Question

What is true about the compensation points in C3 and C4 plants?
A. Compensation point of C3 plants is higher.
B. Compensation point of C4 plants is higher.
C. It is equal.
D. None of these as it is variable.

Answer 1

Hint: Compensation point is reached when photosynthesis occurs at the same rate as that of respiration. Due to an enzyme of the C4 pathway, the compensation point varies between C3 andC4 plants.

Complete answer: In C4 pathway, double fixation of carbon dioxide occurs.
The four-carbon compound obtained is transferred to the bundle sheath cells for the next step (Calvin cycle). The whole process involves an enzyme called PEP carboxylase.
It converts PEP to oxaloacetate. In the question, compensation point refers to a particular time in which the photosynthetic-rate equals to respiration rate.
It indicates a point where net photosynthesis is zero.
In C4 plants, the compensation point is lower due to the high affinity of an enzyme PEP-carboxylase.
In C3 plants no such reason is there and the compensation point is higher.

So, the correct option is A. Compensation point of C3 plants is higher.

Note: Every photosynthetic plant undergoes Calvin cycle.
Many plants are adapted to dry tropical desert regions.
They follow a primary stage to the Calvin Cycle- these plants undergo the C4 pathway.
For this reason are known as C4 plants also e.g. maize, corn, sugarcane, etc.