Question

Cyclic photophosphorylation involves
A. PS-I
B. PS-II
C. PS-I and PS-II
D. P680

Answer 1

Arnon and his coworker in 1954 were the first to show that isolated chloroplast can produce ATP when exposed to light. They called it photophosphorylation. This ATP production occurs through the electron transport chain which is of two types:
A.Non-cyclic
B.Cyclic

Complete answer: In cyclic electron transport system, electrons come back to PS-I hence it is called cyclic transport system. In non-cyclic transport, electrons are not received again by any photosystem. Non-cyclic phosphorylation is the dominant one and it produces more ATP than cyclic phosphorylation. This transport is active in plants when NADPH starts accumulating and CO$_2$ assimilation is checked. It helps in the production of six more ATP production. In this, electrons released by P700 finally come back to PS-I, hence, this transport is called cyclic. The pigments of PS-I absorb a specific wavelength of light beyond 680nm and become photoexcited. After photoexcitation, electrons are released and transferred to the reaction centre (P700) of PS-I. The electrons from P700 reach ferredoxin via A1, A2, and A3 as in the case of noncyclic transport. From reduced ferredoxin, these electrons reach ti plastoquinone(PQ) via cyt-b6. After this, electrons finally reach P700. After PQ the path of electrons is similar to non-cyclic transport. In cyclic transport also, the ATP formation takes place between PQH$_2$ --> cyt-f.
Hence, the correct answer is Option A

Note: Both PS-I and PS-II systems absorb the different wavelengths of light. Both PS-I and PS-II work the same as mitochondria of animal cells in which electron transport occurs via the electron transport system resulting in the formation of ATP.