c4 and cam pathways
maximizing co2 fixation: c4 and cam pathways
Plants that only use the Calvin cycle to fix CO2 are called C3 plants. However, to improve photosynthesis efficiency, different plants have pathways other than just the Calvin cycle. While most plants are C3 (rice, trees), there are some plants that use other metabolic processes to maximize carbon dioxide fixation such as the C4 pathway.
c4 plants
C4 plants maximize carbon dioxide fixation by using an enzyme to fix CO2 into 4-C sugars. The production of 4 carbon sugars is why this process is known as the C4 pathway. Phosphoenolpyruvate carboxylase (PEP carboxylase), the enzyme used in the C4 pathway, does not need oxygen.
C4 plants combine the C3 and C4 processes to provide a efficient way to fix carbon dioxide. The C3 pathway occurs in mesophyll cells in plants while the C3 cycle occurs in bundlesheath cells.
This process allows C4 plants to be more efficient than C3 plants because of the double carbon-fixation. Rubisco, the enzyme C3 plants use to fix CO2 is inefficient in the presence of a lot of oxygen. Oxygen binds to the active site on Rubisco, competing with carbon dioxide in a process called photorespiration. Thus, C4 plants can overcome photorespiration with the C4 pathway.
C4 plants include pineapple, sugarcane, and corn.
C4 plants combine the C3 and C4 processes to provide a efficient way to fix carbon dioxide. The C3 pathway occurs in mesophyll cells in plants while the C3 cycle occurs in bundlesheath cells.
This process allows C4 plants to be more efficient than C3 plants because of the double carbon-fixation. Rubisco, the enzyme C3 plants use to fix CO2 is inefficient in the presence of a lot of oxygen. Oxygen binds to the active site on Rubisco, competing with carbon dioxide in a process called photorespiration. Thus, C4 plants can overcome photorespiration with the C4 pathway.
C4 plants include pineapple, sugarcane, and corn.
cam plants
Crassulacean Acid Metabolism plants (CAM plants) also use C3 and C4 cycles for CO2 fixation. CO2 is taken in through stoma on leaves of plants. However, H2O is also lost at the same time when stoma is opened. Thus, this poses a big problem for desert plants that have to conserve its water. Therefore, while both C3 and C4 processes are still performed in these plants, C3 reactions are performed during the day. C3 reactions do not need CO2 allowing the stomata to be closed as the pathway is carried out. At night, when it is cooler, stomata opens to allow CO2 intake and C4 reactions are performed.
Thus, while the C3 and C4 process are physically separated in C4 plants, the two processes are separated by time in CAM plants. Both processes occur in mesophyll cells for CAM plants.
CAM plants include many desert plants such as cacti.
Thus, while the C3 and C4 process are physically separated in C4 plants, the two processes are separated by time in CAM plants. Both processes occur in mesophyll cells for CAM plants.
CAM plants include many desert plants such as cacti.