C3 Plants use the enzyme rubisco to fix CO2 to RuBP in the mesophyll cells, creating 2 3PG molecules. However, if the weather is hot and dry, their stomata will close causing a buildup of oxygen. because of this, RuBP will bind to oxygen but creates only 1 3PG. CO2 is also released. This whole process of when oxygen binds to rubisco is called photorespiration.
In C4 Plants, however, CO2 combines with PEP to form oxaloacetate. CO2 is taken in via mesophyll cells, and malate is pumped into the bundle sheath cells. CO2 then enters the Calvin Cycle. In hot weather, though, C4 plants' PEP does not combine with oxygen, making it more efficient. C3 Plants, however, are more efficient in moderate temperatures.
CAM Plants live in the dry parts of the world. They partition time (as opposed to C4 plants partitioning space). Stomata are only opened during night, allowing CO2 to come in. CO2 attaches to PEP via PEP Carboxylase to form C4 molecules. during the day, that C4 molecule (malate) releases CO2 into the Calvin Cycle while using ATP and NADPH to create glucose.
CAM Photosynthesis conserves water, it's bad because CO2 can only enter at night.
