagus (or gullet), stomach, small intestine (made up of duodenum, jejunum and ileum), large intestine (made up of caecum and colon), rectum, anus.

Digestive Enzymes

8.

Nutrient	Enzyme	Product of digestion
Starch	amylase	maltose sugar
Protein	protease	amino acids
Fat	lipase	fatty acids and glycerol

2. Bile salts are released into the small intestine where they neutralise acid as it leaves the stomach. The pancreas secretes amylase into the small intestine to digest starch. Amylase works best at neutral pH.

3. The mixture needs to be alkaline at the start of the investigation so that the indicator is pink. Any fatty acids made will gradually decolourise the indicator.