Question

During which stage of photosynthesis is oxygen produced?

• A. Cyclic photophosphorylation
• B. Non-cyclic photophosphorylation
• C. Carbon fixation
• D. Calvin cycle

Answer 1

The correct option is B Non-cyclic photophosphorylation

Oxygen released during photosynthesis comes from the splitting of water. The splitting of water releases protons, electrons and also leads to evolution of oxygen. During non-cyclic photophosphorylation, the electrons from PS-II reach PS-I. The void created in PS-II due to lack of electrons has to be filled for the light reaction to proceed. Hence, there is splitting of water and the electrons released due to splitting of water are taken up by PS-II. The splitting of water also leads to the evolution of oxygen. Hence, oxygen is produced during non-cyclic photophosphorylation.

During cyclic photophosphorylation, electrons released by PS-I pass through the electron transport chain and are again recycled back to PS-I. Hence, the splitting of water is not required during cyclic photophosphorylation to replace the lost electrons.

During the Calvin cycle, there is carbon fixation and formation of glucose.