Chapter-3
PLANT KINGDOM
Reading Material
G. CHANNAIH, PGT (BIOLOGY)
CLASSIFICATION: -
• Artificial System of Classification
• Based on a few characteristics.
• e.g., By Carolous Linnaeus, based on androecium structure • Natural
System of Classification
• Based on natural affinities among organisms
• Included external as well as internal features
• e.g., By George Bentham and J. D. Hooker
• Phylogenetic System of Classification
• Based on evolutionary relationships between the various organism
• e.g., By Hutchinson
Numerical Taxonomy:
• Carried out using computers
• Based on all observable characteristics
• Data processed after assigning number and codes to all the
characters.
Advantage:
Each character gets equal importance and a number of characters can
be considered.
Cytotaxonomy:
• Based on cytological information.
• Gives importance to chromosome number, structure and behaviour.
Chemotaxonomy:
• Based on chemical constituents of the plants.
Importance of Algae:
• At least half of the total carbon dioxide fixation on earth
carried out by them.
• Increase oxygen level in the environment.
• Many species like Laminaria, Sargassum etc. are used as
food.
• Agar obtained from Gelidium and Gracilaria is used in ice-creams
and jellies.
• Algin obtained from brown algae are carrageon from red algae used
commercially
• Chlorella and Spirulina are unicellular algae, rich in protein and
used even by space travellers.
Algae divided into 3 classes:
• Algae are unicellular like Chlamydomonas, colonial like Volvox or
fila mentous like Spirogyra.
• Are simple, thalloid, autotrophic and occur in water, soil, wood etc.
• Help in carbon dioxide fixation by carrying out photosynthesis and
have immense economic importance.
(i) Chlorophyceae
• Green algae. Main pigment is chlorophyll ‘a’ and ‘b’.
• Cell wall has inner layer of cellulose and outer layer of
pectose
. • Has pyrenoids made up of starch and proteins. e.g.,
Chlamydomona, Volvox, Spirogyra.
(ii) Phaeophyceae
• Brown algae due to main pigments chlorophyll ‘a’, ‘c’ and
fucoxanthin.
• Cell wall has cellulose and lignin or gelantinous coating of
algin.
• Has mannitol and laminarin as reserve food material.
• Body divisible into holdfast, stipe and frond.
• e.g., Ectocarpus,
Fucus
Laminaria.
Rhodophyceae
• Red algae due to pigments chlorophyll ‘a’, ‘d’ and r-
phycoerythrin.
• Found on surface as well as great depths in oceans.
• Cell wall as cellulose.
• Reserve food material is floridean starch.
• e.g., Polysiphonia,
Porphyra,
Gelidium
REPRODUCTION IN ALGAE
Vegetative reproduction:
by fragmentation
Asexual Reproduction:
Flagellated zoospores in Chlorophyceae Biflagellated
zoospores in Phaeophycean by non-motile spores in
Rhodophyceae.
Sexual Reproduction:
Isogamous
Anisogamous
oogamous in Chlorophyceae and Phaeophyceae. By non-
motile gametes in Rhodophyceae.
BRYOPHYTES:
Amphibians of plant kingdom
• Occur in damp, humid places.
• Lack true roots, stem or leaves
• Main plant body is haploid.
• Economic Importance:
Food for herbaceous animals
Sphagnum in form of peat is used as fuel and also used for
trans-shipment of living material as it has water holding
capacity, prevent soil erosion, along with lichens are first
colonisers on barren rocks.
• Is divided into two classes Liverworts (thalloid body,
dorsiventral, e.g., Marchantia) and Mosses (have two stages
in gametophyte − creeping, green, branched, filamentous
protonema stage and the leafy stage having spirally arranged
leaves e.g., Funaria.
REPRODUCTION IN BRYOPHYTES: -
• Vegetative reproduction by fragmentation
. • Asexual reproduction by gemmae formed in gemma cups.
• Sexual reproduction:
By fusion of antherozoids produced in antheridium and egg
cell produced in archegonium. This results in formation of
zygote which develops into a sporophytic structure
differentiated into foot, seta and capsule. Spores produced in
a capsule germinate to form free-living gametophyte.
PTERIDOPHYTES:-
• Main plant body is sporophyte which is differentiated into
true stem and leaves.
• Leaves may be small (microsporophyll) as in Selaginella or
large (macrophyll) as in ferns
• Sporangia having spores are subtended by leaf-like
appendages called sporophylls. (Sporophylls may be arranged
to form strobili or cones.)
• In Sporangia, the spore mother cells give rise to spores
after meiosis.
• Spores germinate to form haploid gametophytic structure
called prothallus which is free living, small, multicellular and
photosynthetic.
• Prothallus bears antheridia and archegonia which bear
antherozoids and egg cell respectively which on fertilisation
form zygote. Zygote produces multicellular, well
differentiated sporophyte.
• The four classes are: Psilopsida (Psilotum), Lycopsida
(Selaginella), Sphenopsida (Equisetum) and Pteropsida
(Pteris).
HETEROSPORY:
Two kinds of spores i.e., large (macro) and small (micro)
spores are produced. e.g., Selaginella and Salvinia.
SEED HABIT:
The development of zygote into young embryos takes place
within the female gametophyte which is retained on parent
sporophyte. This is an important step in evolution and is
found in Selaginella and Salvinia among the pteridophytes
GYMNOSPERMS:
• Have naked seeds as the ovules are not enclosed by any
ovary wall and remain exposed
. • Male cone has microsporophylls which bear
microsporangia having microspores which develop into
reduced gametophyte called pollen grain
. • Female cone has megasporophylls which bear
megasporongia having megaspores which are enclosed within
the megasporangium (Nucellus). One megaspore develops
into female gametophyte bearing two or more archegonia.
• Pollen grains carried in air currents reach ovules, form
pollen tube which reach archegonia and release male gametes
which fertilise egg cell and form zygote which produce
embryos. Ovules develop into seeds which are not covered.
ANGIOSPERMS:
The angiosperms are two types
1. Dicotyledons
2. Monocotyledons
• These are Called flowering plants and have seeds enclosed
in fruits. • Divided into two classes − Dicotyledons (have two
cotyledons) and Monocotyledons (have one cotyledon).
• Smallest angiosperm: --- Wolfia
• Large tree: --- Eucalyptus
• Stamen has filament and anther. Anthers bear pollen grains.
Pollen grains have two male gametes.
• Pistil has stigma, style and ovary. Ovary has ovule in which
female gametophyte (embryo sac) develops
• Embryo sac has 7 cells and 8 nuclei. One egg cell, 2
synergids, 3 antipodals and two polar nuclei which fuse to
form secondary nucleus.
• Pollen grain is carried by wind, water etc. reaches to stigma
and produces pollen tube which enters embryo sac
• Double fertilisation: --
One male gamete fuse with egg cell to form zygote which
develops into embryo. Other male gamete fuses with
secondary nucleus which forms triploid primary endosperm
nucleus (PEN). PEN develops into endosperm which
nourishes the developing embryo.
• Ovules develop into seeds and ovaries into fruits.
Germination of seed
Monocot plant
Haploid gametophytic and spore producing sporophytic
generation alternate with each other in this process.
Haplontic: Gametophytic phase dominant.
e.g., Chlamydomonas
Diplontic: Sporophytic phase dominant. e.g., Angiosperms
and Gymnosperms
Haplo-Diplontic: --Intermediate like stage where
gametophytic and sporophytic stage partially dominate at
different stages.
e.g., Bryophytes and Pteridophytes.
Exceptions: Ectocarpus, Polysipnonia are Haplo-diplontic
algae. Fucus is diplontic alga.
