With the help of a schematic diagram des | Class 11 Biology Chapter Plant Kingdom, Plant Kingdom NCERT Solutions

Alternation of Generation takes place between gametophyte and saprophyte that is haploid and diploid phase. Thus this is called the haplodiplontic (or diplohaplontic) life cycle. For example in pteridophytes: It also shows two distinct phases- Gametophytic phase and Sporophytic phase and they comes after one another which shows alternation of generation; this is heteromorphic type or heterologous type.

The life cycle of pteridophytes is dominated by the sporophyte. Reproduction occurs by spores are spread into the air which is developed into haploid gametophytes, contain both male and female sex organs. When the young gametophyte matures, sex organs become active. The male reproductive organ is the antheridium, which produces sperms and the female reproductive organ is the archegonium which produces the egg. They requires water for the sperm to swim to the archegonium and fertilization occurs. Water is needed for dehiscence of antheridia, liberation of flagellated antherozoids, for the movement of antherozoids from antheridia to archegonia, maturation of archegonia and Syngamy.

A diploid zygote grows through the process of mitosis during cell division that produces roots, stems, and a new sporophyte. The sporophytes is again an independent vegetative plant body. Meiosis (cell division) occurs at the time of spore formation. Spore again germinates to produce haploid Gametophytic plants. And the life cycle continues.