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3. PLANT KINGDOM
- E.g. Classification for flowering plants given by George
Bentham & Joseph Dalton Hooker.
Phylogenetic classification systems
- These are based on evolutionary relationships between
the various organisms.
- This assumes that organisms belonging to the same taxa
have a common ancestor.
Other sources to resolve the problems in classification:
o Numerical Taxonomy: It is based on all observable
characteristics. It is now easily carried out using
computers. Number and codes are assigned to all the
characters and the data are processed. Thus hundreds of
characters can be considered giving equal importance.
o Cytotaxonomy: It is based on cytological information
like chromosome number, structure, behaviour etc.
o Chemotaxonomy: It uses the chemical constituents of
the plant to resolve confusions.
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Artificial classification systems
- These are earliest systems of classification.
- They were based on vegetative characters or superficial
morphological characters such as habit, colour, number
and shape of leaves, etc.
- Linnaeus’s artificial system of classification was based
on the androecium structure.
Drawbacks:
- Artificial systems separated the closely related species
since they were based on a few characteristics.
- They gave equal weightage to vegetative and sexual
characteristics. This is not acceptable since the vegetative
characters are more easily affected by environment.
Natural classification systems
- These are based on natural affinities among organisms
and considered external features, internal features (ultra
structure, anatomy, embryology & phytochemistry).
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ALGAE
- Algae are simple, thalloid, autotrophic, chlorophyll☺ Agar (obtained from Gelidium & Gracilaria) is used to
bearing and aquatic (fresh water & marine) organisms.
grow microbes and in ice-creams and jellies.
- They also occur in moist stones, soils and wood.
☺ Some marine brown & red algae produce hydrocolloids
- Some of them also occur in association with fungi
(water holding substances). E.g. algin (brown algae) and
(lichen) and animals (e.g., on sloth bear).
carrageen (red algae). These are used commercially.
- The form and size of algae is highly variable.
☺ Protein-rich unicellular algae like Chlorella & Spirullina
o Microscopic unicellular forms: E.g. Chlamydomonas.
are used as food supplements by space travellers.
o Colonial forms: E.g. Volvox
Algae are classified into 3 classes: Chlorophyceae,
o Filamentous forms: E.g. Ulothrix and Spirogyra.
Phaeophyceae and Rhodophyceae.
Reproduction:
Chlorophyceae (green algae)
- Vegetative reproduction: By fragmentation. Each
- Unicellular, colonial or filamentous.
fragment develops into a thallus.
- They are usually grass green due to the pigments
- Asexual reproduction: By the production of spores. E.g.
chlorophyll a and b localized in chloroplasts.
zoospores (most common). They are flagellated (motile)
- The chloroplasts may be discoid, plate-like, reticulate,
and on germination gives rise to new plants.
cup-shaped, spiral or ribbon-shaped in different species.
- Sexual reproduction: Through fusion of two gametes. It
- Most of them have one or more pyrenoids (storage
is many types:
bodies) located in the chloroplasts. Pyrenoids contain
o Isogamous: Fusion of gametes similar in size. They
protein besides starch.
may be flagellated (e.g. Chlamydomonas) or non- Some algae may store food in the form of oil droplets.
flagellated (non-motile, e.g. Spirogyra).
- They have a rigid cell wall made of an inner layer of
o Anisogamous: Fusion of two gametes dissimilar in
cellulose and an outer layer of pectose.
size. E.g. Some species of Chlamydomonas.
- E.g. Chlamydomonas, Volvox, Ulothrix, Spirogyra & Chara.
o Oogamous: Fusion between one large, non-motile
Reproduction:
(static) female gamete and a smaller, motile male
o Vegetative reproduction by fragmentation or by
gamete. E.g. Volvox, Fucus.
formation of different types of spores.
Benefits of algae:
o Asexual reproduction is by flagellated zoospores
☺ Through photosynthesis, they fix half of the total CO2 on
produced in zoosporangia.
earth and increase the level of dissolved oxygen in their
o Sexual reproduction may be isogamous, anisogamous
immediate environment.
or oogamous.
☺ They are primary producers and form the basis of the
Phaeophyceae (brown algae)
food cycles of all aquatic animals.
- They are found primarily in marine habitats.
☺ Many marine algae (70 species) are used as food. E.g.
- They show great variation in size and form. They range
Porphyra, Laminaria and Sargassum.
from simple branched, filamentous forms (Ectocarpus) to
profusely branched forms (e.g. kelps- 100 m in height).
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Phaeophyceae
Brown algae
Chlorophyll a, c, Fucoxanthin
Mannitol, laminarin
Cellulose and algin
Rhodophyceae
Red algae
Chlorophyll a, d, Phycoerythrin
Floridean Starch
Cellulose
2-8, equal, apical
2, unequal, lateral
Absent
Fresh water, salt water &
brackish water
Fresh water (rare), salt water &
brackish water
Fresh water (some), salt water
(most) & brackish water
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Chlorophyceae
Green algae
Chlorophyll a, b
Starch
Cellulose
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Habitat
Rhodophyceae (red algae)
- They have the red pigment, r-phycoerythrin.
- Majority are marine especially in the warmer areas.
- They occur in both well-lighted regions close to the
surface of water and at great depths in oceans where
relatively little light penetrates.
- The red thalli of most of the red algae are multicellular.
- Some of them have complex body organisation.
- The food is stored as floridean starch which is very
similar to amylopectin and glycogen in structure.
Reproduction:
o Vegetative reproduction: By fragmentation.
o Asexual reproduction: By non-motile spores.
o Sexual reproduction: Oogamous. By non-motile
gametes. It has complex post fertilisation developments.
- E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium.
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Common name
Major pigments
Stored food
Cell wall
Flagellar number &
position of insertion
- E.g. Ectocarpus, Dictyota, Laminaria, Sargassum & Fucus.
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- They have chlorophyll a, c, carotenoids & xanthophylls.
- They vary in colour from olive green to brown depending
upon the amount of a xanthophyll pigment, fucoxanthin.
- Food is stored as complex carbohydrates, which may be
in the form of laminarin or mannitol.
- The vegetative cells have a cellulosic wall usually
covered on the outside by a gelatinous coating of algin.
- Protoplast contains plastids, central vacuole and nucleus.
- Plant body is attached to substratum by a holdfast, and has
a stalk (stipe) and leaf like photosynthetic organ (frond).
Reproduction:
o Vegetative reproduction: By fragmentation.
o Asexual reproduction: By pear-shaped biflagellate
zoospores (have 2 unequal laterally attached flagella).
o Sexual reproduction: Isogamous, anisogamous or
oogamous. Union of gametes occurs in water or within
the oogonium (oogamous species). Gametes are pearshaped (pyriform) bearing 2 laterally attached flagella.
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BRYOPHYTES
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- They are also called amphibians of the plant kingdom
because they can live in soil but need water for sexual
reproduction.
- They occur in damp, humid and shaded localities. Found
in moist shaded areas in the hills.
- Their body is more differentiated than that of algae. It is
thallus-like and prostrate or erect, and attached to the
substratum by unicellular or multicellular rhizoids.
- They lack true roots, stem or leaves. They may possess
root-like, leaf-like or stem-like structures.
- The main plant body is haploid. It produces gametes,
hence is called a gametophyte.
- The sex organs in bryophytes are multicellular.
- The male sex organ (antheridium) produces biflagellate
antherozoids. The female sex organ (archegonium) is
flask-shaped and produces a single egg.
- Antherozoids are released into water where they come in
contact with archegonium. An antherozoid fuses with the
egg to form zygote.
- Zygotes do not undergo meiosis immediately. They
produce a multicellular body called a sporophyte.
- Sporophyte is not free-living but attached to the
photosynthetic gametophyte and derives nourishment
from it. Some cells of the sporophyte undergo meiosis to
produce haploid spores. These spores germinate to form
gametophyte.
Importance of Bryophytes:
☺ Some mosses provide food for herbaceous mammals,
birds and other animals.
☺ Species of Sphagnum (a moss) provide peat. It is used as
fuel. It has water holding capacity so that used as packing
material for trans-shipment of living material.
☺ They have great ecological importance because of their
important role in plant succession on bare rocks/soil.
Mosses along with lichens decompose rocks making the
substrate suitable for the growth of higher plants.
☺ Since mosses form dense mats on the soil, they can
prevent soil erosion.
The bryophytes are divided into liverworts and mosses.
Liverworts
- They grow usually in moist, shady habitats such as banks
of streams, marshy ground, damp soil, bark of trees and
deep in the woods.
- Their plant body is thalloid. E.g. Marchantia. Thallus is
dorsi-ventral and closely appressed to the substrate. The
leafy members have tiny leaf-like appendages in two
rows on the stem-like structures.
- Asexual reproduction: By fragmentation of thalli, or
by the formation of gemmae (sing. gemma). Gemmae
are green, multicellular, asexual buds that develop in
small receptacles (gemma cups) on the thalli. The
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gemmae are detached from the parent body and
germinate to form new individuals.
- Sexual reproduction: Male and female sex organs are
produced on the same or different thalli. Sporophyte is
differentiated into a foot, seta and capsule. After
meiosis, spores are produced within the capsule. These
spores germinate to form free-living gametophytes.
Mosses
- The predominant stage of the life cycle of a moss is the
gametophyte. It consists of two stages.
o Protonema stage: The first stage which develops
directly from a spore. It is a creeping, green, branched
and frequently filamentous stage.
o Leafy stage: The second stage which develops from
the secondary protonema as a lateral bud. They consist
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PTERIDOPHYTES
They include horsetails and ferns.
- The gametophytes bear male and female sex organs
called antheridia and archegonia, respectively.
They are found in cool, damp, shady places though some
may flourish well in sandy-soil conditions.
- Water is required for transfer of antherozoids (male
gametes from antheridia) to the mouth of archegonium.
They are used for medicinal purposes and as soil-binders.
They are also frequently grown as ornamentals.
- Antherozoid fuses with the egg in the archegonium to
form zygote.
Evolutionarily, they are the first terrestrial plants to
possess vascular tissues (xylem & phloem).
- Zygote produces a multicellular well-differentiated
sporophyte (dominant phase of pteridophytes).
In bryophytes, the dominant phase in the life cycle is the
gametophytic plant body. In pteridophytes, the main
- Most of the pteridophytes produce similar kinds of
plant body is a sporophyte which is differentiated into
spores. Such plants are called homosporous. Others
true root, stem and leaves. These organs possess wellproduce two kinds of spores, macro & micro spores.
differentiated vascular tissues.
They are heterosporous. E.g. Selaginella & Salvinia.
The leaves in pteridophyta are small (microphylls) as in
- The megaspores & microspores germinate and give rise
to female and male gametophytes, respectively. The
Selaginella or large (macrophylls) as in ferns.
female gametophytes are retained on the parent
The sporophytes bear sporangia that are subtended by
leaf-like appendages called sporophylls. In some cases
sporophytes for variable periods.
sporophylls may form distinct compact structures called
- Development of the zygotes into young embryos takes
strobili or cones (Selaginella, Equisetum).
place within female gametophytes. This event is a
precursor to the seed habit. It is considered as an
Sporangia produce spores by meiosis in spore mother
important step in evolution.
cells. The spores germinate to give rise to inconspicuous,
small, multicellular, free-living, mostly photosynthetic
- The pteridophytes have 4 classes:
thalloid gametophytes called prothallus.
1. Psilopsida (Psilotum)
2. Lycopsida (Selaginella, Lycopodium)
Prothallus requires cool, damp, shady places to grow.
3. Sphenopsida (Equisetum)
Because of this restricted requirement and the need for
4. Pteropsida (Dryopteris, Pteris, Adiantum)
water for fertilization, the spread of pteridophytes is
limited and restricted to narrow geographical regions.
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of upright, slender axes bearing spirally arranged
leaves. They are attached to soil through multicellular
and branched rhizoids. This stage bears the sex organs.
- Vegetative reproduction: By fragmentation and
budding in the secondary protonema.
- Sexual reproduction: The antheridia & archegonia are
produced at the apex of leafy shoots. After fertilisation,
zygote develops into a sporophyte, consisting of a foot,
seta and capsule. The sporophyte in mosses is more
elaborate than that in liverworts. The capsule contains
spores. Spores are formed after meiosis. Mosses have an
elaborate mechanism of spore dispersal.
- E.g. Funaria, Polytrichum and Sphagnum.
GYMNOSPERMS
specialized roots (coralloid roots) are associated with
Gymnosperms (gymnos: naked, sperma: seeds) are plants
N2- fixing cyanobacteria.
in which the ovules are not enclosed by ovary wall and
remain exposed before and after fertilization. Seeds that
- Stems are unbranched (Cycas) or branched (Pinus,
develop post-fertilization are not covered (naked).
Cedrus).
They include medium-sized trees or tall trees and shrubs.
- Leaves are simple or compound. They are well-adapted
The gymnosperm, Sequoia (giant redwood) is one of the
to withstand extreme temperature, humidity and wind.
tallest tree species.
- In Cycas the pinnate leaves persist for a few years. In
conifers, the needle-like leaves reduce the surface area.
The roots are generally tap roots.
Their thick cuticle and sunken stomata also help to
Roots in some genera have fungal association in the form
reduce water loss.
of mycorrhiza (Pinus). In some others (Cycas) small
Reproduction:
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- The ovules are borne on megasporophylls which may be
clustered to form the female cones.
- Megaspore mother cell undergoes meiosis to form four
megaspores. One of the megaspores enclosed within the
Megasporangium (nucellus) develops into a
multicellular female gametophyte that bears two or more
archegonia. The multicellular female gametophyte is
also retained within megasporangium.
- Unlike bryophytes and pteridophytes, in gymnosperms
the male and the female gametophytes do not have an
independent free-living existence. They remain within
the sporangia retained on the sporophytes.
- 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. The
pollen tube carrying the male gametes grows towards
archegonia in the ovules and discharges their contents
near the mouth of the archegonia.
- After fertilization, zygote develops into an embryo and
the ovules into seeds. These seeds are not covered.
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- Gymnosperms are heterosporous. They produce haploid
microspores and megaspores.
- 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.
strobili
bearing
microsporophylls
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- The
microsporangia are called microsporangiate (male
strobili). The microspores develop into a male
gametophytic generation which is highly reduced and is
confined to only a limited number of cells. This reduced
gametophyte is called a pollen grain. The development
of pollen grains takes place within the microsporangia.
- The cones bearing megasporophylls with ovules or
megasporangia are called macrosporangiate (female
strobili).
- The male or female cones may be borne on the same tree
(Pinus) or on different trees (Cycas).
- The megaspore mother cell is differentiated from one of
the cells of the nucellus. The nucellus is protected by
envelopes and the composite structure is called an ovule.
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ANGIOSPERMS (FLOWERING PLANTS)
polar nuclei. The polar nuclei eventually fuse to produce
- They are an exceptionally large group of plants occurring
a diploid secondary nucleus.
in wide range of habitats. They range in size from tiny,
almost microscopic Wolfia to tall trees of Eucalyptus
- Pollen grains are dispersed from the anthers and carried
(over 100 metres).
by wind or other agencies to the stigma of a pistil. This is
called pollination.
- In angiosperms, the pollen grains and ovules are
developed in specialized structures called flowers. The
- The pollen grains germinate on the stigma and the
seeds are enclosed by fruits.
resulting pollen tubes grow through the tissues of stigma
and style and reach the ovule.
- They are divided into two classes:
o Dicotyledons: They have 2 cotyledons in their seeds.
- The pollen tubes enter the embryo-sac where two male
o Monocotyledons: They have only one cotyledon.
gametes are discharged. One of the male gametes fuses
with the egg cell to form a zygote (syngamy). The other
- Male sex organ in a flower is the stamen. Each stamen
male gamete fuses with the diploid secondary nucleus to
consists of a slender filament with an anther at the tip.
produce the triploid primary endosperm nucleus
The anthers produce pollen grains by mieosis.
(PEN). Because of the involvement of two fusions, this
- Female sex organ in a flower is the pistil or the carpel.
event is termed as double fertilisation, an event unique
Pistil consists of an ovary enclosing one to many ovules.
to angiosperms.
Within ovules are present highly reduced female
- The zygote develops into an embryo (with one or two
gametophytes (embryo sacs).
cotyledons). The PEN develops into endosperm which
- The embryo-sac formation is preceded by meiosis.
provides nourishment to the developing embryo.
Hence, each of the cells of an embryo-sac is haploid.
- Synergids & antipodals degenerate after fertilization.
- Each embryo-sac has a three-celled egg apparatus (one
egg cell & two synergids), three antipodal cells and two
- During these events the ovules develop into seeds and
the ovaries develop into fruit.
PLANT LIFE CYCLES AND ALTERNATION OF GENERATIONS
- In plants, both haploid and diploid cells can divide by
mitosis. This leads to the formation of haploid and
diploid plant bodies.
- Haploid plant body produces gametes by mitosis. This
plant body represents a gametophyte.
- After fertilization, the zygote also divides by mitosis to
produce a diploid sporophytic plant body. Haploid spores
are produced by this plant body by meiosis. These in turn,
divide by mitosis to form a haploid plant body once again.
- Thus, during the life cycle of any sexually reproducing
plant, there is an alternation of generations between
gamete producing haploid gametophyte and spore
producing diploid sporophyte.
- However, different plant groups, as well as individuals
representing them, differ in the following patterns:
1. Haplontic: In this, sporophytic generation is
represented only by the one-celled zygote. There are no
free-living sporophytes. Meiosis in the zygote results in
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plant. The gametophytic phase is represented by the
single to few-celled haploid gametophyte. E.g. All seedbearing plants (gymnosperms & angiosperms).
3. Haplo-diplontic: Bryophytes and pteridophytes exhibit
an intermediate condition (Haplo-diplontic). Both
phases are multicellular and often free-living. However,
they differ in their dominant phases.
MODEL QUESTIONS
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Match the names given in column I with the items in column II
Column I
Column II
a) Adiantum
Bryophyte
b) Sargassum
Angiosperm
c) Sunflower
Algae
d) Riccia
Pteridophyte
Bryophytes are called ‘amphibians of the plant kingdom’. Justify the statement.
Some features of Haplontic and Diplontic life cycles are given below. Arrange them correctly in a table.
 Sporophyte is a single celled zygote
 Meioisis occurs in Zygote
 Sporophyte dominant
 No free living Sporophyte
 Gametophyte dominant
 Meioisis occurs before zygote formation
Match the following.
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B
a. Algae
Naked seeded plants.
b. Pteridophytes
Amphibians of plant kingdom
c. Gymnosperms Flowering plants
d. Angiosperms
Thalloid body, photosynthetic and mainly aquatic
e. Bryophytes
Independent sporophytic and gametophytic phase. Commonly called ferns.
The most characteristic features of angiosperms is double fertilization
a. What is double fertilization?
b. Why is it called triple fusion?
Identify the plant group from the given data.
a. Plant body is not differentiated into root, stem and leaf
b. Reproductive structures are strobili
Some Pteridophytes produce two types of spores.
a. Name the phenomenon
b. This event is an important step in evolution. Explain.
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the formation of haploid spores. The haploid spores
divide mitotically and form the gametophyte. The
dominant, photosynthetic phase in such plants is the
free-living gametophyte. E.g. Algae such as Volvox,
Spirogyra and some species of Chlamydomonas.
2. Diplontic: In this, the diploid sporophyte is the
dominant, photosynthetic, independent phase of the
SANDEEP DALAL
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