Download Pigments

Light-trapping pigments
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Radiant energy from the sun includes a range of wavelengths:
o Visible light, in the range from about 0.4 to 0.7µm
o Infra-red (IR), with wavelengths greater than 0.7µm
o Ultraviolet light (UV), with wavelengths shorter than 0.4µm
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Various pigments can trap light energy:
o Major light trapping pigments are green chlorophylls located on the
grana membranes.
o Other kinds of light-trapping pigments are also found in chloroplasts of
various organisms = accessory pigments.
Pigment
Chlorophyll a
Chlorophyll b
Chlorophyll c
Chlorophyll d
Carotenoids
Phycobilins
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Organisms where found
All plants and all algae
All plants and green algae
Brown algae and phytoplankton
Red algae
All plants and green algae
Red algae
Carotenoids are red, orange and yellow pigments that are normally masked
by the green chlorophylls.
In temperate climates in early autumn, deciduous trees begin to withdraw the
chlorophyll from their leaves, exposing the carotenoids and other pigments
that are normally hidden.
Phycobilins are blue-green (phycocyanin) and red (phycoerythrin) watersoluble pigments.
The various pigments trap light energy of different wavelengths (see figure
below).
The presence of accessory pigments extends the range of light wavelengths
that can be absorbed by a plant and converted to chemical energy.
Light energy absorbed by accessory pigments must be transferred to
chlorophyll a before it can be converted into chemical energy.
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Photosynthesis is most efficient in light of red and blue wavelengths.
These wavelengths do not penetrate very far below the surface of water.
In deeper waters most of the light wavelengths available are blue-green,
which accessory pigments can absorb.
The phycobilins, in particular, contribute to photosynthesis in deeper waters
and these are found in seaweeds.
Seaweeds that have colour when brought to the surface of the water often
look black when looked at in water.