Question

Chemiosmotic theory of ATP synthesis in chloroplast and mitochondria is based on:
A. Membrane potential
B. Accumulation of Na+ ions
C. Accumulation of K+ ions
D. Proton gradient

Answer 1

Hint: The chemiosmotic hypothesis explains how the energy currency, i.e. the ATP is synthesized inside the chloroplast. The ATP synthesis is linked to the transfer of the H+ ions across the thylakoid membrane. The H+ ions accumulate on the inner side of the lumen.

Complete answer:
To solve the given question, we must be well aware of the chemiosmotic hypothesis. The chemiosmotic theory was given by P.Mitchell. It begins with the photolysis of water thus producing protons on the inner side of the lumen. As the electrons move through the photosystems, the transfer of protons takes place from the stroma to the lumen.
There is an enzyme located at the stroma side of the membrane. This enzyme is known as the NADP reductase. We all know that H+ ions are required to change NADP+ to NADPH + H+. These protons or the H+ ions are then removed from the stroma. A proton gradient is made which helps in releasing energy.
Since now we know the chemiosmotic hypothesis, therefore the correct answer to the question is proton gradient.

Note: It must be noted here that the enzyme ATPase allows the proton diffusion back into the membrane. This diffusion releases energy which is further utilized to activate the enzyme ATPase. This enzyme catalyzes the synthesis of Adenosine Triphosphate (ATP).