View source for C4 carbon fixation

== Overview ==
[[C4 carbon fixation]] or the C4 photosynthetic pathway is a process used by plants and other organisms to capture carbon dioxide (CO2) from the atmosphere, which is then used to produce energy-rich molecules like glucose. This process is one of three known photosynthetic processes of carbon fixation in plants, the other two being [[C3 carbon fixation]] and [[CAM photosynthesis]].

== Biochemistry of C4 Carbon Fixation ==
The C4 carbon fixation process is named for the 4-carbon compound that is the first product of carbon fixation in the process, oxaloacetic acid. This process involves the enzyme [[Phosphoenolpyruvate carboxylase]] (PEP carboxylase), which catalyzes the reaction of phosphoenolpyruvate (PEP) with carbon dioxide to form oxaloacetic acid.

[[Image:Detail-50915.jpg|thumb|center|A close-up view of a plant cell showing the chloroplasts and other organelles.|class=only_on_mobile]]
[[Image:Detail-50916.jpg|thumb|center|A close-up view of a plant cell showing the chloroplasts and other organelles.|class=only_on_desktop]]

== Evolution of C4 Carbon Fixation ==
The C4 carbon fixation pathway evolved as an adaptation to high light intensities, high temperatures, and dryness. It is believed to have evolved more than 60 times independently in various plant lineages, making it a classic example of [[convergent evolution]].

== C4 Plants ==
Plants that use the C4 carbon fixation process are known as C4 plants. These include several thousand species in at least 19 families of plants, including the family [[Poaceae]] (grasses), which contains important crops such as maize, sugarcane, and sorghum.

== Advantages and Disadvantages of C4 Carbon Fixation ==
C4 carbon fixation has several advantages over the C3 pathway, particularly in conditions of drought, high temperatures, and nitrogen or CO2 limitation. However, it also has some disadvantages, such as the requirement for additional energy in the form of ATP.

== See Also ==
* [[C3 carbon fixation]]
* [[CAM photosynthesis]]
* [[Photosynthesis]]
* [[Carbon cycle]]
* [[Plant physiology]]

[[Category:Photosynthesis]]
[[Category:Plant physiology]]
[[Category:Biochemistry]]