Investigating Gas Exchange (CIE IGCSE Biology)
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Biology Lead
Investigating Gas Exchange
- Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration
- Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis
- At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide
Photosynthesis and respiration in plants
- During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net intake of carbon dioxide and a net output of oxygen
- We can investigate the effect of light on the net gas exchange in an aquatic plant using a pH indicator such as hydrogencarbonate indicator
- This is possible because carbon dioxide is an acidic gas when dissolved in water
- Hydrogencarbonate indicator shows the carbon dioxide concentration in solution
- The table below shows the colour that the indicator turns at different levels of carbon dioxide concentration
- Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator
- The effect of light can then be investigated over a period of a few hours
- Results from a typical experiment are shown in the table below:
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