A-level set practicals: factors affecting rates of photosynthesis

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This updated version of the SAPS algal balls resource is designed to support the use of practicals across 2015 A-level biology specifications.

Students measure the rate of photosynthesis in comparison to the rate of respiration. Because of this, it is possible to determine the light intensity at which the photosynthesising material is using the same quantity of carbon dioxide in photosynthesis as it is producing in respiration (the light compensation point).

This practical provides the opportunity for skills development in

  • the use of appropriate instrumentation (a colorimeter) to record quantitative measurements
  • the safe and ethical use of organisms to measure plant responses to changing conditions
  • the use of computer modelling, or a data logger to collect data, or the use of software to process data
  • immobilisation of organic material (in this case algae but the technique is often used for enzymes as well)
  • the use of a smart phone as a lux meter (optional)
  • graphical skills (including plotting graphs with lines of best fit and reading off intercept points).

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