CAIE IGCSE Biology 6.1.9 Aquatic Plant Gas Exchange in Light & Dark
Practise using hydrogencarbonate indicator to compare net carbon dioxide exchange by aquatic plants in light and darkness.
- Syllabus
- 2026–2028
- Course
- Biology 0610
Exam points
- explain that hydrogencarbonate indicator turns purple in light when photosynthesis removes carbon dioxide faster than respiration releases it
- explain that hydrogencarbonate indicator turns yellow in darkness when respiration releases carbon dioxide
- state that respiration occurs in both light and darkness while photosynthesis occurs only in light
6.1.9—Effect of light and dark conditions on question 1
A student investigated the effect of light on photosynthesis in algae, using hydrogencarbonate indicator solution.
Carbon dioxide is an acidic gas.
Table 4.1 shows the colour of the hydrogencarbonate indicator solution at different pH values.
Table 4.1
Two test-tubes were set up at the same time. Both contained algae and hydrogencarbonate indicator. At the start of the investigation the hydrogencarbonate indicator was red in both test-tubes.
One test-tube was placed in the dark and one test-tube was placed in the light.
After 20 minutes, the contents of the test-tube in the dark were yellow and the contents of the test-tube in the light were purple.
Explain these results.
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