Question

When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?

Answer 1

Liverwort: In liverworts, the main plant body is haploid (gametophytic). It bears the male and female sex organs that produce gametes. These gametes fuse to form a zygote. The zygote develops on the gametophytic plant-body to form a sporophyte. The sporophyte is differentiated into the foot, seta, and capsule. Many haploid spores are produced as a result of the reduction and division taking place inside the capsule.

Moss: In mosses, the primary protonema (developed in the first stage) develops into the secondary protonema. Both of these stages are haploid or gametophytic. The secondary protonema bears the sex organs, which produce gametes. These gametes fuse to form a zygote. The zygote develops into a sporophyte. Many spores are formed as a result of the reduction and division taking place in the capsule of this sporophyte.

Fern: In ferns, the main plant body is sporophytic. Its leaves are known as sporophylls and these bear the sporangia. Reduction division takes place in these sporangia, thereby producing many spores.

Gymnosperm: In gymnosperms, the main plant body is sporophytic. They bear two types of leaves: microsporophylls and megasporophylls. Reduction division takes place in the microsporangia present on the microsporophylls (producing pollen grains) and in the megasporangia present on the megasporophylls (producing megaspores).

Angiosperm: In angiosperms, the main plant body is sporophytic and bears flowers. The male sex organ in the flower is the stamen, while the female sex organ is the pistil. Reduction division takes place in the anthers of the stamen (producing haploid pollen grains) and in the ovary of the pistil (producing eggs).

Answer 2

1. These plants all exhibit a single gametophytic (n) generation and a single sporophytic (2n) generation life cycle. Their life cycles require reduction division, or meiosis, to create haploid (n) cells from diploid (2n) cells in order to regenerate gametophyte generation following sporophytic generation. According to the fundamental physical characteristics of these groups, it manifests in various body structures. At the conclusion of the sporophytic generation, reduction division occurs in liverworts and mosses, when haploid spores are created by the reduction division of the spore mother cell inside the capsule. To create the dominant gametophytic generation, spores germinate.
2. In ferns, reduction division occurs within the sporangium from the spore mother cell at the conclusion of the dominant sporophytic generation. Spores can be either homosporous (one kind) or heterosporous (two types).
3. In gymnosperms, reduction division occurs at the conclusion of the dominant sporophytic generation. The reduction division of the diploid megaspore mother cell and the diploid microspore mother cell, respectively, inside the megasporangium and microsporangium, produces the megaspore and microspores. In angiosperms, reduction division occurs at the conclusion of the dominant sporophytic generation. The reduction division of the diploid mother cell (microspore) and the diploid megaspore mother cell yields the haploid pollen grain or microspore and the haploid egg cell, respectively. Megasporic division takes place inside the gynoecium (ovary), while microsporic division takes place inside the anther.