[Biology Class Notes] on Difference Between Cyclic and Noncyclic Photophosphorylation Pdf

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.

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 

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 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.