Difference Between Cyclic and Noncyclic Photophosphorylation

Introduction

All plants undergo the vital process of photosynthesis. We know it as the process by which plants manufacture food and the light energy gets transformed into chemical energy. Photosynthesis is the basis of life for green plants and all other organisms in the food chains and food webs. Chlorophyll, sunlight, and carbon dioxide are required for this process. Photosynthesis takes place in all green parts of the plant at the cellular level in the chloroplasts.

  1. The process of photosynthesis takes place in a series of steps, as follows. 

  2. Absorption of sunlight or light energy by chlorophyll.

  3. Conversion of light energy into chemical energy.

  4. Decomposition of water molecules into hydrogen and oxygen.

  5. Transformation of carbon dioxide to form carbohydrates. 

These steps take place in all plants that make their own food but not necessarily in the same order. The entire process can be divided into two major phases, one which is light-dependent and the other, which is light-independent.


What is Photophosphorylation?

The light-dependent reaction phase of photosynthesis is known as photophosphorylation. This process involves producing ATP (three phosphate groups) molecules from the ADP (2 phosphate groups) in the plant cells' chloroplasts in the presence of light. These reactions generate the following two molecules needed for the next stage of photosynthesis by utilizing light energy.

  • The energy storage molecule ATP 

  • The reduced electron carrier NADPH

This process is carried out in the presence of photosystems. They are the functional units for photosynthesis. They consist of complex pigment organizations that absorb and transfer light energy and assist in transferring electrons. They are of 2 types: photosystem I and photosystem II.


Photophosphorylation is of the Following Two Types

  1. Cyclic Photophosphorylation

  2. Non–cyclic photophosphorylation

We will now study these two types of photophosphorylation, their features, and the difference between cyclic and non-cyclic photophosphorylation.


What is Cyclic Photophosphorylation?

Cyclic photophosphorylation is the process in which organisms, especially prokaryotes, bring about the conversion of ADP to ATP to generate energy for the cells' immediate needs. It takes place in the lamellae of chloroplasts.

  • In cyclic photophosphorylation, the electrons move in a circular pattern in photosystem I. 

  • Here, the ATP synthesis is brought about by electron transport that is powered by Photosystem I only.

  • No oxygen or NADPH is produced in this phase.

  • The movement of electrons is from the primary acceptor to ferredoxin via cytochrome B6F found in mitochondria. The electron then passes to plastocyanin and finally returns to chlorophyll, completing a cycle.


What is Noncyclic Photophosphorylation?

Noncyclic photophosphorylation is the other method of photophosphorylation. It results in the synthesis of ATP molecules from ADP using the energy from excited electrons by photosystem II. In this process, the movement of the electrons happens in a noncyclic manner. The excited electrons do not get back to the chlorophyll.


The noncyclic photophosphorylation occurs in two stages and involves two different chlorophyll photosystems, PS I and PS II. 

  • It is a light reaction and occurs in the thylakoid membrane.

  • Noncyclic photophosphorylation produces ATP and NADPH. 

  • The generation of ATP is along with a one-way flow of electrons from H₂O to NADP+.

  • The lost electrons by P680 of PS II are occupied by P700 of PS I.

  • They are not reverted to the energy center. 

  • The complete movement of the electrons is in a non-cyclic manner or a unidirectional manner.

Now that we know about the two types of phosphorylation, let us study the difference between cyclic and noncyclic photophosphorylation.


The table below explains the difference between cyclic and noncyclic phosphorylation.


Differentiate Between Cyclic and Noncyclic Photophosphorylation


Cyclic and Noncyclic Photophosphorylation Class 11 

Feature

Cyclic Photophosphorylation

Non-cyclic Photophosphorylation

Photosystems Involved

Only PS I

Both PS I and PS II

Water

No water is required

Photolysis of water is a requirement

Oxygen

No Molecular Oxygen requirement

Oxygen is required

NADPH

No NADPH synthesis happens

NADPH is synthesized

Purpose

Used to produce additional ATP for immediate cell needs

Products ATP, NADPH, and H+ formed for further light-independent reactions.

Electron Pathway

Electrons cycle back to the reaction center in a circular manner.

Electrons do not get back to the reaction center.

External Electron Donors

Not required

Required from H₂O or H₂S

Photophosphorylation Location

Happens at 2 locations

Only at one place

Light Intensity

Low light intensity

High light intensity is required.


In the photophosphorylation method, there is the formation of ATP from ADP. ATP consists of three phosphor units while the ADP consists of two phosphor units. When there is an addition of an extra phosphor unit to the ADP it is then called the ATP. The cyclic photophosphorylation takes place under both aerobic and anaerobic conditions which is hence an efficient process than the other process. The ATP that is produced from this process is also highly beneficial for the production of energy for plants and the production of oxygen important for humans. Students can now also Check The Difference Between Cyclic and Noncyclic Photophosphorylation via Vedantu where everything regarding the same is provided in many details.


Significance of noncyclic photophosphorylation

  1. Noncyclic electron transport occurs through a sequence of electron transport where there is the reduction of NADP by PS 1 and the PS 1 is reduced by PS 2 and then finally PS 3 is reduced by electrons that arise from photo-oxidation of water.

  2. This electron transport helps release oxygen and photooxidation of water takes place.

  3. The non-cyclic process is important as it supplies assimilatory power in the form of NADPH and  ATP for carbon dioxide assimilation and purifies the atmospheric air.

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FAQs on Difference Between Cyclic and Noncyclic Photophosphorylation

1. How are photosynthesis and photophosphorylation connected to each other?

The process of photosynthesis consists of two phases one is the light reaction phase and the other is the dark reaction phase. The light reaction is the one that depends on the light energy for the reaction to occur. During the light reaction, the photolysis of water takes place. In this reaction the evolution of oxygen takes place. During this light reaction, the energy is captured by the centers of photosystems and then they tend to expel the electrons with great energy. These electrons then pass through a series of complexes which are called the Electron transport system. During the transfer of electrons, there is a phosphorylation reaction that occurs which produces the energy-rich ATP.

2. Are there any similarities between Cyclic and Noncyclic Photophosphorylation?

There are a lot of similarities between Cyclic and Noncyclic Photophosphorylation which can be provided as follows:

  1. Both Cyclic and Noncyclic Photophosphorylation are light-based reactions. They both need light to occur.

  2. Cyclic and Noncyclic Photophosphorylation both consist of the electron transport system

  3. Cyclic and Noncyclic Photophosphorylation both of them produce assimilatory powers

  4. In both the Cyclic and Noncyclic Photophosphorylation there is the formation of ATP.

These are the only similarities found and the rest process differs a lot.

3. What happens during cyclic photophosphorylation?

Cyclic phosphorylation is a process that involves photophosphorylation in which there is an electron released due to the exciting photo center. This process takes place in the stroma lamellae membrane of the chloroplast and the cyclic photophosphorylation only consists of the PS 1 system also called the photosystem 1 system. The lamellae of the grana have both the PS 1 and PS 2 whereas the lamellae membranes of stroma only consist of PS 1 along with the NADP enzyme. The excited electrons do not pass through the NADP and are cycled back to the PS 1 complex with the help of the electron transport chain. Cyclic photophosphorylation is independent of the photolysis of water. Here no oxygen is evolved.

4. What is the process involved in noncyclic photophosphorylation?

The following process takes place in the noncyclic photophosphorylation:

  1. The noncyclic photophosphorylation takes place in the grana of the chloroplasts.

  2. The process starts with the excitation of special types of molecules.

  3. These molecules of chlorophyll then form the reaction centers also called the photo centers.

  4. The accessory pigments and other chlorophyll molecules tend to take in the solar energy and then pass it on to those centers where the reaction occurs.

  5. Thus when a photon is absorbed it is passed on to the special molecule

  6. The pigment molecules which transfer the energy will absorb a wavelength of about 680 nm or lower than that range.

  7. Then the pigment molecules from the PS 1 and PS 2.

5. Why is it important to learn about the Difference Between Cyclic and Noncyclic Photophosphorylation?

Checking out the Difference Between Cyclic and Noncyclic Photophosphorylation helps students to understand how two processes take place in a single plant with the help of light. While both processes occur under the light itself they have different mechanisms and different strategies are involved to complete the process.  Will the end product of the process be the same i.e. the production of ATP which is the energy-providing molecule for plants, they still have different routes of the process that are used. The cyclic process has a more continuous network than the noncyclic ones. The non-cyclic will need external energy for it to move forward. Students can also refer to Vedantu NCERT Solutions for Biology which will enable them to understand more regarding the Difference Between Cyclic and Noncyclic Photophosphorylation.

6. What Happens During Photophosphorylation?

The process of photophosphorylation ensures the conversion of ADP to ATP using sunlight by PS II activation. This process involves the splitting of the water molecule into oxygen and hydrogen protons (H+). This process is known as photolysis. It results in a continuous unidirectional flow of electrons from water to the PS I.


In this process, the electron movement is spontaneous from the donor to the acceptor through an electron transport chain. The ATP is made from the enzyme ATP synthase. This chain, which is responsible for electron transport, is made up of a series of redox reactions. The purpose of these reactions is to sequentially transfer electrons from a high-energy donor to a lower energy acceptor molecule. 


During the function of the electron transport chain, the flow of electrons from the stroma to the thylakoid area results in the production of an electrochemical potential gradient across membranes. ATP is produced by phosphorylation.

7. What are Photosystems?

Photosystems are large complexes of proteins and light-absorbing molecules. They play a key role in the light reactions. Each photosystem has light-sensitive complexes made up of proteins, pigments, and chlorophylls. Photosystems are of two types-PS I and PS II.


When a pigment absorbs a photon, it gets high in energy. It then transfers energy to a neighbouring pigment through electromagnetic interactions in a process called resonance energy transfer. The central part of the photosystem, called the reaction center, thus gets all the energy. PS I consist of the P700, chlorophyll, and other pigments. It converts NADP+ to NADPH2 with light energy. It is located on the external surface of the thylakoid membrane. PS II consists of P680, chlorophyll, and multiple pigments. It is built up of a protein complex that absorbs light energy. It is located on the internal surface of the thylakoid membrane in plant cells. It transfers electrons from water and helps in the dissociation of water molecules. They produce H + protons and oxygen.


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