C3 C4 CAM

First off, C3 plants are called C3 because the CO2 is incorporated into a 3 carbon compound. For the C3 plants, their stomatas are opened during the day. Rubisco is involved in the photosynthesis. Initial fixation of carbon occurs via rubisco, which is the enzyme that catalyzes the first step of the Calvin cycle, the Calvin cycle enzyme that adds carbon dioxide to ribulose biphosphate. The first organic product of carbon fixation is a three-carbon compound (3-phosphoglycerate). Examples of C3 plants are rice, wheat and soy.C3 plants are more productive when in moist areas compared to C4 or CAM plants. They produce less food when their stomatas are closed which is during hot, dry days. C4 plants preface the Calvin cycle with an alternate mode of carbon fixation which forms a FOUR-carbon compound as its first product. They are important to agriculture and some examples are sugarcane and corn. In C4 plants, there are two distinct types of photosynthetic cells, bundle-sheath and mesophyll cells. C4 photosynthesize faster than C3 plants under high light intensity and temperature because carbon dioxide goes directly to the rubisco. CAM plants' stomatas are opened during the night and usually closed during the day. They use water better than C3 plants because their stomatas are opened during the night. They are usually found in deserts. It prevents carbon dioxide from entering the leaves. the mesophyll cells of CAM plants store organic acids made during the
night.
Reference : http://wc.pima.edu/Bfiero/tucsonecology/plants/plants_photosynthesis.htm and Biology Book.