Question

Ferredoxin is a constituent of
A. PS I
B. PS II
C. Hill reaction
D. P-680

Answer 1

Photosynthesis is the process of making food by autotrophs. It occurs in two phases: the light-dependent reactions and the light independent reactions or Calvin cycle. The light-dependent reaction takes place at the thylakoid membrane where chlorophyll absorbs light energy and then converts it into chemical energy with the use of water.

Complete answer:
Chlorophylls and other pigments are arranged as photosystems in the chloroplast. There are two photosystems, PS II or Photosystem II and PS I or Photosystem I. Photosystem I uses chlorophyll a, with reaction centre as P-700. Photosystem II uses a form of chlorophyll with reaction centre P-680. During light reactions, the light energy causes the removal of an electron from chlorophyll a reaction centre of Photosystem II P-680. The excited electron is collected by a series of electron carriers which function in the electron transport chain between water and the final electron-acceptor. Ferredoxin (Fd) is one such electron carrier. It is an iron-containing protein present on the stromal side of the thylakoid membrane. It is a component of PS I. In PS I the ejected electron is trapped by FRS (ferredoxin reducing substance) an unknown compound. The electron from FRS is accepted by ferredoxin (Fd) from which the electron is transferred to NADP+ is reduced to NADPH. The end result of light reaction is the formation of assimilatory power (ATP and NADH).

**Thus, A. PS I is the correct answer. ,/b>

Note: In PS I, electrons are passed on to ferredoxin. In the presence of n NADP+ and a suitable enzyme, two ferredoxin molecules transfer two electrons (one each) to NADP+, which picks up a proton and becomes NADPH.