NCERT Textbook: Plant Kingdom | NCERT Textbooks (Class 6 to Class 12) - CTET & State TET PDF Download

 Page 1


PLANT KINGDOM 29
In the previous chapter, we looked at the broad classification of living
organisms under the system proposed by Whittaker (1969) wherein he
suggested the Five Kingdom classification viz. Monera, Protista, Fungi,
Animalia and Plantae.  In this chapter, we will deal in detail with further
classification within Kingdom Plantae popularly known as the ‘plant
kingdom’.
We must stress here that our understanding of the plant kingdom
has changed over time. Fungi, and members of the Monera and Protista
having cell walls have now been excluded from Plantae though earlier
classifications placed them in the same kingdom.  So, the cyanobacteria
that are also referred to as blue green algae are not ‘algae’ any more.  In
this chapter, we will describe Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms under Plantae .
Let us also look at classification within angiosperms to understand
some of the concerns  that influenced the classification systems. The
earliest systems of classification used only gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc.  They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment. As against this, natural classification systems developed,
which were based on natural affinities among the organisms and consider,
PLANT KINGDOM
CHAPTER  3
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles
and Alternation
of Generations
2020-21
Page 2


PLANT KINGDOM 29
In the previous chapter, we looked at the broad classification of living
organisms under the system proposed by Whittaker (1969) wherein he
suggested the Five Kingdom classification viz. Monera, Protista, Fungi,
Animalia and Plantae.  In this chapter, we will deal in detail with further
classification within Kingdom Plantae popularly known as the ‘plant
kingdom’.
We must stress here that our understanding of the plant kingdom
has changed over time. Fungi, and members of the Monera and Protista
having cell walls have now been excluded from Plantae though earlier
classifications placed them in the same kingdom.  So, the cyanobacteria
that are also referred to as blue green algae are not ‘algae’ any more.  In
this chapter, we will describe Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms under Plantae .
Let us also look at classification within angiosperms to understand
some of the concerns  that influenced the classification systems. The
earliest systems of classification used only gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc.  They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment. As against this, natural classification systems developed,
which were based on natural affinities among the organisms and consider,
PLANT KINGDOM
CHAPTER  3
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles
and Alternation
of Generations
2020-21
30 BIOLOGY
not only the external features, but also internal features, like ultra-
structure, anatomy, embryology and phytochemistry. Such a
classification for flowering plants was given by George Bentham and
Joseph Dalton Hooker.
At present phylogenetic classification systems based on
evolutionary relationships between the various organisms are acceptable.
This assumes that organisms belonging to the same taxa have a common
ancestor.   We now use information from many other sources too to help
resolve difficulties in classification.  These become more important when
there is no supporting fossil evidence.  Numerical Taxonomy which is
now easily carried out using computers is based on all observable
characteristics. Number and codes are assigned to all the characters and
the data are then processed. In this way each character is given equal
importance and at the same time hundreds of characters can be
considered.  Cytotaxonomy that is based on cytological information like
chromosome number, structure, behaviour and chemotaxonomy that
uses the chemical constituents of the plant to resolve confusions, are also
used by taxonomists these days.
3.1 ALGAE
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them
also occur in association with fungi (lichen) and animals (e.g., on sloth
bear).
The form and size of algae is highly variable, ranging from colonial
forms like Volvox and the filamentous forms like Ulothrix and Spirogyra
(Figure 3.1). A few of the marine forms such as kelps, form massive plant
bodies.
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. 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. Fusion of two gametes dissimilar in size, as in species of
Eudorina is termed as anisogamous. Fusion between one large, non-
motile (static) female gamete and a smaller, motile male gamete is termed
oogamous, e.g., Volvox, Fucus.
2020-21
Page 3


PLANT KINGDOM 29
In the previous chapter, we looked at the broad classification of living
organisms under the system proposed by Whittaker (1969) wherein he
suggested the Five Kingdom classification viz. Monera, Protista, Fungi,
Animalia and Plantae.  In this chapter, we will deal in detail with further
classification within Kingdom Plantae popularly known as the ‘plant
kingdom’.
We must stress here that our understanding of the plant kingdom
has changed over time. Fungi, and members of the Monera and Protista
having cell walls have now been excluded from Plantae though earlier
classifications placed them in the same kingdom.  So, the cyanobacteria
that are also referred to as blue green algae are not ‘algae’ any more.  In
this chapter, we will describe Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms under Plantae .
Let us also look at classification within angiosperms to understand
some of the concerns  that influenced the classification systems. The
earliest systems of classification used only gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc.  They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment. As against this, natural classification systems developed,
which were based on natural affinities among the organisms and consider,
PLANT KINGDOM
CHAPTER  3
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles
and Alternation
of Generations
2020-21
30 BIOLOGY
not only the external features, but also internal features, like ultra-
structure, anatomy, embryology and phytochemistry. Such a
classification for flowering plants was given by George Bentham and
Joseph Dalton Hooker.
At present phylogenetic classification systems based on
evolutionary relationships between the various organisms are acceptable.
This assumes that organisms belonging to the same taxa have a common
ancestor.   We now use information from many other sources too to help
resolve difficulties in classification.  These become more important when
there is no supporting fossil evidence.  Numerical Taxonomy which is
now easily carried out using computers is based on all observable
characteristics. Number and codes are assigned to all the characters and
the data are then processed. In this way each character is given equal
importance and at the same time hundreds of characters can be
considered.  Cytotaxonomy that is based on cytological information like
chromosome number, structure, behaviour and chemotaxonomy that
uses the chemical constituents of the plant to resolve confusions, are also
used by taxonomists these days.
3.1 ALGAE
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them
also occur in association with fungi (lichen) and animals (e.g., on sloth
bear).
The form and size of algae is highly variable, ranging from colonial
forms like Volvox and the filamentous forms like Ulothrix and Spirogyra
(Figure 3.1). A few of the marine forms such as kelps, form massive plant
bodies.
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. 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. Fusion of two gametes dissimilar in size, as in species of
Eudorina is termed as anisogamous. Fusion between one large, non-
motile (static) female gamete and a smaller, motile male gamete is termed
oogamous, e.g., Volvox, Fucus.
2020-21
PLANT KINGDOM 31
Figure 3.1  Algae : (a) Green algae   (i) Volvox         (ii) Ulothrix
(b) Brown algae  (i) Laminaria   (ii) Fucus      (iii) Dictyota
(c)  Red algae     (i)  Porphyra    (ii) Polysiphonia
2020-21
Page 4


PLANT KINGDOM 29
In the previous chapter, we looked at the broad classification of living
organisms under the system proposed by Whittaker (1969) wherein he
suggested the Five Kingdom classification viz. Monera, Protista, Fungi,
Animalia and Plantae.  In this chapter, we will deal in detail with further
classification within Kingdom Plantae popularly known as the ‘plant
kingdom’.
We must stress here that our understanding of the plant kingdom
has changed over time. Fungi, and members of the Monera and Protista
having cell walls have now been excluded from Plantae though earlier
classifications placed them in the same kingdom.  So, the cyanobacteria
that are also referred to as blue green algae are not ‘algae’ any more.  In
this chapter, we will describe Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms under Plantae .
Let us also look at classification within angiosperms to understand
some of the concerns  that influenced the classification systems. The
earliest systems of classification used only gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc.  They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment. As against this, natural classification systems developed,
which were based on natural affinities among the organisms and consider,
PLANT KINGDOM
CHAPTER  3
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles
and Alternation
of Generations
2020-21
30 BIOLOGY
not only the external features, but also internal features, like ultra-
structure, anatomy, embryology and phytochemistry. Such a
classification for flowering plants was given by George Bentham and
Joseph Dalton Hooker.
At present phylogenetic classification systems based on
evolutionary relationships between the various organisms are acceptable.
This assumes that organisms belonging to the same taxa have a common
ancestor.   We now use information from many other sources too to help
resolve difficulties in classification.  These become more important when
there is no supporting fossil evidence.  Numerical Taxonomy which is
now easily carried out using computers is based on all observable
characteristics. Number and codes are assigned to all the characters and
the data are then processed. In this way each character is given equal
importance and at the same time hundreds of characters can be
considered.  Cytotaxonomy that is based on cytological information like
chromosome number, structure, behaviour and chemotaxonomy that
uses the chemical constituents of the plant to resolve confusions, are also
used by taxonomists these days.
3.1 ALGAE
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them
also occur in association with fungi (lichen) and animals (e.g., on sloth
bear).
The form and size of algae is highly variable, ranging from colonial
forms like Volvox and the filamentous forms like Ulothrix and Spirogyra
(Figure 3.1). A few of the marine forms such as kelps, form massive plant
bodies.
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. 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. Fusion of two gametes dissimilar in size, as in species of
Eudorina is termed as anisogamous. Fusion between one large, non-
motile (static) female gamete and a smaller, motile male gamete is termed
oogamous, e.g., Volvox, Fucus.
2020-21
PLANT KINGDOM 31
Figure 3.1  Algae : (a) Green algae   (i) Volvox         (ii) Ulothrix
(b) Brown algae  (i) Laminaria   (ii) Fucus      (iii) Dictyota
(c)  Red algae     (i)  Porphyra    (ii) Polysiphonia
2020-21
32 BIOLOGY
Algae are useful to man in a variety of ways. At least a half of the total
carbon dioxide fixation on earth is carried out by algae through
photosynthesis. Being photosynthetic they increase the level of dissolved
oxygen in their immediate environment. They are of paramount
importance as primary producers of energy-rich compounds which form
the basis of the food cycles of all aquatic animals. Many species of Porphyra,
Laminaria and Sargassum  are among the 70 species of marine algae
used as food. Certain marine brown and red algae produce large amounts
of hydrocolloids (water holding substances), e.g., algin (brown algae) and
carrageen (red algae) which are used commercially. Agar, one of the
commercial products obtained from Gelidium and Gracilaria are used to
grow microbes and in preparations of ice-creams and jellies. Chlorella a
unicellular alga rich in proteins is used as food supplement even by space
travellers. The algae are divided into three main classes: Chlorophyceae,
Phaeophyceae and Rhodophyceae.
3.1.1 Chlorophyceae
The members of chlorophyceae are commonly called green algae. The
plant body may be unicellular, colonial or filamentous. They are usually
grass green due to the dominance of pigments chlorophyll a and b. The
pigments are localised in definite chloroplasts. The chloroplasts may be
discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in
different species. Most of the members have one or more storage bodies
called pyrenoids located in the chloroplasts. Pyrenoids contain protein
besides starch. Some algae may store food in the form of oil droplets.
Green algae usually have a rigid cell wall made of an inner layer of cellulose
and an outer layer of pectose.
Vegetative reproduction usually takes place by fragmentation or by
formation of different types of spores. Asexual reproduction is by
flagellated zoospores produced in zoosporangia. The sexual reproduction
shows considerable variation in the type and formation of sex cells and it
may be isogamous, anisogamous or oogamous. Some commonly found
green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara
(Figure 3.1a).
3.1.2 Phaeophyceae
The members of phaeophyceae or brown algae are found primarily in
marine habitats. They show great variation in size and form. They range
from simple branched, filamentous forms (Ectocarpus) to profusely
branched forms as represented by kelps, which may reach a height of
100 metres. They possess chlorophyll a, c, carotenoids and xanthophylls.
They vary in colour from olive green to various shades of brown depending
upon the amount of the xanthophyll pigment, fucoxanthin present in
2020-21
Page 5


PLANT KINGDOM 29
In the previous chapter, we looked at the broad classification of living
organisms under the system proposed by Whittaker (1969) wherein he
suggested the Five Kingdom classification viz. Monera, Protista, Fungi,
Animalia and Plantae.  In this chapter, we will deal in detail with further
classification within Kingdom Plantae popularly known as the ‘plant
kingdom’.
We must stress here that our understanding of the plant kingdom
has changed over time. Fungi, and members of the Monera and Protista
having cell walls have now been excluded from Plantae though earlier
classifications placed them in the same kingdom.  So, the cyanobacteria
that are also referred to as blue green algae are not ‘algae’ any more.  In
this chapter, we will describe Algae, Bryophytes, Pteridophytes,
Gymnosperms and Angiosperms under Plantae .
Let us also look at classification within angiosperms to understand
some of the concerns  that influenced the classification systems. The
earliest systems of classification used only gross superficial morphological
characters such as habit, colour, number and shape of leaves, etc.  They
were based mainly on vegetative characters or on the androecium
structure (system given by Linnaeus). Such systems were artificial; they
separated the closely related species since they were based on a few
characteristics. Also, the artificial systems gave equal weightage to
vegetative and sexual characteristics; this is not acceptable since we know
that often the vegetative characters are more easily affected by
environment. As against this, natural classification systems developed,
which were based on natural affinities among the organisms and consider,
PLANT KINGDOM
CHAPTER  3
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles
and Alternation
of Generations
2020-21
30 BIOLOGY
not only the external features, but also internal features, like ultra-
structure, anatomy, embryology and phytochemistry. Such a
classification for flowering plants was given by George Bentham and
Joseph Dalton Hooker.
At present phylogenetic classification systems based on
evolutionary relationships between the various organisms are acceptable.
This assumes that organisms belonging to the same taxa have a common
ancestor.   We now use information from many other sources too to help
resolve difficulties in classification.  These become more important when
there is no supporting fossil evidence.  Numerical Taxonomy which is
now easily carried out using computers is based on all observable
characteristics. Number and codes are assigned to all the characters and
the data are then processed. In this way each character is given equal
importance and at the same time hundreds of characters can be
considered.  Cytotaxonomy that is based on cytological information like
chromosome number, structure, behaviour and chemotaxonomy that
uses the chemical constituents of the plant to resolve confusions, are also
used by taxonomists these days.
3.1 ALGAE
Algae are chlorophyll-bearing, simple, thalloid, autotrophic and largely
aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them
also occur in association with fungi (lichen) and animals (e.g., on sloth
bear).
The form and size of algae is highly variable, ranging from colonial
forms like Volvox and the filamentous forms like Ulothrix and Spirogyra
(Figure 3.1). A few of the marine forms such as kelps, form massive plant
bodies.
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative reproduction is by fragmentation. Each fragment develops into
a thallus. Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated
(motile) and on germination gives rise to new plants. Sexual reproduction
takes place through fusion of two gametes. 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. Fusion of two gametes dissimilar in size, as in species of
Eudorina is termed as anisogamous. Fusion between one large, non-
motile (static) female gamete and a smaller, motile male gamete is termed
oogamous, e.g., Volvox, Fucus.
2020-21
PLANT KINGDOM 31
Figure 3.1  Algae : (a) Green algae   (i) Volvox         (ii) Ulothrix
(b) Brown algae  (i) Laminaria   (ii) Fucus      (iii) Dictyota
(c)  Red algae     (i)  Porphyra    (ii) Polysiphonia
2020-21
32 BIOLOGY
Algae are useful to man in a variety of ways. At least a half of the total
carbon dioxide fixation on earth is carried out by algae through
photosynthesis. Being photosynthetic they increase the level of dissolved
oxygen in their immediate environment. They are of paramount
importance as primary producers of energy-rich compounds which form
the basis of the food cycles of all aquatic animals. Many species of Porphyra,
Laminaria and Sargassum  are among the 70 species of marine algae
used as food. Certain marine brown and red algae produce large amounts
of hydrocolloids (water holding substances), e.g., algin (brown algae) and
carrageen (red algae) which are used commercially. Agar, one of the
commercial products obtained from Gelidium and Gracilaria are used to
grow microbes and in preparations of ice-creams and jellies. Chlorella a
unicellular alga rich in proteins is used as food supplement even by space
travellers. The algae are divided into three main classes: Chlorophyceae,
Phaeophyceae and Rhodophyceae.
3.1.1 Chlorophyceae
The members of chlorophyceae are commonly called green algae. The
plant body may be unicellular, colonial or filamentous. They are usually
grass green due to the dominance of pigments chlorophyll a and b. The
pigments are localised in definite chloroplasts. The chloroplasts may be
discoid, plate-like, reticulate, cup-shaped, spiral or ribbon-shaped in
different species. Most of the members have one or more storage bodies
called pyrenoids located in the chloroplasts. Pyrenoids contain protein
besides starch. Some algae may store food in the form of oil droplets.
Green algae usually have a rigid cell wall made of an inner layer of cellulose
and an outer layer of pectose.
Vegetative reproduction usually takes place by fragmentation or by
formation of different types of spores. Asexual reproduction is by
flagellated zoospores produced in zoosporangia. The sexual reproduction
shows considerable variation in the type and formation of sex cells and it
may be isogamous, anisogamous or oogamous. Some commonly found
green algae are: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara
(Figure 3.1a).
3.1.2 Phaeophyceae
The members of phaeophyceae or brown algae are found primarily in
marine habitats. They show great variation in size and form. They range
from simple branched, filamentous forms (Ectocarpus) to profusely
branched forms as represented by kelps, which may reach a height of
100 metres. They possess chlorophyll a, c, carotenoids and xanthophylls.
They vary in colour from olive green to various shades of brown depending
upon the amount of the xanthophyll pigment, fucoxanthin present in
2020-21
PLANT KINGDOM 33
them. 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. The
protoplast contains, in addition to plastids, a centrally located vacuole
and nucleus. 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. Vegetative reproduction takes place by fragmentation. Asexual
reproduction in most brown algae is by biflagellate zoospores that are
pear-shaped and have two unequal laterally attached flagella.
Sexual reproduction may be isogamous, anisogamous or oogamous.
Union of gametes may take place in water or within the oogonium
(oogamous species). The gametes are pyriform (pear-shaped) and bear
two laterally attached flagella. The common forms are Ectocarpus, Dictyota,
Laminaria, Sargassum and Fucus (Figure 3.1b).
3.1.3 Rhodophyceae
The members of rhodophyceae are commonly called red algae because of
the predominance of the red pigment, r-phycoerythrin in their body. Majority
of the red algae are marine with greater concentrations found in the warmer
areas. 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.
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.
The red algae usually reproduce vegetatively by fragmentation. They
reproduce asexually by non-motile spores and sexually by non-motile
TABLE 3.1 Divisions of Algae and their Main Characteristics
Classes Common Major Stored Cell Wall Flagellar Habitat
Name Pigments Food Number and
Position of
Insertions
Chlorophyceae Green Chlorophyll Starch Cellulose 2-8, equal, Fresh water,
algae a, b apical brackish water,
salt water
Phaeophyceae Brown Chlorophyll Mannitol, Cellulose 2, unequal, Fresh water
algae a, c, laminarin and algin lateral (rare) brackish
fucoxanthin water, salt
water
Rhodophyceae Red Chlorophyll Floridean Cellulose, Absent Fresh water
algae a, d, starch pectin and (some),
phycoerythrin poly brackish
sulphate water, salt
esters water (most)
2020-21