Question

Even though a very few cells in a $C_4$ plant carry out biosynthetic Calvin pathway, yet they are highly productive. Can you discuss why ?

Answer 1

In $C_4$ plants, biosynthetic Calvin cycle occurs only in bundle sheaths. Despite few number of cells performing Calvin cycle, $C_4$ plants have a high rate of photosynthesis due to (i) Rapid supply of $C{0}_2$ from all mesophyll cells taking part in initial carbon dioxide fixation, (ii) Absence of photorespiration due to absence of photolysis in bundle sheath cells, (iii) Rapid withdrawal of photosynthates from the bundle sheath cells as they lie over the vascular bundles, (iv) Photosynthesis continues even when stomata are closed due to fixation of $C{0}_2$ released through respiration.