Question

In photosystem I, the first electron acceptor is
A. Plastocyanin
B. An iron-sulfur protein
C. Ferredoxin
D. Cytochrome

Answer 1

Hint: Photosystem I is a light-harvesting complex which is located towards the outer surface of the thylakoid membrane, it is important as it transfers the absorbed light and carries out the process of electron transfer creating resonance energy transfer in photosynthesis.

Complete answer: Photosystems are light-harvesting complexes found inside the chloroplast, their main function is to pass on the electrons excited after absorbing light energy to the pigment molecules and carry out the energy generation process, which is essential for photosynthesis.
These photosystems are of two types, that is the photosystem I and the photosystem II, they are named such in the order of their discovery and not concerning which of the photosystems absorbs the light first.

The photosystem I absorbs light of wavelength 700 nm and the photosystem II absorbs light of wavelength 680 nm.
Photosystem I is located on the outer surface of the thylakoid and photosystem II is located towards the inner side of the thylakoid membrane.
The first electron acceptor in the case of photosystem I is $A_0$ which is modified chlorophyll. After which it gets transferred to phylloquinone, phylloquinone then transfers it to Ferredoxin.
And since other two molecules are not given in the option,

Hence, the correct option is (C),Ferredoxin

Note: The naming of PS I and PS II is solely based on their discovery and not on any other criteria. Ferredoxin or iron-sulphur protein helps in electron transport and is not involved in photosystem I and plastocyanin is a copper-containing protein used in electron transport.