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How To Set Up and Demonstrate Light Intensity and Photosynthesis for GCSE

How To Set Up and Demonstrate Light Intensity and Photosynthesis for GCSE

In this video, Denise Ralph will show you how to demonstrate photosynthesis using pondweed. This practical is an essential part of the GCSE Biology curriculum, focusing on understanding the vital process of photosynthesis in plants.

This experiment is ideal for teaching the following key learning objectives:

  1. Carbon Dioxide Requirement: Explore how the addition of a bicarbonate solution provides the necessary carbon dioxide for the photosynthetic process.
  2. Light as an Essential Factor: Understand the role of light, mimicked by a lamp in this experiment, in driving photosynthesis.
  3. Oxygen Production: Observe the release of oxygen bubbles from the cut end of the pond weed as a direct result of the photosynthetic activity.



You will need:

  • Fresh pond weed (elodea or similar) – 2-3 cm cut
  • Test tube
  • Bicarbonate of soda solution (3 spatula full in 50 ml water)
  • Retort stand with a clamp
  • Lamp (light source)
  • Water


  1. Measure three spatulas full of bicarbonate of soda and dissolve it in 50 ml of water. Stir until it’s well-mixed.
  2. Set up the retort stand with a clamp on a stable surface.
  3. Take the fresh pond weed and cut it to a length of about 2-3 cm. Place the cut end of the pond weed in the test tube, making sure the cut part is facing upward.
  4. Pour the prepared bicarbonate of soda solution into the test tube until the pond weed is fully submerged. This bicarbonate solution provides carbon dioxide necessary for photosynthesis.
  5. Firmly fix the test tube into the clamp on the retort stand. Ensure that the pond weed is fully immersed in the bicarbonate solution.
  6. Position the lamp in such a way that it shines directly on the pond weed in the test tube. The light source is essential for the process of photosynthesis.
  7. Switch on the lamp to initiate the photosynthesis process.
  8. Watch for the appearance of bubbles coming from the cut end of the pond weed. These bubbles are oxygen produced during photosynthesis. You can also use a stirring rod to gently stir the solution, which can help in the release of any trapped oxygen.
  9. Record the observations, noting the time it takes for bubbles to appear and any other changes you observe.

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.

Important safety precautions and tips:

    • Use a transparent test tube to easily observe the bubbles.
    • Ensure that the lamp is at an appropriate distance to provide sufficient light for photosynthesis.
    • Repeat the experiment with variations, such as changing the distance of the lamp or using different concentrations of bicarbonate solution, to explore the effects on the rate of photosynthesis.

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