The algae also known as sea weeds, pond scrubs, frog spittle and water mosses (L.alga = sea weeds Gr.phykos – sea weeds) are studied under algology (Gr.phykology phykos-sea weeds+logos- dis-course or study. They are simple plants with autotiophic nutrition. They are chlorophyll bearing organisms (and their colourless relatives ) which are thalloid and have not differentiated as roots, stems and leaves.
Their occurrence is universal and found in all kinds of habitats in fresh as well as sea waters, soil, on within other plants and even animals, rock stones, in desert sand and snow fields. Based on their habitat they are classified as aquatic growing in fresh and brackish water, terrestrial (edaphophytes), on rocks and stones (lithophytic), halophytic growing in water of high concentrations of salinity, psammon algae of sandy beaches, thermal algae of hot waters near hot springs, cryophytic algae (on ice or snow) forming different colours of the snow. Epiphytic algae occurring within the cells of other plants, Epizoic and endozoic occurring on shells of mollusces, nose of fishes and within Paramecium, Hydra and molluces. There are also algae parasitic on plants and animals. Planktonic algae, shell bearing algae and alga of lichens are also algae.
The thallus in alga varies from (1) motle unicellular (Chlamy-domonas; Phacus), (2) motile colonial (Volvox; Eudorina), (3)Palmelloid (Chlamydomonas; Palmella dendroid (Prasinodadus), Coccoid (Chlorella), filamentous (Spirogyra; Nostoc), heterotrichous (Fritschiella), siphonaceous)uniaxial (Botrydium(Batrachospermum), multiaxial (Polysiphonia) and parenchymatous(Sargassam).
The size is microscopic (0.5 mm in dia in Chlamydomonas to as large as 30 m or even more (Macrocystis). Each cell is found by a typical cell wall in all cases except in Euglena and Gymnodinium where the cytoplasmic membrane called pellicle is present. The cell wall is bilayered composted mainly of cellulose and pandes with sub-stances like pectin, chitin, algin and fucoidon. In a few alga the wall is fortified with calcium, silica and magnesium carbonate.
The motile member, zoospore and gametes of many algae bear flagella consisting of 2 central tubules surrounded by 9 peripheral tu-bules enclosed in a membrane. Flagella may be equal or unequal in length, inserted apically or laterally and may be tinsel or whiplash.
The cytoplasm contains contractile vacuoles, mitochondria, eyespot, chloroplast, nucleus, pyrenoids, chondriosormes and Golgi bodies. In the prokaryotic blue green algae these are absent.
The pigments in the alage vary with the group. They are chlo-rophyll a, chlorophyll b,-caroteneβ and xanthophylls. Phycobilins are present in Rhodophyceae and blue green algae.
The food reserve is in the form of starch. But fats and oils are also present in certain groups. Laminarin and mannitol are in phaeophyceae, Floridian starch, floridoside and mannoglycerate are the chief reserve products in Rhodophyceae.
The reproduction in alga is by (1) vegetative (2) asexual and (3) sexual process. The vegetative propagation is fragmentation, fis-sion, akinete formation, tuber, hormogonia and formation of adventi-tious thalli.
Asexual reproduction takes place by release of protoplasts in the form of zoospores, synzoospore, aplanospore, hypnospore, autospore, auxospore, carpospore, tetraspore, cyst, etc., These ger-minate into a new plant. Sexual reproduction takes place by the union of cytoplasm and nuclear material of two gametes of two or-ganisms of the same species on three different ways viz., (1) Isogamy (fusion of morphologically similar gametes) (2) Anisogamy (fusion of morphologically dissimilar gametes) and (3) Oogamy (female is im-mobile and the male gamete is small and motile).
The algae are important as food (Chlorella, Scenedesmus,Laminaria, Spirulina) as medicine (Chlorella ) as nitrogen fixingfertilizer (blue green algae) as fodder (Laminairia, Sargassum andFicus) and in the industrial preparations. Agar-agar is produced from Gelidium and Gracillaria.Iodine is from Laminaria and Macrocystis, carragenin (from Chondrus crispus), alginic acid from Laminaria and filter aids (diabomaceous earth) from diatom are in-dustrially important products.
The widely accepted Fritsch classification is outlined below. This algae were divided to (XI) classes (= phyceae) including the procaryotric blue green algae which is grouped in class Myxophyceae.
Copyright © 2018-2020 BrainKart.com; All Rights Reserved. Developed by Therithal info, Chennai.