A student investigated the effect of light intensity on the rate of photosynthesis.
The diagram shows the apparatus the student used.
This is the method used.
1. Set up the apparatus as shown in the diagram above.
2. Place the lamp 10 cm from the pondweed.
3. Turn the lamp on and count the number of bubbles produced in one minute.
4. Repeat with the lamp at different distances from the pondweed

The teacher suggests putting the boiling tube into a beaker of water during the
investigation.
Suggest why this would make the results more valid.
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