C3, C4, and CAM Plants

C3 plants is the first organic product of carbon fixation, a three-carbon compound, 3-phosphoglycerate. C3 plants produce less food when their stomata close on hot and dry days and ribisco can only accept O2 in replace of CO2, which means that the Calvin cycle would have more O2 than CO2. This then results in a process known as photorespiration where it produces no food and generates no ATP. Photorespiration decreases photosynthetic output.
C4 plants form a four-carbon compound as its first product which includes bundle-sheath cells and mesophyll cells as two types of photosynthetic cells. Bundle-sheath cells are arranged into tightly packed sheaths around the veins. Mesophyll cells are found between the bundle sheath and the left surface. The enzyme PEP carboxylase adds CO2 to PEP, therefore being able to fix CO2 efficentiely when ribisco cannot. Within the bundle-sheath cells, the four-carbon compound releases CO2, and mesophyll cells pump CO2 into the bundle sheath cells.
CAM plants open their stomata during the night and close them during the day. They close their stomata during the day because it helps desert plants conserve water, as well as prevent CO2 from entering the leaves. When the leaves are opened during the nighttime, the plants take up CO2. The mesophyll cells store the organic acids they make during the night until the morning when their stomata close. Therefore, during the day, the light reactions that supply ATP and NADPH for the Calvin cycle release CO2 from the organic compound that was made the night before.

Source: Campbell book