Question

The first electron acceptor in photosystem-I of the cyclic photophosphorylation is
(a)Cytochrome
(b)Plastocyanin
(c)Ferredoxin
(d)Plastoquinone

Answer 1

Hint: It is a small reductase enzyme consisting of iron and sulfur also known as ‘biological capacitors’ which can accept and release electrons by changing the oxidation state of iron.

Complete answer:
The process of photosynthesis was the phosphorylation of ADP to produce ATP by the use of sunlight. Photosynthesis occurs in two-phase – the first phase- light reaction, the second phase- dark reaction. The light reaction occurs in chloroplast. The light reaction consists of a two-step reaction- photolysis of water and phosphorylation. Photophosphorylation involves the only photosystem I occur in bacteria called cyclic photophosphorylation where involvement of both the photosystem I and II occurs in the plant called non- cyclic photophosphorylation. Cyclic photophosphorylation occurs when plants have enough amount of NADH and there is no need of producing more NADH by the use of both the photosystems I and II.

Additional Information:
-Cyclic photophosphorylation occurs in aerobic and anaerobic conditions in bacteria containing a single photosystem.
-Cyclic photophosphorylation is operated at a very high rate in the bundle sheath chloroplast of certain C4 plants.
-The electron released by P700 in the presence of light is passed as the primary acceptor, ferredoxin, plastoquinone, cytochrome complex, plastocyanin, and finally back to P700.
-In non- cyclic photophosphorylation the electron is passed from P680 to primary acceptor, plastoquinone, cytochrome complex, plastocyanin, and finally to P700 where the electron is taken up by the primary acceptor and ultimately passed to NADP.
-Non- cyclic photophosphorylation needs constant requirement of a water molecule.

So, the correct answer is, ’ferredoxin.’

Note:
 -The sunlight is used to create a high energy electron donor and a low energy acceptor.
-The yield in non- cyclic photophosphorylation is not sufficient for the requirement of carbon dioxide assimilation.
-The cell has a high demand for ATP contains high photosystem I activity but very little photosystem II activity.
-The photosystem I am also known as P680 and photosystem II is also known as P700.