Required Practical: Photosynthesis Rate (AQA GCSE Combined Science: Trilogy: Biology): Revision Note

Investigating photosynthesis

• Aim: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed

• The most commonly used method to measure the rate of photosynthesis is to measure or observe the oxygen released from aquatic plants

• To prevent heating the plant, there are two options:

  • using a glass tank between the lamp and the plant

  • using an LED bulb that releases very little heat energy

Diagram showing the setup for the investigation using aquatic plants

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Method

1. Place a piece of pondweed (Elodea or Cabomba are often used) into a beaker of water

2. Use a light a set distance from the plant

3. Record the number of bubbles produced in one minute

4. Repeat the experiment at least twice for each distance and calculate the mean number of bubbles

5. Repeat steps 2–4 for different distances

Improvements

• Use a gas syringe to collect the volume of gas produced

Variables

• Different variables can be investigated using this method - the diagram above shows the setup for light as the independent variable

• To investigate carbon dioxide, use different concentrations of sodium hydrogencarbonate in the beaker

• To investigate temperature, change the temperature of the beaker containing the pondweed

Results

• A graph of the independent variable against the number of bubbles produced per minute can be drawn to see the pattern or trend

A graph of distance from the lamp against number of bubbles per minute

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