photosynthesis

How are plants affected by light?
During photosynthesis oxygen is produced. How much photosynthesis occurs depends on how much light there is. You can measure the amount of oxygen produced using sensors connected to the computer. And you can start to explore how photosynthesis in plants is affected by light.

What you need
Live pond weed, such as Elodea. Keep this warm and illuminated before you use it, flask, 10g/L sodium hydrogen carbonate NaHCO3 solution, oxygen probe, oxygen sensor, light sensor and data logger.

Set up the oxygen sensor. Leave this for 15 minutes or so to stabilise. Connect the oxygen sensor to the interface. Connect the light sensor too. If the oxygen sensor is adjustable, you may be able to calibrate it to read 21% oxygen in room air. If the light sensor is adjustable use the broadest range.
Start up the sensing software, with luck it will automatically recognise the sensors you attached, otherwise you will have to do this yourself.
Get the software to record for 30 minutes. See if the sensors are responding within their range.
Shield the plant from light for the first 10 minutes or so. Use ambient light for the next 15 minutes. Use bright light for the remaining time.

Questions

  • Is oxygen produced steadily during photosynthesis? How does the light level affect photosynthesis?
  • Could heat from the light source affect your experiment?
  • How could you find out whether different coloured light affected? Do you think that there a point where more light has little extra effect?
  • What sort of graph would you expect if you left your experiment running over several days?
  • What happens to the production of oxygen overnight? Is there a daily pattern to the change in photosynthesis? Collect readings over several days, using a data logger, to find out. This device allows you to collect readings over several days without needing the computer running.

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