Question

$C_4$ and $C_3$ pathways of CAM plants are separated by

• A. Bundle sheath
• B. Mesophyll and bundle sheath cells
• C. Mesophyll and bundle sheath chloroplasts
• D. Time

Answer 1

Answer: (D)

Time

Certain plants, especially succulents which grow under extremely xeric conditions, fix carbon dioxide in dark. These plants are termed as CAM (Crassulacean Acid Metabolism) plants. In these plants, stomata remain open at night but closed during the day (in light).

1. In this CO${}_2$ combine with PEP to form OAA in presence of PEP carboxylase like C4 plants.

2. OAA converted to malic acid in the presence of NADH. Malic acid produced in dark as a result of acidification.

3. Malic acid converted to pyruvic acid and evolve CO${}_2$ during the day when stomata are closed. This process is termed as deacidification.

The CO${}_2$ released by deacidification accepted by RuBP and fixed to carbohydrate by C${}_3$ cycle.

Hence, the correct answer is 'Time'.