Question

Why are $C_4$ plants special ?
(i) Have a special type of leaf anatomy.
(ii) Tolerate higher temperatures.
(iii) Show a response to high light intensities.
(iv) Lack of a process called photorespiration.
(v) Have greater productivity of biomass.

• A. All of these
• B. (i), (ii), (iii) and (iv)
• C. (i), (iii) and (iv)
• D. (i) and (ii)

Answer 1

The correct option is A All of these

In $C_4$ plants, the ${\mathrm{CO}}_2$ is first bound to a phosphoenolpyruvate in mesophyll cell resulting in the formation of four-carbon compound (oxaloacetate) that is shuttled to the bundle sheath cell where it will be decarboxylated to liberate the ${\mathrm{CO}}_2$ to be utilised in the $C_3$ pathway. In this mechanism, the tendency of rubisco enzymes to photo respire, or waste energy by using oxygen to break down carbon compounds to ${\mathrm{CO}}_2$ , is minimised. Most $C_4$ plants have a special leaf anatomy (called Kranz anatomy) in which the vascular bundles are surrounded by bundle sheath cells, show a response to highlight intensities, lack photorespiration and have a greater productivity of biomass. Examples of $C_4$ plants include sugarcane, maize, sorghum, amaranth, etc.