Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
6
Digestion
_Why do we digest food (pages 56–57)____________
PRACTICAL Using a ‘model gut’ (pages 56–57)
1. Explain what your results show about the gut and digestion.
The results show that starch cannot pass out of the gut into the blood, but glucose can.
Therefore, starch has to be digested into glucose in order for it to be used by the body.
2. Suggest why it is better to use a boiling tube in this experiment, rather than a beaker, which would
hold more water.
The quantity of glucose going into the water from the visking tubing is likely to be small.
The more water there is, the more dilute the glucose solution will be, and if it is too dilute,
the clinistix will not detect it.
Discussion point
How good a model of the gut and blood system do you think this apparatus is Justify your opinion.
The visking tubing has similar properties to the lining of the gut and so from that point of view
the model is good. Blood is mostly water so using water as a model for blood is reasonable.
However, there are other tissues in the gut between the lining and the blood vessels, and other
substances in the gut and the blood which may affect the process, so the model has some
weaknesses. As the experiment is qualitative rather than quantitative, the model is adequate.
_What food needs digesting (pages 57–58)_________
Question
1. When people need energy very rapidly (e.g. athletes before strenuous exercise, diabetics with low
blood sugar levels) they take glucose tablets or drinks. Why would glucose be a particularly good
source of rapid energy
Glucose is high in energy and is already a simple sugar which can pass through the gut wall
without being digested. It would therefore get into the blood quicker than most other
carbohydrates.
PRACTICAL How do we know what our food contains
(page 58)
1. The more sugar there is in the solution, the further the colour change in the Benedict’s solution
goes. This gives an indication, but not a measure, of how much glucose is in the solution. Suggest
how you might get an actual measure of the amount of glucose in a solution, using the Benedict’s
test.
If you did the test with a series of different concentrations of glucose, and ran it for a set
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