Biology XI:3. Plant Kingdom (6 Plant Life Cycles)

Plant Life Cycles There is alternation of generations between haploid gametophyte and diploid sporophyte in the life cycle of a plant. In plants, both haploid and diploid cells can divide by mitosis. Hence, there are two different plant bodies − haploid and diploid. The haploid plant body produces gametes by mitosis and represents a gametophyte. Mitotic division is encountered in diploid cells when zygote divides by mitosis to produce sporophytic plant body after fertilization. This sporophyte produces haploid spores by meiosis. Spores in turn undergo mitosis to form haploid plant body. Types of Life Cycles in Plants Haplontic Life cycle In this, sporophyte is represented by one-celled zygote. There is no free living sporophyte. Zygote undergoes meiotic division to produce spores, which divide mitotically and form gametophyte. Gametophyte is the dominant phase in this life cycle as it is dominant, free living, and photosynthetic. Algae such as Spirogyra and some species of Chlamydomonas have this type of life cycle. Diplontic Life Cycle In this case, diploid sporophyte is the dominant phase as it is free living and photosynthetic. Gametophyte is single to few-celled. Example − All seed-bearing plants, gymnosperms, and angiosperms, some algae-like Fucus Haplodiplontic Life Cycle Intermediate condition Both gametophyte and sporophyte are free-living and multicellular, but have different dominant phases. In Bryophytes, haploid gametophyte is dominant, independent, and photosynthetic. It alternates with short-lived multicellular sporophyte totally or partially and is dependent on gametophyte for nutrition and anchorage. In Pteridophytes, diploid sporophyte is dominant, independent, and photosynthetic. It alternates with short-lived haploid gametophyte, which is independent of sporophyte.