Required Practical: Photosynthesis Rate (AQA GCSE Biology)
Revision Note
Written by: Lára Marie McIvor
Reviewed by: Lucy Kirkham
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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
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
A graph of distance from the lamp against number of bubbles per minute
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