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A Handbook of Biology
PÏGMËÑTS ÏÑVØLVËD ÏÑ PHØTØSÝÑTHËSÏS
Pigments are substances that have the ability to absorb light, at specific
wavelengths.
Chromatography shows the following leaf pigments:
Chlorophyll a (bright or blue
green in chromatogram)
Chlorophyll b (yellow green)
Xanthophylls (yellow)
Carotenoids (yellow to yellow-
orange)
Chlorophyll b
Carotenoids
Chlorophyll
400
500
600
Wavelength (nm)
700
a
Absorbance of light by
chloroplast pigments
FÜÑÇTÏØÑS ØF ÅÇÇËSSØRÝ PÏGMËÑTS:
Rate of photosynthesis
Absorption
Light absorbed
Wavelength of light in nanometres (nm)
400
500
600
700
3
2
1
They
absorb
light
at
different
wavelength and transfer the energy
to chlorophyll .
They protect chlorophyll a from
photo-oxidation.
The
absorption
spectrum
&
action spectrum coincide closely
showing
that
photosynthesis
is maximum in the blue & red
regions of the spectrum.
The
graphs
also
show
that
chlorophyll a is the chief pigment
associated with photosynthesis
4
PHØTØSÝSTËMS
Pigments are organised into two Photosystems called Photosystem I
(PS I) & Photosystem II (PS II). These are named in the sequence of their
discovery.
Each
photosystem
has
a
chlorophyll
a
molecule
and
accessory pigments bound to
proteins.
Each
photosystem
have
all
pigments (except one molecule
of chlorophyll a) form a light
harvesting complex (LHC or antennae).
Rate of photosynthesis
(measured by O release)
2
400
500
700
600
Wave length of light (nm)