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Q1.
Light intensity, carbon dioxide concentration and temperature are three factors
that affect the rate of photosynthesis.
How would you investigate the effect of light intensity on the rate of
photosynthesis?
The image below shows some of the apparatus you might use.
You should include details of:
• how you would set up the apparatus and the materials you would use
• the measurements you would make
• how you could make this a fair test
(Total 6 marks)
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To measure the effect of light intensity on photosynthesis, place a pondweed plant in a beaker of water (so that the water levels is not a limiting factor). Then place the light approximately 20cm away from the beaker and switch it on. Use a timer to count 60 seconds and then after the timer is done, count the number of bubbles which is produced (the bubbles will be of oxygen which is a product of photosynthesis). record the results and increase the distance of the lamp by another 20 cm and redo the above steps. repeat this until the distance of the lamp is one meter away from the beaker. To make this fair, repeat the experiment to get multiple values in order to calculate a mean/average which is more fair. Use the same pondweed plant and lamp to make it fair.
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I used the same type and same length of pondweed each time.
I kept the temperature the same by using a water bath.
I made sure the amount of carbon dioxide stayed the same by adding the same amount of sodium hydrogencarbonate to the water.
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