Classification of Plant Kingdom


IMPORTANT POINTS
Five kingdom classification system was given by Whittaker on the basis of following four criteria :
(i) Cell structure
(ii) Body Structure
(iii) Mode of nutrition – Autotrophic and Heterotrophic
(iv) Major ecological role.
The five kingdoms are Monera, Protista, Fungi, Plantae and Animalia.
The three-domain system is closely based on five-kingdom system.
The Eukarya are then divided into 4 kingdoms :
Protistsa, Fungi, plantae and anamalia.
Viroids were discovered by Diener from infectious agents which are even smaller than viruses. It
consists of a very simple structure and short RNA strand viroids lack protective protein coat known as
capsid.
Viruses are self reproducing and obligate parasite in living cells : They Viroids remain inactive
and behave as non-living things. When they enter inside of the living cells, they are active and behave as
living organisms Because of this they are intermediate between living and non-living things. They are also
called as living chemical.
Algae, Fungi and Lichens are included under thallophyta. The gametophytic plant body is thalloid,
without differentiation in to true root, stem and leaves. Zygote does not develop into embryo. Algae
have Chlorophylls and they synthesize their one own food so it is Autotrophs, while Fungi are non
chlorophylls and they do not Synthesize their own food so it own is called heterotrophs. The lichens,
show symbiotic relationship between algae and fungi components.
Bryophytes are non vascular plants. After fertilization Zygote undergoes divisions to form embryo.
The life cycle of bryophytes has two distinct phases.
(1) Gametophytic phases – Haploid, main, autotrophic and gametes formative
(2) Sporophytic phase – Diploid, Subsidiary, heterotrophic, spores formative.
Pteridophytes have vascular tissues, and develop the embryo. The life cycle of pteridophytes
shows alternation of generation. Gemetophytic phase is haploid, subsidiary, short lived and Gametes
producing while sporophytic phase is diploid, main long lived and spores producing.
Gymnosperm is sporophytic. It is differntiated into root, stem and leaves. Ovules are naked and
not enclosed by the ovary therefore recognized as a gymnosperm. The sporophytic and gametophytic
phases alternate with each other to complete the life cycle. Gametophytic phase is haploid, subsidiary,
short lived and under ground and sporophytic phase is diploid, Main, long and as a whole plant.
Endosperm develops before fertilization, ovules are orthotropous and true fruits are lacking because,
of the absence of ovary.

Read More  Cell structure

In angiosperms, sporophytic plant body is in the form of herbs, shrubs, trees, climbers or lianas.
Ovules are enclosed in the ovary therefore, recognized as angiosperms. Endosperm is developed after
fertilization. Members of this group show double fertilization. After fertilization ovules are transformed
into seeds and ovary into fruit. The plant life cycle shows alternation of generation.
Bentham and Hooker classified the angiosperms into two classes. (1) Dicotyledon and (2)
Monocotyledon.

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