Question

How is photosynthesis similar in C₄ plants and CAM plants?

(A) In both cases, only photosystem I is used.

(B) Both types of plants make sugar without the Calvin cycle.

(C) In both cases, rubisco is not used to fix carbon initially.

(D) Both types of plants make most of their sugar in the dark.

Short answer

a. The option “In both cases, only photosystem I is used” is false.

b. The option “Both types of plants make sugar without the Calvin cycle” is false.

c. The option “In both cases, rubisco is not used to fix carbon initially” is true.

d. The option “Both types of plants make most of their sugar in the dark”isfalse.

Step-by-step solution

Carbon fixation in C4 and CAM plants

To avoid water loss in dry climates, C4 and CAM plants have adopted a specialized method to work efficiently. In C4 plants, carbon fixation occurs in mesophyll cells, and the Calvin cycle occurs in the bundle sheath cells.

On the other hand, CAM plants employ temporal separation where carbon fixation and the Calvin cycle occur in the same cell but at different times. Carbon fixation occurs at night, but the Calvin cycle occurs in the day to synthesize sugar.

Explanation of option (A)

In all plants, electrons from water flow to PSII, then to PSI, and finally to NADP⁺ to produce NADPH.

Thus, all the plants use photosystem I.

Therefore, the given option is false.

Explanation of option (B)

The Calvin cycle is the second phase of photosynthesis after light reaction, where they fix carbon to produce sugar.

Thus, plants cannot make sugar without the Calvin cycle.

Therefore, the given option is false.

Explanation of option (C)

Carbon fixation occurs in most plants when CO₂ combines with RuBP (ribulose 1, 5-bisphosphate). Rubisco is the enzyme that catalyzes the combining of RuBP and CO₂. However, rubisco is not an efficient enzyme in hot and dry climates, where the carbon dioxide concentration is low.

Thus, rubisco is not involved in C4 and CAM plants during photosynthesis.

Therefore, the given option is true.

Explanation of option (D)

All the plants fix carbon and synthesize sugar during the day. However, CAM plants fix carbon at night, but they synthesize sugar during the day to avoid water loss.

Thus, C4 and CAM plants do not produce sugar at the same time, that is, in the dark.

Therefore, the given option is false.