Question

Evolution of oxygen during photosynthesis is a

• A. Light reaction
• B. Dark reaction
• C. Respiratory influence
• D. Both light and dark reactions.

Answer 1

The correct option is A Light reaction

Photosynthesis is an anabolic process happening in green plants during which plant body synthesizes its own food material by taking carbon dioxide from atmosphere and water from the soil in presence of sunlight. It proceeds in the sequence of light phase and dark phase.

Light phase is also known as the photochemical phase because it is a light dependent phase. Reactions that take place during the light phase are known as light reactions. During this phase, the formation of high-energy chemical intermediates ATP and $NADP{H}_2$ takes place. ATP and $NADP{H}_2$ are the assimilatory power of photosynthesis. Light phase also includes light absorption, water splitting and release of oxygen. Two photosynthetic units called Photosystem I and Photosystem II are involved in the light phase. Evolution of oxygen during the light reaction is a result of the splitting of water. The electrons that were removed from PS II during non-cyclic photophosphorylation must be replaced. This is achieved by electrons available due to the splitting of water. Water is split into $H^{+}$, [O] and electrons. The proton and oxygen formed by splitting of water are released within the lumen of the thylakoids.

$2H_{2}O$ $⟶$ $4H^{+}$ + $O_2$ + $4e^{-}$