Difference Between Cyclic And Noncyclic Photophosphorylation: Noncyclic Photophosphorylation

Table: Difference Between Cyclic And Noncyclic Photophosphorylation

Definition Of Photophosphorylation

Photophosphorylation is a process by which light energy is used in the light-dependent reactions for photosynthesis to synthesise ATP from ADP and inorganic phosphate. This activity is an essential part of the light energy conversion into chemical energy stored in the form of ATP and occurs within the membranes of thylakoids inside chloroplasts.

Photophosphorylation is a part of the photosynthetic process by which ATP and NADPH are produced, the essential energy carriers for the subsequent cycle of Calvin. These molecules carry energy and reduce power to drive carbon dioxide into glucose and other organic compounds supporting plants' energy needs for survival and growth.

There are two different pathways of photophosphorylation producing ATP in the light reactions of photosynthesis: cyclic and noncyclic photophosphorylation. Cyclic photophosphorylation involves only PS I, and it produces ATP without the generation of NADPH or oxygen. In contrast, noncyclic photophosphorylation involves both PS II and PS I and produces both ATP and NADPH with the release of oxygen as a byproduct. Both are essential steps of light-dependent reaction, although the two processes play different roles in supporting the overall photosynthetic process.

Cyclic Photophosphorylation

Cyclic photophosphorylation is light-dependent and the process by which ATP is produced using only Photosystem I and involves the cyclic flow of electrons. This does not yield NADPH or oxygen and seems to be mainly implicated in replenishing ATP levels when their levels are needed more than those of NADPH.

Definition And Process

• Light Absorption: Light absorption by photosystem I excites electrons.

• Electron Transport: The electrons transfer through a series of transport proteins in the thylakoid membrane.

• ATP Synthesis: The energy from electron transport is used by ATP synthase to drive the synthesis of ATP.

• Return of Electron: This step is completed by cycling back the electrons to Photosystem I.

Key Components

• Photosystem I (PS I): This is the light-harvesting complex where electrons get excited.

• Electron Transport Chain (ETC): This is a series of proteins that translocate excited electrons and generate a proton gradient.

• ATP Synthesis: In this process, ATP is produced using the energy from the proton gradient.

Products Of Cyclic Photophosphorylation

• ATP is produced through the cyclic electron flow.

• Significance and Functions

• ATP Supply: Provides ATP for other cellular processes.

• Balancing ATP/NADPH: Maintains the level of ATP when there is excess NADPH.

Noncyclic Photophosphorylation

Noncyclic photophosphorylation involves both photosystems, PS II and PS I, and the overall result of this process is the formation of molecules of ATP and NADPH with the release of oxygen gas. It forms a part of the light-dependent reaction of photosynthesis and provides energy and reducing power to the Calvin cycle.

Definition And Process

• Light Absorption: Light is absorbed by photosystem II and results in the splitting of the water molecule.

• Electron Transport: The electrons are passed through the electron transport chain, thus creating a proton gradient.

• ATP and NADPH Synthesis: The energy from this gradient of protons drives the process of synthesising ATP. These electrons reduce NADP+ into NADPH.

• Oxygen Release: Water is split to release oxygen as a byproduct.

Key Components

• Photosystem II, PS II - A complex responsible for water-splitting and light absorption.

• Photosystem I, PS I - A complex involved in producing NADPH.

• Photolysis (Water Splitting): break-down of water to supply electrons

• Electron Transport Chain: transport of electrons from PS II to PS I with concomitant formation of a proton gradient.

• Reduction of NADP+: NADPH Formation

• Noncyclic Photophosphorylation Products

• ATP: Due to the electron transport chain, a proton gradient is formed.

• NADPH: From the reduction of NADP+.

• Oxygen: A by-product of water-splitting

Functions and Significance

• ATP and NADPH Supply: The Calvin cycle is supplied with energy and reducing power.

• Oxygen Production: This is necessary for respiration in aerobic organisms.

Role In Photosynthesis

• Cyclic: Mainly maintains the concentration of ATP used by a wide range of cellular processes.

• Noncyclic: Produces ATP and NADPH both of which are crucial for the Calvin cycle and hence overall photosynthetic efficiency.

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