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Early experiments

•  Experiment on a variegated leaf

•  Experiment on a leaf covered with black

paper

•  Experiment on a leaf enclosed in a test

tube containing some KOH soaked cotton

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Joseph Priestley

Discovered that plants restore to

the air whatever breathing animals

and burning candles remove.

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Jan Ingenhousz

He showed that sunlight is essential to

the plant process that somehow

purifies the air fouled by burning

candles or breathing animals.

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Julius von Sachs

He proved that the green parts in

plants is where glucose is made and

that the glucose is stored as starch.

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T.W. Engelmann

He described first action spectrum of

photosynthesis and observed that the

bacteria accumulated in the region of blue

and red light of the split spectrum.

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Cornelius van Niel

He demonstrated that photosynthesis is

essentially a light-dependent reaction in

which hydrogen from a suitable oxidisable

compound reduces carbon dioxide to

carbohydrates

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Pigments involved in

photosynthesis

•  Chlorophyll a

•  Chlorophyll b

•  Xanthophylls

•  Cartenoids

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Light reaction

•  Light absorption

•  Water splitting

•  Oxygen release

•  Formation of high-energy chemical

intermediates

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Electron transport

Cytochromeb f

6

P680

P680*

P700

P700*

NADP

+

NADPH

Ferredoxin

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Chemiosmotic hypothesis

PhotosystemII

Cytochromes

b and f

PS I

Lumen

H

+

H

+

H

+

H

+

H

+

H

+

H

+

F

0

F

1

ATP

ADP

ATP Synthase

NADP

+

NADPH

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The Calvin Cycle

•  Carboxylation

•  Reduction

•  Regeneration

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The C4 Cycle

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Photorespiration

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Factors affecting photosynthesis

External

•  Availability of sunlight

•  Temperature

•  CO2 concentration

•  Availability of water

Internal

•

Number, size, age and

orientation of leaves

•

Mesophyll cells and

chloroplasts

•

Internal CO2

concentration

•

Amount of chlorophyll