Tag: alternation of generations

Haplo-diplontic type of life cycle involves the clear alternation of generations between a haploid gamete producing gametophyte and a diploid spore-producing sporophyte. Both bryophytes and pteridophytes exhibit this kind of life cycle pattern.

In a diplontic life cycle, the dominant free-living phase is the diploid (2n). The sporophyte is photosynthetic. The gametophytic phase is represented by single to few-celled haploid gametophyte. All seed-bearing plants, i.e., gymnosperms and angiosperms exhibit this type of life cycle.

The carrot is a root vegetable, usually orange in colour, though purple, black, red, white, and yellow cultivars exist. The carrot is a biennial plant. Carrots are a domesticated form of the wild carrot, Daucus carota, native to Europe and southwestern Asia. The plant probably originated in Persia and was originally cultivated for its leaves and seeds. The most commonly eaten part of the plant is the taproot, although the stems and leaves are eaten as well. 

The plant body  or the vegetative phase is diploid in pteridophytes, gymnosperms and angiosperms. The reproductive structures like the stobili in pteridophytes, ovules and microsporangium,  anther are also diploid. Here, only the reproductive cells undergo meiosis or gametogenesis to give rise to male and female gametes that are haploid. These fuse to produce a  diploid zygote. So, the gametophytic stage is restricted and of a very short duration as compared to the sporophytic stage. therefore, sporophyte is a dominant phase.

Algae are mostly haploid. They show haplontic lifestyle i.e. for the most part of the life haploid is the dominant stage. Fusion of gametes results in diploid sporophyte in algae which undergoes meiosis to form haploid gametophyte. There are no free-living sporophytes. The gametophyte is the dominant phase.

Monocarpic plants are those plants that flower and fruit only once and then die. They are also called as semelparous plants. Most perennial plants are polycarpic. They flower many seasons in a lifetime. However, certain perennial plants are monocarpic. They flower only once and die after that. However, it can live up to 40 years before it flowers. Example includes Bambusa, Agave.

Sporophyte develops by diploid zygote and hence is diploid. Spores are produced on sporophyte by meiosis and hence are haploid. Haploid spores develop mitotically into the haploid multicellular gametophyte. Thus, spores and gametophyte exhibit haploid condition while sporophyte is diploid.