Question

The first carbon dioxide acceptor in plants is:
A. Phosphoenolpyruvate
B. Ribulose 1,5-diphosphate
C. Oxalo-acetic acid
D. Phosphoglyceric acid

Answer 1

Hint: The first $CO_2$ acceptor is a 3 carbon molecule.

Complete answer: Photosynthesis is a process by which all green plants, some bacteria, and some autotrophs convert light energy of the sun into chemical energy and simultaneously produce glucose from carbon dioxide and water.
1. Oxygen is released out as a by-product of this process.
2. Every photosynthetic plant undergoes the Calvin cycle.
3. Many plants are adapted to dry tropical desert regions. Their photosynthetic process is different from others.
4. They follow a primary stage to the Calvin Cycle- these plants undergo the C4 pathway.
For this reason, they are known as C4 plants also e.g. maize, corn, sugarcane, etc.
5. In the pathway, a double fixation of carbon dioxide occurs.
It is also called the Hatch-Slack pathway and it suggests the name of the scientists who discovered this process.
6. In this case, the primary acceptor is a 3-C molecule called phosphoenolpyruvate (PEP).
It is located in the mesophyll.
7. The reaction of fixation is catalyzed by an enzyme- PEP carboxylase.
8. It is the initial carboxylation enzyme.
9. Now, the first stable product is formed in mesophyll which is oxaloacetic acid (OAA).
It is a 4-C compound.
10.Later, it is further converted into malic acid, another 4-C compound.
11. These organic acids are then transferred to bundle sheath cells where OAA is broken down. As a result, a 3-C molecule formed and is released.

So, the correct option is A. Phosphoenolpyruvate.

Note: The mesophyll of C4 plants do not have RuBisCO enzyme.