Question

Define photophosphorylation and non-cyclic photophosphorylation.

Answer 1

Hint: Photophosphorylation is a process where ATP is formed by conversion of ADP TO ATP by utilising the sunlight energy.

Complete answer:
In plants during photosynthesis the sunlight activates the PSII ( photosystem II), the activated PSII causes the splitting of water to oxygen and hydrogen particles, where this process is said to be photolysis.

Once the photolysis did, this results in the continuous flow of electrons through the electron transport chain in PSII, at this time in the presence of ATP synthase ATP will be formed, and this whole process is said to be photophosphorylation. It got this name as phosphorylation occurs in the presence of sunlight.

Based on the direction of transport of electrons in the electron transport chain in PS( photosystem), they are classified into the following types:
- Cyclic photophosphorylation: In this electron in electron transport system moves cyclically.
- Non-cyclic photophosphorylation: In this electrons move in a non cyclic manner, here the whole movement of electrons is unidirectional.
But there are some similarities and differences between cyclic and non-cyclic phosphorylation.

Cyclic-photophosphorylation:
- It occurs in a cyclic manner
- It occurs in photosystem I, where p700 is activated.
- Here electron again reverted to PSI
- Only ATP is produced, water is not required so there are no byproducts such as oxygen
- This process mainly occurs in bacteria.

Non-cyclic photophosphorylation:
- It occurs in a unidirectional way, which means electrons are not reverted.
- It occurs in both PSI and PSII
- Here both ATP and NADH are produced.
- Water is utilised, and oxygen is the byproduct.
- Occurs in all green plants.

Note: To understand this question knowledge of light reaction and dark reaction is necessary.
And critical terms such as phosphorylation: which means an addition of phosphate.
As it occurs in the presence of light, it is termed as photophosphorylation.