C3 Pathway
Most plants assimilate C into sugar using a single step (in Calvin cycle)
CO2 + RuBP ? 2PGA
- ribulose bisphophate (RuBP) - 5 C
- phosphoglycerate (PGA) - 3 C
Each turn of Calvin cycle makes one C available to synthesize glucose
Problem:
- enzyme RuBP carboxylase (Rubisco), which is responsible for assimilation of C, has low affinity for CO2, therefore leaves need lots
- Rubisco also facilitates oxidation of RuBP when [O2] high & [CO2] low, therefore photosynthesis is inefficient and self-limiting
- to deal with this, plants keep their stomates open - water loss!!!