C3 plants have no mechanism of inhibiting the enzyme rubisco from potentially wasting resources by fixing to both O2 and CO2 which causes water loss in hot, arid environments through the stomata being continually open. CAM plants generally live in drier areas, so they only open their stomata at night, which allows them to conserve resources like water. They both use the Calvin cycle to create glucose from CO2, and utilize the rubisco enzyme; however, they are just metabolic pathways that are suited to different environments.
