NEETBotanyPhotosynthesis in Higher Plants
In the leaves of a C ₄ plant such as maize, where is the enzyme RuBisCO exclusively located and what is its primary activity in these cells?
Options
- AMesophyll cells; acts primarily as a carboxylase
- BBundle sheath cells; acts as both carboxylase and oxygenase equally
- CBoth mesophyll and bundle sheath cells; acts primarily as a carboxylase
- DBundle sheath cells; acts primarily as a carboxylase
Correct answer
D. Bundle sheath cells; acts primarily as a carboxylase
Step-by-step solution
In C ₄ plants, there is a spatial separation of the initial carbon fixation and the Calvin cycle (Kranz anatomy). The mesophyll cells lack RuBisCO and instead contain PEP carboxylase, which fixes CO ₂ into a 4-carbon acid. This 4-carbon acid is transported to the bundle sheath cells, where it is decarboxylated. This process creates a high concentration of CO ₂ around RuBisCO, which is exclusively located in the bundle sheath cells. Because of this high intracellular CO ₂ concentration, the competitive binding stron