Question

In photosystem-I, the first electron acceptor is :

• A. ferredoxin
• B. cytochrome
• C. plastocyanin
• D. an iron-sulphur protein

Answer 1

The Correct Option is D

In the process of photosynthesis, Photosystem I (PSI) plays a crucial role in the light-dependent reactions. It is responsible for the transfer of electrons which ultimately leads to the synthesis of NADPH. In Photosystem I, when light energy is absorbed, it excites electrons to a higher energy level. These high-energy electrons need an acceptor to initiate the electron transport chain.

The first electron acceptor in Photosystem I is an iron-sulphur protein, commonly referred to as Fe-S protein. These proteins contain clusters that are capable of rapidly accepting and transferring electrons.

Let's evaluate the options given:

1. Ferredoxin: Although ferredoxin is an electron acceptor, it is involved after the initial electron transfer from PSI, specifically transferring electrons to NADP⁺.
2. Cytochrome: Cytochromes are part of the electron transport in Photosystem II, not the primary acceptors in PSI.
3. Plastocyanin: This is part of the electron transport chain between Photosystem II and Photosystem I, not the initial acceptor for PSI.
4. An iron-sulphur protein: Correct answer. These proteins initially receive electrons directly from Photosystem I upon excitation by light.

Thus, the correct answer is: an iron-sulphur protein.