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Photosynthesis in Higher Plants — BIOLOGY STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceBIOLOGYPhotosynthesis in Higher Plants5 Marks
Question
Describe the basic characteristics of a photosystem and explain how photosystem I differs from photosystem II.
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Answer

  • Photosystems are the discrete units of organisation of the pigments in the thylakoid (grana) membranes.
  • Each photosystem has about 250-400 pigment molecules, which include chlorophyll a, that forms the reaction centre and other accessory pigments, chlorophyll b, carotene and xanthophyll, forming the antenna of light harvesting complex (LHC).
  • Chlorophyll a that forms reaction centre has two absorption maxima, at 680 nm and 700 nm; these pigments are designated as P680 and P700.
  •  
PS I
PS II
It is constituted by those chlorophyll P700 and other pigment molecules which absorb light energy and pass on to P700.
It is constituted by those chlorophyll P680 and accessory pigments that pass on light energy to P680.
The reaction centre is P700
The reaction centre is P680
The electrons emitted by this come back as de-energized electrons.
The electrons emitted by this do not come back, but are replaced by electrons generated by photolysis of water.
It is involved only in non-cyclic photophosphorylation.
It is involved both in cyclic and non-cyclic photophosphorylation.

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