Biological World Working as a Scientist Making and Recording Observations
Investigating Light and Photosynthesis A student in a different class has designed the investigation shown in Fig. 3.5.1. You have been asked to change it to examine the relationship between light intensity and the rate of photosynthesis. The hypothesis is ʻThe greater the light intensity, the greater the rate of photosynthesis’.
Step 1: Collect the necessary equipment and position the lamp approximately 50 cm away from the Canadian Pondweed. Do not turn on the lamp.
1 Consider the factors that are likely to affect the rate of photosynthesis. You must collect data on factors such as: z Distance between the lamp and beaker with Canadian Pondweed.
z Mass of sodium hydrogencarbonate.
z Wattage of bulb.
2 Make a list of at least five other factors that are key to the relationship between light intensity and the rate of photosynthesis. You must collect this data to help you test the hypothesis. Decide what equipment you will need to take and record these measurements.
Water Light
Canadian Pondweed
Lamp Fig. 3.5.1
Set-up to investigate the relationship between light intensity and rate of photosynthesis
Step 2: Now turn on the lamp. Wait for three minutes and then record the number of bubbles that drift up through the boiling tube over the next 60 seconds.
Step 3: Move the lamp 10 cm closer to the Canadian Pondweed. Wait three minutes and then, once more, record the number of bubbles that drift up through the boiling tube over the next 60 seconds. Repeat three more times until you have reached a distance of 10 cm between the Canadian Pondweed and the lamp.
3 Record your results in a table.
4 Comment on the trend that you have observed and compare with other groups in the class. Does this trend support the original hypothesis?
5 Comment on likely sources of error. How could you change the investigation to improve accuracy? Consider a suitable control for this investigation.
