Figure 3.11 Leaf cell arrangements for C3 versus C4 plants. (a) C3 plants conduct all steps of photosynthesis in the chloroplasts of the mesophyll cells. (b) In C4 plants, the initial step of carbon assimilation and the light reactions take place in the chloroplasts in mesophyll cells. However, the CO2 that has been assimilated is then transported to the bundle sheath cells where the Calvin cycle takes place.