Plant Kingdom - Notes | Class 11 | Part 6: Plant Life cycles and alternation of generations
Plant Kingdom Notes - Plant Life Cycles and Alternation of Generations
Plant Life Cycles and Alternation of Generations
In plants, both haploid and diploid cells can divide by mitosis. This forms haploid and diploid plant bodies.
Haploid plant body (gametophyte) produces gametes by mitosis.
After fertilization, the zygote also divides by mitosis to produce a diploid plant body (sporophyte). This produces haploid spores by meiosis.
Spores divide by mitosis to form a haploid plant body.
Thus, during the life cycle of any sexually reproducing plant, there is an alternation of generations between gametophyte (n) and sporophyte (2n).
Patterns of Plant Life Cycles
Haplontic: In this, sporophytic generation is represented only by the zygote. There are no free-living sporophytes. Zygote undergoes meiosis to form haploid spores. They divide mitotically to form gametophyte. The dominant, photosynthetic phase is the free-living gametophyte. E.g., Algae such as Volvox, Spirogyra and some species of Chlamydomonas.
Diplontic: In this, diploid sporophyte is the dominant, photosynthetic, independent phase. Gametophytic phase is represented by the single to few-celled haploid gametophyte. E.g., An alga, Fucus sp., and all seed-bearing plants (gymnosperms and angiosperms - the gametophytic phase is few to multi-celled).
Haplo-diplontic: It is the intermediate condition between haplontic and diplontic. Both gametophyte and sporophyte are multicellular and often free-living. But they have different dominant phases. E.g., Bryophytes and Pteridophytes.
