Answer:
Three groups of plants that bear archegonia are
bryophytes, pteridophytes and gymnosperms.
Life cycle of a pteridophyte The life cycle
of a pteridophyte consists of two morphologically distinct phases:
(i) The gametophytic phase
(ii) The sporophytic phase.
These two phases come one after another in the life
cycle of a pteridophyte. This phenomenon is called alternation of generation.
The gametophyte is haploid with single set of chromosomes. It produces male sex
organs antheridia and female sex organs archegonia.
(i) The antheridia may be embedded or projecting
type. Each antheridium has single layered sterile jacket enclosing a mass of
androcytes.
(ii) The androcytes are flask-shaped, sessile or
shortly stalked and differentiated into globular venter and tubular neck.
(iii) The archegonium contains large egg, which is
non-motile.
(iv) The antherozoids after liberation from
antheridium, reaches up to the archegonium fuses with the egg and forms a
diploid structure known as zygotes.
(v) The diploid zygote is the first cell of
sporophytic generation. It is retained inside the archegonium and forms the
embryo.
(vi) The embryo grows and develop to form
sporophyte which is differentiated into roots, stem and leaves.
(vii) At maturity the plant bears sporangia, which encloses
spore mother cells.
(viii) Each spore mother cell gives rise to four haploid
spores which are usually arranged in tetrads.
(ix) The sporophytic generation ends with the production of
spores.
(x) Each spore is the first cell of gametophytic
generation. It germinates to produce gametophyte and completes its life cycle.
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