CHA P TER
03
Plant Kingdom | 27
PLÅÑT KÏÑGDØM
28 | A Handbook of Biology
In plantae 5 groups are included – Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms.
It includes all eukaryotic chlorophyll-containing organisms commonly
called plants.
A few members are partially heterotrophic such as insectivorous plants
or parasites. Bladderwort and venus fly trap are example of insectivorous
plants and Cuscuta is a parasite.
Life cycle of plants has two distinct phases – the diploid sporophytic and
the haploid gametophytic – that alternate with each other.
SÝSTËM ØF BÏØLØGÏÇÅL ÇLÅSSÏFÏÇÅTÏØÑ
ÅRTÏFÏÇÏÅL ÇLÅSSÏFÏÇÅTÏØÑ SÝSTËMS
These are based on the external features : E.g.,
Linnaeus’s artificial system of classification was based
on the androecium structure.
It is the earliest classification system used only gross
superficial morphological characters including colour,
number habit and shape of leaves etc.
Aristotle was the earliest to attempt a more scientific
1
basis for classification.
Aristotle used simple morphological characters to
classify plants into trees, shrubs and herbs.
Aristotle divided animals into two groups, those
which had red blood (Enaima) and those that did not
(Anaima).
Aristotle is called father of Zoology, father of Biology
and father of Embryology.
ÑÅTÜRÅL ÇLÅSSÏFÏÇÅTÏØÑ SÝSTËMS
These are based on natural affinities among organisms. E.g. 2
Classification for flowering plants given by George Bentham
and Joseph Dalton Hooker.
PHÝLØGËÑËTÏÇ ÇLÅSSÏFÏÇÅTÏØÑ SÝSTËMS
These are based on the evolutionary relationships.
Numerical taxonomy:
It is based on all observable characteristics. It is easily carried out using
computers. Number & codes are assigned to all the characters and the
data are processed. Thus, hundreds of characters can be considered
giving equal importance.
Plant Kingdom | 29
Cytotaxonomy: It is based on cytological information like chromosome
number, structure, behaviour etc.
Chemotaxonomy: It uses chemical constituents of plants.
ÅLGÅË (PHÝÇØLØGÝ)
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms.
Found in moist stones, soil and wood.
Some of them occur in association with fungi (lichen) and animals (e.g.,
on sloth bear).
The form and size of algae is highly variable. The size ranges from the
microscopic unicellular forms like Chlamydomonas, to colonial forms
like Volvox and to filamentous forms like Ulothrix and spirogyra.
A few of the marine forms such as kelps, form massive plant bodies.
Vegetative reproduction: By fragmentation. Each fragment
develops into a thallus.
Asexual reproduction: By the production of spores. E.g.
zoospores (most common). They are flagellated (motile) and
on germination gives rise to new plants.
Sexual reproduction: Through fusion of two gametes. It may be:
Isogamous: Fusion of gametes similar in size. They may be
flagellated (e.g. Chlamydomonas) or non flagellated (non
motile, e.g. Spirogyra).
Anisogamous: Fusion of two gametes dissimilar in size. E.g.
Some species of Chlamydomonas.
Oogamous: Fusion between one large, non motile (static)
female gamete and a smaller, motile male gamete. E.g.
Volvox, Fucus.
Spirogyra Chlamydomonas
30 | A Handbook of Biology
Examples of Algae
BËÑËFÏTS ØF ÅLGÅË
Through photosynthesis, they fix nearly half of the total CO2 on earth and
increase the level of dissolved oxygen.
Many marine algae (70 species) are used as food. E.g. Porphyra,
Laminaria and Sargassum.
Some marine brown & red algae produce hydrocolloids (water holding
substances). E.g. Algin (brown algae) and carrageen (red algae). These
are used commercially.
They are primary producers and the basis of the food cycles of all
aquatic animals.
Agar (from Gelidium & Gracilaria) is used to grow microbes and in ice-
creams and jellies.
Chlorella and Spirulina are unicellular algae, rich in proteins and are
used as food supplements even by space travellers.
Algae include 3 classes: Chlorophyceae, Phaeophyceae and Rhodophyceae.
ÇHLØRØPHÝÇËÅË (GRËËÑ ÅLGÅË)
They are usually grass green due to the pigments chlorophyll a and
b in chloroplasts.
The chloroplasts may be discoid, plate like, reticulate, cup shaped,
spiral or ribbon shaped in different species.
Most of them have one or more pyrenoids (storage bodies) located
in the chloroplasts Pyrenoids contain protein besides starch.
(AIPMT 2012)
Some algae store food in the form of oil droplets.
Have a rigid cell wall made of an inner layer of cellulose and outer
layer of pectose.
Some commonly from green algae are Chlamydomonas, Volvox,
Ulothrix, Spirogyra and Chara.
Plant Kingdom | 31
Vegetative reproduction: By
fragmentation or by formation of
different types of spores. (AIPMT 2012)
Asexual reproduction: By flagellate
RËPRØDÜÇTÏØÑ zoospores produced in zoosporangia.
Sexual reproduction: By sex cell
formation and may be isogamous,
anisogamous or oogamous.
PHÅËØPHÝÇËÅË (BRØWÑ ÅLGÅË)
1 They vary in colour from olive green to brown depending upon
the amount of xanthophyll pigment, fucoxanthin. (AIPMT 1997)
Food is stored as complex carbohydrates, which may be in
the form of laminarin or mannitol. (AIPMT 1997)
2
3 The vegetative cells have a cellulosic wall usually covered on
the outside by a gelatinous coating of algin. (AIPMT 1997)
Protoplast contains plastids, central vacuole and nucleus. 4
5 Plant body is attached to substratum by a holdfast, has a stalk
(stipe) and leaf like photosynthetic organ (frond).
E.g. Ectocarpus, Dictyota, Laminaria, Sargassum, Fucus and
Kelps.
6
32 | A Handbook of Biology
Vegetative reproduction: By
fragmentation.
Asexual reproduction: By pear-
RËPRØDÜÇTÏØÑ shaped biflagellate zoospores (have
2 unequal laterally attached flagella).
Sexual reproduction: Isogamous,
anisogamous or oogamous. Union
of gametes occurs in water or within
the oogonium (oogamous species).
Gametes are pear- shaped (pyriform)
bearing 2 laterally attached flagella.
RHØDØPHÝÇËÅË (RËD ÅLGÅË)
They have the red pigment, r-phycoerythrin
Found in marine water and in warmer areas.
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.
E.g. Polysiphonia, Porphyra, Gracilaria and Gelidium
Vegetative reproduction: By
fragmentation.
Asexual reproduction: By non-motile
RËPRØDÜÇTÏØÑ spores.
Sexual reproduction: Oogamous. By
non-motile gametes. It has complex
post fertilisation developments.
Plant Kingdom | 33
Division of Algae and their main characteristics
Chlorophyceae Phaeophyceae Rhodophyceae
Classes
(Green algae) (brown algae) (Red algae)
Major Chlorophyll a, c, Chlorophyll a, d,
Chlorophyll a, b
pigments fucoxanthin phycoerythrin
Mannitol,
Stored food Starch Floridean Starch
laminarin
Cellulose , pectin
Cellulose and
Cell wall Cellulose and polysulphate
algin
esters
2-8, equal, 2, unequal,
Flagella Absent
apical lateral
Fresh water, salt Fresh water Fresh water (some),
Habitat water & brackish (rare), salt water salt water (most) &
water & brackish water brackish water
BRÝØPHÝTËS (BRÝØLØGÝ)
Commonly growing in moist shaded areas in the hills.
They are non-vascular terrestrial plants in which diploid sporophyte lives
as a parasite on an independent haploid gametophyte.
They are called amphibians of the plant kingdom because they can live
in soil but need water for sexual reproduction.
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.
34 | A Handbook of Biology
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.
ÏMPØRTÅÑÇË ØF BRÝØPHÝTËS
Some mosses provide food for herbivorous mammals, birds
and other animals.
Species of Sphagnum (a moss) provide peat. It is used as fuel.
It has water holding capacity so it is used as packing material
for trans-shipment of living material. (AIPMT 2006)
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.
LÏVËRWØRTS
Grow in moist, shady habitats.
Plant body of a liverwort is thalloid. Eg. Marchantia
Leafy members have tiny leaf-like appendages in two rows on the stem-
like structures.
Plant Kingdom | 35
Asexual reproduction: By fragmentation of thalli
e.g. Marchantia, (NEET 2013) or by the formation
01 of gemmae (sing. gemma). Gemmae are green,
multicellular, asexual buds that develop in small
receptacles (gemma cups) on the thalli. Gemmae
detach from the parent body and germinate to
form new individuals.
Sexual reproduction: Male and female sex organs
02
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.
MØSSËS
The predominant stage of the life cycle of a moss is the gametophyte. It
consists of two stages.
Protonema stage: The first stage which develops directly from a spore. It
is a creeping, green, branched and frequently filamentous stage.
Leafy stage: The second stage which develops from the secondary
protonema as a lateral bud. They consist 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.
36 | A Handbook of Biology
PTËRÏDØPHÝTËS
Primitive seedless vascular plants that have conspicuous
sporophytic plant body and inconspicuous gametophytes.
They include horsetails and ferns.
Used for medicinal purposes and as soil-binders. Frequently
grown as ornamentals.
Found in cool, damp, shady places though some may flourish
in sandy soil conditions.
In bryophytes, the dominant phase in the life cycle is the
gametophytic plant body. In pteridophytes, the main plant
body is a sporophyte which is differentiated into true root, stem
and leaves.
The leaves in pteridophytes are small (microphylls) as in
Selaginella or large (macrophylls) as in ferns.
The sporophytes bear sporangia that are subtended by leaf-
like appendages called sporophylls. In some cases sporophylls
may form distinct compact structures called strobili or cones
(Selaginella and Equisetum).
Sporangia produce spores by meiosis in spore mother cells.
The spores germinate to give rise to inconspicuous, small,
multicellular, free-living, mostly photosynthetic thalloid
gametophytes called prothallus.
The gametophytes bear male and female sex organs called
antheridia and archegonia respectively.
Water is needed for transfer of antherozoids (male gametes
from antheridia) to the mouth of archegonium. (NEET 2016,
AIPMT 2009)
Antherozoid fuses with the egg in the archegonium to form
zygote.
Zygote produces a multicellular well-differentiated sporophyte
(dominant phase of pteridophytes).
Most of the pteridophytes produce similar kinds of spores
(homosporous plants). Others produce two kinds of spores,
macro & micro spores. They are heterosporous. E.g. Selaginella
& Salvinia. (AIPMT 2008)
The megaspores & microspores germinate and give rise to
female and male gametophytes, respectively. The female
gametophytes are retained on the parent sporophytes for
variable periods. (AIPMT 2011)
Within female gametophytes, zygotes develop into young
embryos. This event is a precursor to the seed habit. It is
considered as an important step in evolution.
Plant Kingdom | 37
THË PTËRÏDØPHÝTËS HÅVË 4 ÇLÅSSËS:
1. 2. 3. 4.
Psilopsida: E.g. Lycopsida: E.g. Sphenopsida: Pteropsida:
Psilotum Selaginella, E.g. Equisetum E.g. Dryopteris,
Lycopodium Pteris, Adiantum
(walking fern)
GÝMÑØSPËRMS
The gymnosperms (gymnos: naked, sperma: seeds) are plants
in which the ovules are not enclosed by any ovarian wall and
remain exposed, both before and after fertilisation. The seeds
that develop post fertilisation, are not covered, i.e., are naked.
They include medium-sized trees or fall trees and shrubs.
Out of the gymnosperms, the giant redwood tree Sequoia is
one of the tallest tree species.
Roots are generally tap roots.
Stems are unbranched (Cycas) or branched (Pinus and Cedrus).
Roots in some genera have fungal association in the form of
mycorrhiza (E.g. Pinus).
In plants like Cycas, small specialized roots (coralloid roots) are
associated with N2-fixing cyanobacteria.
Leaves are well adapted to with stand extremes of temperatures,
humidity and wind. In conifers, needle-like leaves reduce the
surface area. Their thick cuticle and sunken stomata help to
reduce water loss.
Reproduction: Gymnosperms are heterosporous. They produce
haploid microspores and megaspores.
Some leaves are modified into sporophylls. They are compactly
and spirally arranged along an axis to form strobili or cones.
Sporophylls bear sporangia in which spores are produced.
38 | A Handbook of Biology
SPØRØPHÝLLS ÅRË ØF 2 TÝPËS:
Microsporophylls: They are arranged to form male strobili
(microsporangiate). They bear microsporangia. The microspores develop
into male gametophytes. It is highly reduced and confined to only a limited
number of cells. This gametophyte is called a pollen grain. The pollen grains
are developed within the microsporangia.
Megasporophylls: They are arranged to form female strobili
(macrosporangiate). They bear megasporangia (ovules).
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
nucellus. The nucellus is protected by envelops and the composite
structure is called an ovule.
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.
ÅÑGÏØSPËRMS
Angiosperms are flowering plants
Specialised reproductive structures are
flowers
Seeds are enclosed in fruits
Ovary – develops into fruit
Ovules – develop into seeds
Double – fertilisation is characteristic
feature of angiosperms. (AIPMT 2002)
Pollination occurs with the help of insects, birds, water or wind
Size range is from tiny, almost microscopic Wolfia to tall trees of
Eucalyptus (over 100 metres).
They provide us with food, fodder, fuel, medicines and several other
commercially important products.
Plant Kingdom | 39
DÏÇØTS
Seeds having two cotyledon
Eg. Mustard, Pea, Beans
MØÑØÇØTS
Seeds having only one cotyledon
Eg. Grasses, wheat, Rice
PLÅÑT LÏFË ÇÝÇLËS ÅÑD ÅLTËRÑÅTÏØÑ ØF GËÑËRÅTÏØÑS
Plants cells divide by mitosis to grow and
Gametophyte (n)
produce different plant bodies like haploid
and diploid. Haploid plant bodies are called
Divides by mitosis
gametophyte and diploid plant bodies are
called sporophyte.
Gametes (n)
Sexually reproducing plants exhibit
alternation of generations between
Fertilisation
gametophyte (n) and sporophyte (2n) in a
complete life cycle.
Zygote (2n)
PÅTTËRÑS ØF PLÅÑT LÏFË ÇÝÇLËS Divides by mitosis
HÅPLØÑTÏÇ LÏFË ÇÝÇLË Sporophyte (2n)
Gametophyte generation – dominant;
photosynthetic and free-living. Divides by meiosis
In sporophytic generation, there is only one-
celled zygote which is not free-living and Spores (n)
undergoes meiosis to form spores that divide
mitotically to produce new gametophyte Divide by mitosis again
Examples: Volvox and Spirogyra and some
New gametophyte (n)
species of Chlamydomonas.
40 | A Handbook of Biology
Gametophyte
(n)
Spores
HAPLONTIC LIFE Gametogenesis
(n)
CYCLE
Meiosis Syngamy
Zygote
(2n)
DÏPLØÑTÏÇ LÏFË ÇÝÇLË
Sporophytic generation is dominant; photosynthetic and independent.
Gametophytic generation is microscopic and represented by single to
few-celled (e.g., Fucus) haploid gametophyte.
Examples: All seed-bearing plants (gymnosperms and angiosperms)
follow this pattern, where the gametophytic phase is few to multicell.
(AIPMT MAINS 2011)
Sporophyte
(2n)
Zygote
DIPLONTIC LIFE Meiosis
(2n)
CYCLE
Syngamy
Gametophyte/
Gametes (n)
Gametogenesis
Plant Kingdom | 41
HÅPLØ-DÏPLØÑTÏÇ LÏFË ÇÝÇLË
Both gametophytic and sporophytic stages are multi-cellular and free-
living.
It is an intermediate condition between haplontic and diplontic life
cycles.
In bryophytes, haploid gametophyte is dominant, independent,
photosynthetic and alternates with short-lived multicellular sporophyte.
In pteridophytes, diploid sporophyte is dominant, independent,
photosynthetic and alternates with short-lived multicellular haploid
gametophyte.
Examples: Byrophytes and pteridophytes, alga Ectocarpus, Polysiphonia
and kelps.
Sporophyte
(2n)
Zygote
(2n)
Meiosis
HAPLO-DIPLONTIC
LIFE CYCLE
Syngamy
Spores
(n)
Gametogenesis
Gametophyte
(n)
