text: There are two main kinds of photosynthesis.  One kind is C3 photosynthesis and the other kind is C4 photosynthesis.  The main difference between them is that more water is conserved in C4 photosynthesis than in C3 photosynthesis.  C4 photosynthesis uses a different pathway to get CO2 into its photosynthetic cells. In order to perform this different CO2 transport mechanism C4 photosynthesis requires more energy from the absorption of light in the P700 independant photosystems, which just create energy.  So C4 plants conserve more water, but require more energy to perform their photosynthesis.  \nThe reason why all plants don't use the same kind of photosynthesis is because plants in some tropical areas grow where water is sparse so they must conserve water, and since they are in a sun rich area they are able to absorb more light to create energy.   The C3 plants live in cooler regions that tend to have more abundant water sources.  So C3 plants do not have to conserve water and grow where light is not as plentiful so they are not able to create extra energy from the absorption of extra light.  Therefore plants growing in temperate regions use C3 photosynthesis.\n\n\nNote: Plants do not choose what type of photosynthesis they use.  Plants will either only perform C3 photosynthesis or they will only perform C4 photosynthesis.