Photosynthesis is the process by which plants use the energy in sunlight to synthesise material from air and water for growth. The chemical equation for this process is shown below.

6CO₂+ 6H₂O C₆H₁₂O₆+ 6O₂

This investigation focuses on the production of oxygen by plants during the photosynthesis process. The investigation aim is to assess how light intensity affects the rate at which photosynthesis occurs and the rate of oxygen production.

You have a sprig of elodea (underwater) plant a test tube filled with water. A light source will be placed at different distances from the test plant. The oxygen is given off in the form of bubbles which you need to count using the tally counter.

Set the light source at 100cm from the elodea
Press start and using the counter, record the number of bubbles produced over one minute
Now, set the light source at 120cm from the elodea
Press start and using the counter, record the number of bubbles produced over one minute
Continue to do this for set distances of 140cm, 160cm, 180cm and 200cm

From your observations and data table, what effect does light have on the rate of photosynthesis?

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