Other investigations

Investigating the need for carbon dioxide in photosynthesis

  • Destarch a plant.
  • Expose one leaf to sodium hydroxide, which will absorb carbon dioxide from the surrounding air.
  • Expose another leaf to water (control experiment), which will not absorb carbon dioxide from the surrounding air.
  • Place the plant in bright light for several hours.
  • Test both leaves for starch using the 4-step starch test.

Results

Only the leaf that has been exposed to carbon dioxide will photosynthesise and therefore test positive for starch, showing that carbon dioxide is necessary for photosynthesis.

Investigating the production of oxygen

Photosynthesis oxygen experiment

If the rate of photosynthesis increases (e.g. by increasing the light intensity) the number of oxygen bubbles or volume of oxygen produced will also increase.

Measuring the volume of oxygen produced is more accurate than counting the bubbles of oxygen produced.

An oxygen electrode connected to a data logger can be used to measure the change in oxygen concentration.