Question

In noncyclic photophosphorylation, water is used for the hydrolysis of ATP. D. the oxidation of NADPH. the excitation of chlorophyll. E. the synthesis of chlorophyll. the reduction of chlorophyll.

Answer 1

10. Photosynthesis is the synthesis of glucose from carbon dioxide and water in presence of sunlight. It has two stages-light and dark reactions. In light reaction, there is production of ATP and NADPH. There is photolysis of water occurring along with release of oxygen.

Non-cyclic phosphorylation is a part of light reaction wherein the electrons do not move in cyclical fashion. It involves both photosystems- I and II. There is reduction of NADP+ occurring in non-cyclic phosphorylation. Light energy will excite electrons in photosystem II that pass through a series of electron carriers to generate ATP via ATP synthase. The electrons are then accepted by photosystem I. In photosystem I, there is also excitation of electrons by sunlight. Electrons in photosystem I are used to generate reducing power NADPH.

The electrons that excited from photosystem II will be accepted by photosystem I. Thus, photosystem II compensates for the electrons in photosystem I. In order to compensate from electrons transferred to photosystem I by photosystem I, a water molecule undergoes photolysis. Photolysis of water releases electrons that are accepted by photosystems II. Photolysis of water leads to its oxidation and loss of electrons.

Oxidation reaction is a loss of electrons by the molecule. Conversely in reduction, electrons are accepted by the molecule. As chlorophyll in photosystem II accepts the electrons that are released by photolysis of water, reduction of chlorophyll occurs. Thus, photolysis of water is required for reduction of chlorophyll.

Excitation of chlorophyll occurs in response to sunlight. Chlorophyll is synthesized prior to initiation of photosynthesis. Hydrolysis of ATP is required for production of NADPH by photosystem I. Oxidation of NADPH is required for reduction of carbon dixoide in Calvin Benson cycle (dark reaction).

Right choice: C. reduction of chlorophyll.