Question

What is the site of ${C_3}$cycle in ${C_3}$ and ${C_4}$ plants?
A. In ${C_3}$ plant – Mesophyll cells and ${C_4}$ plant – Bundle Sheath cells
B. In ${C_3}$ plant – Bundle Sheath cells and ${C_4}$ plant – Mesophyll cells
C. In ${C_4}$ plant – Bundle Sheath cells and ${C_3}$ plant – Bundle Sheath cells
D. In ${C_3}$ plant – Mesophyll cells and ${C_4}$ plant – Mesophyll cells

Answer 1

Carbon is fixed into three-carbon sugars from carbon dioxide during the ${C_3}$ cycle of the chemical reactions inside the plants. A single type of chloroplast is involved in it. The ${C_4}$ cycle is designed to efficiently fix $C{O_2}$ at low concentrations and plants that use this cycle are known as ${C_4}$ plants. First these plants fix carbon dioxide into a four carbon compound $\left( {{C_4}} \right).$Two types of chloroplast are involved in this.

Complete answer:
In the ${C_4}$ ​plants, photosynthesis takes place in the chloroplast of a thin-walled mesophyll cell and a four-carbon acid is got over by a thick-walled bundle sheath cell where the calvin cycle takes place. In the ${C_3}$ ​plants, 3-carbon sugar is produced which can easily diffuse into mesophyll cells, and into the stroma of chloroplasts, where the Calvin cycle takes place. Hence, the site of ${C_3}$ cycle or Calvin cycle in ${C_3}$ plants are mesophyll cell and in ${C_4}$ plants are bundle sheath cell (A layer of cells surrounding the vascular bundles in leaves). So, the correct answer for this is option (A) 'In ${C_3}$ ​plant - mesophyll cell and In ${C_4}$ ​plant - Bundle sheath cell'.

Note: ${C_3}$ does not have the bundle Sheath cells. In the ${C_4}$ pathway, the Calvin cycle takes place in the bundle sheath cells. Six turns taken by the calvin cycle to fix 6 carbon atoms from carbon dioxide. These six turns require energy input for 12 AATP and 12 NADPH mol. in reduction.