DIVISION CHLOROPHYTA

  1. Occurrence: Majority members of this class are freshwater. are found in ponds, lakes, streams, moist rocks and damp plat Some species are marine.
  2. Vegetative structure: They have variety of vegetative struct Some are unicellular. Some are multicellular. Motile forms have to kur flagella. They have acronematic (whiplash) type of flap
  3. Cell structure: Cell is surrounded by cell wall. Cell ha layers. Inner layer is composed of cellulose. Outer layer has pe, Protoplast is divided into two parts: cytoplasm and nuclet,nucleus is embedded in the cytoplasm. Nucleus contains a nuclear membrane, chromatin network, one or two nucleoli. Cytoplasm contains membranous bound organelles.

    4. Pigments and plastids: Their pigments are chlorophyll a, chlorophyll b, carotene and xanthophylls. These pigments are present in chloroplasts. Few species have orange red pigment called heamotochrome. It masks the green colour of green pigment. The shape of chloroplast may be discoid, band shaped or stellate. Each chloroplast contains pyrenoids. The reserve food material is starch.

    5. Vegetative reproduction: Vegetative reproduction occurs by simple cell division and fragmentation. Some species produces special propagules. Unicellular species divide by simple cells division. Fragmentation occurs in filamentous forms.

    6. Asexual reproduction: Spore formation is common method of asexual reproduction. They produce different types of spores:

    (a)      Zoospore: These are motile spores. They have 2-4 flagella. These spores are produced in zoosporangia.

    (b)  Aplanospores: These are non-motile spores. They have thin wall.


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    (c)   Hypnospore: The non-motile spores with thick wall are called aplanospore.

    (d)  Akintes: A spore formed singly in a cell whose wall is distinct from the parent cell is called akinete.

    7. Sexual reproduction: Sexual reproduction may be isogamy, anisogamy or oogamy. Gametes are produced in gametangia. Zygotes secretes thick wall to become zygospore. There are two types of species:

    • Homothallic: In this case, gametes of the same plant can fuse with each other.

    Heterothallic: In this case, gametes of different plants fuse with each other.

    Sometimes, gametes develop into new plants with out fusion. It forms spores called parthenospore. This phenomenon is called parthenogenesis.

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