Question

RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in C4 plants?

Answer 1

Part 1: RuBisCO
RuBisCO (Ribulose Bisphosphate Carboxylase Oxygenase) is an enzyme which is very important for the process of photosynthesis. It acts as both carboxylase and oxygenase.

Part 2: Anatomy of C4 plants
The arrangement of mesophyll and bundle sheath cells in the leaf of C4 plants is different from C3 plants. The parenchymatous cells which are a type of ground tissue present in the leaf are called mesophyll cells. The cells surrounding the vascular bundles is called the bundle sheath cells. In C4 plant these mesophyll cells are clustered around the bundle sheath cells and forms a shape which is similar to the wreath. This arrangement seen in the leaf of C4 plants is called Kranz anatomy.

Part 3: Significance of Kranz anatomy
But in C4 plants the loss of energy molecules due to photorespiration is reduced as the concentration of $C{O}_2$is high in the bundle sheath cells. Due to the high concentration of $C{O}_2$ in the bundle sheath cells, RuBisCO acts as a carboxylase and calvin cycle occurs. Thus there is more carboxylation in C4 plants.