Comparison of cyclic and noncyclic photophosphorylation process and key differences
Photosynthesis is referred to as the process of converting the light energy of the Sun into chemical energy. During this process, the light energy gets captured and is then used to convert carbon dioxide and water to glucose and oxygen.
Photosynthetic processes can be divided into two categories: oxygenic and anoxygenic. Both work on the same principles, although plants, algae, and cyanobacteria use oxygenic photosynthesis the most.
Light energy transfers electrons from water (H2O) taken up by plant roots to CO2 to make carbohydrates during oxygenic photosynthesis. The CO2 is "reduced," or gains electrons, while the water is "oxidised," or loses electrons, in this process. Along with carbs, oxygen is generated.
6CO2 + 12H2O + Light Energy → C6H12O6 + 6O2 + 6H2O
"Anoxygenic Photosynthetic Bacteria," anoxygenic photosynthesis uses electron donors that aren't water and don’t produce oxygen. Green sulfur bacteria and phototrophic purple bacteria are among the microorganisms that undergo this activity.
CO2 + 2H2A + Light Energy → [CH2O] + 2A + H2O
However, this entire process of photosynthesis occurs in two different processes:
Light reaction and dark reaction.
Light Reaction
The light reaction of the photosynthesis occurs in the chloroplast inside the grana. In this reaction, the light energy is converted to chemical energy in the form of ATP and NADPH. In this reaction, when phosphate is added in the presence of sunlight or by the process of ATP synthesis by cells, it is referred to as photophosphorylation. Carotenoids make up the accessory pigments. The chlorophyll in the thylakoid membrane of chloroplasts absorbs the energy from the sun. Two-electron transport chains generate ATP and NADPH, which are then transferred to ATP and NADPH. During the process, both water and oxygen are utilised.
Dark Reaction
In the dark reaction of photosynthesis, the energy which is produced in the light reaction is used for converting carbon dioxide into carbohydrates. This reaction happens in the stroma of the chloroplasts. The nighttime reactions of photosynthesis are propelled by the energy provided by ATP (made during the light reactions). The phrase "dark reactions" does not imply that the reactions take place at night or that darkness is required. It means that the reactions can continue regardless of how much light is present. The phrase is solely used to differentiate between dark and light reactions, both of which require light.
Students can refer to the Light Dependent Reactions page for more information.
What is Photophosphorylation?
Otto Kandler published the first experimental evidence for photophosphorylation in vivo in 1950, utilising intact Chlorella cells and interpreting his findings as light-dependent ATP production. With the use of P32, Daniel I. Arnon identified photophosphorylation in isolated chloroplasts in vitro in 1954. In 1956, he released his first review of early photophosphorylation studies.
Photophosphorylation is the process in which light energy is used from photosynthesis to convert adenosine diphosphate (ADP) to adenosine triphosphate (ATP). It is the process in which the energy-rich ATP molecules are synthesised by the transfer of the phosphate group to the ADP molecule during the presence of sunlight.
Photophosphorylation is of Two Different Types:
Non-cyclic photophosphorylation
Difference Between Cyclic and Non-Cyclic Photophosphorylation
Cyclic Photophosphorylation
Cyclic photophosphorylation is a process that results in the movement of the electrons in a cyclic way to synthesise the ATP molecules. In this process, the plant cells convert ADP to ATP to gain immediate energy for their cells. The process of cyclic photophosphorylation generally occurs in the thylakoid membrane and makes use of Photosystem I and Chlorophyll P700.
Non-cyclic Photophosphorylation
Non-cyclic photophosphorylation is a process that results in the movement of the electrons in a non-cyclic way to synthesise the ATP molecules by using the energy from the excited electrons that are provided by Photosystem II.
Students Can Check All Other Biology-related Topics for Their Reference-
FAQs on Difference Between Cyclic and Noncyclic Photophosphorylation in Photosynthesis
1. What is the difference between cyclic and non cyclic photophosphorylation?
The main difference between cyclic photophosphorylation and non-cyclic photophosphorylation is that cyclic produces only ATP, while non-cyclic produces ATP, NADPH, and O₂.
- Cyclic photophosphorylation involves only Photosystem I (PSI) and electrons return to the same reaction center.
- Non-cyclic photophosphorylation involves both Photosystem II (PSII) and Photosystem I, and electrons do not return.
- Water is split (photolysis) only in non-cyclic photophosphorylation, releasing oxygen.
- NADPH is formed only in non-cyclic photophosphorylation.
2. What is cyclic photophosphorylation?
Cyclic photophosphorylation is a light-dependent reaction of photosynthesis in which electrons cycle back to Photosystem I and generate only ATP.
- Occurs in the thylakoid membrane of chloroplasts.
- Involves only PSI (P700).
- Electrons move through the electron transport chain and return to PSI.
- No NADPH formation and no oxygen release.
3. What is non cyclic photophosphorylation?
Non-cyclic photophosphorylation is a light reaction where electrons flow from water to NADP⁺, producing ATP, NADPH, and oxygen.
- Involves both Photosystem II (P680) and Photosystem I (P700).
- Water undergoes photolysis to replace lost electrons.
- Electrons move in a linear pathway called the Z-scheme.
- Produces ATP via chemiosmosis and NADPH via NADP⁺ reduction.
4. Why is oxygen produced only in non cyclic photophosphorylation?
Oxygen is produced only in non-cyclic photophosphorylation because it involves the photolysis of water in Photosystem II.
- Water splits into electrons, protons (H⁺), and oxygen.
- The released electrons replace those lost by PSII.
- Cyclic photophosphorylation does not split water, so no oxygen is formed.
5. Which photosystems are involved in cyclic and non cyclic photophosphorylation?
Cyclic photophosphorylation uses only Photosystem I, while non-cyclic photophosphorylation uses both Photosystem II and Photosystem I.
- Cyclic: PSI (P700) only.
- Non-cyclic: PSII (P680) first, then PSI (P700).
- PSII is responsible for water splitting in non-cyclic flow.
6. How does cyclic photophosphorylation produce ATP?
Cyclic photophosphorylation produces ATP through an electron transport chain that creates a proton gradient used in chemiosmosis.
- Light excites electrons in PSI.
- Electrons pass through carriers like cytochrome complex.
- Protons are pumped into the thylakoid lumen.
- ATP synthase uses the proton gradient to form ATP.
- Electrons return to PSI, completing the cycle.
7. What is the Z-scheme in non cyclic photophosphorylation?
The Z-scheme is the linear flow of electrons from water to NADP⁺ through PSII and PSI during non-cyclic photophosphorylation.
- Electrons start at water and move to PSII.
- They pass through the electron transport chain to PSI.
- Finally, electrons reduce NADP⁺ to NADPH.
- The energy changes resemble a “Z” shape when plotted graphically.
8. When does cyclic photophosphorylation occur in plants?
Cyclic photophosphorylation occurs when the plant requires extra ATP but not additional NADPH.
- Happens when NADP⁺ availability is low.
- Balances the ATP/NADPH ratio for the Calvin cycle.
- Common under high light intensity or stress conditions.
9. What are the similarities between cyclic and non cyclic photophosphorylation?
Both cyclic and non-cyclic photophosphorylation are light-dependent reactions that produce ATP in the thylakoid membranes of chloroplasts.
- Both require light energy.
- Both involve an electron transport chain.
- Both generate ATP through chemiosmosis and ATP synthase.
- Both are part of the light reactions of photosynthesis.
10. Why is non cyclic photophosphorylation more common than cyclic photophosphorylation?
Non-cyclic photophosphorylation is more common because it produces both ATP and NADPH, which are required for the Calvin cycle.
- Provides reducing power in the form of NADPH.
- Supplies ATP for carbon fixation.
- Releases oxygen as a by-product, supporting aerobic life.
- Cyclic photophosphorylation mainly acts as a supplementary pathway to adjust ATP levels.
