Investigating the effect of light intensity on the rate of photosynthesis of Elodea


In this experiment the rate of photosynthesis is measured by counting the number of bubbles rising from the cut end of a piece of Elodea. The plant will be exposed to different light intensity in order to establish the correlation between light and rate of photosynthesis.  The independent variable is the light and carbon dioxide intake, the dependent variable is the number of released bubbles and the constant variable is the strand of Elodea.


  • 2 test tubes in which to put the Elodea in
  • Elodea plants kept in a tank
  • Water I which to put the Elodea in as to observe the bubbles
  • Liquid CO2 in order to speed up the reaction


  1. Pour water into the two test tubes and add a strand of Elodea in each one, cutting the top off as to increase the photosynthesis rate.
  2. Add CO2 in order to speed up the reaction.
  3. Put one tube in the shade and expose the other to daylight.
  4. Observe the bubbles in both tubes after 1minute.



  • There were some bubbles in the light and no bubbles in the shade. This indicates that photosynthesis has a positive correlation with light. The more light is present the faster the process.

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