Specify how a pentose phosphate is a CO 2 acceptor in the dark reaction of photosynthesis.

Pentose phosphate i.e. ribulose 1, 5-bisphosphate (RuBP) accepts the CO 2 in the first step of dark reaction or Calvin cycle. The pentose phosphate along with CO 2 undergoes carboxylation in the presence of an enzyme RuBisCO to form an unstable 6C containing molecule which splits and give 2 molecules of phosphoglyceric acid (PGA).

Specify how the C 4 photosynthetic pathway increases CO 2 concentration in bundle sheath cells of sugarcane.

The C 4 pathway acts as a mechanism to build up high concentrations of CO 2 in the chloroplasts of the bundle sheath cells because (i) In the mesophyll cells: Atmospheric CO 2 is fixed by PEP carboxylase enzyme to form OAA and then to malate which moves into the bundle sheath cells of sugarcane. (ii) In bundle sheath cells : malate converts into the pyruvate to release CO 2 . Thus, there is always a supply of CO 2 in the form of malate in the sugarcane.

What is RuBisCO? Explain its role in C 3 and C 4 photosynthesis.

RuBisCO stands for ribulose 1,5-bisphosphate carboxylase-oxygenase. It is the first enzyme that is involved in the dark reaction to produce glucose molecules. In C3 and C4 plants, the RuBisCO enzyme catalyzes the carboxylation process in the mesophyll cells of C3 plants and bundle sheath cells of C4 plants.

Give the importance of C 4 plants.

The importance of C4 plants: (i) C4 plants have Kranz anatomy(the plants have additional bundle sheath cells near the vascular bundle cells). Thus, C4 plants can avoid wasteful processes like photorespiration. (ii) They have high productivity than C3 plants.