Plant Kingdom

Plant life cycles

  • The haplontic life cycle is a single somatic phase and is haploid called gametophyte that may be unicellular, multicellular (or) colonial, which gives rises to gametes.
  • The gametes fuse to form a zygote which remains single-celled.
  • The zygote does not multiply, neither it gives rises to a multicellular diploid structure.
  • After a certain rest period, zygote undergoes meiosis to form haploid nucleus are meiospores which will again form a gametophyte.
  • An alternation of generation is absent since the plant does not have 2 cytologically distinct phases.
  • Examples: Volvox, Chlamydomonas, Spirogyra, Ulothrix, Chara, Oedogonium etc.,
  • In a diplontic life cycle, there is a single somatic phase which is a diploid structure often called a sporophyte, which possesses sex organs to produce gametes.
  • Gametes re-unite to form the zygote which forms sporophyte and hence gametes are the only haploid structures.
  • Alternation of generation is absent in the history of the diplontic cycle.
  • Eg. Cladophora glomerata, Fucus , Sargassum , Caulerpa, Gymnosperms and Angiosperms.
  • The life cycle involving 2 well developed vegetative individuals, gametophyte and sporophyte is called as Haplo – diplontic life cycle, which clearly possesses an alternation of generation
  • Examples: Dictyota, Bryophytes and Pteridophytes.
  • Apospory is the formation of gametophyte directly from the sporophyte
  • Apogamy is the formation of sporophyte directly from gametophyte.

View this video for the topic from 0:17 to 10:26

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