When light shines on pondweed, Elodea sp, bubbles of gas are released. The rate at which bubbles of gas are produced can be used to measure the rate of photosynthesis. An investigation was carried out to study the effect of different colours of light on the rate of photosynthesis in the pondweed. The apparatus was set up as shown in the diagram below. The pondweed was exposed to one colour of light and left for 5 minutes before measurements were taken. The time taken for the release of 20 bubbles were recorded.