Class 12th Biology Chapter 1 - Sexual Reproduction In Flowering Plants

NCERT Solutions for Class 12 Biology Chapter 1: This chapter is about Sexual Reproduction in Flowering Plants. We are going to cover the topics like Flower structure, Development of gametophytes, seeds, Pollination, Double Fertilization,etc. We have prepared this article very carefully and tried to include all those important topics and notes from the chapter which you can use in your preparation for 12th exam or any other upcoming competitive exams.

 

In this chapter we have covered all the topics related to Sexual Reproduction In Flowering Plants which are listed below:-

Flower
Structure of flower
Placentation
Aestivation
Development of Male gametophytes
Microsporogenesis
Development of Female Gametophyte 
Megasporogenesis
Pollination
Fertilization
Germination of pollen grains
Emasculation
Parthenocarpy 
Parthenogenesis
  

       Sexual reproduction in flowering plants

When new organisms is formed by the fusion of  one male gamete and the other female gamete of two parent and this process is known as sexual reproduction.

A flower is compressed shoot which consists of sepals , petals, stamens and carpels which are successive lateral organs.

There are two sporophylls one is stamen (microsporophylls) and the other is carpel (megasporophylls).

Filament,anther and connective are the three types of stamen.

The sexual reproduction in flowering plants is of three steps:-

1.Pre fertilization

2.Double fertilization

3.Post fertilization

The Structure of flower is 

Thalamus or Receptacle

The swollen part at the end of the stalk or pedicel is called thalamus or Receptacle.

There are 4 sets of appendages  

The outer one two sets is accessory whorls and the inner two sets essential whorls.

1.Accessory whorls

Sepals are the accessory whorls which  form the calyx and petals, and they make the corolla.

2.Essential whorls

Microsporophylls or stamens which form the androecium and carpels ( megasporophylls), and they form the gynoecium.

Perianth

The monocotyledons , calyx and corolla are undifferentiated in many plants which is known as perianth.

Tepals

Tepals are the individual members.

Stamen

 It is a slender organ which is differentiated to to proximal sterile part , which is filament and there is a distal fertile part which is the anther.

Further the carpels is divided into three parts which are :-

.Ovary

.Style

.Stigma

Structures and Events of Pre Fertilization

1.Pollen grain formation

2.Embryo sac formation

3.Pollination

4.Pollen pistil interaction

Locules 

 One or more chambers in ovary is known as locules .

Placentation

The pattern of arrangement of ovule in the ovary is called placentation.

Types of placentation

. Marginal

.Axile

. Parietal

.Free Central

.Basal

.Superficial

Complete flower – it consists of all the four whorls.

Incomplete – It consists of only one or two whorls.

Connective

Pair of sporangia where a strip of tissue lies.

Aestivation

The arrangement of petals /sepals in floral bud with other members of same whorl .

There are various types of aestivation are present.

.Valvate

.Twisted

.Imbricate

.Vexillary

Development of male gametophyte and anther.

There are two anther lobes in a typical anther and in each anther lobe there are two pollen chambers (microsporangia).

The wall is made up of epidermis, endothecium, single layer of tapetum and one or more middle layers.

Microsporogenesis

 From the sporogenous tissue the formation of microspores is called microsporogenesis.

Tetrahedral, Isobilateral, Decussate and Linear fashion or T-Shaped are the microspores which is formed from the microspore of mother cell.

Pollinium

 All microspores in a pollen sac from a single mass in the members Asclepiadaceae family is called Pollinium.

Two wall layers in pollen grain

. Exine – the outer thick ornamental .It is composed of sporopollenin.

.Intine – the inner thin .

The pollen grain is divided into two unequal cells.The smaller one is generative cell and larger one is vegetative cell, the smaller one or generative cell divides by mitotic method and this leads to  formation of two non motile male gametes.

Development of Female Gametophyte and Ovule

Types of ovules

.Orthotropous

.Anatropous

.Campylotropous

.Hemitropous 

.Amphitropous

.Circinotropous 

Pollenkit 

The exine of insects pollinated flower is covered by a yellowish viscous & sticky substance.

Pollen Banks

It is a collection of types of pollen containing male genetic material.They are preserved in liquid nitrogen at -196°C.They are used as crop breeding in pollen Banks.It is used to store the pollen for very long time for ex situ conservation.

Nucellus

The parenchymatous body which is present on the ovary which develops the ovule within it.

Integuments

The nucleus is protected by one or two sheath which is knows as integuments

Micropyle

The small opening at the one end of the integument.

Funicle

The stalk by which the ovule is attached to the placenta is called funicle.

Hilum

It is the point where the body of the ovule and the funicle is attached.

Chalaza

The merging point or the basal part of the ovule where nucleus, funicle and integuments are merged.

Megasporogenesis

The development of megaspore within ovule or megasporangium .

The embryo sac or mature gametophyte is consist of two polar nuclei, one egg, two synergids and three antipodals.

The embryo sac of this type is known as Monosporic 8-nucleate embryo sac or Polygonum type .

Pollination

The transfer of pollen grains from the anther of flower to the stigma of the other flower or same flower.

Self Pollination

The transfer of pollen grains from the anther of flower to the stigma of the same plant.

Autogamy

The transfer of pollen grains from the anther of flower to the stigma of the same flower .

Geitonogamy

The transfer of pollen grains from the anther of flower to the stigma of the flower in a same plant.

The two adaptation for self pollination are.

.Homogamy In this the anther & stigma mature at same time.

.Cleistogamy  In this the flowers which never open are produced.

Cross Pollination or Allogamy or Xenogamy

The transfer of pollen grains from the anther of flower to the stigma of the another flower.

Some contrivances are-

Dichogamy At different time the stigma of flowers and the maturation of pollens takes place.

Protogyny Before the maturation of pollen grains the stigma becomes receptive.

Protandry Before stigma becomes receptive the anthers shed their pollen grains.

Herkogamy The structure of anthers & styles where autogamy is mechanically impossible.

Heterostyly  Styles of different length in a dimorphic flowers.

Types & agents of Cross Pollination

.Anemophily- The pollen grain is transferred through wind.

.Hydrophily- The pollen grain is transferred through water .

.Entomophily- The pollen grain is transferred through insects.

.Ornithophily- The pollen grain is transferred through birds.

.Cheiropteriphily- The pollen grain is transferred through bats.

.Malacophily- The pollen grain is transferred through slugs.

Fertilization

It is the fusion of two sexual reproductive units which are dissimilar called gametes.

Strasburger was the first who discovered the process of Fertilization in 1884.

 

 

Emasculation

The removal of stamens from female parent and they shed their pollens before bursting.

Double Fertilization

 The fusion of male nucleus with the egg and the other with polar nuclei which is unique to angiosperms is known as double Fertilization.

A phenomenon first discovered by S.G.Nawaschin 1897 in Lilium and Fritillaria species.

Germination of pollen grains and growth of it

When the pollen has landed in the stigma the process starts it absorbs water and it swells and produce a pollen tube which penetrates the stigma and it push it to the style and the wall of ovary.

Entry of pollen tube into ovule

When it reaches to ovary , the pollen tube goes towards the ovules.It may enter through one way which are-

.Porogamy-The pollen tube enters through micropyle.

.Chalazogamy-The pollen tube enters through chalaza end.Ex-Casuarina

.Mesogamy-The pollen tube enters through integuments.Ex-Populus

Totipotency

It is defined as that every living cell is capable of regenerating a whole organism.

Fruits

It is the ripened ovary.

Pericarp

The outer epicarp , middle mesocarp and inner endocarp.

True fruit

When a fruit is obtained from the ovary. ex-guava.

False fruit

When a fruit is obtained not only from the ovary but with the addition of floral parts.

SEED

It is the mature ovule which contains the embryonic plant and have stored food material and protective coat .

Aril

In seeds , a structure develops which is bright in colours as an outgrowth which is known as aril.

They are classified into 2 categories on basis of number of cotyledons.

1.Dicotyledonous seeds

a.Exalbuminous – mango, pea

b.Albuminous -pineapple

2.Monocotyledonous seeds

a.Exalbuminous -Amorphophallus

b.albuminous- Cereals

On basis of presence or absence of endosperm

1.Albuminous or endospermic

2.Exalbuminous or Non endospermic 

Parthenogenesis

In sexual reproduction in which development of eggs occurs without the participation of sperm cells.

Haploid in Datura is discovered by Blakeslee in 1922

Parthenocarpy

Fruits are formed without fertilization.

Parthenocarpic fruits may be produced-

1.Pollination absence

2.Fertilizarion Failure

3.Zygotic Sterility

Apomixis

In this process the reproduction of seed is done without fertilization or by asexual methods.

Three types of apomixis

1.Non recurrent

2.Recurrent

3.Adventive

Triple Fusion

The primary endosperm nucleus in angiosperms is formed when one male gamete fuse with two polar nuclei.

Polyembryony

When more than one embryo is present in a seed then it is called polyembryony.

In  angiosperms there are four types polyembryony found which are:-

1.Cleavage polyembryony ,it develops by splitting of proembryo.

2.Within the same ovule the formation of more than one embryo.

3.From the sporophytic cell of ovule the development of embryo sac.

4.From other cell of embryo sac  than egg the formation of embryos.

 It was first Discovered by Antony Van Leeuwenhoek in 1719.

Necrohormone theory is discovered by Haberlandt in 1921,22.

Kappert in 1933 proposed Recessive gene theory.

Endosperm 

It is the nourishing tissue in seed which is formed in embryo sac.

It is triploid.

Three types of endosperm are

1. nuclear

2.cellular

3.helobial 

Apogamy

 Without fertilization the development of sporophyte from gametophyte.

Micropropagation

It is the technique by which propagation of cell, tissue & organ culture involves.

Incompatibility

Pistol carrying the functional female gamete fails to set seed following pollination with viable and fertile pollen is capable of bringing fertilization in another pistol and they two are incomplete is called incompatibility.

It may be interspecific or intraspecific

Two types of self incompatibility are

1.Heteromorphic

2.Homomorphic

Embryo

Embryogenesis.

Development of embryo from the diploid zygote is known as embryogenesis.

 Entry of pollen tube  in the embryo sac

They enter from the micropylar end.

Discharge of male gametes from pollen tube

When the pollen tube enters into the embryo sac, the pollen tube bursts at the tip from where two male gamates are released.

Double Fertilization

 The fusion of male nucleus with the egg and the other with polar nuclei which is unique to angiosperms is known as double Fertilization.

 

 

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