Download PLANT KINGDOM Chapter 3

PLANT KINGDOM
Chapter 3
PLANT KINGDOM
-ve
Prerequisites
Learning Objectives
3.1 Algae
3.2 Bryophytes
3.3 Pteridophytes
3.4 Gymnosperms
3.5 Angiosperms
3.6 Plant Life Cycles and Alternation of
Generations
Summary
PREREQUISITES
Our earth is bestowed with immense biological diversity having evolved during nearly 3.5 billion years
of life on earth. The plant kingdom comprises more than 400,000 different kinds of plants occupying
different habitats throughout the world.
On account of their diversity and the large number of organisms, it became necessary to
classify them into different groups.
To make the study of organisms easier, scientists put together similar things into groups.
This process of grouping similar things is called classification.
Wittaker(1969) suggested five kingdom classification – Monera, Protista, Fungi, Animalia and Plantae.
The present chapter deals with classification within Plantae popularly known as Plant Kingdom and
the details of each division – Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.
25
www.sciencetuts.com
PLANT KINGDOM
Let us have a glance at classification within angiosperms to
understand the concerns that influenced the classification
systems. The earliest system of classification was Artificial.
The artificial system of classification used only superficial
morphological characters such as habit, colour, number
and shape of leaves etc. They were mainly based on few
vegetative characters.
fig.3.1 Whittaker
The artificial systems gave equal weitage to vegetative and sexual characteristics; this is not acceptable,
because the vegetative characteristics are more easily affected by environment.
Later Natural Classification System was developed which were based on natural affinities among the
organisms, and considered 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 J.D. Hooker.Eichler proposed
phylogentic classification system based on evolutionary relationships between various groups.
This assumes that organisms belonging to the same taxa have a common ancestor. To resolve difficulties
in classification where there is no supporting fossil evidence, information from various sources are used by
taxonomists like
1. Numerical Taxonomy
Is now easily carried out by using computers. It is based on 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 weightage and simultaneously hundreds of characters can be considered.
2. Cytotaxonomy
It is based on cytological information like chromosome number, structure and behavior.
3. Chemotaxonomy
It uses chemical constituents of the plant to resolve confusion.
LEARNING OBJECTIVES
To understand the basis of classification in plant kingdom.
To gain knowledge about different divisions in the plant kingdom.
To know different types of life cycles and alternation of generation in plants.
26
www.sciencetuts.com
PLANT KINGDOM
INTRODUCTION
Plant kingdom
CRYPTOGAMAE
PHANEROGAMAE
ALGAE
FUNGI
ANGIOSPERMAE
GYMNOSPERMAE
THALLOPHYTA BRYOPHYTA PTERIDOPHYTA
HEPATICAE
EQUISITINAE
MUSCI
LYCOPODINAE
MONOCOTS
DICOTS
FILICINEAE
Thallophyta
(Thallos = undifferentiated; phyton – plant)
Thallus refers to a plant body, which is not differentiated into true roots, stem and leaves.
Gemma cup
Rhizoids
fig.3.2 Marchantia
fig.3.3 Marchantia
The thallus may range from microscopic unicellular to macroscopic multicellular forms. Vascular
tissues (xylem and phloem) are absent.
Sex organs are simple and mostly unicellular. If multicellular sterile envelop is absent.
Embryo is not formed. These are simplest plants.
27
www.sciencetuts.com
PLANT KINGDOM
Archegoniophore
Gemma cup
Rhizoids
fig.3.4 Marchantia
THALLOPHYTA
FUNGI
ALGAE
Algae
Chlorophyll bearing thallophytes are called “algae”. The study of algae is known as “phycology” or
“algology”.
Phykos = sea weeds
Logos = discourse
fig. 3.1.1 ALGAE
The word algae was first coined by Linnaeus.
Algae are characterised by the following features.
1.Habitat
They are predominantly aquatic and occur in marine as well as fresh water habitats. They are also
present on moist stones, soils, wood or association with fungi (lichen).
fig.3.1.2 Aquatic water
fig.3.1.3 Marine water
28
www.sciencetuts.com
PLANT KINGDOM
2. Form and size
Algae exhibit great variation in size and form. The size ranges from microscopic(0.5m diameter) unicellular forms like Chlamydomonas to motile colonial forms
like Volvox, filamentous forms like Ulothrix and Spirogyra. A few marine forms such as Kelps, form
massive plant bodies.
fig.3.1.4 ALGAE
fig.3.1.5 Unicellular
fig.3.1.6 Chlamydomonas
fig.3.1.7 Volvox
fig.3.1.8 Ulothrix
fig.3.1.9 Spirogyra
3. Nutrition
Algae are characterised by the presence of chlorophyll, hence their mode of nutrition is autotrophic.
chlorophyll
fig.3.1.10 Chloroplast
fig.3.1.11Chloroplast
4. Cell wall
Cell wall is made up of cellulose.
5. Reserve Food:
In the form of starch.
6. Reproduction:
Algae reproduces by 3 methods – vegetative, asexual and sexual methods.
29
www.sciencetuts.com
PLANT KINGDOM
Vegetative reproduction
In filamentous form the thallus breaks into pieces which can grow into new filaments.This is called
fragmentation. Each fragment develops into a thallus.
Asexual reproduction
Is by the production of different types of spores – Zoospores, Aplanospores, Akinetes, Autospores, Endospores,
Exopores, Cysts and Auxospores. The most common type of spores is zoospores. They are flagellated, motile
and naked cells produced during favourable conditions. Zoospores on germination give rise to new plants.
Sexual reproduction
Sexual reproduction occurs at the end of the growing season. It involves fusion of two gametes.
Fusion of 2 gametes is of 3 types.
a) Isogamy: The fusion of morphologically similar gametes (similar in size) is called isogamy. The
gamates can be flagellated
Eg: Chlamydomonas (or) non-flagellated, Spirogyra.
fig.3.1.12 Chlamydomonas
fig.3.1.13 Chlamydomonas
b) Anisogamy: Fusion of morphologically
dissimilar gametes (dissimilar in size) is called
anisogamy.
Eg: Species of Chlamydomonas.
fig.3.1.14 Chlamydomonas
c) Oogamy:Fusion between one large, non motile female gamete and a smaller motile male gamete
is termed as oogamous.
Eg: Volvox, Fucus.
fig.3.1.16 Fucus
fig.3.1.15 Volvox
30
www.sciencetuts.com
PLANT KINGDOM
Uses of Algae
Algae are useful to man in a variety of ways.
1. Half of the total CO2 fixation on earth is carried out by Algae – Primary producers.
2. Algae as food: They are rich in proteins, vitamins and minerals.
eg: Chlorella (high protein and lipid content), Laminaria, Sargassum; Porphyra (Soups, Salads,
Vegetables).
fig.3.1.17 Chlorella
fig.3.1.18 Laminaria
3. Fodder and fertilier: E.g. Gracilaria fed to hens
yielded more eggs. Laminaria is used as stock feed.
Spirulina when fed to fishes, poultry and cattle, their
productivity increased.Tolypothrix increase the fertility
of rice fields. Biofertilizers Spirulina – used as Manure.
Nostoc, Anabaena can fix atmospheric N2 and there
by increasing soil fertility.
fig.3.1.19 Porphyra
fig.3.1.20Gracilaria
4. Commercial products:
Algin- is extracted from cell wall of Fucus, Laminaria is used in preparation of flame proof fabrics,
plastics, paints, gauze material in surgicaldressing, soups, sauces, ice cream and as thickner in
cosmetics, textiles and pharmaceutical industry.
Algin
Sauce
Plastics
Soups
Paints
Ice-Cream
fig.3.1.21
31
www.sciencetuts.com
PLANT KINGDOM
Agar Agar – obtained from Gelidium and Gracilaria are used as culture medium for growing algae,
fungi, and bacteria. It is used in making capsules of antibiotics and as laxative.
Algae
Fungi
Capsules
Bacteria
fig.3.1.22
Carragenin: Extracted from cell wall of Chondrus, Gigartine is used in textile, leather, cosmetics and
brewing industry.
Diatomite: Is used as filter for oils and clearing solvents. It is used as insulating the boilers and blast
furnaces, making tooth paste, metal polishes and paints. Used as absorbant for nitroglycerine
in the manufacture of dynamite etc.
5. Antibiotic and Medicine: Chlorellin is obtained from Chlorella - effective against a number of
pathogenic bacteria. Extracts of Digenea, Codium – effective vermifuge. Agar Agar is used for treating
prolapsed stomach. Laminaria is modern tool for abortion. Sea weeds – effect on gall bladders,
pancreas, kidneys, uterus and thyroid glands.
6. Sewage disposal: Algae help in bacterial decomposition of sewage. E.g. Euglena, Scenedesmus.
The mineral rich water is used for irrigation and the algae can be used as manure and animal feed.
7. Algae as research material: Chlorella – used
in investigation in photosynthesis. Blue green
algae are used in studies on nitrogen fixation.
Research in genetics and cytology are carried out
in Acetabularia.
fig.3.1.23 Agar Agar
8. Soil reclamation: Blue green algae can be used to help reclaim saline and alkaline soils.
32
www.sciencetuts.com
PLANT KINGDOM
CLASSIFICATION OF ALGAE
Algae are divided into 11 classes. They are based on photosynthetic pigments, nature of storage products,
nature of cell wall components, type of flagella and details of cell structure.
They are Cyanophyceae, Chlorophyceae,Charophyceae, Euglenophyceae, Xanthophyceae,Chrysophyceae,
Bacilleriophyceae, Phaeophyceae, Pyrrophyceaes, Cryptophyceae and Phodophyceae.
Chrysophyceae
Cyanophyceae
Euglcnophyceae
Xanthophycase
Chlorophyceae
fig.3.1.24
The main classes
Chlorophyceae
Rhodophyceae
Phaeophyceae
CHLOROPHYCEAE
1. The members of chlorophyceae are commonly known as green algae.
2. They are mostly aquatic fresh as well as marine.
3. The plant body may be unicellular, colonial or filementors.
33
www.sciencetuts.com
PLANT KINGDOM
fig.3.1.25 Volvox
fig.3.1.26 Aquatic water
fig.3.1.27 Bacteria
4. Photosynthetic pigments are chlorophyll a, chlorophyll b, carotene and xanthophyll. The
chloroplasts may be discoid, plate like, reticulate, cup shaped, spiral, or ribbon shaped.
5. Usually green algae have rigid cell wall made of an inner layer of cellulose and outer layer of
pectose.
6. The reserve food is stored in the form of starch. Most of the member have storage bodies called
pyrenoids located in the chloroplasts. Pyrenoids contain protein. Some algae store food in the form of
oil droplets.
7.Reproduction
a) Vegetative reproduction: Takes place by fragmentation.
b) Asexual reproduction: Takes place by means of spores called zoospores produced in zoosporangia. They
are associated with 2 or 4 whip like flagella of equal length.
c) Sexual reproduction: Is of isogamous anisogamous and oogamous
Example of Green algae Chlamydomonas, Volvox, Spirogyra, Ulothrix, Chara & Oedogonium.
fig.3.1.28 Volvox
fig.3.1.29 Chlamydomonas
fig.3.1.30 Chara
PHAEOPHYCEAE
1. The phaeophycean members are commonly called brown algae. and are found mostly in marine
habitats.
2. The degree of morphological complexity is greater (great variation in size and form). They range
from simple unbranched, filamentous form to profusely branched forms. Which may reach a height of
100m.
3.The photosynthetic pigments are chlorophyll a, b, c, carotene, xanthophyll. The brown colour of
brown algae is due to an accessory golden brown pigment called Fucoxanthin.
34
www.sciencetuts.com
PLANT KINGDOM
4.Reserve food is complex carbohydrates which is
in the form of laminarin and mannitol.
5.Fucosan vesicles are usually present in the cells.
6.The cell wall is made up of 2 layers, the outer
layer is a slimy layer and is made up of cellulose.
fig.3.1.31 Laminaria
7.Reproduction: Vegetative reproduction takes place by fragmentation. Asexual reproduction is by
biflagellate zoospores that are pear shaped and have 2 unequal laterally attached flagella.
RHODOPHYCEAE
Sexual reproduction – isogamy, anisogamy and oogamy.
Eg: Fucoxanthin, Dictyota.
1.Rhodophyta are commonly called red algae. They are called because of the presence of red
pigment, r-phycoerythrin
2.They are mostly marine.
3.The red thalli of the red algae are multicellular.
4.Photosynthetic pigments are chloroerythrin and
blue pigment phycocyanin are also present.
5.The reserve food materials are stored in the form
of Floridean starch. Which is similar to amylopectin
and glycogen in structure.
6.Flagellated cells are totally absent.
fig.3.1.32 Polysiphonia
7.Reproduction:They reproduce vegetatively by fragmentation. They reproduce asexually by non motile
sporesand sexually by non motile gametes. Sexual reproduction is oogamous and accompanied by complex
post fertilisation developments.
Eg: Polysiphonia, Porphyra.
Bryophytes
Bryophytes include the various Mosses and Liverworts that are found growing in moist shaded areas
in the hills.
Bryophytes are small group of primitive plants which are commonly called “Amphibians” of the
Plant Kingdom.
fig.13.2.1 Mosses
fig.13.2.2 Liverworts
35
fig.13.2.3 Amphibians
www.sciencetuts.com
PLANT KINGDOM
The word bryophyte (Bryon = moss, Phyton = plant) was coined by Brown. The study of bryophytesis
called Bryology.
Bryon = moss
Phyton = plant
1.Bryophytes chiefly occur in damp, shady and humid localities.
2.The plant body is a gametophyte (because it
produces gametes). It is thallus like in primitive
form (Riccia). In higher bryophytes the plant body
is differentiated into rhizoids, stem and leaves.
The stem is prostrate or erect, and attached to the
substratum by unicellular or multicellular rhizoids.
They are organs of absorption and fixation.
fig.13.2.4 Mud land
Archegoniophore
Gemma cup
Rhizoids
fig.13.2.6 Riccia-bubbling
fig.13.2.5 Marchantia
3.Nutritionally, the plant body is independent, and is the conspicuous phase of the life cycle.
4.The gametophytes lack vascular tissues – xylem and phloem.
5.Bryophytes reproduce vegetatively – tubers, gemmae, protonema etc.
fig.13.2.7 Tubers
fig.13.2.8Gemmae
fig.13.2.9 Protonema
6.Sexual reproduction is oogamous type. The sex organs are antheridia (male) and oogonia (female)
which are always multicellular.
fig.13.2.10Oogonia
fig.13.2.11 Antheridia
36
www.sciencetuts.com
PLANT KINGDOM
7. The male gametes are motile and biflagellate called antherozoids produced in male sex organ called
antheridia.
8. The female sex organ is called archegonium is flask shaped having venter and long neck. The egg
is retained with in the archegonial venter so that fertilisation is internal.
fig.13.2.13 Sporophyte
fig.13.2.12 Archegonium
9. Presence of water is necessary for fertilisation and dehiscence of sex organs. Antherozoids are released
into water where they come in contact with archegonium.
10. An antherozoid fuses with the egg to produce the zygote.
11. The zygote produces multicellular body called
sporophyte. The sporophyte is dependent on
gametophyte for nutrition
12.The sporophyte produces haploid spores which
germinate to produce gametophyte.
fig.13.2.14 Gametophyte
Economic importance
1 .Some mosses provide food for herbaceous mammals, birds and other animals.
2. Sporophytes of sphagnum (moss) provide peat, which is used as fuel.
fig.13.2.15 Sphagnum 2
fig.13.2.16 Sphagnum 3
fig.13.2.17 Sphagnum
3. As packing material for transport shipment of living material.
4. They decompose rocks and make the substrate suitable for growth of plants.
5. They form dense mats on the soil, they reduce the impart of falling rain and prevent soil erosion.
fig.13.2.18 Burren-plants-limestone-rocks
fig.13.2.19 Bryophyta in open place
37
www.sciencetuts.com
PLANT KINGDOM
Liverworts
1. The members of this class are popularly known as liverworts, since the thallus shows liver shaped
lobes.
2. They grow mostly in moist shady habitats such as banks of streams, marshy grounds, damp soil,
base of trees.
3. The gametophyte is dorsiventrally differentiated. The leafy members have tiny leaf like appendages
in two rows on the stem like structures. Ventral surface of the thallus shows unicellular rhizoids. Sex
organs develop on the dorsal surface of the leaf thallus. They are multicellular.
fig.13.2.20
fig.13.2.21 Marchantia
4. Asexual reproduction takes place by fragmentation of
thalli or by the formation of speciaised structures called
“Gemmae”. Gemmae are green, multicellular, asexual buds
which develop in small receptacles called gemma cups
located on the thalli. The gemmae become detatched from
the parent body and germinate to form new individuals.
fig.13.2.22 Marchantia
5. During sexual reproduction male and female sex organs are produced either on the same or on
different thalli.
Rhizoids
fig.13.2.23 Archegonium
fig.13.2.24
6. Water is essential for fertilisation.
7. The sporophyte is simple capsule in primitive forms
(Riccia) or may be distinguished into foot, seta and
capsule (Marchantia). The sporophyta lacks columella.
The endothecium produces sporogenous tissue.
Spores are produced with in the capsules. These
spores germinate to form independent gametophytes
[male gametophyte \ female gametophyte]. Sporophyte
is entirely parasitic on the gametophyte
ex: Riccia, Marchantia.
38
fig.13.2.25 Marchantia
fig.13.2.26 Riccia
www.sciencetuts.com
PLANT KINGDOM
Mosses
1. The class bryopsida includes advanced bryophyte commonly called as mosses.
2. The plant body is gametophyte (it is differentiated into axis leaves and rhizoids). It consists of 2
stages.
fig.13.2.27 Moses
fig.13.2.28 Gametophyte
3. The gametophyte is distinguished as branched
prostrate filamentous juvenile stage called protonema.
The protonemal stage is transitory. It develops directly
from spores.
4. The second stage is erect, leafy shoot called
gametophore. It develops from secondary protonema
as a lateral bud. They consist of slender, upright are
bearing spirally arranged leaves. The gametophore
is persistent. They are attached to the soil through
multicellular and branched rhizoids. This stage bears
sex organs.
fig.13.2.29 Livewort life cycle
5.Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema.
6.In sexual reproduction, sex organs antheridia and archegonia are produced at the apex of leafy
shoots.
fig.13.2.30 Marchantia
fig.13.2.31 Protonema
After fertilisation, the zygote develops into a sporophyte, consisting of foot, seta and capsule. The
capsule contains spores. Spores are formed after meiosis eg: Funaria, polytrichum.
fig.13.2.32 Funaria
fig.13.2.33 Polytrichum
39
www.sciencetuts.com
PLANT KINGDOM
Pteridophytes
Pteridophyta is considered as highly evolved group of Cryptogams. The protonemal a special position
as the first land plants. The ptetidophytes are also called vascular cryptogams as they possess xylem
and phloem. Thus they are included as first group in tracheophyta. Pteridophytes are nicknamed as
“botanical snakes”.
fig.3.3.2 Pholem
fig.3.3.1 Xylem
Pteridophytes
They are characterised by the following features.
1. Pteridophytes are found in cool, damp, moist and shady places.
2. The plant body is a sporophyte and is differentiated into true root, stem and leaves.
fig.3.3.3 True root
fig.3.3.4 Stem
fig.3.3.5 Leaves
3. The root system is of adventitious type.
4. The stem may be aerial or rhizomatous.
5. The organs possess well differentiated vascular tissues.
6. The leaves are small (microphylls) as in scalaginella or large (macrophylls) as in ferns.
7. The sporophytes bear sporangia that are subtended by leaf like appendages called sporophylls.
The sporophylls may form distinct compact structure called stobili or cones (selaginella, Equisetum).
fig.3.3.6 Selaginella
fig.3.3.7 Equisetum
40
www.sciencetuts.com
PLANT KINGDOM
8. The sporangia produces spores which produce free living photosynthetic, thalloid gametophytes
called prothallus. The gametophyte bear sex organs called antheridia and archegonia.
9. Water is essential for transfer of antherozoids. The male gametes released from Antheridia to the
mouth of Archegonia.
10. Fusion of male gamete with the egg present in the archegonium result in the formation of zygote.
Zygote produces sporophyte which is dominant phase.
11. In pteridophytes of all the spores are of similar kind. They are called homosporous.Selaginella
and saleria produce two kinds of spores – macro (large) micro (small) spores – heterosporous.
Megaspores and microspores germinate and give rise to female and male gametophytes. The
development of the zygote into young embryos take place within the female gametophyte. This event
is a precursor to the seed habit, considered an important step in evolution.
Pteridophytes
Psilopsida (Psilotum)
Lycopsida (Lycopodium, Selaginella)
Sphenopsida (Equisetum)
Steropsida (Pteris, Adiantum)
Gymnosperms
Gymnosperms are seed bearing plants (gymnous = naked; sperma = seed).
gymnos = naked
sperma = seeds
The ovules are not exposed by ovary wall and remain exposed.
Thus they occupy intermediate position between pteridophytes and angiosperms.Gymnosperms are
the primitive seed plants gymnosperms are characterized by the following features.
1. Most of the genera are entirely extinct and only few are living.
2.Generally the x gymnosperms are xetrophytes.
3.They are predominantly woody plants – few are climbers.
4.The sporophytic plant is evergreen the tallest living gymnosperm is sequoia.
5.The roots are generally tap roots, Roots in some genar have fungal association in the form of
Mycorrhiza(pinus) while in cycas, the roots are called corolloid roots and are associated with N2 fixing
cyanobacteria.
41
www.sciencetuts.com
PLANT KINGDOM
fig.3.4.1 Mycorrhiza (Pinus)
fig.3.4.2 Cycas
6. The stems are unbranched – Cycas, branched – Pinus.
7. The leaves may be simple or compound. Cycas – pinnate leaves. The leaves are well adapted to
withstand extremes of temperature, humidity and wind. Conifers – needle like leaves reduce the surface area. Thick cuticle and sunken stomata reduce water loss.
8. Gymnosperms are heteroporous. They produce haploid microspores and megaspores. The spores
produced within sporangia are arranged spirally along an axis to form compact strobili or cones
The strobili bearing microsporophylls and microporangia are called male strobili. The microspores
develop into male gametophyte which is reduced called pollen grain. The development of pollen
grains take place within microsporangia.
The cones bearing megasporophylls with ovules are called female strobili. The ovules borne on
megasporophylls may be clustered to form female cones. Megaspore mother cell divides meioticelly
to form 4 megaspores. One of the megaspore enclosed within the megasporangium develops into
female gametophyte that bears 2 or more archegonia or female sex organs. The female gametophyte
is also retained within megasporangium.
The gametophytes remain within the sporangia retained on the sporophytes. The pollen grain is
released from the microsporophytes. They are carried by air currents and come in contact with the
opening of the ovules borne on megasporophylls.
The pollen tube carrying the male gametes grow towards archegomia in the ovules and discharge
their contents near the mouth of archegonia. After fertilization, zygote developes into an embryo and
ovules into seeds. Seeds are exposed.
Angiosperms
Angiosperms constitute highly advanced plants which dominate the present vegetation. As the name
indicate, in angiosperms, the ovules and seeds are enclosed in a sac like structure called ovary (fruit)
(angio = sac; sperma = seed)
fig.3.5.1
fig.3.5.2 Coconut
42
www.sciencetuts.com
PLANT KINGDOM
The angiosperms exhibit the following features
1. Angiosperms are large group of plants occurring in wide range of habitate and their size varies
from tiny wolfia to tall trees – Euclayptus
2. The sporophyte is the dominant phase of life history. It is differentiated into root, stem and leaf.
fig.3.5.3 Euclayptus
fig.3.3.4 True root
fig.3.3.5 Stem
fig.3.3.6 Leaves
3. The leaves show distinct venation.
4. Vascular tissues are well developed.
fig.3.5.7
fig.3.5.8
5. Distinct secondary growth is seen.
6. Sexual reproduction is carried out by flowers which may be unisexual or bisexual.
Corolla
Androecium
Calyx
Gynoecium
fig.3.5.9 Parts of flower
7. Androecium and gynoecium are essential sex
organs. They are surrounded by non-essential
organs like calyx and corolla.
8. Pollen grains are produced by anthers of the
stamen. Pollen grain is the male gametophyte.
Female Sex organ is pistil. Pistil consists of ovary
with ovules.
Anther
Pollen grains
Stamen
Pistil
Overy
Ovule
fig.3.5.10
43
www.sciencetuts.com
PLANT KINGDOM
9. Within the ovule, the female gametophyte or embryo
sac is produced (haploid). Embryo sac has v3 celled egg
apparatus – one egg cell and 2 synergids, 3 antipodal
cells and 2 polar nuclei. This is termed as “Pollination”.
The pollen grains germinate on the stigma and the
resulting pollen tubes grow through style and reach
ovule. The pollen tube enters embryo sac where 2 male
cell to form zygote.
Antipodals
Polar nuclei
Synergids
fig.3.5.11
Zygote
Embryo
fig.3.5.12
The other male gamete fuses with diploid secondary nucleus to produce triploid primary endosperm
nucleus.Because of the involvement of 2 fusions this event is termed as double fertilisation.The
zygote develops into embryo and primary endosperm nucleus develops embryo.
The synergids and antipodals degenerate after fertilisation. The ovules develop into seeds and the
ovaries develop into fruit.
10. Pollination is indirect as ovules are enclosed in ovary.
11. The male gametes are non motile.
Egg
male Gametes
Zygote
Gametes
fig.3.5.13
44
www.sciencetuts.com
PLANT KINGDOM
12. Water is not essential for fertilisation.
13. Angiosperms are characterized by double fertilization and triple fusion.
14. Endosperm is the post fertilized product and is triploid.
15. As a result of post fertilization changes fruit formation takes place. Fruit encloses seeds.
Angiosperm includes 2 classes - Dicotyledons and monocotyledons
Dicotyledons
Bean, Sun flower.
fig.3.5.14 Bean
fig.3.5.15 Sun flower
1. Two cotyledons are seen in the seed.
2. Root system is tap root.
3. Leaves show reticulate venation.
4. Flowers are tetramerous or pentamerous
Class dicotyledonae is divided into 3 groups.
a.Polypetalae
fig.3.5.16 Soy taproot
b.Gamopetalae
c.Monochlamydae
Monocotyledons
Monocotyledons: eg Rice, wheat, sugarcane.
fig.3.5.17 Wheat
fig.3.5.18 Rice
fig.3.5.19 Sugarcane
1. Single cotyledon is seen in the seed.
2. Root system is of adventitious types.
3. Leaves are with parallel venation.
4. Flowers are trimerous.
45
www.sciencetuts.com
PLANT KINGDOM
Plant Life Cycles and Alternation of Generations
The sequence of events through which an organism passes from zygote to the zygote of the next
generation constitutes its life cycle
Spore
Zygote
Diploid (2N)
Meiosis
Haploid
gametophyte
Metosis
Fertilization Haploid (N)
male
Female
Gametes Gametes
Egg cell
Diploid
sporophyte
Spores
Fertilization
Embry
Meito
osis
o
sis
Meit
Sperm cell
Gametophytes
Female
2n
Male 2n
Haplonic Life cycle
Haplo-diplontic Life cycle
Microspore
mother cell
Anther
Stigma
Style
Microsporangium
Filmate
Flower
Megaspore
mother cell
Overy
Sporophyte
Megasporegium
(Ovule)
Microspore
gemetophytic
(n)
Generation
Sporophytic
(2n)
Generation
Microspore
(pollen gain)
Embro
Male
gamectophyte
Zygote
Egg
Diplontic Life cycle
fig.3.6.1
The haploid plant produces gametes by mitosis. This plant body represents gametophyte. After
fertilization, zygote divides by mitosis to produce diploid sporophytic plant body haploid spores are
produced by meiosis and form haploid plant body once again.
Thus during life cycle of sexually reproducing plant, haploid gametophyte and spore producing diploid
sporophyte.
Life cycles are of following types
1.Haplontic Life cycle
Sexual reproduction always involves cyclic alternation between a haploid and a diploid condition.
Towards the end of growing season, the gametophyte plant. Plant produces gametes. The gametes
fuse to form zygote.
46
www.sciencetuts.com
PLANT KINGDOM
Zygote
The zygote undergoes meiosis producing 4
haploid spores. The spore germinates to produce
gametophyte plant.There is alternation between a
prolonged haploid vegetative gametophyte plant
and a single called diploid zygote. Such a life cycle
is called haplontic life cycle. It is primitive type
characterised by zygote meiosis.
Diploid (2N)
Metosis
Fertilization Haploid (N)
male
Female
Gametes Gametes
Spores
Meito
osis
sis
Meit
Gametophytes
fig.3.6.2 Haplontic Life cycle
Eg: spirogyra, chlemydomonas and oedogonium
fig.3.6.3 chlemydomonas
fig.3.6.5 oedogonium
fig.3.6.4 spirogyra
2.Diplontic Life cycle
e.g. all seed bearing plants
The diploid sporophyte is the dominant phase in the life cycle, the sex organs produce gametes. The
haploid condition is limited to the gametes alone. The gametophyte is represented by haploid cells,
the gametes only. The sporophyte plant in the life cycle alternates with a few haploid cells called the
gametes. Such a life cycle is called diplontic life cycle.
Haplo – diplontic Life cycle: eg: Bryophytes and pteridophytes exhibit an intermediate condition
called heplodiplontic. Both phases are multicellular and often free living. They differ in their dominant
phases.
Anther
Stigma
Microspore
mother cell
Style
Microsporangium
Filmate
Flower
Overy
Sporophyte
Megasporegium
(Ovule)
Sporophytic
(2n)
Generation
Embro
Spore
Meiosis
Haploid
gametophyte
Microspore
Megaspore
mother cell
Egg cell
Diploid
sporophyte
gemetophytic
(n)
Generation
Microspore
(pollen gain)
Male
gamectophyte
Sperm cell
Fertilization
Embry
o
Female
2n
Male 2n
fig.3.6.7 Haplo-diplontic Life cycle
fig.3.6.6Haplo-diplontic Life cycle
47
www.sciencetuts.com
PLANT KINGDOM
A dominant independent photosynthetic, thelloid or exact phase is represented by haploid
gametophyte and it alternates with short lived multicellular sporophyte totally or partially dependent on
the gametophyte for its anchorage and nutrition.
E.g. Bryophytes
A diploid sporophyte is represented by dominant,
independent, photosynthetic vascular plant body.
It alternates with multicellular, autotrophic
independent but short lived haploid gametophyte.
Eg: Polytrichum
fig.3.6.8 Polytrichum
Algae are generally haplontic; Ectocarpus,polysiphonia, kelps are haplo-diplontic.fucus is diplontic.
fig.3.6.9 Fucus
SUMMARY
Plant kingdom includes algae, bryophytes, pteridophytes gymnosperms and angiosperms.
Algae are chlorophyll bearing simple, thalloid, autotrophic, aquatic organisms.
Depending up on the type of pigmentation, cell wall components, resume food, flagella and cell
structure, algae are classified into many class
Chlorophyceae, Rhodophyceae and Phaeophyceae etc.,
Algae reproduce vegetatively by fragmentation, asexually by spores and sexually by gametes.
Isogamy, Anisogamy and Oogamy.
Bryophytes are land plants but depends on water for reproduction.
The plant body is differentiated and possess root – like, stem – like and leaf – like structures.
They are divided into liverworts and mosses.
The plant body of liverworts is thalloid and dorsiventral whereas mosses have upright, slender axes
bearing spirally arranged leaves.
The main plant body of a bryophyte is gamete producing and is called gametophyte.
It bears antheridia and archegonia.
The gamets fuse to forms zygote which produces multicellular body called sporophyte.
48
www.sciencetuts.com
PLANT KINGDOM
It produces haploid spors. Spores germinate to form gametophytes.
In pteridophytes – plant body is sporophyte and is differentiated into root, stem and leaves.
Vascular tissues are well developed. The sporophytes bear sporangia which produces spores.
The spores germinate to form gametophyte.
The gametophyte bears sex organs – Antheridia and Archegonia. Water is essential for festilisation.
The zygote formed after fertilization produces sporophyte.
In Gymnosperms ovules are naked. After fertilisation seeds remain exposed so they are called naked
seeded plants.
The microspores and megaspores produced in the respective sporangia are borne on sporophylls.
The micro and megasporophylls are spirally arranged to form male and female cones.
The pollen grain germinates and pollen tube releases male gamete into the ovule.Where it fuses with
egg cell in archegonia.
Zygote developes into embryo and ovules into seeds.In angiosperms flower is the reproductive part
with stamen and pistil.
The anther produces pollen grains (male gametophyte). Pistil consists of ovary enclosing many
ovules. Ovule is the female gametophyte which contains egg cell. Pollen tube enters embryo sac and
releases two male gamets.
One male gamete fuses with egg cell (syngamy) and other fuses with diploid secondary nucleus
(triple fusion).
This phenomenon of two fusions is called double fertilization.Angiosperm is divided into 2 classesDicots and monocots.
During the life cycle of a sexually reproducing plant, there is alternation of generations between
gamete producing haploid gametophyte and spore producing diploid sporophyte.
Different plant groups show different patterns of life cycles – haplontic diplontic or haplodiplontic.
49
www.sciencetuts.com