AQA GCSE Biology

Revision Notes

4.1.4 Required Practical: Photosynthesis Rate

Investigating Photosynthesis

  • Aim: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed
  • You will:
    • measure the volume of oxygen produced by the pondweed as the light intensity changes as the light source is moved
    • measure and calculate rates of photosynthesis
    • extract and interpret graphs of photosynthesis rate involving one limiting factor
  • The most commonly used method to measure the rate of photosynthesis is to measure or observe the oxygen released from aquatic plants

Investigating the effect of changing light intensity on the rate of photosynthesis, downloadable IGCSE & GCSE Biology revision notes

Diagram showing the setup for the investigation using aquatic plants

Method

  • Place a piece of pondweed (Elodea or Cabomba are often used), into a beaker of water
  • Use a light a set distance from the plant
  • Record the number of bubbles observed in three minutes
  • Repeat steps for different distances

Improvements

  • Use a gas syringe to collect the volume of gas produced
  • Repeat the experiment at least twice for each distance and calculate the mean number of bubbles
  • Use of a glass tank between lamp and plant to prevent heating of the plant, or using an LED bulb that releases very little heat energy

Variables

  • Different variables can be investigated using this method. The three diagrams show the setup for 3 independent variables: light, carbon dioxide and temperature

Results

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

Graph RP6, downloadable IGCSE & GCSE Biology revision notes

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

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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