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The digestive tract runs from the mouth through the oesophagus, stomach, small intestine and large intestine to the anus. Muscles move food along by squeezing in waves: peristalsis.

In the mouth, teeth break food into smaller pieces. Saliva moistens it and contains an enzyme that begins to break down starch.

The stomach is extremely acidic (pH 1.5–2.5). Its enzyme pepsin starts digesting protein, and the food becomes a soupy mix called chyme.

Experiment: Does chewing make a difference?

1. Put the same amount of water (for example 100 ml) at the same temperature into three cups.
2. Prepare three sugar cubes: leave one whole, break one into 4 pieces, and crush one into small grains with the back of a spoon (this is 'chewing').
3. Add each one to its own cup at the same time and stir each in the same way (for example, one stir every 10 seconds).
4. Time how long it takes until you can see no sugar left.
5. Repeat the test twice more and work out the mean time for each.

Sugar	Time trial 1 (s)	Trial 2 (s)	Trial 3 (s)	Mean (s)
Whole cube	Predict which will dissolve first.
4 pieces	Predict which will dissolve first.
Crushed	Predict which will dissolve first.

Questions

1. Put these in order: stomach, mouth, large intestine, oesophagus, small intestine.

2. What do the liver and the pancreas each add to help digestion?

3. What did your sugar experiment show? Use your mean times.

4. How did you keep your test fair?

Sources for every fact on this sheet: echoesof.science/school/digestion/sources/

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