Investigating the Rate of Photosynthesis | Biology for GCSE/IGCSE - Year 11 PDF Download

Investigating the Rate of Photosynthesis

• The plants typically used for this experiment are Elodea or Cabomba, which are types of pondweed.
• During photosynthesis, oxygen gas is produced and released by the plant.
• When the plant is submerged in water, the released oxygen can be observed as bubbles emerging from the cut end of the pondweed.
• The number of bubbles produced per minute can be counted to measure the rate of photosynthesis.
• A higher number of bubbles per minute indicates a faster rate of photosynthesis.
• For greater accuracy, the oxygen released can be collected in a test tube inverted over the pondweed for a longer period, and the volume of oxygen collected can be measured.

This practical experiment can be used in the following ways:

Investigating the effect of changing light intensity

• This can be achieved by positioning a lamp at various distances from the beaker containing the pondweed.

Investigating the effect of changing temperature

• This can be done by changing the temperature of the water in the beaker

Investigating the effect of changing carbon dioxide concentration

• This can be achieved by dissolving varying amounts of sodium hydrogen carbonate in the water within the beaker.

• Care must be taken when investigating a condition to keep all other variables constant in order to ensure a fair test
• For example, when investigating changing light intensity, a glass tank should be placed in between the lamp and the beaker to absorb heat from the lamp and so avoid changing the temperature of the water as well as the light intensity