The diagram shows a set-up used to investigate the effect of light intensity on the rate of photosynthesis. A pond weed was placed inside a beaker and the gas bubbles released were counted per minute.

Light intensity (watts): 0, 3, 10, 16, 25, 30, 35, 40. Number of gas bubbles released per minute: 0, 7, 20, 31, 43, 47, 50, 50. (Plot the graph on paper.)

1. aUsing your graph, determine the number of bubbles released per minute at a light intensity of 20 watts. [2]
2. bName the gas collected during the investigation. [1]
3. cExplain the observation made from the light intensity of 35 to 40 watts. [2]
4. dWrite down the conclusion that could be made from the investigation. [1]

You'll mark your own answer against the marking guide when you hand it in.