2- SEXUAL REPRODUCTION IN FLOWERING PLANTS

CHAPTER NO.2 SEXUAL REPRODUCTION IN FLOWERING PLANTS

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

(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

(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.

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

(d) young anthers

2. The cells of which layer provide nourishment to the the microscope

(a) middle layer

(b) tapetum

(d) epidermis

3. Development of pollen grains is known as

(a) microsporogenesis

(b) microgametogenesis

(d)none of a and b

4.Tetrad of pollen grain have internal layer which break the plamodesmal connection is

(a) Callose

(b) tapetum

(d) none of above

5.Pollen Mother Cell Give Rise To

(a) two pollen grains

(b) 4 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.

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

(d) Cholera

3. Development of Male gametophyte is known as

(a) microsporogenesis

(b) microgametogenesis

(d)none of a and b

4.Microspore mother cell divides into

(a) two cells

(b) four cells

(d) 6 cells

5.Pollen grain is covered by

(a)exine and intine

(b)epidermis

(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.

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

(d) none of above

2. The part which determine compatibility-incom patibility of pollen grain is

(a) style

(b) ovary

(d) hilum

3. Nucellus is surrounded by

(a) integuments

(b)funiculus

(d) ovary

4. The ovules are attached to ovary with

(a) placenta

(b) hilum

(d) none of the above

5. Nucellus is equivalent to

(a) microsporangium

(b) ovary

(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.

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

(d)8

Q. 2. During megasporogenesis, which division takes place inside the

megaspore mother cell to form megaspores?

(a) mitosis

(b) meiosis

(d) none of these

Q.3. The functional megaspore undergoes divisions to form the embryo sac:

(a) two mitotic divisions

(b) three mitotic divisions

(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

(d) 7 nuclei 8 cells

Q. 5. The central cell is made up of:

(a) two polar nuclei

(b) one polar nuclei

(d) two egg cells

Q. 6. The cells present towards the chalazal end of embryo sac are:

(a) egg apparatus

(b) anti podal cells

(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

(d) Gossypium

3. Which of the following pollination occurs in a closed flower?

(a) Decliny

(b) Cleistogamy

(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

(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

(d) male gametes with two eggs

3. The transfer of pollen from the anther to stigma is called:

(a) Pollination

(b) Fertilization

(d) Diffusion

4. Generative nucleus divides forming:

(a) 2 male nuclei

(b) 3 male 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

(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

(d) haploid

2. In the angiosperms, the endosperm is formed:

(a) before fertilization

(b) after fertilization

(d) None of the above

3. Which of the tissue culture will form a triploid plant:

(a) endosperm

(b) pollen

(d) ovule

4. The polar nuclei and male gamete fuse to form:

(a) secondary nucleus

(b) zygote

(d) PEN

5. The white edible part of maize is:

(a) pericarp

(b) seed coat

(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

(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

(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

(d) Funiculus

2. Seed bud is:

(a) Plumule

(b) Tegmen

(d) Mesocotyl

3. Tegmen is the name of

(a) Embryo shoot

(b) Embryonic node

(d) Inner seed coat

4. The micropyle in a seed helps the entry of:

(a) Water

(b) pollen tube

(d) none

5. Seed may be defined as:

(a) Ripened ovule

(b) fertilized ovary

(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

(d) None of the above

2. In plants, apomixis pertains to plant development;

(a) From root cuttings

(b) From cuttings of stem

(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

(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

(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

(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?

Chapter 2 Sexual Reproduction IN Flowering Plants

Plus Two

Saturday, 30 January 2021

Chapter 2 Sexual Reproduction IN Flowering Plants

Chapter 2 Sexual Reproduction IN Flowering Plants

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