Environmental Factor on Rate of Photosynthesis

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19. Investigation of the effects of environmental factors on the rate of photosynthesis
The rate of photosynthesis of a photosynthetic plant is affected by factors such as light quality, light intensity, carbon dioxide concentration and temperature. A convenient way of investigating the effects of these factors on the rate of photosynthesis is to measure the volume of oxygen given off by a plant in a given time. When a particular factor is being investigated, it is essential that other factors are kept constant and, if possible, at optimum levels so that no other factors are limiting. Pondweeds, like Hydrilla and Ceratophyllum, are suitable plant materials for this investigation. It is advisable to use plant materials that have been well illuminated for three or four hours before the experiment.

Fig.1 Experimental set up

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A. To investigate the effect of light quality on the rate of photosynthesis Procedure 1. 2. 3. 4. 5. Cut the stem of a well-illuminated piece of Hydrilla to about 10 cm long. Place it with cut surface upwards, in a boiling tube filled with 0.25% sodium hydrogencarbonate solution. Wrap the tube with red cellophane. Set up the apparatus as shown in Fig.1. Stand the tube in a beaker of water at room temperature. Record the temperature of the water, which acts as a heat shield, and check it at intervals throughout the experiment. It should remain constant and the water should be renewed if necessary. 6. 7. 8. Put a 100-watt table lamp at 20 cm from Hydrilla. Turn on the lamp. Wait for about 5 minutes for Hydrilla to equilibrate. Suck the sodium hydrogencarbonate solution from the tube into the pipette. Close the clip and record the initial reading. Make sure that the clip is tightened to prevent the solution in the pipette from falling. 9. After a fixed period of time (e.g. 5 minutes), record the final reading in the pipette and calculate the volume of gas collected. 10. Repeat steps (2)...