As we all are well aware, photosynthesis is the process of producing carbohydrates by green plants using carbon dioxide and water in the presence of sunlight. Here we will discuss Cyclic Photophosphorylation & Non-Cyclic Photophosphorylation.
The two-step process comprises:
- The light reaction takes place in the grana of the chloroplast. Here light energy gets converted to chemical energy as ATP and NADHP. In this very light reaction, the addition of phosphate in the presence of light or the synthesizing of ATP by cells is known as photophosphorylation.
- While in the dark reaction, the energy produced previously in the light reaction is utilized to fix carbon dioxide to carbohydrates. The location where this happens is the stroma of the chloroplast.
Cyclic photophosphorylation just accomplishes the ADP to ATP process for immediate energy for these cells. This process uses only Photosystem I and the chlorophyll P700. It transports the cyclic electron. Electrons here travel in a cyclic manner and electrons travel back to photosystem I and only ATP is produced. Another point to be noted is that photolysis or water splitting is absent, oxygen is not evolved and also this system is mostly predominant in bacteria.
While noncyclic photophosphorylation uses both photosystem I and photosystem II acting in series. In this, it transports a noncyclic electron. The active reaction center in noncyclic photophosphorylation is P680 and electrons travel in a non-cyclic manner. The electrons from photosystem I is accepted by NADHP. In this process, both NADHP and ATP are produced. The process of photolysis or water splitting is present unlike cyclic photophosphorylation and towards the end, oxygen is evolved as a byproduct. The system happens to be mostly predominant in green plants.
Let’s summarize photophosphorylation. Photophosphorylation refers to the use of light energy to ultimately provide the energy to convert ADP to ATP and so replenishing the energy currency in living beings.
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