Question

1. Explain how the oxidation of water and PQH, during the light reactions contributes to the formation of ATP. 2. a. What is the original source of the electron used in the reduction of NADP+ to NADPH? b. What photosystem is most directly related to this reduction event. 3. What photosystem is associated with the formation of Oxygen gas (O2) and where do the oxygen atoms in O2 gas come from?
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Answer 1

1. Explain how oxidation of water and PQH2 during the light reactions contributes to the formation of ATP.

The oxidation of water in photosystem II releases electrons, protons, and oxygen atoms. These electrons are then used to reduce plastoquinone (PQ) into plastoquinol (PQH2) which then passes the electrons to cytochrome b6f complex and to the photosystem I. The protons released from oxidation of water and Q cycle generate a transmembrane proton gradient across the thylakoid lumen. This proton gradient is used for ATP production from ADP.

2. A. What is the original source of the electron used in the reduction of NADP⁺ to NADPH?

The electrons used in the reduction of NADP⁺ to NADPH come from water molecule upon its oxidation.

B. What photosystem is most directly related to this reduction event?

Photosystem I is most directly related to the reduction of NADP⁺ to NADPH.

3. What photosystem is associated with the formation of oxygen gas (O₂) and where do the oxygen atoms in O₂ gas come from?

Photosystem II is associated with the formation of oxygen gas (O₂).

The oxygen atoms in O₂ gas come from water molecule upon its oxidation at photosystem II.