Alternation of Generation in Different Divisions of Plants
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Question
Write about the sporophyte evolution in Bryophytes.
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Solution
Bryophytes:
Bryophytes are non- vascular terrestrial plants.
They are known as the amphibians of the plant kingdom as they require water for their propagation.
They have two stages in their life cycle i.e sporophyte and gametophyte.
Sporophyte:
Sporophyte is a diploid, multicellular plant structure in bryophtes.
It develops from the fertilized gamete formed by the gametophytic stage of the plant.
It produces spores through asexual, meiotic division.
These spores proliferate to become gametophytes.
Gametophyte:
Gametophyte is a haploid, multicellular plant structure in bryophytes.
It develops from spores formed by the sporophytic body.
it produces haploid gametes through mitotic division.
These gametes fuse to form a zygote that develops into a sporophyte.
Evolution of sporophyte in bryophytes:
There are mainly two theories regarding the evolution of sporophytes:
Theory of progressive evolution.
Theory of regressive evolution.
Theory of progressive evolution:
According to this theory, the early sporophyte of bryophytes was uncomplicated and almost all of the sporogenous tissue was fertile (e.g., Riccia) and from this type of sporophyte, the more complex sporophytes (e.g., mosses) are said to have evolved by the process of progressive sterilisation of potential sporogenous tissue.
This theory is also known by the name of “theory of sterilisation”.
Theory of regressive evolution:
According to this theory, the simplest sporophyte of Riccia (which is composed of a simple capsule) is the most advanced kind which is said to have evolved by the simplification or progressive reduction of the more complicated sporophytes (foliose with complex assimilatory tissue and functional stomata) of mosses (e.g. Funaria, Pogonatum, Polytrichum etc.).
This theory is also known as “retrogressive theory”
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