2- SEXUAL REPRODUCTION IN FLOWERING PLANTS
CHAPTER NO.2 SEXUAL REPRODUCTION IN
FLOWERING PLANTS
A5
SIMPLIFIED LEARNING MATERIAL
SEXUAL REPRODUCTION:-
Sexual reproduction is the process of development of new organisms through the
formation and fusion of gametes. Gametes are not directly formed by the
sporophytic structures of flowering plants. Instead, they produce spores and
then gametophytes. The organs specialized to perform sexual reproduction in
angiosperms are flowers.
FLOWERS-Flowers
are specialized condensed shoot of an angiospermic plant in which the shoot
apical meristem gets transformed into floral meristem for carrying out sexual
reproduction through progressive specialization of leaves into floral
appendages.Like a branch, it may develop in the axil of small leaf like
structure
called bract.Flowers are formed over mature plants
in response to hormone induced
structural and physiological changes in shoot
apices. Shoot apices are transformed into an inflorescence over which floral
primordia develop.The primordia grow into floral buds which undergo anthesis
(opening of floral bud) and form flower. A typical flower has a broad base or
thalamus over which are born four whorls of floral parts:---
1.SEPALS-Sepals
constitutes the lower accessory whorl or outermost series of green flattened or
foliaceous floral organs which are mainly meant for protecting other floral
parts in the bud condition. The sepals having colour other than green are
called petaloid.
2.PETALS-Petals
constitutes the upper or inner series of accessory floral organ which are leaf
like flattened but brightly coloured to attract pollinating organisms. Petals
with greenish Tinge is called sepaloid.
3.STAMENS-
A stamen or male reproductive organ of flower is made up of two parts -a stalk
like filament and knob like terminal anther.
4.CARPELS-Carpels
are female parts of a flower develop from the central region of thalamus. A
flower may have one or more carpels. They may be free or fused. The free
occuring unit of gynaecium is called pistil. Pistil is flask shaped structure.
It has basal swollen ovary, stalk like style and a terminal receptive part
called stigma. Ovary has one or more chambers or loculi.
The sepals and petals are accessory or non essential
floral organs as they have only supportive role.Stamens and carpels are called
essential floral organs as these are the reproductive structures of flower.
LET US KNOW WHAT WE LEARNT ?
(A)VERY SHORT ANSWER TYPE QUESTIOS:
MCQs:-----
1. Coloured sepals are known as
a) petals
b)petaloid
c)sepaloid
d)none of the above
Ans. (b)
(The sepals other than green coloured are known as
petaloid).
2. Stamens Consists Of Filament And
a) anther
b) stigma
c) style
d) pollen grains
Ans- (a) anther
3. Stamens are the:
a) accessory whorl
b) essential whorl
c) both a and b
d) none of these
Ans-(b)
(Stamens and carpels take part in formation of
gametes,thus known as essential whorl).
4.Broader base of flower is known as
(a) thalamus
(b)pedicel
(c) anther
(d) pistil
Ans-(a)
(Broaderbase of the flower is thalamus to which
other parts are attached)
5.Flower is a modified
(a) root
(b) leaf
(c) shoot
(d) none of the above
Ans-(c)
(Flower is a modified shoot meant for sexual
reproduction)
Fill ups:-----
1. Sticky part in the pistil is called.......
Ans - Stigma
2. w+. IS a modified shoot meant for sexual
reproduction.
Ans- Flower
True/False:-----
1. Atypical flower has three whorls.
Ans-False (A typical flower has for whorls sepals,
petals,stamens and carpels).
2. A flower may have one or more carpels.
Ans-True (A flower may consists of one or more carpels)
3.Green petals are known as petaloid.
Ans-False (Because green petals are known as
sepaloid).
(B) SHORT ANSWER TYPE QUESTIONS:
1. Write short note on parts of a flower.
2. What are essential floral organs?
(C) LONG ANSWER TYPE QUESTIONS:
1. Draw a well labelled diagram of a typical
bisexual flower. Also discuss different parts of flower.
A6
STAMEN-
Stamen is male reproductive organ or microsporophyll of a flower. It consists of two parts filament and anther.Filament is long and slender stalk. It is attached proximally to thalamus,petals or tepals. Distally it bears an anther.
Anther is a a broader knob like a fertile part of stamen. It
consists of generally two lobes. The two anther lobes are separated in the
anterior
region by a deep groove but are attached to each
other on the back side by sterile Parenchymatous tissue called connective.
Connective possesses a vascular strand.
STRUCTURE OF ANTHER
It is bilobed tetragonal oblong knob like fertile
part of stamen. Each anther lobe has 2 chambers. The two chambers of an anther
lobe possess long and cylindrical pollen sacs or microsporangia. Thus a
bilobed anther is tetrasporangiate. Rarely, an
anther lobe has only one microsporangium for example Wofia. The four
microsporangia of an anther lie at its four corners. They run parallel to one
another.All microsporangia are covered by well defined common epidermis. The
cells of epidermis become stretched and shrivel off at maturity. The
microsporangia develop hypodemally in anther from. strips of
archesporial cell that is development of
microsporangium is eusporangiate. The archesporial cells divide Periclinally to
form outer subepidermal parietal cells and inner sporogenous cells. The
parietal
cells divide further by periclinal walls to produce
a 3-5 layered microsporangial wall consisting of endothecium,middle layer and
tapetum.
MICROSPORANGIUM:Microsporangium
or future pollen sac is a cylindrical sac which appear circular in transverse
section. It consists of two parts outer wall and
Central homogenous sporogenous tissue.
Microsporangia wall has four types of
layers epidermis,endothecium, middle layer and tapetum. The outer 3 perform the
function of protection in the young anther and mechanism of dehiscence in the
ripe anther.
TAPETUM:Tapetum
is of two types amoeboid and secretory. In amoeboid type the
tapetal cells fuse to form a plasmodium or
Periplasmodium because it passes in between thesporogenous tissue to nourish
them. The cells of secretory pass out substances over the sporogenous cell for
their growth and differentiation. Ultimately both the types of tapetum
degenerate.
FUNCTIONS
OF TAPETUM:
1 Nourishment of developing microspore mother cell
and pollen grains.
2 It produces lipids rich ubisch granules containing
sporopollenin for exine formation, pollen kit in case of entomophilous pollen
grains,special proteins for the pollen grains to recognise compatibility and
hormone IAA.
3. It secretes enzymes like callase responsible for
the degradation of
callose around for pollen tetrad.
MICROSPOROGENESIS:Sporogenous
tissue fills the whole interior of a microsporangium. Its cell divide with the
growth of anther and increase their number.Ultimately they are transformed into
microspore or pollen mother cell (MMC) or (PMC). The latter are diploid that is
they possess two sets of
chromosomes. The microspore mother cell or
microsporocytes develop an internal layer of callose which breaks the
plasmodesmal
connections among them.
The separated mother cells
round off and undergo meiosis to produce tetrads of haploid microspores or
pollen grains. The phenomenon is
called microsporogenesis. The pollen grains or
tetrad grow and separate from one another. Usually the arrangement of
microspore in a tetrad is tetrahedral or isobilateral.
Let us know what we learnt?
(A)VERY SHORT ANSWER TYPE QUESTIONS
1.Which part of the flowering plant contain
sporogenesis tissue
a) stamen
(b) Pollen
(c) microspores
(d) young anthers
2. The cells of which layer provide
nourishment to the the microscope
(a) middle layer
(b) tapetum
(c) endothecium
(d) epidermis
3. Development of pollen grains is known as
(a) microsporogenesis
(b) microgametogenesis
(c) both a and b
(d)none of a and b
4.Tetrad of pollen grain have internal
layer which break the plamodesmal connection is
(a) Callose
(b) tapetum
(c) middle layer
(d) none of above
5.Pollen Mother Cell Give Rise To
(a) two pollen grains
(b) 4 pollen grains
(c) 5 pollen grains
(d) tree pollen grains
Fill ups
1. Archesporial cell divides into parietal and.............
2. ........ outermost layer of anther.
True/False
1.Tapetum degenerate in ripened anther.
2.Epidermis provide protection to the Sporogenous
tissue.
3.PMC cell give rise to four microspores.
ANSWER KEY (Part A)
1.d (Sporogenous cells are present in an anther
which give rise to pollen grains).
2 .b (The main function of the tapetum is to provide
nourishment to the pollen grains).
3.a (The phenomenon of formation of pollen grains is
known asmicrosporogenesis).
4.a (callose deposited between the microspores and
break down the
connections).
5.b (Pollen mother cells divide meiotically to
produce four pollen grains)
Fill ups
1.Sporogenous cells 2.epidermis
True/False
1.True (At the time of dehiscence of anther tapetum
also degenerate in mature anther).
2.True (Epidermis is the outermost layer which
provide protection to the sporogenous cells).
3.True(PMC divide meiotically to give rise to four
microspores.)
(B)SHORT ANSWER TYPE QUESTIONS
1. Draw well labelled diagram of stamen.
2. Write a short note on microsporogenesis.
3.What are functions of tapetum?
(C) LONG ANSWER TYPE QUESTIONS
1. Write a note on microsporangium.
2. Discuss the structure of anther.
A7
SIMPLIFIED LEARNING MATERIAL
MICROSPORES AND POLLEN GRAIN:Microspore is single
celled microscopic structure with dense cytoplasm and uni-nuclear. Pollen grain
develops from a microspore. Pollen grain has 2-3 cells in it.The mature pollen
grain has large vegetative or tube cell and a small generative cell.
STRUCTURE OF POLLEN GRAIN:It
is commonly globular in outline, though several other shapes are also found.
The diameter is 25-50 pmeter. There is highly resistant wall on the outside and
cellular contents inside. It has two layers outer exine and inner intine.Intine
is pectocellulosic in nature. Exine is made up of a highly resistant fatty
substance called sporopollenin. It is not degraded by any enzyme.
The study of external morphology of mature pollen
grain is called PALYNOLOGY.
POLLEN VIABILITY:It
is the period for which pollen grains retain the ability to germinate. It is 30
minutes in rice and wheat. In others the period of viability is long even
months in some members of family rosaceae. Pollen viability depends upon
environmental conditions of temperature and humidity.It is possible to store
pollen grains for years in liquid nitrogen (-196° C) in pollen banks for later
used in plant breeding programmes.
POLLEN ALLERGY:Pollen
grains are produced in large number ,especially in anemophilous
flowers.They float in air and enter respiratory
tract.Some individuals
develop allergy to them,producing respiratory
disorders like rhinitis,asthma and bronchitis(Bronchial allergy-hay fever)
POLLEN PRODUCTS:The
pollen grains especially the ones collected by bees are being used for a
variety of purposes like nature cure,cosmetics and as food
suplements.Pollen grains are believed to be rich in
nutrients.
STRUCTURE AND DEVELOPMENT OF OF MALE
GAMETOPHYTE (MICROGAMETOGENESIS)
Pollen grains or microspore is the first cell of male gametophyte and represent Immature male gametophyte. Development of male gametophyte is precocious that is it begins inside the microsporangium.When first formed the microspore has a centrally placed nucleus embedded in dense cytoplasm covered by plasma membrane. The
protoplast divides mitotically to form two unequal
cells-small generative cell and large tube or vegetative cell.
The tube cell has a vacuolate cytoplasm which is
rich in the food reserves and cell organelles. Its nucleus become large and
irregular.The generative cell is spindle shaped to spherical in outline with in
dense cytoplasm surrounding a prominent nucleus. In some species the generative
cell divide into two non motile male gametes prior to the dehiscence of anther
and release of pollen grains. Therefore at the time of pollination the pollen
grain is either two celled-(tube cell+generative
cell) or three celled-(tube cell+two male gametes).
Let us know what we learnt?
(A)VERY SHORT ANSWER TYPE QUESTIONS
MCQs
1.Pollen grains can be stored for longer
period at
a) 100°C
(b) -196°C 1
(c)-37°C
(d)- 200°C
2. Pollen grains may cause
(a) Hay fever
(b) Enteric fever
(c) pneumonia
(d) Cholera
3. Development of Male gametophyte is known
as
(a) microsporogenesis
(b) microgametogenesis
(c) both a and b
(d)none of a and b
4.Microspore mother cell divides into
(a) two cells
(b) four cells
(c) five cells
(d) 6 cells
5.Pollen grain is covered by
(a)exine and intine
(b)epidermis
(c) both a and b
(d) none of above.
Fill ups
1. Pollen viability in rice and wheat
is.............
2. ...:... Outermost layer of pollen grains.
True/False
1.Exine can be degraded by enzyme
2.Pollen grains are rich in nutrients.
3.PMC cell give rise to two nonmotile male gametes.
ANSWER KEY(Part A)
1.b (pollen grains can be stored in liquid nitrogen)
2 .a (pollen grains may cause bronchitis to human
beings ,al;so known as hay fever).
3.b (The phenomenon of formation of Male gametes is
known asmicrogametogenesis).
4.b (Diploid microspore mother cell is divided
meiotically into four haploid cells).
5.a (Outer layer is exine,inner layer is intine)
Fill ups
1. 30 minutes
2.exine
True/False
1.False
(Because exine is made up of highly resistant fatty substance
sporopollenin which is not degraded by any enzyme).
2.True
3.False
(Becaue non motile gametes are formed from
generative cell)
(B)SHORT ANSWER TYPE QUESTIONS
1. Draw well labelled diagram of mature pollen
grain.
2.Write a short note on microgametogenesis.
3.What are pollen products?
(C) LONG ANSWER TYPE QUESTIONS
1.Draw well labelled diagrams of microgametogenesis.
A8
PISTIL or CARPEL:---The
female reproductive organ Gynoecium represent the female component of a flower.
It may consist of only one carpel (monocarpellary), two carpels (bicarpellary),
three carpels
(tricarpellary), or many carpels (multicarpellary).
Each carpel represents a
megasporophyll. Gynoecium is apocarpus- if the
carpels are free for example Ranunculus. It is syncarpous- if carpels are fused
for example Hibiscus,Poppy. The basal part of carpels must fuse for syncarpous
condition. Parts of styles and stigmas can be free.
The free unit of gynoecium is called PISTIL. A
pistil has three parts-STIGMA,
STYLE and OVARY.
STIGMA-Stigma
is the terminal receptive part of the pistil which function as
landing platform for the pollen grains. It also
determines the compatibility-
incompatibility of pollen grains.
STYLE-Style
is elongated narrow stalk that connects the ovary with the stigma.
OVARY-Ovary is the
basal swollen part of the pistil. It has an ovarian cavity with one or more
chambers or locules and ovule bearing parenchymatous cushions called placentae
(singular Placenta).Ovary may have one ovule for example: wheat, paddy and mango.Ovary
may also have several ovules for example: papaya, watermelon.
STRUCTURE OF A TYPICAL (AN ANATROPOUS)
OVULE: ---
Ovule is an integumented megasporangium found in
spermatophytes which develop into seed after fertilization. An angiosperm ovule
is typically an ovoid and whitish structure. It occurs inside ovary where it is
attached to the parenchymatous cushion called placenta. The ovule is stalked.
The stalk is called funiculus or funicle. The point of attachment of the body
of the ovule with the funiculus is known as hilum. In the typical
ovule(Anatropous ovule)
the funiculus is fused with the body of ovule
lengthwise beyond the hilum. It
gives rise to a longitudinal ridge called raphe.
Funiculus contains a vascular
strand for the supply of nourishment to the
ovule.The body of the ovule consists of a mass of parenchymatous cells called
nucellus. It is equivalent to megasporangium. It is surrounded by
integuments.
The integuments leave a narrow pore for
passage at one end of the ovule it
is known as micropyle. The place of origin of the
integuments usually lies at
the opposite end. It is termed as chalaza.
TYPES OF OVULES:-----
Depending upon the configuration and orientation of
the body of ovule in
relation to funiculus,there are SIX types of ovules.
1.Orthotropous ovule4t
is the simplest and primitive ovule. In this type of
ovule micropyle, chalaza and funiculus lie in
vertical plane.
2.Anatropous ovule-It
is completely inverted ovule turned back 180 degrees
on its stalk. It is typical as it is present in 82%
of Angiosperms.
3.Hemitropous ovule-tIn
this type of ovule,the body of ovule is turned through
90 degrees, micropyle and chalaza lie in straight
line.
4.Campylotropous_ovule-A
curved ovule with micropyle almost touching
funiculus.Hilum,Chalaza and Micropyle lie nearby.
5.Amphitropous ovule-A
partly inverted ovule in which both Nucellus (body)
and Embryo sac are curved.
6.Circinotropous_ovule4in
circinotropous ovule, the length of funiculus increased so it covers the whole
ovule. The body of the Ovule is turned through 360 degrees.
LET US KNOW WHAT WE HAVE LEARNT!
(A) VERY SHORT ANSWER TYPE QUESTIONS:
a) MCQs
1. In apocorpus condition the carpels are
(a)free.
(b)fused
(c) both a and b
(d) none of above
2. The part which determine compatibility-incom
patibility of pollen grain is
(a) style
(b) ovary
(c) stigma
(d) hilum
3. Nucellus is surrounded by
(a) integuments
(b)funiculus
(c) Chalaza
(d) ovary
4. The ovules are attached to ovary with
(a) placenta
(b) hilum
(c) funiculus
(d) none of the above
5. Nucellus is equivalent to
(a) microsporangium
(b) ovary
(c) ovule
(d) megasporangium
b) Fill ups
1. A narrow pore in integuments is known as........
2. Carpels are fused
in................condition.
c) True/False
1. Pistil has four parts.
2. Chalaza is opposite to the micropyle.
3. Style is the receptive part of pistil.
ANSWER KEY
MCQs:
1.a (In apocarpous condition the carpels are free
whereas in syncarpous condition carpels are fused)
2.c (Stigma is the receptive part of pistil which
determine the compatibility-incompatibility of pollen grains)
3.a (Nucellus which is equivalent to megasporangium
is surrounded by integuments)
4.a (Ovules attached to ovary with parenchymatous
cushions called placenta)
5.d (Nucellus is equivalent to megasporangium which later on develops into
embryo sac)
Fill ups:
1.Micropyle
2.Syncarpous
True/False:
1.False (Pistil has three parts that is stigma,
style and ovary)
2.True (The place of origin of integuments is
opposite to the
micropyle that is known as Chalaza)
3.False (Stigma is the receptive part of of pistil)
(B) SHORT ANSWER TYPE QUESTIONS:
1. What are apoCorpus and syncorpus pistil?
2. Define micropyle and Chalaza.
Draw a well labelled diagram of pistil.
(C) LONG ANSWER TYPE QUESTIONS:
3. Draw well labelled diagram of typical
(anatropous) ovule.
A9
INTRODUCTION
MEGASPOROGENESIS:The
process of formation of four HAPLOID megaspores from one
DIPLOID megaspore mother cell (MMC), through ME!OSIS
is called megasporogenesis.
EMBRYOSAC:Inside
the ovule, is present a mass of cells called nucellus. In the
nucellus is the embryo sac. The embryo sac is called
the female gametophyte.
MONOSPORIC DEVELOPMENT EMBRYOSAC:
The MMC megaspore mother cell, undergoes meiotic
division and forms four megaspores. In a majority of flowering plants, one of
the megaspores is functional while the other three degenerate. Only the
functional megaspore develops into the female gametophyte (embryosac). This
method of embryo sac formation from a single megaspore is termed as monosporic
development.
DEVELOPMENT OF THE FEMALE GAMETOPHYTE
The nucleus of the functional megaspore divides
mitotically to form two nuclei which move to the opposite poles, forming the
2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in
the formation of the 4-nucleate and later the 8-nucleate stages of the embryo
sac.Now 8 nucleate embryo sac is formed. These nuclear divisions do not result
in the formation of cell wall, means they are strictly free nuclear.
Cell walls are formed after 8 nuclei are formed. Six
of the eight nuclei are surrounded by cell walls and organised into cells; the
remaining two nuclei, called polar nuclei are organized in a large central
cell.
ORGANIZATION OF CELLS IN EMBRYO SAC
Three cells are grouped together at the micropylar
end and constitute the egg apparatus. The egg apparatus, in turn, consists of
two synergids and one egg cell. The synergids have special cellular thickenings
at the micropylar tip called filiform apparatus, which play an important role
in
guiding the pollen tubes into the synergid.
Three cells are at the chalazal end and are called
the antipodals.The large central cell which has two polar nuclei lies below the
egg apparatus. Thus, a typical angiosperm embryo sac, at maturity, though
8-nucleate is 7-celled.
LET US KNOW WHAT WE HAVE LEARNT!
PART(A) VERY SHORT ANSWER TYPE
QUESTIONS
a) MCQs:-
Q.1. The number of megaspores formed from
one megaspore mother cell is:
(a) 1
(b) 2
(c) 4
(d)8
Q. 2. During megasporogenesis, which
division takes place inside the
megaspore mother cell to form megaspores?
(a) mitosis
(b) meiosis
(c) both
(d) none of these
Q.3. The functional megaspore undergoes
divisions to form the embryo sac:
(a) two mitotic divisions
(b) three mitotic divisions
(c) one meiotic division one mitotic division
(d) one meiotic division two mitotic division
Q.4. The embryo sac in angiosperms has:
(a) 8 nuclei 7 cells
(b) 8 nuclei 8 cells
(c) 7 nuclei 7 cells
(d) 7 nuclei 8 cells
Q.
5. The central cell is made up of:
(a) two polar nuclei
(b) one polar nuclei
(c) egg cell and synergid
(d) two egg cells
Q. 6. The cells present towards the
chalazal end of embryo sac are:
(a) egg apparatus
(b) anti podal cells
(c) synergids
(d) polar nuclei
b) FILL IN THE BLANKS:
1. When only one megaspore out of the megaspore
tetrad develops into the female gametophyte then this type of development is
called .
2. The process of formation of from is called
megasporogenesis
3. The filiform apparatus is present in
c) TRUE/FALSE:
1. The egg apparatus is present towards the chalazal
end of the embryo sac.
2. The embryo sac of the ovule is called female
gametophyte.
3. The egg apparatus is made up of one egg cell and
one synergid.
ANSWER KEY PART (A)
a) MCQs. :—
1.c- 4, (Because megaspore mother cell undergoes
meiosis and 4
daughter cells are produced)
2. b — meiosis. (Since megasporogenesis involves
formation of megaspores and female gametes, meiosis has to take place)
3. b — 3 mitotic division. (8 nuclei are formed in embryo
sac this will take
place by 3 mitotic divisions)
4.a-8 nuclei 7 cells. (After 3 mitotic division, 8
nuclei are formed which
organize into 7 cells, 3 at micropylar end, 3 at the
chalazal end, 1 containing two nuclei at the centre. It is called central cell)
5. a — two polar nuclei. (Of the 8 nuclei formed
after 3 mitotic divisions, 3
arrange at the micropylar end, 3 at the chalazal end
and 2 are left. They
form the central cell)
6. b — antipodals. (Egg apparatus is at the
micropylar end, polar nuclei at
the centre. Synergids are part of the egg apparatus.
Those at the
chalazal end are antipodals)
b) FILL UPS:--
1. monosporic
Hint: When only one of the megaspore remain
functional and the rest three of the four degenerate then this type of
development is called monosporic development.
2. megaspores, megaspore mother cell
Hint: Megasporogenesis is formation of megaspores
from megaspore mother cell.
3. synergids
Hint: The finger like projections present in the
synergids is called filiform
apparatus.
c) TRUE/FALSE
1. False
Hint: Egg apparatus is present towards the
micropylar end
2. True
3. False
Hint: Egg apparatus is made up of one egg cell and
two synergids
PART-B SHORT ANSWER TYPE QUESTIONS
1. Define megasporogenesis.
2. What do you mean by monosporic development? Where
is it seen?
3. What is the function of synergids?
PART-C LONG ANSWER TYPE QUESTIONS
1. Describe the development of female gametophyte in
angiosperm with
suitable diagrams.
2. Describe the organization of the different cells
in the embryo sac and
write their different functions.
A10
INTRODUCTION
Pollination:
Transfer of Pollen Grains from Anther of a stamen to
the Stigma of a pistil is termed pollination.
Aided by several agencies like wind, water, and
insects.
Pollen grains shed by mature anther need to reach up
to stigma to bring about ‘Double Fertilisation’ (Characteristic of Flowering
Plants).
Successful pollination causes fruit and seed
formation leading to production of various products of commercial use.
Plays a vital role in an economy.
TYPES
Depending on the source of pollen, pollination can
be divided into three
types.
1. Autogamy:
Auto means ‘self’ and ‘gamy’ means ‘fusion’ ; so Autogamy means transfer of
pollen grains from anther to the stigma of same flower of same plant.
Also known as self pollination.
Genetically and ecologically both self-pollination.
Such flowers remain open to increase chance of
self-pollination .
Both Stamen & Carpel should mature at same time
to ensure self-
pollination.
Two Types:Chasmogamy
in Chasmogamous Flowers & Clesitogamy in
Clesitogamous Flowers
a) Chasmoqamous Flowers:
Flowers which remain open. Anthers and stigma
brought close by growth, bending or folding. Examples: Vinca, Mirabilis.
b) Clesitogamous Flowers:
Flowers which remain closed. Anthers and stigma lie
close to each other.
When anthers dehisce in the flower buds, pollen
grains come in contact with the stigma to cause pollination.
Assured self pollination; no new characters.
Cleistogamy occurs late in flowering season in plants
like Oxalis,
Balsam etc.
2. Geitonogamy:
‘Geiton’ means ‘neighbour’ & ‘gamy’ means ‘fusion’ so Geitonogamy means
transfer of pollen grains from the anther to the stigma of another flower of
the same plant.
3. Xenogamy: ‘Xeno’
means ‘stranger’ & ‘gamy’ means ‘fusion’ so
Xenogamy means transfer of pollen grains from the
anther to the stigma of
another flower of the different plant of same
species.
Also known as Cross pollination.
Genetically and ecologically both cross-pollination.
It brings genetically different types of pollen
grains to the stigma.
Cross-Pollination is generally brought out by both
Abiotic (Wind,water) as well as biotic agencies (Insects, birds, bats, snails,
etc.)
LET’S SEE HOW MUCH WE HAVE GRASPED!
(A) VERY SHORT ANSWER TYPE QUESTIONS
a) MCQs:-
1. The transfer of pollen from the anther
to stigma is called
a) Pollination
b) Fertilization
c) Adoption
d) Diffusion
2. Both chasmogamous and cleistogamous
flowers are present in
(a) Helianthus
(b) Oxalis
(c) Rosa
(d) Gossypium
3. Which of the following pollination
occurs in a closed flower?
(a) Decliny
(b) Cleistogamy
(c) Dichogamy
(d) None of these
4. Geitonogamy is
a) Both genetically and ecologically self
pollination
b) Genetically cross pollination but ecologically
self pollination
c) Genetically self pollination but ecologically
cross pollination
d) None of above
b) Fill Ups. :--
5. is another term for Cross-pollination.
6. type of pollination is advantages like evolution
of new characters.
7 flowers remain open.
c) True/ False:--
8. Pollination involves pollen grains of plants of
different species.
9. Xenogamy is carried out with the help of various
agencies.
10. Both Stamen & Carpel should mature at same
time to ensure self-pollination in Chasmogamous Flowers.
(B) SHORT ANSWER TYPE QUESTIONS
1. Write difference between Autogamy and
Geitonogamy.
2. Write a note on characters of Chasmogamous
Flowers.
(c) LONG ANSWER TYPE QUESTIONS
1. What is pollination? What are its various types
according to the source of
pollen?
Answer Key - Part-A
a) MCQs.:--
1. (a) Pollination
2. (b) Oxalis
3. (b) Cleistogamy
4. (c) Genetically self pollination but ecologically
cross pollination; Because
in geitonogamy gametes are from same plant hence
genetically self-pollination whereas two different flowers are involved hence
cross-pollination.
b) Fill Ups.:--
5. Xenogamy
6. Xenogamy; Because it involves cross of two
genetically different plants
hence possibilities of new characters for better
chances of survival are more.
7. Chasmogamous Flowers.
c) True/ False:—
8. False; Pollination involves transfer of pollen
grains of plants of same species. Because pollen grains of different species
would not be able to germinate on stigma of different plants due to
non-matching of species specific proteins on both pollen and stigma’s surface.
9. True ; Xenogamy is aided by both Abiotic (Wind,
water) as well as biotic
agencies (Insects, birds, bats, snails, etc.)
10. True; Because maturity of both Stamen &
Carpel at same time would provide enhanced chances of self-pollination in
Chasmogamous Flowers.
A11
INTRODUCTION
Pollination Recap. :--
Transfer of Pollen Grains from Anther of stamen to
the stigma of carpel or pistil is termed pollination, which is aided by several
agencies like wind, water, and animals.
What is the Need for External Agent?
Pollen grains need some agent to reach up to stigma
in XENOGAMY.
In case of xenogamy, or cross pollination different
flowers of different plants (of same species) are involved.
Hence this need becomes requirement especially in
such case.
TYPES OF POLLINATING AGENCIES:-Depending
on the nature of pollinating agency, they are categorized broadly into two
categories—ABIOTIC & BIOTIC
1. Pollination by Wind (Anemophilly) :
Transfer of pollen grains from anther to the stigma of a pistil with help of
wind is termed Anemophily.Such flowers are known as Anemophilous flowers.
CHARACTERISTICS OF ANEMOPHILOUS
FLOWERS:
Flowers are small and not so brightly
coloured.Sepals & petals are either
indistinguishable or absent.
Nectar & Odor absent (as flower need not to
attract some living organism).
Well exposed stamens (so that pollen grains can be
easily dispersed).
Pollen grains are large in number (in order to
compensate the loss during pollination) & light (so that pollen grains can
be easily carried away).
Feathery stigma (in order to trap air-borne pollen
grains).
Example — Mostly Grasses
2. Pollination by Water (Hydrophilly):
Transfer of pollen grains from anther to the stigma of a pistil with help of
water is termed Hydrophily.Such flowers are known as Hydrophillous flowers.
CHARACTERISTICS OF HYDROPHILOUS
FLOWERS:
Quite rare; limited to 30 genera mostly monocots
like Vallisneria,Hydrilla, Zostera etc.
Not all aquatic plants pollinated by water.
Such flowers have no need to attract some living
organism to pollinate hence have some characters common with Anemophilous
flowers such as:
Small sized,
dull flowers with nectar & odor absent.
Floral parts are un-wet able (in order to avoid
desiccation in water).
Pollen grains are without exine.
Stigma is long and sticky.
ll. Biotic Agencies :
Biotic agencies,animals like Insects, birds, bats, snails,humans help in pollination.
1. ENTOMOPHILLY :
Transfer of pollen grains from anther to the stigma of a pistil with help of
insects is termed Entomophily. Such flowers are known as Entomophillous
flowers.
Such flowers need to attract insects to pollinate
hence they are adapted
accordingly.
Insects get
attracted to beautiful blooms & fragrance of the flowers.
Once they
visit the flowers, the presence of nectar (food) as a reward provokes repeated
visits to same or different flowers leading to pollination.
It’s a
win-win situation for both of them; as insects get their food & flowers get
pollinated hence form a very beautiful example of mutualism.
Both can’t _
survive without each another.
Leads to
co-evolution of pollinator-plant.
CHARACTERISTICS OF ENTOMOPHILOUS
FLOWERS:
Flowers are generally large and brightly coloured.
Nectar & Odor present
Bees pollinate sweet-smelling flowers
Flies &
Beetles pollinate foul-smelling flowers (because these
mistake it for rotten meat).
Stamens and carpels are inserted (as nectaries are
mostly present deep-seated in the flower).
Pollen grains are sticky (so that pollen grains can
stick to insect body).
Sticky stigma (so that sticky pollen grains can get
attached to it).
2. ORNITHOPHILLY:
Transfer of pollen grains from anther to the stigma of a pistil with help of
birds is termed Ornithophilly. Such flowers are known as Ornithophillous
flowers.
Ornithophillous flowers being pollinated by birds,
also have to offer reward to visiting birds for pollination.
Few birds specialized for the same only can perform
ornithophilly.(Small sized birds with long beaks)Like Sun-birds & Humming
Bird (Smallest bird)
As such flowers need to attract birds to pollinate
hence they are adapted accordingly.
CHARACTERISTICS OF ORNITHOPHILOUS
FLOWERS:
Flowers
whorls are leathery & sturdy to hold weight of the bird.
Abundant
watery nectar enriched in sugars.
Brightly
coloured like red, orange, yellow etc.
Funnel shaped
corolla
Plants like Bombax, Bottle-brush, and Agave.
Bignonia etc are ornithophillous.
Let’s see how much we have grasped!
(A) VERY SHORT ANSWER TYPE QUESTIONS
a) MCQs:
1. Which of the following source of
pollination is abiotic in nature?
a) Wind
b) Birds
c) Insects
d) Bats
2. In which type of pollination, flowers
are pollinated by insects?
a) Anemophillly
b) Hydrophilly
c) Entomophily
d) Chiropterophily
3. Anemophilous flowers are:
a) Large and showy
b) With light pollen
c) With nectar
d) Having Un wet able pollen grains
4. Vallisneria shows:
a) Hydrophily
b) Anemophily
c) Entomophily
d) Ornithophily
5. In which type of pollination, flowers
are pollinated by bats?
a) Anemophillly
b) Hydrophilly
c) Entomophily
d) Chiropterophily
b) FILL UPS:
6. is term for plants pollinated by snails.
7. no. of pollen grains are produced in anemophilous
flowers.
c) TRUE/FALSE:
8. Floral parts are unwettable in case of
hydrophilous flowers.
9. Entomophilous flowers and their pollinators don’t
exhibit co-evolution.
10. Ornithophilous flowers have large amount of
sugary nectar.
(B) SHORT ANSWER TYPE QUESTIONS
1. Write a note on characters of hydrophilous
flowers.
2. Write a note on differences between anemophilous
& entomophilous
flowers.
3. What are various characters that attract insects
towards entomophilous
flowers?
(C) LONG ANSWER TYPE QUESTIONS
1. Write a note on various biotic agencies that help
in pollination.
ANSWER KEY- PART(A)
a) MCQs:
1. (a) Wind; Because rest all options are living
(birds, insects, bats) wheras
wind is non-living hence abiotic.
2. (c) Entomophily; Entomon means insects &
phily means_fusion hence entomophily is answer.
3. (b) With light pollen; Anemophilous flowers have
light pollen because
being wind-pollinated, light pollen grains can be
easily carried away by wind.
4. (a) Hydrophily; As male flowers or their pollen
are drifted by water currents to reach female flowers.
5. (c) Chiropterophily; As cheir means hand, pteros
means wing, phily means
fusion, hence Chiropterophily is correct option.
b) FILL UPS:
6. Malacophily, Malakos means soft (referred to snails),
phily means fusion,
and hence Malacophily is correct answer.
7. Large, because lots of pollen grains are wasted
in anemophily (non-directional pollination) hence in order to compensate the
loss, a large no. of pollen grains is formed in anemophilous flowers.
c) TRUE/FALSE:
8. True, In order to avoid desiccation in water.
9. False, Entomophilous flowers and their
pollinators exhibit co-evolution.
Because changing environmental conditions affect
both plant & their pollinators, hence to continue their association, both
have to evolve simultaneously hence co-evolution.
10. True, because sugary nectar serves as food for
birds.
A12
INTRODUCTION
As you all are now well known to the phenomenon of
io cliauen, Le, transfer of pollen grains from the anther of
stamen to the stigma of pistil is called
pollination.Now let us study about .° 2) “.:c05hs, GS Soe eroeean oF coe Pefor
ore pelore fae oeicexs of tar ozones,( fusion of male and female gametes)
inside the ovule.
All the events—from pollen deposition on the stigma
until pollen tubes enter the ovule, are together referred to as pollen-pistil
interaction. It is a dynamic process involving pollen recognition followed by
promotion or inhibition of the pollen. It is reaction between proteins present
over the pollen grains and the stigma.
POLLEN PISTIL INTERACTION
Pollination does not guarantee the transfer of the
right type of pollen (compatible pollen of the same species as the stigma).
Often,pollen of the wrong type, either from other species or from the same
plant (if it is self-incompatible), also land on the stigma.The pistil has the
ability to recognise the pollen, whether it is of the
right type (compatible) or of the wrong type
(incompatible).If it is of the right type, the pistil accepts the pollen and
promotes post-pollination events that lead to fertilisation.If the pollen is of
the wrong type, the pistil rejects the pollen by preventing pollen germination
on the stigma or the pollen tube growth in the style.The ability of the pistil
to recognise the pollen followed by its
acceptance or rejection is the result of a
continuous interaction between pollen grain and the pistil. This interaction is
mediated by chemical components of the pollen interacting with those of the
pistil.
EVENTS OF POLLEN PISTIL INTERACTION
Recognition of compatible pollen by the pistil.
Germination of pollen on the stigma to form pollen
tube. The pollen tube grows through the germ pores
The contents of the pollen grain move into the
pollen tube, which grows through the tissues of the stigma and style and
reaches
the ovary.
The pollen tube contains two male gametes formed
from the division if the generative cell.
Pollen tube reaches the ovary and enters the ovule
through the micropyle. After that the pollen tube enters one of the synergids
through the filiform apparatus. The filiform
apparatus of the synergids guides the entry of the pollen tube into the ovule
and brings about opening of the pollen tube whereby male gametes are discharged
and one fuses with the egg cell to form zygote and the other fuses with the
central cell to form the primary endosperm cell.
SIGNIFICANCE OF POLLEN PISTIL
INTERACTION:
The knowledge of pollen pistil interaction helps the
plant breeders in manipulating pollen pistil interaction, even in incompatible
pollinations, to get desired hybrids.
SELF INCOMPATIBILITY:
This is a genetic mechanism which causes
self-sterility and prevents self-pollen (from the same flower or other flowers
of the same plant) from fertilising the ovules by inhibiting pollen germination
or pollen tube growth in the pistil, after the process of pollen-pistil
interaction.
Self- incompatibility or self- sterility occurs when
similar sterile genes e.g. Siand S2 are present in pollen grains and stigma.
OUTBREEDING
To overcome the phenomenon of self-incompatibility,
out-breeding or out-crossing method is adapted.Continued self-pollination
result in inbreeding depression which results in homozygous genes. So flowering
plants have developed many devices to discourage self-pollination and to
encourage cross-pollination. This is known as outbreeding.
OUTBREEDING DEVICES:
Plants have evolved outbreeding methods or devices
like the following.
In some species, pollen release and stigma
receptivity are not synchronised. Either the pollen is released before the
stigma
becomes receptive or stigma becomes receptive much
before the release of pollen.
In some other species, the anther and stigma are
placed at different positions so that the pollen cannot come in contact with
the stigma of the same flower. Both these devices
prevent autogamy.
The third device to prevent self-pollination is the
production of
unisexual flowers. If both male and female flowers
are present on the same plant such as castor and maize (monoecious), it
prevents autogamy.
Another device to prevent inbreeding is self-incom
patibility.
LET US KNOW WHAT WE HAVE LEARNT!
PART A: VERY SHORT ANSWER TYPE
QUESTIONS:
a) MCQs.:--
1. Outbreeding devices:
a) Discourage self-pollination
b) Encourage cross-pollination
c) Both
d) None of these
2. The structure which guides the pollen
tube into the synergid is:
a) Filiform apparatus
b) Antipodals
c) Polar nuclei
d) None of these
3. Polien pistil interaction determines the
of the pollen:
a) Compatibility
b) Colour
c) Nature
d) Maturation
4. What causes the pollen rejection in the
pistil?
a) Style
b) Nucellus
c) Similar sterile genes in pollen and pistil
d) Stigma
5. Knowledge of pollen pistil interaction
helps the plant breeder:
a) To manipulate incompatibility and get desired
hybrids
b) To stop the growth of pollen tube
c) Both of these
d) None of these
b) FILL UPS.:—
1. In pollen pistil interaction, after the right
type of pollen is recognized by the pistil the pollen will on the stigma.
2. Pollen pistil interaction is mediated by
components of the pollen and pistil.
3. Pollen tube contains formed by division of
generative cell.
c) TRUE / FALSE:--
1. In self-incompatibility self-pollen will not
germinate on the pistil
(True/False).
2. Production of unisexual flowers is an outbreeding
device
(True/False).
3. Pollination guarantees the transfer of right type
of pollen
(True/False).
ANSWER
KEY-PART-A
a)
MCQs.:--
1. c — Both. (because outbreeding devices encourage
cross pollination and discourage self-pollination)
2. a - filiform apparatus. (filiform apparatus in
the synergids guides
the entry of the pollen tube into the synergids)
3. a— compatibility. (pollen pistil interaction
determines the suitability of the pollen to carry out sexual reproduction. If
it is compatible it will grow and fertilization will take place)
4. c — similar sterile genes (The compatibility of
the pollen with pistil
is mediated by chemicals- proteins of the sterile
genes. )
5. a— manipulate incompatibility and get desired hybrids.(Knowledge
of pollen pistil interaction will help the plant breeder to
manipulate pollen pistil interaction according to
his needs and get better hybrids)
b) FILL UPS.:—
1. germinate
Hint: when compatible pollen is recognized by pistil
it will grow on
the stigma and ensure fertilization.
2. chemical (Proteins)
Hint: chemical substances present in the pistil and
pollen are
responsible for pollen pistil interaction.
3. two male gametes
Hint: the generative cell divides into two male
gametes which enter the pollen tube and fertilize the cells in the ovule
c) TRUE/FALSE:--
1. True
2. True
3. False
Hint: pollination does not guarantee the transfer of
right type of
pollen
PART-B SHORT ANSWER TYPE QUESTIONS
1. Name the four strategies involved to prevent
self-pollination and
encourage cross pollination in flowers.
2. Write the function of the filiform apparatus.
3. What is the significance of pollen pistil
interaction?
PART-C LONG ANSWER TYPE QUESTIONS
1. What is self-incom patibility? Why does self-pollination
not lead to seed formation in self-incompatible species?
2. What are the different events involved in pollen
pistil interaction?
A13
INTRODUCTION
Dear students, after studying the assignments
no.10,11 and 12 you are now well known about pollination and Pollen- Pistil
interaction.
Angiosperms are flower-bearing plants and are the
most diverse group of terrestrial plants.
The flowers form the reproductive part of
angiosperms with separate male and female reproductive organs. Each contains
gametes — sperm and egg cells, respectively.
In flowering plants, fertilization is a process of
sexual reproduction, which
occurs after pollination and germination of pollen
grain.
In the course of fertilization, male gametes get
transferred into the female
reproductive organs through pollinators and the
final product will be the formation of the embryo in a seed.
One vegetative cell and two male gametes are found
in a pollen grain when it is shed at the three celled stages
GROWTH OF POLLEN TUBE:
Sexual reproduction of flowering plants requires
delivery of the sperm(male gamete) to the egg(female gamete).
The process begins with deposition of the pollen
grain, containing the male gametes, delivered by an insect, wind or other
means, on the female stigmatic tissue.
If the pollen—stigma interaction is compatible, the
pollen grain hydrates
and germinates (pollen tube comes out of the pollen
grain through germ pore), shortly following landing on the stigma.
During germination, a defined area in the pollen
plasma membrane —the tip growth domain to which post-Golgi vesicles are
targeted and fused, promoting directional growth —is established, and the
pollen
tube elongation begins, often reaching astounding
rates of growth.
During the elongation process, the pollen cytoplasm.
vegetative nucleus and two sperm cells are transported within the tube, which
grows through intercellular spaces in the pistil.
ENTRY OF POLLEN TUBE :
The events from pollen deposition on the stigma to
the entry of pollen tube in to the ovule is called pollen-pistil interaction.
It is a dynamic process which involves recognition
of pollen and to
promote or inhibit its germination and growth.
The growth of pollen tube towards the ovary, ovule
and embryo sac is due to the presence of chemotropic substances, (proteins).
The pollen tube after travelling the whole length of
the style enters into the ovary locule where it is guided towards the micropyle
of the ovule by a structure called obturator.
ENTRY OF POLLEN TUBE INTO THE OVULE:
There are three types of pollen tube entry into the
ovule:
1. Porogamy:
when the pollen tube enters through the micropyle.
2.Chalazogamy:
when the pollen tube enters through the chalaza.
3.Mesogamy:
when the pollen tube enters through the integument.
After reaching the embryo sac, a pore is formed in
pollen tube wall at its apex or just behind the apex.
The content of the pollen tube (two male gametes,
vegetative nucleus and cytoplasm) are discharged into one of the two
synergids, into which the pollen tube enters.
The pollen tube does not grow beyond it, in the
embryo sac. The tube nucleus disorganizes.
DOUBLE FERTILIZATION:
Double fertilization is the chief trait of flowering
or Angiospermic plants.One of the male gametes fertilizes the egg resulting in
the formation of a zygote, Generative Fertilization and the other male gamete
unites with two polar nuclei of the central cell, for the formation of an
endosperm
Vegetative Fertilization & Triple Fusion.
THE STAGES INVOLVED IN DOUBLE FERTILIZATION ARE:-
Germination of pollen to form pollen tube in the
stigma;
Growth of pollen tube in the style;
Direction of pollen tube towards the micropyle of
the ovule;
Entry of the pollen tube into one of the synergids
Discharge of male gametes;
Syngamy and triple fusion
LET US KNOW, WHAT WE HAVE LEARNT!
PART A- VERY SHORT ANSWER TYPE
QUESTIONS:
(a) MCQs type questions ;
1. The fusion of female reproductive
nucleus with the male reproductive _..
nucleus is known as:
(a) Adoption
(b) Excretion
(c) Fertilization
(d) Regeneration
2. Double fertilization is due to the
fusion of
(a) male gametes with egg and synergid
(b) male gametes with egg and secondary nucleus
(c) male gametes with egg and polar nuclei
(d) male gametes with two eggs
3. The transfer of pollen from the anther
to stigma is called:
(a) Pollination
(b) Fertilization
(c) Adoption
(d) Diffusion
4. Generative nucleus divides forming:
(a) 2 male nuclei
(b) 3 male nuclei
(c) 2 female nuclei
(d) 3 female nuclei
5. The two nuclei at the end of the pollen
tube are called:
(a) Generative nucleus and stigma
(b) Sperm and ovum
(c) Tube nucleus and a generative nucleus (d) Tube
nucleus and sperm
(b) True/ False:
1. When the pollen tube enters through the
integument is called chalazogamy.
2. One of the male gametes fertilizes the egg.
3. The flowers form the reproductive part of
angiosperms.
(c) Fillups :
1. When the pollen tube enters through the
micropyle,it is called
2. The pollen tube opens into the through the
micropyle.
3. The events from pollen deposition on the stigma
to the entry of pollen tube in to the ovule is called
ANSWER KEY - PART A
(a) MCQs:
1. (C )The fusion of female reproductive nucleus
with the male reproductive nucleus is known as Fertilization
2. (B) Double fertilization is due to the fusion of
male gametes with egg and secondary nucleus
3. (A) The transfer of pollen from the anther to
stigma is called Pollination
4. (A) Generative nucleus divides forming 2 male
nuclei
5. (C) two nuclei at the end of the pollen tube are
called Tube nucleus and a generative nucleus
(b) TRUE / FALSE:
1. False -Mesogamy: when the pollen tube enters
through the integument.
2. True- and the other unite with 2 polar nuclei for
the formation of an endosperm.
3. True - The flowers form the reproductive part of
angiosperms with separate male and female reproductive organs.
(c) FILL UPS:
1. Porogamy
2. Ovule
3. Pollen - Pistil Interaction
PART -B SHORT ANSWER TYPE QUESTIONS
1. Which are the three cells found in a pollen grain
when it is shed at the
three celled stages?
2. Draw the diagram of a mature embryo sac and show
its 8-nucleate 7-celled nature. Show the following parts: antipodals,
synergids, egg,central cell, polar nuclei.
3. What are the end products of double fertilization?
PART -C LONG ANSWER TYPE QUESTIONS
1. What is double Fertilization and Triple Fusion?
Explain its events.
A14
INTRODUCTION
The endosperm is very vital part of the fertilized
embryo sac. An endosperm
forms the surrounding tissue of the growing embryo.
They are the primary storage tissue and their main function is to provide
starch and other nutrients to the growing embryo. Endosperm formation precedes
embryo development.
Development of Endosperm :
We need to understand what gives rise to the
endosperm.
Aphenomenon called as ‘double fertilization, which
we discussed in
assignment no. 13.
Each pollen grain consists of two male gametes.
Once they reach the ovary, one of the male gametes
fuses with the female gamete and forms the diploid zygote.
The other male gamete fuses with the central cell
which is diploid,resulting in the formation of a triploid endosperm.
Thus, the endosperm can be polyploid as well in
certain cases. But, in
gymnosperms, the endosperm is haploid.
This simultaneous occurrence of SYNGAMY and TRIPLE
FUSION is called DOUBLE FERTILIZATION and leads to the formation of the zygote
and primary endosperm nucleus.
FORMATION OF ENDOSPERM:The
ptimary endosperm cell formed after triple fusion divides repeatedly and form TRIPLOID
endosperm tissue, which is filled with reserve food materials for the embryo.
TYPES OF ENDOSPERMS :On
the basis of formation of endosperm it is of three types.
1. Nuclear Endosperms:
In this type, the divisions are free-nuclear
divisions, where each nuclear
division is not followed by formation of a cell
wall.
They may or may not form a cell wall towards later
stages.
With the nuclear divisions, the nuclei are pushed
towards the periphery of the cell giving rise to a large vacuole in the centre.
This type of endosperm is the most common type and
is found in maize,
wheat, areca nut and coconut.
The endosperm of the coconut gives rise to a large
central vacuole that gets eventually filled up with the nutritious coconut
water. It has white kernel of solid multinuclear endosperm outside and milky
free nuclear liquid endosperm (NARIAL PANI) in the center.
2. Cellular Endosperms:
This type is the opposite of the nuclear endosperm.
In this type, cell wall
formation follows each ceil division.
Thus, the endosperm divides into many segments.
There might not be coherency in the divisions and
they can happen along different planes.
Cellular divisions of the endosperm consequently
lead to the formation of
the coconut meat (NARIAL GIRI)
Plants like petunia and Dhatura have this kind of
endosperm.
3. Helobial Endosperms:
This is an intermediate form between the Nuclear and
Cellular types. In this type, cell wall formation follows the first nuclear
division to produce two un equal chambers. The first cell division occurs along
the transverse plane giving rise to clear larger micropylar and smaller
chalazal ends.
But the subsequent nuclear divisions do not lead to
cell wall formation, in both the chambers.
Once the number of division in the micropylar end
begin to increase, the
chalazal end starts to degenerate or disintearate.
FUNCTIONS OF ENDOSPERM
Itis the primary storage tissue and their main
function is to provide starch and other nutrients to the growing embryo.
LET US KNOW WHAT WE HAVE LEARNT!
PART A- VERY SHORT ANSWER TYPE
QUESTIONS:
a) MCQs:
1. The primary endosperm nucleus is:
(a) tetraploid
(b) triploid
(c) diploid
(d) haploid
2. In the angiosperms, the endosperm is
formed:
(a) before fertilization
(b) after fertilization
(c) along with fertilization
(d) None of the above
3. Which of the tissue culture will form a
triploid plant:
(a) endosperm
(b) pollen
(c) megaspore
(d) ovule
4. The polar nuclei and male gamete fuse to
form:
(a) secondary nucleus
(b) zygote
(c) triple fusion
(d) PEN
5. The white edible part of maize is:
(a) pericarp
(b) seed coat
(c) endosperm
(d) seed
b) True / False:
1. The fusion of male gamete with the egg cell is
called pollination .
2. Once the number of division in the micropylar end
begin to increase,the chalazal end starts to grow .
3. The endosperm of the coconut gives rise to a
large central vacuole that gets eventually filled up with the nutritious
coconut water.
c) Fill ups:
1. Endosperm development takes place from the in the
embryo sac.
2. Endosperm mostly contains as a food reserve.
3. Coconut water is the example of a
ANSWER KEY PART-A
a) MCQs:
1. b - The primary endosperm nucleus is triploid
2. b - Inthe angiosperms, the endosperm is formed
after fertilization.
3. a — endosperm tissue culture will form a triploid
plant.
4.d - The polar nuclei and male gamete fuse to form
PEN
5. c - The white edible part of maize is endosperm.
b) True / False:
1. False
Hint -The fusion of male gamete with the egg cell is
called syngamy or fertilization.
2. False
Hint - Once the number of division in the micropylar
end begin to increase, the chalazal end starts to degenerate.
3. True
c) Fillups:
1. triploid cell (3n) PEN- (primary endosperm cell.)
2. starch
3. Liquid endosperm.
PART B - SHORT ANSWER TYPE QUESTIONS:
1. Which are the nuclei that fuse to form endosperm?
2. Which is the most common type of endosperm
development?
3.Write about most common method of endosperm
development .
PART C - Long answer type questions
1. Explain the major event, taking place in a
flowering plant just after fertilization.
A15
INTRODUCTION
Father of Indian embryology is P.Maheswari.
After the process of double fertilization, two
structures are formed:
ZYGOTE in generative fertilization and ENDOSPERM in
vegetative fertilization, or triple fusion.
Embryo develops from zygote by a process called
EMBRYOGENESIS.
Embryogenesis starts after the formation of
Endosperm.
During embryogenesis, zygote undergoes mitotic
divisions and
Cell division increases the number of cells in the
developing embryo and Oe help to form specialized tissues and organs to form an
organism.
PROCESS OF EMBRYO FORMATION IN DICOTS:
Embryo develops at the micropylar end of the embryo
sac, where zygote is
situated.
Embryo does not start dividing until certain amount
of endosperm is formed. This assured the nutrition to the developing embryo.
Zygote start dividing and in early stages embryogeny
in dicot and monocot is almost same .
Zygote give rise to the PROEMBRYO and subsequently
to theGLOBULAR, HEART SHAPED and MATURE EMBRYO.
The ZYGOTE divide to form two cells, the HYPO-BASAL
CELL (basal)toward ...micropylar end and EPI-BASAL CELL toward chalazal end.
EPIBASAL CELL divides repeatdly to produce a row of
4-8 cells that constitute SUSPENSER .
The TERMINAL CELL divides in various planes to
produce a cluster of cells called PROEMBRYO. (fig. d)
The SUSPENSOR pushes the PROEMBRYO to the ENDOSPERM.
The endosperm gives the nutrition to developing
embryo.
The PROEMBYRO divides in variously planes to form a
globular mass as depicted in (fig f)
Ultimately it takes the heart shaped in outline
(fig. g)
A few cells of embryo near to the suspensor develops
in to HYPOCOTYL and RADICLE .
Others cells give rise to EPICOTYL, PLUMULE and COTYLEDONS.
In DICOTS there are TWO COTYLEDONS. (Fig.h)
The mature embryo with all organs are depicted in
the diagram, so all
the organs of the embryo develope from BASAL CELL.
RADICLE is the FUTURE ROOT of next generation.
PLUMULE give rise to SHOOT SYSTEM.
PART A: VERY SHORT ANSWER TYPE
QUESTIONS:
a) MCQs.:--
1. The dicot embryo has:
a) Cotyledons
b) Radicle
c) Both
d) None of these
2. The future root stored in which organ of
embryo?
a) Cotyledons
b) Antipodals
c) Radicle
d) None of these
3. Growing embryo take its nutrition from :
a) Ovule
b) Suspensser
c) Endosperm
d) Cotyledon
4. Father of indian embryology is:
a) P.Maheshwari
b) Swaminathan
c) R. Mishra
d) none of the above
5. Heart shaped embryo is the feature of :
a) Dicot embryo
b) Monocot
c) Both of these
d) None of these
b) FILL UPS.--
1. Embryo develops at the ............... end in the
ovule.
2. Stored food in the dicot embryo is present in
.................
3. Suspensor pushes the pro-embryo toward
...................
c) TRUE / FALSE:--
1. In dicot there is one cotyledon in the seed.
2. Epibasal cell give rise to suspensor.
3. During seed germination shoot system is formed
from plumule.
a} MCQs. :--
1. (c) both. (cotyledon, plumule, radical are part
of dicot embryo. )
2. (c )radicle (it give rise to root )
3. (c) endosperm
4. (a) P. Maheshwari
5. (a) dicot Embryo
b) FILL UPS.:-
1. Micropylar
2. Cotyledons
Hint: food stored in cotyledon for seed germination.
3. Endosperm (to takes nutrition)
c) TRUE/FALSE:--
1. False , (Di- means two, there are two cotyledons
in dicot seed.)
2. True
3. True
PART-B SHORT ANSWER TYPE QUESTIONS
1. What is the embryogenesis?
2. Differentiate between hypocotyl and epicotyl.
3. Draw the well labeled diagram of dicot embryo.
PART-C LONG ANSWER TYPE QUESTIONS
1. Give the detail process of embryo formation in
dicots with diagrams.
A16
INTRODUCTION
Zygote is the first cell of next generation.
Embryo is the diploid cell developing from zygote.
It starts to develop at the micropylar end of the zygote.
Embryogeny refers to the stages of embryo
development.
Development of embryo starts only after endosperm
formation started.
This assure the nutrition to the developing embryo
.ALL THE STAGES of MONOCOT EMBRYO development ARE SAME as in DICOT EMBRYO.
It started with the fertilized egg, then passes
through 2- celled stage , 8-
celled stage , heart shaped and finally in to mature
embryo in DICOTS.
DEVELOPMENT OF MONOCOT EMBRYO:--
In monocots, about one half of the terminal cell
derivatives function as shoot apex , rest cells show rapid rate of cell
division in the formation of single terminal cotyledon .
The zygote elongates and then divides transversely
to form basal and terminal cells.
The basal cell produces a large swollen vesicular
suspensor cell, may function as haustorium.
The terminal cell divides transversely, produces 2-
cells .
The top cell after a series of divisions, form
plumule and a single cotyledon, also called scutellum.
Scutellum grows rapidly and pushes plumule to one
side.
The middle cell after many divisions forms hypocotyl
and radical.
STRUCTURE OF MONOCOT EMBRYO:--
Monocot embryo has only one cotyledon.
In grass family this cotyledon is called scutellum,
situated toward lateral
side of embryonal axis.
This is the axis at its lower end has radicle and
root cap which is covered
by a sheath called coleorhiza.
If this covers the plumule, called the coleoptile.
This coleoptile and coleorhiza is develops from
scutellum.
The part of axis above the level of attachment of
scutellum is called epicotyl,
it has as shoot apex and few leaf primordia.
Epicotyl is rudiments second cotyledon.
LET US KNOW WHAT WE HAVE LEARNT!
PART- A: VERY SHORT ANSWER TYPE
QUESTIONS:
(a)_MCQs :
1. The first cell of next generation is:
(a) zygote
(b) cotyledon
(b) both
(d) none
2. The first division of monocot embryo is:
(a) longitudinal
(b) transverse
(c) periclinal
(d) none of the above
3. Which of the following have monocot
seed/s :
(a) maize
(b) rice
(d) both
(d) none
4. Radicle and root cap is covered by:
(a) coleorhiza
(b) coleoptile
(b) scutellum
(d) seed coat
5. The plumule gives rise to:
(a) shoot system
(b) root System
(b) both
(d) none
6. Epicotyl represents:
(a) root
(b) shoot
(c) rudiment cotyledon
(d) ail the above
(b) Fill Ups:
1. Growing embryo draw the nutrition
from...................
2. Formation of embryo is called...................
3. Suspensor is formed from...................
(c) True /False:
1. In monocot embryo there are two cotyledons.
2. The suspensor cell may function as haustoria.
3. Plumule is covered by a sheath called coleorhiza.
ANSWER KEY: PART-A
(a) MCQs:
1. (a) Zygote (Hint: as whole embryo formed from it)
2. (b) transverse ( Hint: as depicted in diagram )
3. (c) both
4. (a) Coleorhiza (Hint: this is a sheath which
cover radicle ).
5. (a) Shoot System
6. (c) Rudiment second cotyledon
(b) FILL UPS:
1. Endosperm
2. Embryogeny
3. Basal cell
(c) TRUE/FALSE:
1. False (Hint: Mono means one, so it has one
cotyledon.)
2. True
3. False: (Hint: It is covered by coleoptile. )
PART-B: SHORT ANSWER TYPE QUESTIONS
1. Differentiate between monocot and dicot embryo.
2. Draw a well labelled diagram of mature monocot
embryo.
3. Differentiate between epicotyl and hypocotyl .
PART-C: LONG ANSWER TYPE QUESTIONS
1. Write in detail, the process of monocot
embryogeny with diagrams.
A17
INTRODUCTION
The seeds and fruits are the results of
fertilization or sexual reproduction in plants.The ovary in angiosperms
develops into the fruit wnereas the ovules become the seeds enclosed within the
fruit. Seeds are found both in gymnosperms and
angiosperms.
SEED
Seed is a fertilized ovule. Integuments of ovule
harden to form Seed coat,
however micropyle is still present on the seed coat.
Basic structure of a seed consists of
the following parts:
Seed coat:
Hard outer covering of the seed
Radicle:
Root tip which later gives rise to the entire root system
Plumule:
Shoot tip which later gives rise to the entire shoot system
Cotyledons:
Seed leaves
Based on the number of cotyledons, seeds are of two
types:
Dicotyledonous seed: Seed with two cotyledons.
Monocotyledonous seed: Seed with one cotyledon.
SEED COAT
Outer covering of the seed which is
composed of two layers:
Testa : thick outer layer.
Tegmen: thin inner layer.
HILUM
Scar on seed coat through which the seed was
attached to the fruit.
MICROPYLE
Asmall pore on the seed through which oxygen &
water exchange occurs during seed germination.
COTYLEDONS
Seed leaves
Food storage
Provide nourishment to the developing radicle &
plumule
RADICLE
Embryonic root
PLUMULE
Embryonic shoot
SEED COAT
Fused with pericarp
Endosperm
Bulky part within which lies the small embryo
Massive & starchy endosperm
Aleurone layer
Special tissue surrounding the endosperm
COTYLEDON
Single cotyledon termed as Scutellum
Incontact with endosperm through an epithelial layer
Plumule
Embryonic shoot covered by protective layer
Coleoptile
RADICLE
Embryonic root covered by protective layer
Coleorrhiza
APPLICATIONS OF SEEDS IN DAILY LIFE:
Seeds are extremely useful in agriculture.
Some of the important applications of seeds are:
Help plant species to be colonized in different
areas
Provide nourishment to young seedlings
Ensure protection to the young embryo
Results in variations with new genetic combinations
Can be easily stored for future usage
Long term viability of most of the seeds
FRUITS
The fruit is broadly divided into the pericarp which
is the various covering
layers of the fruit and the seed or seeds which are
present inside it. The pericarp of a fruit can be further divided into:
Exocarp- It is the outermost layer which is formed
from the outer layer or the epidermis
Mesocarp- Is the second or the middle layer which is
often juicy and varies
in thickness in different fruits
Endocarp- It is the innermost layer and also is
different in different kinds of
fruits.
When a fruit develops exclusively from the ovary,
itis called a true fruit but, when in addition to the ovary, some other floral
parts like petals, bracts or thalamus also participate in the formation of the
fruit, then it is known as false fruit.e.g. Apple, Strawberry.
In some species fruits do not have seeds. They
develop without fertilization.
Such fruits are called PARTHENOCARPIC fruits.
e.g.Banana.
LET US KNOW WHAT WE HAVE LEARNT!
PART-A VERY SHORT ANSWER TYPE
QUESTIONS:-
(a) MCQs:
1. Outer seed coat is:
(a)Testa
(b) Tegmen
(c) Hilum
(d) Funiculus
2. Seed bud is:
(a) Plumule
(b) Tegmen
(c) Ovule
(d) Mesocotyl
3. Tegmen is the name of
(a) Embryo shoot
(b) Embryonic node
(c) Cotyledon
(d) Inner seed coat
4. The micropyle in a seed helps the entry
of:
(a) Water
(b) pollen tube
(c) male gamete
(d) none
5. Seed may be defined as:
(a) Ripened ovule
(b) fertilized ovary
(c) the gynoecium
(d) embryo
(b) True/False:-
1. Some seeds have no cotyledons.
2. Warmth is necessary for the germination of seeds.
3. All seeds have two cotyledons.
(c) Fill in the Blanks:-
1. The remnants of nucellus present in the seed
called............
2. Hilum of seed is.........
ANSWER KEY- PART-A
a) MCQs:
1. (a) Testa-inner to testa is tegmen
2. (c) Ovule.
3. (d) Inner seed coat
4. (a) Water and gases
5. (a) Ripened ovule.
b) TRUE/FALSE:
1. false
2. true
3. false
c) FILL IN THE BLANKS:
1. Perisperm
2. Scar of funiculus
PART-B SHORT ANSWER TYPE QUESTIONS:-
1. Banana is a true fruit but is also a
parthenocarpic fruit. Give reason.
2. Why is apple referred to as a false fruit?
PART-C LONG ANSWER TYPE QUESTION:-
3. Explain the structure of a maize grain with the help
of a labelled diagram.
A18
INTRODUCTION
Apomixis, derived from two Greek word 'APO"
(away from) and “mixis” (act of mixing or mingling).
APOMIXIS is a type of reproduction in which sexual
organs of related structures take part but seeds are formed without union of
gametes.
The first discovery of this phenomenon is credited
to Leeuwenhoek as early as
1719 in Citrus seeds.
The genotype of the embryo and resulting plant will
be the same as the seed parent.
This is clonal seed production.
DEVELOPMENT OF EMBRYO WITHOUT SEXUAL
FUSION
Sexual life cycle is “short-circuited”
Genotypes of developed plants are identical to the
parental plant.
Discovered by Leuwenhoek (1719) in citrus seed
GAMETOPHYTIC APOMIXIS
If the unfertilized cells give rise to a mega
gametophyte
Diplospory - MMC (Megaspore Mother Cell) cells give
rise to a megagametophyte or an embryosac.
Apospory - The embryo sac originates from the any
diploid cell except megaspore mother cell either directly by mitosis and/or
after interrupted meiosis.
Androgenesis - The embryo sac originates from
generative nucleus of pollen
tube cells, the most common mechanism of apomixis in
higher plants characterized by the presence of multiple embryo sacs.
SPOROPHYTIC APOMIXIS
If the unfertilized cells give rise directly to an
embryo;
Adventitious embrony (Sporophytic budding ) : Embryo
directly develops from nucellus or integuments ( no production of embryo sac)
e.g.mango , citrus.
TYPES OF APOMIXIS BASED ON OCCURRENCE:-
1. Non recurrent: - Hapioid Embryo develops from any
HAPLOID cell of embryo sac.
2. Recurrent apomixis: Diploid Embryo sac develops
without meiosis from diploid cell e.g.
a) Diplospory: Embryo sac develops from diploid MMC.
b) Apospory: Embryo sac develop from any diploid
vegetative cell of ovule,and then, embryo is developed from diploid egg cell.
3. Adventitious embrony (Sporophytic budding):
Embryo directly develop
from nucellus or integuments (no production of
embryo sac) e.g. mango,citrus.
IMPORTANCE OF APOMIXIS:
It produces seed progeny which are exactly the same
as the mother plant.Thus apomixis helps in the preservation of good characters
over generations for crop plants.
It helps in the production of hybrid seeds with a
combination of desirable characters. It also prevents the loss of specific
characters from a hybrid because there is no mixing of gametes or absence of
fertilization.
Ithelps in the cost-effective and time-efficient
production of seeds.
POLYEMBRYONY
It is the phenomenon in which two or more embryos
are produced ina _ seed.”
Polyembryony means that more than one embryo
develops within a single seed. It
is also known as adventitious embryony (Nucellar
embryony or Nucellar budding).This condition may result from many reasons but
one of the most
common reasons being the nucellar embryony.
Sometimes more than one nucleus develops within the
embryo sac, which may
lead to development of more than one embryo.Further,
cleavage of pro-embryo during early stages of development may be other reason
for development of multiple embryos as in case of conifers.Among fruit crops
polyembryony is quite common in mango and citrus.
Polyembryony can develop from several distinct
causes.Specific cells in the nucellus or sometimes in integuments have
embryos.Genetically, these embryos have the same genotype as the parental plant
and are
apomictic.
Adventitious embryony occurs in many plant species
but is most common in citrus and mango.In these species, both zygotic and
apomictic embryos are produced.In other species (e.g. Opuntia), no pollination
or fertilization is needed.
Polyembryony is common in mango and citrus. In
trifoliate orange (Poincirustrifoliata) several seedlings arise from one seed
of these seedlings, one seedling, usually the weakest may be sexual, and the
others arise apomictically from cells in the nucellus, which are diploid copies
of the mother plant.
SIGNIFICANCE OF POLYEMBRYONY:
1. Seedlings develop a better root system and show
better yield.
2. Seedlings are free from diseases.
3. For large scale production of uniform plants,
induced polyembryony is very
suitable.
4. Artificial seeds can be formed by somatic embryos
which are also suitable for
field planting.
LET US KNOW WHAT WE HAVE LEARNT!
PART-(A) VERY SHORT ANSWER TYPE
QUESTIONS:-
(a) MCQs:
1. Apomixis is a form of:
(a) Vernalization
(b) Parthenogenesis
(c) Parthenocarpy
(d) None of the above
2. In plants, apomixis pertains to plant
development;
(a) From root cuttings
(b) From cuttings of stem
(c) Without fusion of gametes
(d) Fusion of gametes
3. The reason why hybrid seeds have to be
produced every year is:
(a) hybrid seed industry tends to increase the cost
of seeds
(b) hybrid plants turn sterile in coming years
(c) show more heterosis in coming years
(d) hybrid vigour is not maintained in more than one
generation as segregation of genes is initiated in the second generation
4. Inadventive embryony, a type of
apomixis, the embryo develops directly from the:
(a) Zygote
(b) accessory embryo sacs in the ovule
(c) antipodals or synergids in an embryo sac
(d) integuments or nucellus
5. This is true about apomixis:
(a) There is no fertilization involved in both
apomixis and parthenocarpy
(b) Apomixis produces progeny genetically identical
to mother cells
(c) Apomixis is observed in angiosperms and
gymnosperms
(d) All of the above
(b) True/False:-
1. Apomixis is highly significant in producing
hybrids.
2. If hybrids are made into apomicts, there is no
segregation of characters
in the hybrid progeny.
3. Polyembryony was first noted in Mangifera .
(c) Fillin the Blanks:-
1.____ may be defined as occurrence of two or more
embryos in one
ovule.
2. In 1908 termed the term apomixis.
ANSWER KEY: PART-A
a) MCQs:
1. (b) Parthenogenesis is formation of embryo from
single gamete.
2. (c) Apo means without and mixis means fusion
3. (d) Hybrid vigour reduces due to crossing during
fertilization.
4. (d) Adventitive means any part other than actual
part.
5. (d) All are true for apomixis.
b) True/False:
1. false (apomixis is significant)
2. true (as there is no fertilization and hence no
crossing)
3. false (No,apomixis was first noticed in citrus)
c) Fill in the Blanks:
1. Polyembryony
2. Winkler
PART-(B) SHORT ANSWERS TYPE QUESTIONS:-
1. Explain the term polyembryony. How is it
exploited commercially?
2. Is there any difference between apomixis and
parthenocarpy? Explain the benefits of each.
PART- (C) LONG ANSWERS TYPE QUESTION:-
1. What is apomixis and what is its importance?