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Photosynthesis in Higher Plants

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Describe carbon reactions of the Cpathway. Does this pathway also operate in Cplants ?

Calvin Cycle (C3 cycle).
The steps involved in C3 cycle are discussed below:

(a) Carboxylation : It is the fixation of CO2 into a stable compound. the reaction is catalysed by RuBP carboxylase enzyme. In this the ribulose 1, 5 -bisphosphate reacts with carbon dioxide to give 3-PGA (3 phosphoglyceric acid).

(b) Reduction : In this step carbohydrate is formed at the expense of ATP and NADPH. Two molecules of ATP are utilized for phosphorylation and two NAdph for the reduction of COmolecule fixed. 6 molecules of CO2 and 6 turns of cycle are required for removal of one molecule of glucose from pathway. 

(c) Regenration - In this step the CO2 acceptor molecule RuBP is regenerated.


Where CO2 assimilation occurs in CPlants ?

In bundle sheath cells.

Name the first stable compound formed in C3 cycle.

3-phosphoglyceric acid (PGA)

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.

 What is stroma ?

Stroma is matrix or the cytoplasm of chloroplast where dark reaction of photosynthesis takes place.

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.