Question

In the chart of photophosphorylation, what does 'a' represent?

• A. Cyt a
• B. Cyt $a_3$
• C. FRS
• D. PQ

Answer 1

The correct option is D PQ

In cyclic electron transport pathway:

1. The P${}_{700}$ pigment complex absorbs solar energy. They transfer their energy to PS I reaction centre- P${}_{700}$. The outer valance electron of excited P${}_{700}$ is raised to a higher energy level which is captured by the primary acceptor of PS I. The primary acceptor transfers electron to ferredoxin.

2. Reduced ferredoxin, unable to reduce NADP${}^{+}$ returns the electron to PS I via cytochrome b${}_6$, plastoquinone (PQ), cytochrome f and plastocyanin.

3. The electron transport is called cyclic because the electron emitted from PS I returns back to PS I passing through several intermediate carriers.

Hence, the correct answer is 'PQ'.