Photosynthesis

The CAM pathway evolved in plants that live in very arid and dry environments, such as cacti. In a plant using the CAM pathway, the stomata of the plant stay shut during the day to prevent water loss.  At night, they open to allow carbon dioxide to diffuse into the plant.  The carbon dioxide is stored in a four-carbon molecule called malate, the same that was used in the C4 pathway.  

 

During the day, while the stomata are closed, the plant uses the stored carbon dioxide from the night before to perform the light independent reactions.  Because all of the carbon dioxide is concentrated around RuBisCO, it very rarely makes mistakes that result in oxygenation.  The concentrated carbon dioxide is then run through the Calivn Cycle to produce carbohydrates. Therefore, both C4 and CAM eliminate the issue of oxygenation that C3 has at the cost of some of the plant's energy.

 

This pathway is like an assembly line worker who only works half-time.  He/she lets all of the parts pile up during the night while he/she sleeps, and then the next morning, he/she assembles all of the parts that piled up around him/her.  Again, this employee does not make mistakes, but he/she only works during the day.