Photosynthesis Question 47

47. Which one occurs both during cyclic and noncyclic modes of photophosphorylation?

[1994]

(a) Involvement of both PS I and PS II

(b) Formation of ATP

(c) Release of $O_2$

(d) Formation of NADPH

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Answer : b

Hints & Solution

(b) Cyclic photophosphorylation can be used to produce a steady supply of ATP in the presence of sunlight. However, ATP is a highly reactive molecule and hence cannot be readily stored within the cell. Non-cyclic photophosphorylation produces NADPH in addition to ATP (this requires the presence of water). In the Z-scheme, electrons are removed from water (to the left) and then donated to the lower (non-excited) oxidized form of P680. Absorption of a photon excites P680 to P680*, which “jumps” to a more actively reducing species.



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