Q.Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.

Three groups of plants that bear archegonia are the bryophytes, the pteridophytes and the gymnosperms.

Life cycle of a bryophyte (a moss):

• The dominant, conspicuous plant is the haploid gametophyte, which bears the sex organs.
• The male organ, the antheridium, makes biflagellate antherozoids; the flask-shaped archegonium holds a single egg.
• Water is needed for the swimming antherozoids to reach the egg; their fusion forms the zygote.
• The zygote grows into a sporophyte (foot, seta and capsule) that stays attached to the gametophyte for nourishment.
• Cells in the capsule undergo meiosis to form haploid spores, which germinate into new gametophytes.

The archegonium is the flask-shaped female sex organ that holds a single egg. It appears in three groups of plants: the bryophytes (mosses and liverworts), the pteridophytes (such as ferns), and the gymnosperms.

Take the moss, a bryophyte, as an example of the full cycle:

• The gametophyte dominates. In a moss the conspicuous, long-lived plant is the haploid gametophyte. It passes through two stages — first a creeping, branched, filamentous protonema that grows from the spore, and then an upright leafy stage that bears spirally arranged leaves and is anchored by multicellular, branched rhizoids. It is this leafy stage that carries the sex organs.
• Sex organs and gametes. At the tips of the leafy shoots sit the antheridia and archegonia. The antheridium produces biflagellate antherozoids (the male gametes), while each archegonium contains a single egg.
• Fertilisation needs water. The antherozoids are released into a film of water and swim through it to reach the archegonium. Only then can a male gamete fuse with the egg to form the zygote — which is why water is essential for a moss to reproduce sexually.
• The sporophyte forms. The zygote does not divide by meiosis at once; it grows into a sporophyte made of a foot, a seta and a capsule. This sporophyte stays attached to the green gametophyte and draws nourishment from it, and it is better developed than that of a liverwort.
• Spores and the return to the gametophyte. Inside the capsule, some cells undergo meiosis to form haploid spores, and the moss even has an elaborate mechanism for scattering them. Each spore germinates to produce a new gametophyte, completing the cycle.