Question

The saturation point of carbon dioxide in $C4$ plants is?
A. $390\mu l/L$
B. $450\mu l/L$
C. $460\mu l/L$
D. $360\mu l/L$

Answer 1

As we know, every plant uptakes carbon dioxide which are necessary for its growth, cell development, maturity and other varied functions. Saturation point of plants means the marginal or end point of any plant from here no further receive of photosynthesis or any other substances taken. Photosynthesis increases as carbon dioxide increases until the saturation point arrives. Enriching the air with carbon-dioxide enables plants to more effectively utilize light which also helps in reaching saturation.

Complete answer:
Option A $390\mu l/L$- the carbon-dioxide saturation point is usually low in $C4$ plants. The reason behind the low saturation point is the greater efficiency of carbon-dioxide fixation which is done through PEP-carboxylase.
So, option a is not correct.
Option B $450\mu l/L$- the optimum carbon-dioxide concentration of $C3$ plants are $450\mu l/L$. hence it can not be the saturation point for $C4$ plants.
So, option B is not correct.
Option C $460\mu l/L$- the atmospheric saturation of carbon-dioxide is around $0.039\%$. It has the proportion of gases in the atmosphere like nitrogen which is the highest atmospheric gases that is eighty percent.
So, option C is not correct.
Option D $360\mu l/L$- the optimum carbon-dioxide concentration or saturation point is low compared to $C3$ plants in $C4$ plants. It is $360\mu l/L$.
so, option D is correct.

Hence, Option D) is the correct answer.

Note:
As we discussed already about how saturation points affect plants. Now let us know about $C4$ plants efficiency. At high temperatures $C4$ plants are more efficient. This is because their saturation point is low compared to $C3$ plants. $C4$ plants have higher optimum temperature for photosynthesis than $C3$ plants due to the carbon-dioxide concentrating system. plants take the sunlight in the morning and carbon dioxide at night and make their food at that particular time.