Question

Explain why do the linear and cyclic electron flows exist

Answer 1

Ans.

Cyclic Electron Flow - This pathway is used by green plants when their is excess of NADH available and they are in need of synthesis of ATP.It occurs in the chloroplasts. Photosystem I takes part in this pathway and there is no production of oxygen or NADPH. The pathway produces ATP and ADP through cyclic photophosphorylation by means of pumping of protons through the thylakoid membrane. The main reason why a cyclic electron flow exists is the fact that the ATP produced from linear electron flow is not sufficient enough for the assimilation of CO2, thus it fills the energy gap by the help of cyclic electron flow pathways.

Noncyclic/Linear Eectron Flow - This pathway is used when the photosystem II absorbs light and the electrons moves towards higher energy levels to be captured by the primary electron acceptor. When the electrons moves back down the chain the lowered energy levels triggers the thylakoid membrane to produce ATP through the process of Chemiosmosis.This production of ATP that takes place in the chloroplast with the help of light energy is called Linear or non-cyclic photophosphorylation. It is the energy produced in this process that provides the energy during calvin cycle for the synthesis of glucose.