1.
PIGMENTS:
The colour of the
algal thallus which varies in different classes of algae is due to the presence
of definite chemical compounds in their cells. These are called pigments. Each
pigment has its own characteristic colour. The particular colour that a thallus
has is due to the predominance of one pigment in combination with several
others. For example brown algae have predominance of Fucoxanthin and
phycophenin while red algae and blue green algae have phycoerythrin and phycocyanin
respectively. Each group of algae has
its own particular combination of pigments and characteristic colour which is
not found in other group.
The photosynthetic
pigments of algae are of three kinds – Chlorophylls,
Carotenoids and Phycobillins or Billoproteins.
Chlorophyll
pigments are fat
soluble compounds and are of five different types, i.e., chlorophyll a, b, c, d and e.
Out of these, chlorophyll a is
universally present in all the groups of algae whereas chlorophyll b, c, d and e have restricted distribution.
Carotenoids are fat soluble yellow coloured
pigments and are sub-divided into carotene,
xanthophylls and carotenoid
acids.
Phycobillins are water soluble blue (phycocyanin) and red (phycoerythrin) coloured pigments and are
present in Cyanophyceae and Rhodophyceae.
2. FOOD
RESERVES
The primary product
which accumulates as food reserve in algae is the polysaccharides.
Polysaccharides however vary in different algal groups. They may be found as
starch, lamanarian paramylon and leucosin.
True
starch is a
typical food reserve of only two algal divisions namely, Chlorophyta and
Charophyta. The two other kinds of characteristic starches are Cyanophycean starch and Floridean starch. The former is the
characteristic food reserve of Cyanophyta and the later is the characteristic
food reserve of Rhodophyta. Lamanarian
is a food reserve found in brown algae. Paramylon
is a characteristic food reserve of Euglenoids and Leucosin is peculiar to Xanthophyta, Bacillariophyta and
Chrysophyta.
Besides polysaccharides, a
proteinaceous compound Cyanophycin
is found only in the cells of blue-green algae. Manitol, is a food reserve which was primarily considered to be
unique to the brown algae has recently been reported to occur in few red algae.
Fats occur as food reserve in
appreciable amount in the cells of Xanthophyta, Bacillariophyta and
Chrysophyta.
(Both pigments and food reserves has its occurrence in different
divisions of algae and thus provide the key source for the classification of
algae.)
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