Question

What is the relationship between an increase in light intensity and photosynthetic rate in leaves from a corn plant? How does this relationship compare with what you observed for tomato plants?

Answer 1

The relationship between light intensity and photosynthetic rate is that if the intensity of the light is high then the rate of photosynthesis will increase. However the rate of photosynthesis will only increase to an extent after intensity of light reaches a certain point photosynthesis rate will stay still.

Answer 2

A corn plant is a C4 plant, while tomatoes are C3. They therefore exhibit different CO2 fixation strategies.

In C3 plants, CO2 diffuses into bundle-sheat cells and is fixated by RuBisCO into phospho-glycerate, marking the beginning of the calvin cycle.

In C4 plants, CO2 is solubilized first in mesophyllic cells by carboanhydrase, and then fixated into oxaloacetate by the PEP carboxylase. The C4-body is then transferred into bundle-sheath cells, and decarboxylated, releasing CO2 into the bundle-sheath cell. These cells also contain RuBisCO, with re-fixates CO2 and from here, the normal calvin cycle commences.
This fixation strategy is more energy-consuming than in C3 plants. Photosynthesis is therefore weaker when light intensity is low. But it makes up for it under strong lights, and here's why:

RuBisCO is far less efficient in fixating CO2 than in fixating O2, which is a by-product of photosynthesis. In C3 plants, the excess O2 will inhibit the work of RuBisCO if photosynthesis rates are high (for instance: under high light intensity). In C4 plants, because CO2 is enriched in the bundle-sheat cells, you get a vastly higher photosynthesis level, because RuBisCO can work efficiently even under high light intensity.

See Graph.