C4 Plants

C₄ Plants

Both high light intensity and high temperature favor photorespiration. C4 plants provide a way out. They have (a) high photosynthetic rates, (b) low rates of water loss ( transpiration ), low photorespiration rates and (d) high growth rates.

In C4 plants CO2 is fixed, released and fixed again. Sites of first CO2 fixation is separate from Calvin cycle ( spatially separated ).

C3 Plants	C4 Plants
1. Product of CO2 fixation is 3 carbon intermediate 3-PG	Product of first CO2 fixation is 4 carbon intermediate OAA
2. consumes 3 ATP / CO2	Consumes 5 ATP / CO2
3. O2 is acceptable	O2 is not acceptable
4. less efficient utilization of CO2	Most efficient utilization of CO2
5. 4 enzymes are light activated	7 enzymes are light activated.
6. CO2 gas is fixed	CO2 in aqueous state ( HCO3 - ) is first fixed