Thallophyta
Algae
(1) The branch of botany dealing with the study of algae is called as phycology or algology.(2) It is derived from the Greek word Phykos which means 'alga' or 'sea weed'.(3) They are simple, autotrophic non-vascular plants having unicelled sex organs and no embryo formation.(4) According to Fritsch, (1935) the designation alga must include all holophytic organisms.(5) Specialized habitats(a) Cryophytes: Plants growing on snow or ice are called as cryophytes.(b) Thermophytes: Plants growing in hot water are called as thermophytes(c) Epiphytes: Several algal forms grow on other plants (algae, angiosperms) as epiphytes. e.g., Oedogonium, Cladophora, Vaucheria etc.(d) Endophytes: Some blue-green algae grows as endophytes inside other plants e.g., Anabaena growing inside the leaf of Azolla (fern)(e) Epizoic: Algae growing on the bodies of animals are described as epizoic. e.g., Cladophora crispata grows on snail shell.(f) Endozoic: Algae growing inside the body of animals. e.g., Chlorella grows with in the tissue of Hydra.(g) Symbiotic forms: Some algae like Chlorella, Nostoc etc. growing in symbiotic relationship with members of Ascomycetes and Basidiomycetes (Fungi) constitute the lichen.(6) Parasites: The alga Cephaleuros virescens grows a parasite on the tea leaves.(7) Thallus organization: The algae show a considerable variation in the organization of the thallus.(i) Unicellular forms: Several members of algae are unicelled. They may be motile (Chlamydomonas) or non-motile (diatoms).(ii) Multicellular forms: The multicelled algae show a considerable range in their organization.(a) Colonial: A colony consists of independent organisms. While the colony of Volvox is motile, that of Hydrodictyon is fixed.(b) Planeloid: Here the vegetative cells of the alga get surrounded by a mucilagenous matrix e.g., Tetraspora.(c) Dendroid: Here the colony appears like a microscopic tree. There is secretion of mucilage from the polar end e.g., Ecballocystis.(d) Filamentous: The filaments may be uniseriate or multiseriate, free floating or attached, unbranched (Ulothrix) or branched (Cladophora).(e) Siphonous: An aseptate, multinucleate (coenocytic) condition of a filament or thallus constitutes the siphonous habit e.g., Vaucheria.(f) Parenchymatous: Parenchymatous organization of the thallus has been observed in many members of brown algae (Sargassum, Laminaria), red algae (Gracillaria, Porphyra) and a few green algae (Chara, Ulva) etc.(8) Classification: Linnaeus (1754) differentiated a group of plant and called as 'algae' where he included lichens and liverworts also. Fritsch (1935) classified algae into 11 classes as under :(i) Chlorophyceae (Green algae)(ii) Xanthophyceae (Yellow-green algae)(iii) Chrysophyceae(iv) Bacillariophyceae (Diatoms)(v) Cryptophyceae(vi) Dinophyceae (Dinoflagellates)(vii) Chloromonadineae(viii) Euglenineae (Euglenoids)(ix) Phaeophyceae (Brown algae)(x) Rhodophyceae (Red algae)(xi) Myxophyceae or Cyanophyceae (Blue green algae)Salient features of some selected classes(i) Chlorophyceae
(a) Plants fresh water or marine.(b) Forms unicelled to parenchymatous.
(c) Cells showing eukaryotic organization.(d) Chief pigments – Chlorophyll a, b; a, b, g– carotenes, lycopene, lutein, violaxanthin.(e) Reserve food – Starch and oils.(f) Zoospore formation occurs.(g) Male gametes flagellate.(h) Flagella identical.(i) Sexual reproduction – Isogamous, anisogamous or oogamous.(ii) Xanthophyceae
(a) Plants generally fresh water.
(b) Forms unicelled to siphonous.(c) Cells showing eukaryotic organization.(d) Chief pigments – Chlorophyll a,e and beta–carotene, violaxanthin, neoxanthin.(e) Reserve food – Chrysolaminarin and oils.(f) Zoospore formation occurs.(g) Male gametes flagellate.(h) Flagella non-identical (unequal).(i) Sexual reproduction – Isogamous, anisogamous or oogamous.(iii) Phaeophyceae
(a) Plants marine
(b) Forms unicelled to parenchymatous(c) Cells showing eukaryotic organization(d) Chief pigments – Chlorophyll a, c; beta–carotene, fucoxanthin, lutein, violaxanthin, diatoxanthin.(e) Reserve food – Laminarin, mannitol and oils.(f) Zoospore formation occurs.(g) Male gametes flagellate.(h) Flagella unequal.(i) Sexual reproduction – Isogamous , anisogamous or oogamous.(iv) Rhodophyceae
(a) Plants generally marine.
(b) Forms filamentous to parenchymatous.(c) Cells showing eukaryotic organization.(d) Chief pigments – Chlorophyll a, d is present but chlorophyll c is absent; a, b–carotene, lutein, violaxanthin, fucoxanthin, myxoxanthin, g–phycoerythrin, g–phycocyanin and allophycocyanin.(e) Reserve food – Floridean starch, galactan –SO4 polymers.(f) No zoospore formation.(g) Male gametes non-flagellate.(h) Sexual reproduction by specialized type of oogamy.(i) Life cycle haplobiontic or diplobiontic.(v) Myxophyceae (Cyanophyceae)
(a) Plants generally fresh water, a few forms marine.
(b) Forms unicelled to filamentous.(c) Cells showing prokaryotic organization.(d) Chief pigments – Chlorophyll a; b-carotene; luteins, myxoxanthin, oscillaxanthin, c-phycocyanin, c-phycoerythrin, allophycocyanin.(e) Reserve food – Cyanophycean starch (glycogen) and cyanophycin (protein).(f) No zoospore formation.(g) No flagellate bodies.(h) No sexual reproduction.
No comments:
Post a Comment