PLANT KINGDOM – Algae – General Science Notes – For W.B.C.S. Examination.

প্ল্যান্ট কিংডম (উদ্ভিদসর্গ) – শেওলা – সাধারণ বিজ্ঞানের নোট – WBCS পরীক্ষা।

Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a variety
of other habitats: moist stones, soils and wood.Continue Reading PLANT KINGDOM – Algae – General Science Notes – For W.B.C.S. Examination.

Some of them also occurin association with fungi (lichen) and animals (e.g., on sloth bear).The form and size of algae is highly variable (Figure 3.1). The sizeranges from the microscopic unicellular forms like Chlamydomonas, to
colonial forms like Volvox and to the filamentous forms like Ulothrix and
Spirogyra. A few of the marine forms such as kelps, form massive plant
bodies.
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. These gametes can be
flagellated and similar in size (as in Chlamydomonas) or non-flagellated
(non-motile) but similar in size (as in Spirogyra). Such reproduction is
called isogamous. Fusion of two gametes dissimilar in size, as in some
species of Chlamydomonas is termed as anisogamous. Fusion between
one large, non-motile (static) female gamete and a smaller, motile male
gamete is termed oogamous, e.g., Volvox, Fucus.

Algae are useful to man in a variety of ways. At least a half of the total
carbon dioxide fixation on earth is carried out by algae through
photosynthesis. Being photosynthetic they increase the level of dissolved
oxygen in their immediate environment. They are of paramount
importance as primary producers of energy-rich compounds which form
the basis of the food cycles of all aquatic animals. Many species of Porphyra,
Laminaria and Sargassum are among the 70 species of marine algae
used as food. Certain marine brown and red algae produce large amounts
of hydrocolloids (water holding substances), e.g., algin (brown algae) and
carrageen (red algae) which are used commercially. Agar, one of the
commercial products obtained from Gelidium and Gracilaria are used to
grow microbes and in preparations of ice-creams and jellies. Chlorella a
unicellular alga, rich in proteins is used as food supplement even by
space travellers. The algae are divided into three main classes:
Chlorophyceae, Phaeophyceae and Rhodophyceae.

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