Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Archegonium is the female sex organ that produces the female gamete or egg. It is present in the life cycles of mosses (bryophytes), pteridophytes, and gymnosperms.
Life cycle of a moss.
Gametophytic stage is the predominant stage of the moss lifecycle. The Gametophytic stage consists of two stages
(i). Protenema stage – this is the first stage which develops directly from a spore.
(ii). Leafy stage – this is the second stage which develops from the secondary protonema as a lateral bud.
They consist of upright slender axes which bears spirally arranged leaves. Rhizoids are the multicellular structure that attaches the mosses to the soil. This stage bears the sex organs. The male (antheridia) and female (archegonium ) sporangia are formed at the apex of the leafy shoots. Cells within the sporangium of the sporophyte undergo meiosis to produce male and female spores, respectively. These spores divide mitotically to produce multicellular male and female gametophytes. The sperm and eggs are produced mitotically in the antheridia and archegonia, respectively. Sperm are carried to the archegonia in water droplets. After fertilisation, the sporophyte generation develops in the archegonium and remains attached to the gametophyte and the cycle is completed.
Write a note on economic importance of algae and gymnosperms.
When and where does reduction division take place in the life cycle of a liverwort, a moss, a fern, a gymnosperm and an angiosperm?
What is the basis of classification of algae?
Mention the ploidy of the following: protonemal cell of a moss; primary endosperm nucleus in dicot, leaf cell of a moss; prothallus cell of a ferm; gemma cell in Marchantia; meristem cell of monocot, ovum of a liverwort, and zygote of a fern.
