Question

Chemiosmotic hypothesis of ATP synthesis in chloroplast is based on
a. Accumulation of $K^{+}$ ions
b. Proton gradient
c. Accumulation of $Na^{+}$ ions
d. Membrane potential
e. Increase in pH of lumen

Answer 1

Hint: ATP synthesis is due to gradient development across the thylakoid membrane of chloroplast and proton accumulation takes place inside of the chloroplast that is, lumen. The source of these protons is water. Water dissociates and forms protons and oxygen.

Complete answer:
Plants are the source of food and nutrition to all other organisms present on the Earth. These plants observe sunlight and with the help of sunlight plants prepare their food and produce oxygen as well. This wonderful process takes place inside the leaves which contain chloroplast, a food production house of plant cells.

Chloroplasts are complex and undergo many processes for the production of food that is glucose for itself and oxygen for other animals for respiration. CO_{2} undergoes C_{3} and C_{4} mechanisms to convert into food. Water present in the cells dissociates and forms proton and oxygen molecules.

This oxygen molecule comes out of the cell to the atmosphere through the stomata. Proton produced goes to the lumen of the chloroplast and produces a gradient across the thylakoid membrane which helps in the production of ATP in the cell.

Due to gradients produced by the protons across the membrane, movement of protons from higher concentration to lower concentration takes place and during this movement ATP production takes place.

So, we can conclude that Protein gradient is responsible for the ATP synthesis in Chemiosmotic hypothesis.
Hence, the correct answer is option (B).

Note: This hypothesis was given by P. Mitchell. Water dissociates by photolysis in the lumen of the thylakoids. Protons produced are also transported from the stroma of the chloroplast to the thylakoid lumen during the NADP reductase catalyzed reaction.