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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