Question

what is the difference between C3, C4, and CAM plants ?

Answer 1

C3 carbon fixation is a metabolic pathway for carbon fixation in photosynthesis. This process converts co2 and ribulose bisphosphate into 3-phosphoglycerate through the following reaction:

6 CO2 + 6 RuBP → 12 3-phosphoglycerate

In C4 , carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.
Since every CO2 molecule has to be fixed twice, the C4 pathway is more energy-consuming than the C3 pathway. The C3 pathway requires 18 ATP for the synthesis of one molecule of glucose while the C4 pathway requires 30 ATP. But since otherwise tropical plants lose more than half of photosynthetic carbon in photorespiration, the C4 pathway is an adaptive mechanism for minimizing the loss.

There are several variants of this pathway:
*The 4-carbon acid transported from mesophyll cells may be malate as above, or may be aspartate.
*The 3-carbon acid transported back from bundle-sheath cells may be pyruvate as above, or alanine.
*The enzyme which catalyses decarboxylation in bundle-sheath cells differs. In maize and sugarcane, the enzyme is NADP-malic enzyme, in millet, it is NAD-malic enzyme, and in Panicum maximum it is PEP carboxykinase.