How does light intensity, chlorophyll concentration and oxygen concentration affect photosynthesis?
Increasing light intensity = more light available to the plant (more electrons in chlorophyll molecules can be excited at any point in time) = greater rate of photosynthesis. Eventually you'll reach a point though were increasing light intensity further has no effect on the rate of photosynthesis (if you've got a graph of the rate of photosynthesis this corresponds to a plateau)
Greater chlorophyll concentration = more chlorophyll molecules available to absorb light at any point in time = greater rate of photosynthesis
Increasing oxygen concentration may increase the rate of photosynthesis slightly, but probably only if the plant was in an environment depleted of carbon dioxide. Increasing O
2 concentration would increase the rate of aerobic respiration in the plant, increasing the rate at which CO
2 is produced by aerobic respiration. If we increase this rate of CO
2 output the plant is more rapidly able to use that CO
2 for photosynthesis (as part of the light-independent stage). Most likely though the plant will have a plentiful supply of CO
2 from the atmosphere, so this increase in CO
2 output from aerobic respiration will have only a negligible effect on the rate of photosynthesis