Question

Energy required for $ATP$ synthesis in$PS II$ comes from

• A. proton gradient
• B. electron gradient
• C. reduction of glucose
• D. oxidation of glucose

Answer 1

Answer: (A)

proton gradient

Answer 2

Photosystem $II (PS II)$ is a photosynthetic pigment system alongwith some electron carriers that is located in the appressed part of the grana thylakoids. $PS II$ has chlorophyll $a$, chlorophyll $b$ and carotenoids. It picks up electron released during photolysis of water. The same is extruded on absorption of light energy. As the extruded electron passes over cytochrome $b_{6}-f$ complex, it energises passage of protons picked up by $PQ$ to create protons gradient for synthesis of $ATP$ from $ADP$ and inorganic phosphate. This photophosphorylation is non-cyclic.