As light intensity increases to 800 (units), the rate of photosynthesis also increases. This is because a higher light intensity results in an increased rate of the light dependent reaction. However, when light intensity increases above 800, the rate of photosynthesis remains constant. This is because the light intensity is no longer the limiting factor, meaning that something else must be limiting the rate of photosynthesis. This could be carbon dioxide concentration or water availability. CO2 is required for the light independent stage of photosynthesis (the Calvin cycle) whereas water is required to produce H+ and e- for the electron transport chain.
Explanation:
I hope this would be enough to get the 4 marks. The main point is that the rate does not increase each time light intensity increases, because there is a limiting factor that is affecting the rate of the light independent reaction.
