To investigate the effect of light intensity on the rate of photosynthesis

GCSE: Biology

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We know that the equation for photosynthesis is:

6H2O + 6CO2 C6H12O6 + 6O2
Light Energy


Or


Water + Carbon Dioxide Glucose + Oxygen
Light Energy

This equation, along with knowledge that we already have, shows us that water, carbon dioxide and light are needed for photosynthesis to occur. It is difficult to show how rich in minerals certain water is, or how much carbon dioxide is getting to the plant, so we will base our experiment on light energy. Similarly, it is difficult to decipher exactly how much sugar is produced, so we will measure the amount of oxygen given off in a set period of time. We will use an aquatic plant (a hydrophyte) to ensure that any oxygen that is present will have been created by the plant (the oxygen would not have been present at the start of the experiment if under water). We have decided to use Elodea (Canadian pond weed) for this experiment. We will count how many bubbles of oxygen are produced per minute, to work out the rate of photosynthesis at different light intensities. We will decide the distances to set the light to after seeing the results of our preliminary work.
Method

i) Apparatus

We will need:
1) Lamp (60W bulb)
2) Plant (Canadian Pond Weed)
3) Scalpel (to cut the plant)
4) Tweezers (to put the plant into the test tube)
5) Test tube containing the plant
6) Test tube rack
7) Stop clock (digital for accuracy)
8) Ruler (1 metre… accurate to 1mm)
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