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PinkMonkey Online Study Guide-Biology
Red algae (Rhodophyta)
These are exclusively marine, found in deep waters
attached to rocks.
General Characteristics
(i) These are always multicellular, filamentous, radially symmetrical or compressed forms. There is no true parenchymatous construction.
(ii) The cell wall is made up of two layers. The inner
one is of cellulose while the outer one is of pectic compounds with
mucilaginous envelope.
(iii) The cytoplasm is uninucleate and shows a central
vacuole. The chromatophores are with naked pyrenoids.
(iv) The pigments are chlorophyll-a, chlorophyll-b, carotene and xanthophyll. However, the green color of chlorophyll-a is masked by red pigment, phycoerythrin and blue pigment phycocyanin.
(v) Food is stored in the form of chemically distinctive starch called floridean starch.
(vi) The reproduction is vegetative by fragmentation,
asexual by non-flagellated, haploid carpospores, monospores or tetraspores,
and sexual by formation of non-flagellate, non-motile male gametes and
an egg, thus oogamous.
(vii) The life-cycle shows either haploid forms or regular alternation of generations between similar haploid and diploid stages.
Examples: Agardhiella, Palysiphonia, Batrachospermum, Gracilaria, etc.
Figure 14.32 Types of Rhodophyta
Economic importance : The gelatinous substance
extracted from red algae (Gelidium, Gracilaria) is used
to prepare agar as a medium for bacterial and fungal cultures, in preparation
of ice-cream, jelly, cosmetics, medicines, etc. in Japan. Agar is also
used in printing and dying processes in textile industry. Some species
(Porphyra) are used as food.
Evolutionary significance : It appears that this group has taken its origin from some unicellular, non-ciliate ancestor as it shows non-flagellated spores and gametes.
Figure 14.33 Life cycle of a typical alga
Economic importance of algae : Algae are of certain
economic importance to mankind. They serve as initial food producers and
the first link in the aquatic food chain, both fresh water and marine.
Some of the fresh water algae and sea-weeds are used as vitamin-rich food.
Brown algae contain iodine and algin. Some red algae are the source of
agar jelly, used in the preparation of ice creams and culture media. However,
algae sometimes cause contamination of water and some of them release
many toxic substances killing millions of fish and other animals drinking
this water.
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