Chapter 3
Plant Kingdom
Syllabus: Classification
of plants into major groups; Salient and distinguishing features and a few examples of Algae, Bryophyta, Pteridophyta,
Gymnospermae (Topics excluded
– Angiosperms, Plant Life Cycle and
Alternation of Generations)
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PLANT
KINGDOM IS DIVIDED INTO FIVE DIVISIONS |
||||
|
1.
ALGAE |
2.
PTERIDOPHYTA |
3.
BRYOPHYTA |
4.
GYMNOSPERMS |
5.
ANGIOSPERMS |
1. ALGAE
Structure
1.
Algae are chlorophyll-bearing.
2.
These are simple and thalloid
(that lacks distinct organs, such
as stems, leaves, and roots).
3.
Autotrophic.
4.
The form and size of algae is highly variable, ranging from colonial forms like Volvox and the filamentous forms like Ulothrix and Spirogyra.
5. A few of the marine forms such as kelps, form massive plant bodies.
Habitat
1.
Largely aquatic (both fresh
water and marine) organisms.
2.
They occur in a variety of other habitats: moist stones, soils and
wood.
3.
Some of them also occur in association
with fungi (lichen) and animals (e.g., on sloth bear). 
Reproduction
1. The algae reproduce by vegetative, asexual, and sexual methods.
Vegetative reproduction
i) Vegetative reproduction is by
fragmentation.
ii) Each fragment develops into a
thallus.
Asexual reproduction
1.
Asexual reproduction is by the production of different types of spores, the most common
being the zoospores.
2. They are flagellated (motile) and
on germination gives rise to new plants.
5
Sexual
reproduction
1. Sexual reproduction takes place
through fusion of two gametes.
Depending
on the size and structure, the gametes can be divided into three types:-
1.
Isogamous 2. Anisogamous 3. Oogamous
i)
Isogamous: These gametes
can be flagellated and similar in size (as in Ulothrix) or non
flagellated (non-motile) but similar in size (as
in Spirogyra). Such
reproduction is called isogamous.
ii)
Anisogamous: Fusion of two gametes dissimilar in size, as in species of Eudorina is termed as anisogamous.
iii)
Oogamous: Fusion between one large, nonmotile (static) female
gamete and a smaller, motile male gamete is termed oogamous, e.g., Volvox, Fucus.
Importance
of Algae
1.
At least a half of the
total carbon dioxide fixation
on earth is carried out by algae through
photosynthesis.
2.
Being photosynthetic they increase the level of dissolved oxygen in their immediate environment.
3.
As primary producers of energy-rich compounds form the basis of the food cycles of all aquatic animals.
4.
Many species of Porphyra, Laminaria and Sargassum
are among the 70 species of marine algae used as food.
5.
Chlorella a unicellular alga rich in
proteins is used as food supplement even by space travellers.
Classification
of Algae
The
algae are divided into three main classes: Chlorophyceae,
Phaeophyceae and Rhodophyceae.
1. Chlorophyceae:
i) The members of chlorophyceae are commonly called green algae.
ii) The plant body may be unicellular, colonial or filamentous.
iii)
They are usually grass green due to the dominance of pigments chlorophyll a and b.
3. The pigments are localised in
definite chloroplasts.
4.
The chloroplasts may be discoid
(disc shape), plate-like, reticulate (net like), cup-shaped, spiral or
ribbon-shaped in different species.
5.
Most of the members have one or more storage bodies called pyrenoids
located in the
chloroplasts. Pyrenoids
contain protein besides starch.
6.
Green algae usually have a rigid cell wall made of an inner
layer of cellulose and an outer layer of pectose.
Reproduction:
1. Vegetative reproduction usually
takes place by fragmentation .
2. Asexual reproduction is by flagellated zoospores produced
in zoosporangia.
3.
The sexual reproduction shows considerable variation in the type and formation
of sex cells and it may be isogamous, anisogamous or oogamous.
4.
Some commonly found green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra
and Chara.
Phaeophyceae
1. The members of phaeophyceae or brown algae are found
primarily in marine habitats.
2. They range from simple branched,
filamentous forms
(Ectocarpus) to profusely branched forms
(kelps ) which may
reach a height of 100 metres.
3. They possess chlorophyll a, c, carotenoids (colour pigments)
and xanthophylls.
4. They vary in colour from olive
green to various shades of
brown depending upon the amount of
the xanthophyll pigment
(yellow colour) , fucoxanthin (brown colour) present in them.
5.
Food is stored as complex carbohydrates, which may be in the form of laminarin or
mannitol.
6.
The vegetative cells have a cellulosic wall usually covered on the outside by a
gelatinous coating of algin.
7.
The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the frond.
Reproduction:
1. Vegetative reproduction takes
place by fragmentation.
2.
Asexual reproduction in most brown algae is by biflagellate zoospores that are pear-shaped (nashpati) and have two unequal laterally attached flagella.
3. Sexual reproduction may
be isogamous, anisogamous or oogamous.
i) Union of gametes may take
place in water or within the oogonium (oogamous species).
ii) The gametes are pyriform (pear-shaped) and bear two laterally attached
flagella.
iii) The common forms are
Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus.
Rhodophyceae
1.
The members of rhodophyceae are commonly called red algae because of the predominance of the red pigment, r-phycoerythrin with chlorophyll
a and d in their body.
Habitat
1. Majority of the red algae are
marine.
2.
They occur in both well-lighted
regions close to the surface of water and
also at great depths in oceans where relatively little light penetrates.
Structure
1. The red thalli of most of the
red algae are multicellular.
9
2.
The food is stored as floridean
starch which is very similar to
amylopectin and glycogen in
structure.
Reproduction
1. Vegetative reproduction by
fragmentation.
2. Asexual reproduction by non-motile spores.
3. Sexual reproduction by non-motile gametes.
i) Sexual reproduction is
oogamous and accompanied by complex post fertilisation developments.
ii)
The common members are: Polysiphonia, Porphyra , Gracilaria and Gelidium. 
3.2
BRYOPHYTES
Habitat
1.
Bryophytes include the various mosses and liverworts that are found commonly
growing in moist shaded areas in the
hills.
2.
Bryophytes are also called
amphibians of the plant
kingdom because these plants can live in
soil but are dependent on water for sexual reproduction.
3. They usually occur in damp,
humid and shaded localities.
Structure
1. The plant body of bryophytes is
more differentiated than that of algae.
2.
It is thallus-like and prostrate or erect, and attached to the substratum by
unicellular or multicellular
rhizoids.
3. They lack true roots, stem or
leaves.
4. They may possess root-like,
leaf-like or stem-like structures.
Reproduction
1. The plant body has two parts: sporophyte and
gametophyte.
2. The main plant body of the
bryophyte is
haploid (Gametophyte) and it’s the stage which is
for longer time period and perform
photosynthesis.
3. It produces gametes.
4. The sex organs in bryophytes
are multicellular.
(Note: Sporophyte phase is non photosynthetic and
hence depend on gametophyte part for the
nutrition.)
Male sex organs
1. The male sex organ is called antheridium.
2. They produce biflagellate antherozoids.
Female sex organs
1.
The female sex organ called archegonium is
flask-shaped and produces a single egg.
2.
The antherozoids are released into water where they
come in contact with archegonium.
3. An antherozoid fuses with the egg to produce the zygote.
4. Zygotes do not undergo
reduction division immediately.
5. Zyogtes produce a multicellular body called a sporophyte on the gametophyte.
6.
The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.
7.
Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores.
8.
These spores germinate to produce gametophyte.
Classification of Bryophytes
The bryophytes are divided
into
i) liverworts and
ii) mosses.
Habitat
1.
The liverworts grow usually in moist, shady habitats such as banks
of streams, marshy ground, damp soil,
bark of trees and deep in the woods.
2.
The plant body of a liverwort is thalloid, e.g., Marchantia.
3.
The thallus is dorsiventral and closely appressed to the
substrate.
Reprduction
i) Asexual reproduction ii) Sexual reproduction
i) Asexual reproduction
1.
Asexual reproduction in liverworts takes place by fragmentation of thalli, or by the formation of specialised structures called gemmae (sing. gemma).
2.
Gemmae are green, multicellular, asexual buds, which develop in small
receptacles called gemma cups located on the
thalli.
3.
The gemmae become detached from the parent body and germinate to form new individuals.
ii) Sexual reproduction
1.
During sexual reproduction, male and female sex organs are
produced either on the same or on
different thalli.
a)
Male sex organs
i.
The male sex organ is called antheridium.
ii.
They produce biflagellate antherozoids.
b)
Female sex organs
2.
The female sex organ called archegonium is flask-shaped and produces a single egg.
3.
The antherozoids
are released into water where they
come in contact with archegonium.
4.
An antherozoid fuses with the egg to produce the
zygote.
5.
Zygotes do not undergo reduction division immediately.
6.
Zyogtes produce a multicellular body called a sporophyte on the gametophyte.
7.
The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.
8.
Some cells of the sporophyte undergo reduction division
(meiosis) to produce haploid spores.
9.
These spores germinate to produce gametophyte.
Mosses
Reproduction
1.
The predominant stage of the life cycle of a moss is the gametophyte which
consists of two stages.
2. The first stage is the protonema stage, which
develops directly from a spore.
3.
It is a creeping, green, branched and frequently filamentous stage.
i) Asexual ii) Sexual
i) Asexual
1.
The second
stage is the leafy stage, which develops from the secondary protonema as a lateral bud.
2.
They consist of upright, slender axes bearing spirally arranged
leaves.
3.
They are attached to the soil through multicellular and branched
rhizoids.
4.
This stage bears the sex
organs.
5.
Vegetative reproduction in mosses is by fragmentation and budding in the secondary
protonema.
ii) Sexual
1.
In sexual reproduction, the sex organs antheridia and
archegonia are produced at the apex of
the leafy shoots.
2.
After fertilisation, the zygote develops into a
sporophyte, consisting of a foot, seta and
capsule.
3.
The capsule contains spores. Spores are formed after meiosis.
4.
Common examples of mosses are Funaria, Polytrichum and Sphagnum
Pteridophyta
1.
The main plant body is diploid.
2.
The Pteridophytes include horsetails (Equisetum) and
ferns. Pteridophytes are used for
medicinal purposes and as soil-binders.
3.
Evolutionarily, they are the first terrestrial plants to possess
vascular tissues –
xylem and phloem.
Habitat
1.
The pteridophytes are found in cool, damp, shady places though some may
flourish well in sandy-soil
conditions.
Structure
1.
In pteridophytes, the main plant body is a sporophyte which is differentiated into true root, stem and leaves.
2.
These organs possess well-differentiated
vascular tissues.
3.
The leaves
in pteridophyta are small (microphylls) as in Selaginella or large (macrophylls) as in ferns.
4.
The sporophytes bear sporangia that
are subtended by (supported by) leaf-like appendages called sporophylls
(leaf).
5.
In some cases sporophylls (leaf) may form distinct compact
structures called strobili
or
cones (Selaginella, Equisetum).
Types
of Spores
1.
In majority of the pteridophytes all the spores are of similar kinds; such plants are called homosporous.
2.
Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous.
3.
The megaspores and microspores germinate and give rise to
female and male gametophytes,
respectively.
4.
The female gametophytes in these plants are retained on
the parent sporophytes for variable
periods.
Reproduction
1.
The sporangia produce spores
by meiosis in spore mother
cells.
2.
The spores germinate to give rise to inconspicuous (not easily noticed or seen), small but multicellular, free-living, mostly photosynthetic thalloid gametophytes
called prothallus (true vascular tissues are absent).
|
Sporophyte (2n) → meiosis → spores (n) →
grow into → Gametophyte (n) → produces gametes → fertilization
→ zygote (2n) → grows into → Sporophyte (2n) |
3.
These gametophytes require cool, damp, shady places to
grow.
4.
The gametophytes bear male and female sex organs called antheridia
and archegonia, respectively.
5.
Water is required for transfer of antherozoids – the male
gametes released from the antheridia, to
the mouth of archegonium.
6.
Fusion of male gamete with the egg present in the
archegonium result in the formation of zygote.
7. Zygote thereafter produces a
multicellular well-differentiated sporophyte which
is the dominant phase of the
pteridophytes.
8.
The development of
the zygotes into young embryos take place within the female gametophytes.
9.
This event is a precursor
to the seed habit considered an important step in evolution.
Classification
The
pteridophytes are further classified into four classes: Psilopsida (Psilotum); Lycopsida (Selaginella, Lycopodium), Sphenopsida (Equisetum) and Pteropsida (Dryopteris, Pteris, Adiantum).
GYMNOSPERMS
1. The gymnosperms (gymnos : naked,
sperma : seeds) are plants in which the ovules are not enclosed
by any ovary wall and
remain exposed, both before and after fertilisation.
2.
Gymnosperms include medium-sized
trees or tall trees and shrubs.
3.
One of the gymnosperms, the giant redwood tree Sequoia is one of the tallest tree species.
4.
The roots are generally tap roots.
Symbiotic
relationship
1.
Roots in some genera have fungal association in the form of mycorrhiza (Pinus), while in some
others (Cycas) small specialised roots called coralloid
roots (Coralloid
roots are thick, fleshy) are associated with N2 - fixing
cyanobacteria.
Structure
1.
The stems are unbranched (Cycas) or branched (Pinus, Cedrus).
2. The leaves may be simple or compound. Pinnate leaves are compound, meaning they consist of multiple leaflets.
3. In Cycas the pinnate leaves persist for a few years.
4. In conifers, the needle-like leaves reduce the surface area.
Reproduction
1.
The dominant stage is
sporophyte stage.
2.
The gymnosperms are heterosporous; they produce haploid microspores
and megaspores.
3.
The two kinds of spores are produced within sporangia that are borne on sporophylls which are arranged spirally along an axis to form
lax or compact strobili or cones.
4.
The strobili bearing microsporophylls and microsporangia
are called microsporangiate or male strobili/cone.
5.
The microspores develop into a male gametophytic
generation which is highly reduced and
is confined to only a limited number of cells.
6.
This reduced (microspores give rise to male gametophyte
after meiosis) gametophyte
is
called a pollen
grain.
7.
The development of pollen grains take place within the
microsporangia.
8.
The cones bearing megasporophylls with ovules or
megasporangia are called
macrosporangiate or female strobili.
9.
The male or female cones or strobili may be borne on the same tree (Pinus).
10.However, in cycas male cones and megasporophylls are borne on different trees.
11.The megaspore mother cell is differentiated from one of
the cells of the nucellus.
12.The nucellus (It is a
tissue present in the megasporophyll which gives the nutrition to the egg)
is protected by envelopes and the
composite structure is called an ovule.
13.The ovules are borne on megasporophylls which may be
clustered to form the female cones.
14.The megaspore mother cell divides
meiotically to form four megaspores.
15.One of the megaspores (the other three megaspores will degenerate) enclosed within the megasporangium develops into a multicellular female gametophyte that bears two or more archegonia or female sex organs.
16.The multicellular female gametophyte is also retained within megasporangium.
17.Unlike bryophytes and
pteridophytes, in gymnosperms the male and the female gametophytes do not have an independent
free-living existence.
18.They remain within the sporangia retained on the
sporophytes.
19.The pollen grain is released from
the microsporangium. They are carried in air currents and come in contact with the opening of the
ovules borne on megasporophylls.
20.The pollen tube carrying the male
gametes grows towards archegonia in the ovules and discharge their contents near the mouth of
the archegonia.
21.Following fertilisation, zygote
develops into an embryo and the ovules into seeds. These seeds are not covered.
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