Page 5 - LN-PHOTOSYNTHESIS IN PLANTS

The pigments involved in the process of photosynthesis are called photosynthetic
pigments. These pigments provides different shades of green in the leaves in
different plants or in the leaves of same plant.
These pigments can easily be separated out by chromatographic technique (paper
chromatography). On the basis of their significance, the photosynthetic pigments are
of two types
(i) Primary pigments The pigment forms the main molecule of photosystem, e.g.,
Chlorophyll- a, b.
(ii) Accessory pigments. These support the function of primary pigments, e.g.,
Xanthophylls and carotenoids.
A cinematographic separation of the leaf pigments shows that it is not only the
single pigment, which is responsible for the colour in the leaves. Instead the different
shades in leaf are due to four different pigments that have different ability to absorb
light at specific wavelength.
Different pigments present in leaf described below
(a) Chlorophyll-a (C 55H 72O 5N 4M g) This is bright or blue green in the chromatogram. It is
known to be the chief plant pigment associated with photosynthesis.
(b) Chlorophyll-b (C 55H 70O 6N 4M g) This is yellow green in colour.
(c) Xanthophylls This is yellow in colour. These pigments are oxidised carotenoids.
(d) Carotenoids This is yellow to yellow-orange in colour. They are also known as
‘antenna pigment’.
Chlorophyll is the most abundant plant pigment found if the plants in the world. It
contains magnesium (Mg ) metal as its constituents.
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Absorption Spectrum
It is the curve that shows the amount of different wavelength of lights absorbed by a
substance. The graph given below shows the ability of chlorophyll-a to absorb lights
of different wavelength.
Chtorophyll-a shows the maximum absorption peak at 450 nm and also shows
another peak at 650 nm.

Absorption spectrum is constituted by the pigments like violet, blue, orange and red
(400-500 and 600-700 nm).
The Emission spectrum is constituted by yellow and yellow-green pigment (500-600