Feb. 2, 2006 Colonies of flagellated cells

Дата канвертавання27.04.2016
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Feb. 2, 2006

  • Colonies – daughter cells from asexual reproduction remain together by contact or mucilage

    • Flat or spherical

    • Cells like chlamydomanas

  • Evolution:

    • Small, unspecialized colonies → large, specialized Volvocine Series

    • Common Development Feature:

      • Cell divisions determine # of cells in new colony

      • Colony inverts to orient cells w/flagella outwards

  • Initial colony – plakea (in spherical colonies plakea turns inside out)

  • Colonies with fixed # of cells at formation – coenobia (syn o bia)

  • Progression in Evolution:

    • No cells increases

    • Develops anterior and posterior ends anterior – larger eyespots, specialized cells for reproduction

    • Differentiation between gametes, isogamy (2 flagellates), anisogamy (2 flagellates, different sizes), oogamy (sperm, egg)

  • Volvox (see diagrams in scanned notes) – largest member of volvocine series (500 – 50,000 cells)

    • Usually 16 cells w/o flagella

    • Gonidia – cells division to plakea

    • Volvox w/internal daughter colonies – eventually parent dies, releasing daughters

    • Sexual process uses inducers (see diagram in scanned notes for details)

    • Sperm pocket – 64 elongate cells in plate w/flagella – swims to female (attractant?)

    • Most advanced green colonial algae but evolutionary dead end

  • Tetrasporales (Palmelloid aggregations)

    • Recall chlamydomonas temporary palmelloid stage w/sheath holding non-flagellated cells… in tetrasporales, palmelloid stage is permanent

    • Gloecystis (small groups)

    • Tetraspora (large tubes, sheets up to several cm)

    • Cells like chlamydomonas, w basal bodies, eyespots

  • Chlorococcum – fresh water (see diagram of life cycle)

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