Photosynthesis is an endothermic reaction- this means energy is transferreed from the environment in the process.


Plants use glucose in five main ways:

  • For respiration
  • Making cellulose
  • Making amino acids
  • Stored as oils or fats
  • Stored as starch

Limiting factors:

  • Not enough light slows down the rate of photosynthesis
  • Too little carbon dioxide also slows it down
  • The temperature has to be just right
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1) First you place the pondweed in a boiling tube of water and then place it in a test tube rack, then you place a light source at a specific distance from the pondweeds.

2) Then you turn on the lamp and the pondweed is left to photosynthesise for a set amount of time and the oxygen released will collect in the capillary tube.

3) At the end of the experiment, the syringe is used to draw the gas bubble in the tube up alongside a ruler and the length of the gas bubble is measured. This is proportional to the volume of CO2 produced.

4) Any variables that could affect the results should be controlled:

  • The temperature and the time
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