THALLOPHYTA – ALGAE (part – 1), Biology

Algae (singular: alga) are photosynthetic, eukaryotic organisms that do not develop multicellular sex organs. Algae can be unicellular, or they may be large, multicellular organisms. Algae can occur in salt or fresh waters, or on the surfaces of moist soil or rocks. The multicellular algae develop specialized tissues, but they lack the true stems, leaves, or roots

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General characters of algae

  • Eukaryotic, autotrophic, chlorophyllous, cryptogamic, thallophytes.
  • Aquatic either fresh water or marine.
  • They are found in many forms. Unicellular (e.g., Chlamydomonas), colonial (e.g., Volvox)
  • Reserve food is mainly starch.
  • Vegetative reproduction:It takes place by fragmentation.
  • Asexual Reproduction:Zoospores. aplanospores, hypnospores, akinetes, palmella stage etc.
  • Sexual Reproduction: Sex organs are unicellular or multicellular with all fertile cells and none jacketed. Embryonic stage is absent.

Green Algae (Chlorophyceae)

General characters

  • Mostly freshwater (Spirogyra, Ulothrix, Chara, Chlamydomonas, Volvox etc) and some are marine (Acetabularia, Ulva etc).
  • Photosynthetic pigments are chlorophyll a, chlorophyll b and carotenoids.
  • Thylakoids are in group of 2-20 per lamella.
  • Pyrenoids present.
  • Three types of life cycle occur in green algae: Haplontic life-cycle e.g., Ulothrix, Spirogyra, Chlamydomonas(zygotic meiosis occurs).Diplontic life-cycle e.g., Caulerpa(gametic meiosis). Diplohaplontic life cycle e.g. Ulva, Cladophora.