Question

In mechanism, photophosphorylation is most similar to

(A) substrate-level phosphorylation in glycolysis.

(B) oxidative phosphorylation in cellular respiration.

(C) carbon fixation.

(D) reduction of NADP+.

Short answer

a. The option “substrate-level phosphorylation in glycolysis” is false.

b. The option “oxidative phosphorylation in cellular respiration” is true.

c. The option “carbon fixation” is false.

d. The option “reduction of NADP+” is false.

Step-by-step solution

Step 1: Photophosphorylation

In light reactions of photosynthesis, the synthesis of ATP occurs by phosphorylation of ADP through chemiosmosis. This process is called photophosphorylation. Light energy is utilized to accomplish this reaction. It occurs on the thylakoid membranes of the chloroplast.

Explanation of option (A)

In substrate-level phosphorylation, ATPs are produced from ADPs by using phosphate groups of other substrates that are on higher energy and give lower-energy products. In photophosphorylation, light energy is used to synthesize ATPs.

Thus,substrate-level phosphorylation in glycolysisis different fromphotophosphorylation.

Therefore, the given statement is false.

Explanation of option (B)

Oxidative phosphorylationis the same process as photophosphorylation except for the sites where they occur and the purpose. But both are mostly similar. They use chemiosmosis for ATP production, in which an electron transport chain occurs.

In this process, electrons are transferred through a sequence of carriers that generate proton motive forces. An ATP synthase helps in ATP production by using these forces.

Thus, oxidative phosphorylation and photophosphorylation both involve an electron transport chain.

Therefore, the given statement is true.

Explanation of option (C)

Carbon fixation is the process by which CO₂ molecules are connected to organic molecules and help produce sugars in dark reactions of photosynthesis, but photophosphorylation involves ATP production during light reactions of photosynthesis.

Thus, carbon fixation is very different from photophosphorylation.

Therefore, the given statement is false.

Explanation of option (D)

Reduction of NADP into NADPH also occurs in light reactions, but it is not similar to photophosphorylation. It produces reducing powers.

Thus, NADPH production is not similar to photophosphorylation.

Therefore, the given statement is false.