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Question
Name three groups of plants that bear archegonia. Briefly describe the life cycle of any one of them.
Solution 1
The three groups of plants that bear archegonia are bryophytes, pteridophytes and gymnosperms.
Life cycle of a bryophyte is as follows : The main plant body of bryophyte is gametophytic (n), which is independent and may be thallose (no differentiation in root, stem, leaves), e.g., Riccia, or may be foliose (having leafy axis), e.g., Funaria. The dominant phase in the life cycle of Funaria is the gametophyte, which occurs in two stages, the protonema stage and the erect, leafy gametophytic plant.
The leafy gametophyte consists of an upright, slender axis (stem-like) that bears spirally arranged leaves and is attached to the substratum by multicellular, branched rhizoids. Vegetative reproduction takes place
by fragmentation; by the buds formed in secondary protonema, etc. The sex organs, antheridia and archegonia are produced in dusters at the apices of the leafy shoots. Antheridia produces antherozoids and archegonia produces egg. Antherozoid (male gamete) and egg (female gamete) fuse and form zygote. Zygote develops into a sporophyte; which is differentiated into foot, seta and capsule, and spores are produced in the capsule.
Spores, on reaching a suitable substratum, germinate to produce a filamentous juvenile stage. called the primary protonema, which later produces secondary protonema that forms erect leafy plants
Solution 2
Archegonium is the female sexual organ that produces the female gamete or egg. It is present in the life cycles of bryophytes, pteridophytes, and gymnosperms.
Life cycle of a fern (Dryopteris)
Dryopteris is a common fern with pinnately-compound leaves. The main plant's body is sporophytic. Many sporangia are borne on the lower surfaces of its mature leaves. Each sporangium has spore mother cells, which undergo meiosis to produce haploid spores. On maturing, these spores dehisce and germinate to give rise to a heart-shaped gametophyte called prothallus.
The prothallus bears the male and female sex organs called antheridia and archegonia, respectively. The antheridia produce sperms that swim in water to reach the archegonia. The egg is produced by the archegonia. As a result of fertilisation, a zygote is formed. The zygote forms an embryo, which in turn develops into a new sporophyte. The young plant comes out of the archegonium of the parent gametophyte
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