Name: Kranz Anatomy - The Ring of Cells
Uploaded: 2019-07-19
Duration: 5 min 1 s
Description: Let's learn about the characteristic features of certain plants responsible for the process of photosynthesis and photorespiration.

Question

Where does non-cyclic photophosphorylation take place? Describe the process. Why is the process referred to as non-cyclic.

Accepted Answer

The process of photophosphorylation is in which the electron expelled by the exciting photo center does not return to it. This process is called non-cyclic photophosphorylation.

The non-cyclic photophosphorylation is carried out in collaboration with both photosystems I and II.

1. During this, oxygen is produced by the photolysis of water: A water molecule splits into hydrogen and oxygen ions in the illuminated chloroplasts. It requires solar energy, an oxygen-evolving complex (OEC), and an electron carrier (Yz) is needed that is present on the inner surface of the thylakoid membrane. The enzyme has four Mn (Manganese) ions. The liberation of O₂ also requires two other ions, Ca²⁺ and Cl^-. Electron carrier (Yz) transfers the released electrons to P680.

2. Production of NADPH and ATP:

The electrons released during the photolysis of water are picked up by the P680 reaction center of photosystem II.

On receiving a photon of light energy the reaction center expels an electron. It is the primary reaction of photosynthesis during which light energy converts to chemical energy. The phenomenon is also known as quantum conversion. The electron released from the reaction center of photosystem II is picked up by the electron carrier pheophytin. Then electron passes through a series of carriers and loses their energy at every step in the downhill direction. These electron carriers include plastoquinone (PQ), cytochrome bf complex, and plastocyanin (PC). While passing over the cytochrome complex, the electron loses sufficient energy for the creation of proton gradient and synthesis of ATP from ADP and inorganic phosphate.

The process is called photophosphorylation (non-cyclic). From plastocyanin, the electron is picked up by the trap center P700 of photosystem I. On absorbing a photon of light energy, P700 pushes out the electron with the gain of energy. The electron passes through different carriers X (a special chlorophyll molecule), FeS, ferredoxin, and NADP-reductase. The latter gives electrons to NADP⁺for combining with H⁺ ions to produce NADPH.

This process is referred to as the non-cyclic as the electron released from the system doesn’t come back to the system, but is used to reduce the NADP⁺.

Where does non-cyclic photophosphorylation take place? Describe the process. Why is the process referred to as non-cyclic.

Important Questions on Photosynthesis in Higher Plants

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