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Photosynthesis in Higher Plants

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Class 10 Class 12

What is photosystem ? Which is the pigment that acts as reaction centre ? Describe the interaction of photosystem I and photosystem II.

Photosystem : It is a group of pigment molecules and electron acceptors which take part in oxidation and reduction reaction in photosynthesis for producing ATP and NADPH.

Reaction Centre : Chla molecules  act as reaction centres. The Chla of speacial types form different reaction centres like P680 in PS II and P700 in PS I.

Interaction of PS I and PS II :

PS I and PS II are interlinked in following two

ways :

Ist way : P680 reaction centre of PS II takes energy from sunlight. Then, it emits electron which pass through number of electron acceptors and then go to P700, a reaction centre of PSI.

IInd way : The P700 takes energy from sunlight via harvesting molecule and its electron is emitted. This electron passes through primary acceptor x and then to ferrodoxin and after this to NADP reductase.

During photolysis of H2O, the H2O splits into H+ and OH. The OH changes into H2O, O2 and electrons are released which go to P680 molecule. The H+ goes to NADP reductase which combines NADP, H+ and e form assimilatory power called NADPH

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Where CO2 assimilation occurs in CPlants ?

In bundle sheath cells.
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What is stroma ?

Stroma is matrix or the cytoplasm of chloroplast where dark reaction of photosynthesis takes place.
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Why Rubisco is not affected by O2 in C4 plants ?

O2 is formed in mesophyll cells while Rubisco is present in bundle sheath cells. Therefore Rubisco does not come in contact with O2 and is thus not affected by it.
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Name the first stable compound formed in C3 cycle.

3-phosphoglyceric acid (PGA)
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What are grana ?

Grana are the stacks of thylakoids embedded in the stroma of a chloroplast. They are the sites of light reaction of photosynthesis.
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