Photosynthesis in Higher Plants

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In green plants, H2O is the hydrogen donor and is oxidised to O2.

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Purple and green sulphur bacteria use H2S as H-donor. So the ‘oxidation’

product is sulphur or sulphate and no O2 is produced.

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Thus, he inferred that the O2 evolved by the green plant comes from H2O,

not from CO2. This was later proved by using radioisotopic techniques.

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Therefore overall correct equation for photosynthesis is:

Light

2

2

6

12

6

2

2

6CO

12H O

C H O +6H O+6O

+

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PHØTØSÝÑTHËSÏS: SÏTË ÅÑD PÏGMËÑTS

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Photosynthesis occurs in green

leaves & other green parts of the

plant.

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Chloroplasts are present in the

mesophyll cells of leaves so that

they get optimum quantity of

incident light.

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Chloroplast

contains

a

membranous system. It consists

of grana, stroma lamellae and

fluid stroma.

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Each granum is a group of membrane-bound sacs called thylakoids

(lamellae). They contain leaf pigments.

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The membrane system traps light energy and synthesizes ATP and

NADPH. It is called light reaction.

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In stroma, enzymatic reactions incorporate CO2 into the plant for

synthesizing sugar, which in turn forms starch. It is called dark reaction.

It does not mean that they occur in darkness or that they are not light

dependent.

(AIPMT 2009)

Lamella

Thylakoid

Granum

Starch granule

Chloroplast DNA

Ribosome

Stroma

Lipids of Drop

Inner membrane

Intermembrane space

Outer membrane