Question

Which one is false about kranz anatomy?

• A. Bundle sheath have large chloroplast and less developed grana.
• B. Mesophyll cells have large chloroplasts.
• C. It is found in atriplex, sugarcane, maize.
• D. Plant having it have better photosynthesizing power than $c_3$ plants.

Answer 1

The correct option is B Mesophyll cells have large chloroplasts.

In some plants, the first stable product after the fixation of $C{O}_2$ is a 4 carbon dicarboxylic acid called Oxaloacetic acid (OAA). Such plants are called C4 plants. Examples are sugarcane, maize, some other monocot and dicot plants.

C4 plants have characteristic leaf anatomy and dimorphic Chloroplasts:

1. The leaf mesophyll consists of compactly packed cells and is not differentiated into palisade and spongy mesophyll.

2. The vascular bundles in leaves are surrounded by distinct bundle sheath of radially enlarged parenchyma cells.

3. The Chloroplasts in leaves are dimorphic: granal and agranal chloroplasts.

Chloroplasts in the mesophyll cells are smaller and possess grana and chloroplasts in the bundle sheath cells are larger and without grana.

This type of anatomy in C4 plants is called Kranz anatomy

Unlike C3 plants, photosynthesis of C4 plants is not inhibited by $O_2$.

They have a very low $C{O}_2$ compensation point which is the ambient $C{O}_2$ concentration at which the rate of $CO_2$ uptake (for photosynthesis) is balanced by the rate of $C{O}_2$ evolution. For C3 plants it's value is 20-100μl/litre and for C4 plants it's value is 0-5μl/litre.

So, bundle sheath cells have the $C{O}_2$ concentrating mechanism and there is suppression of photorespiratory loss of $C{O}_2$. Therefore C4 plants have better photosynthesizing power than C3 plants.

So, the correct answer is B.