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Kingdom Plantae — Biology STD 11 Science — Question

Maharashtra BoardEnglish MediumSTD 11 ScienceBiologyKingdom Plantae5 Marks
Question
Explain in detail three classes of algae.
✓

Answer

  1. Chlorophyceae includes green algae.
  2. These are mostly fresh water (few brackish water and marine).
  3. Plant body is unicellular, colonial or filamentous.
  4. Cell wall contains cellulose.
  5. Chloroplasts are of various shapes like discoid, plate-like, reticulate, cup-shaped, ribbon-shaped or spiral with chlorophyll a and b.
  6. Reserved food is in the form of starch.
  7. Pyrenoids are located in the chloroplast.
  8. Green algae like Chlorella are rich in protein, hence used as food even by space travelers, e.g. Chlamydomonas, Spirogyra, Chara, Volvox, Ulothrix, etc.

    Characteristics of Phaeophyceae (Brown algae):
  1. These algae are mostly marine, rarely fresh water.
  2. Plant body is simple branched, filamentous (e.g. Ectocarpus) or profusely branched (e.g. Petalonia).
  3. Cell wall has cellulose, fucans and algin.
  4. Photosynthetic pigments like chlorophyll-a, chlorophyll-c and fucoxanthin are present.
  5. Mannitol, laminarin are stored food materials. Body is usually differentiated into holdfast, stalk called stipe and leaf-like photosynthetic organ called frond.
  6. Many species of marine algae are used as food. e.g. Laminaria, Sargassum.
  7. Some species are used for the production of hydrocolloids (water holding substances), e.g. Ectocarpus, Fucus, etc.

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