Question
Explain non-cylic photophosphorylation in plants. Why is this process called so?
OR
Where does non-cyclic photophosphorylation take place? Describe this process. Why is this process called so?✓
Answer
- Non-cyclic photophosphorylation occurs in lamellae of grana.
- It begins with the absorption of light by P680 in PS II.
- The electrons become excited and jump over into an orbit farther away from the atomic nucleus.
- These electrons are picked up by the primary electron acceptor, which passes them into an electron transport system, consisting of cytochromes.
- These electrons are not used by any component of the ETS, but are transferred to PS I.
- Simultaneously, light of wavelength 700 nm is absorbed by PS I, which becomes excited and releases electrons.
- These electrons are transferred to another electron acceptor, from where they are transferred to NADP+; NADP+ is reduced (along with the protons formed by photolysis) to NADPH + H+.
- Both ATP and NADPH are formed during this electron flow.
- Since the electrons lost from PS II do not return to PS II, but are replaced by those from water, the process is called non-cyclic.
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