CBSE Class 12 Biology Sexual Reproduction In flowering Plants Notes Set A

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Sexual Reproduction In flowering Plants Class 12 Biology Revision Notes

Class 12 Biology students should refer to the following concepts and notes for Sexual Reproduction In flowering Plants in standard 12. These exam notes for Grade 12 Biology will be very useful for upcoming class tests and examinations and help you to score good marks

Sexual Reproduction In flowering Plants Notes Class 12 Biology

class_12-biology_concept_250

 FLOWER

♦ Site of sexual Reproduction.

 Male and female reproductive organs are borne on flowers.


PARTS OF A FLOWER:

Four whorls – calyx (sepals), corolla (petals), androecium (Male

reproductive organ), gynoecium (Female reproductive organs)         class_12-biology_concept_251

Function of calyx:protects the bud.

Function of corolla :attracts insects by its colour


Male Reproductive Organ

 Androecium consists of Stamens.

 Stamen consists of anther, filament & connective (when anther is bilobed)

 Anther bilobedhas 4 Microsporangia.

Refer fig. 2.1 of NCERT (L.S. OF A FLOWER WITH DIFFERENT PARTS)


MICROSPOROGENESIS:The process of formation of micro spores from pollen mother cell through

meiosis iscalled microsprogenesis.

Tapetum :Inner most layer of wall of microsporangium .Cells have dense cytoplasm. Generally have more than

one nucleus .Nourishes the developing pollen grain

Microspore mother cell (2n)

Meiosis

Microspore (n)

Mitosis

Pollen grains (n)

class_12-biology_concept_252


LAYERS OF ANTHER WALL


Pollen grains have two outer walls; i) Exine ii) Intine

 Exine is made of sporopollenin.(Hardest natural substance). Intine is made of cellulose and pectin.

 Mature pollen grains have two cells – largevegetative cell & small generative cell.

 Generative cell forms two male gametes bymitotic division.

Pollen grains (Refer fig 2.7 of text book)shed in 2-celled /3celled stage


Gynoecium / carpel (the female reproduuctive organ)

(Structure of anatropous ovule) Megasporangium

Each Carpel consists of ovary, style &stigma.

 Ovules are attached to ovary by placenta.

 Funicle – stalk of ovule

 Hilum, a region where funicle is attached

 Integuments –cover embryo sac.

 Micropyle – a pore for entry of pollen tube &to imbibe water. 

class_12-biology_concept_253

 

Megasporogenesis

CBSE Class 12 Biology - Sexual Reproduction Inflowering Plants
                    Megaspore mother cell (2n)
                                  ↓               Meiosis
                       4 Megaspores (n)
                   (3 megaspores degenerate, 1 remains functional)
                                  ↓
                   Funtional Megaspore (n) (Divides 3times by mitosis)
                                  ↓
                  8 Nucleated Embryo Sac formed
                                                   ↓
                                           3 cells group at micropylar end -the egg cell(n) & 2 synergids(n)
                                 ↓      
                         3 cells at chalazal end called antipodals(n)
                    ↓ 
                2 polar nuclei at center(n each )

       Ref fig 2.7 and 2.8 of text book

 

POLLINATION– transfer of pollen from anther to stigma. Agents of pollination –air, water, insect.bat,bird,man.

CBSE Class 12 Biology - Sexual Reproduction Inflowering Plants

 

Double fertilization
¤ Pollen grains germinate on stigma & pollen tube grows through style.
¤ Pollen tube reaches micropyle& releases two male gametes into embryo-sac
Fertilisation is the process of fusion of male& female gametes (n+n) to form a diploid(2n)zygote.

 

Syngamy: Fusion of one male gamete(n) with egg (n) Zygote(2n)Produced First Fusion  Fusion of two Polar Nuclei(n+n=2n)  Second fusion. Male Gamete(n) Fuses with the fusion product of the two polar nuclei(3n)Third Fusion fusion of male gamete with egg cell.

¤ Double fertilization: i)Fusion of male gamete with egg – First fertilization ,SYNGAMY
ii)Fusion of fusion product of polar nuclei with male gamete – Second fertilization .TRIPLE FUSION Refer fig 2.13 in NCERT

Post fertilisation changes:
Stages of embryo development after fertilization:

1. Zygote divides by mitosis into suspensor & embryo cells
2. Suspensor cell forms a globular basal cell which remains embedded in the endosperm & a multicellular suspensor bearing the embryo
3.Globular embryo becomes heart-shaped & then mature embryo with radicle, plumule&Cotyledons
 Primary endosperm nucleus – divides repeatedly to form endosperm, food for theembryo.
  Mature ovary becomes fruit.
  Mature ovule becomes seed.
  True Fruit develops only from the ovary, e.g. mango, tomato
  False Fruit develops from parts of the flowerother than the ovary e.g. apple, peach etc.

Seeds two types: i) Albuminous (with Endosperm)
ii) Non albuminous(without Endosperm)

Special mechanism of reproduction:-

I) Apomixis- Production of seeds without fertilisation e.g.
species of Astereceae and grasses.
ii) Polyembryony- Occurrence of more than one embryo in a seed e.g.Orange.

CBSE Class 12 Biology - Sexual Reproduction Inflowering Plants

Outbreeding devices:
Continued self-pollination result in breeding depression. Flowering plants have developed many devices to discourage self-pollination & encourage cross-pollination such as Bearing unisexual flowers Unisexuality Anther & stigma mature at different times Dichogamy Anther & stigma placed at different positions Heterostyly Pollen grains of a flower donot germinate on the stigma of the same flowerSelf incompatibilityartificial HybridisationHeterostyly

CBSE Class 12 Biology - Sexual Reproduction Inflowering Plants






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Chapter 1 Reproduction in Organisms
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Chapter 2 Sexual Reproduction In Flowering Plants
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CBSE Class 12 Biology Sexual Reproduction In flowering Plants Notes Set A
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CBSE Class 12 Biology Sexual Reproduction In flowering Plants Notes Set C
Chapter 3 Human Reproduction
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Chapter 4 Reproductive Health
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CBSE Class 12 Biology Reproductive Health Study Guide
Chapter 5 Principles of Inheritance and Variation
CBSE Class 12 Biology Genetics Notes
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Chapter 6 Molecular Basis of Inheritance
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Chapter 7 Evolution
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Chapter 8 Human Health and Diseases
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Chapter 9 Strategies for Enhancement In Food Production
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Chapter 10 Microbes In Human Welfare
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Chapter 11 Biotechnology Principles and Processes
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CBSE Class 12 Biology Biotechnology Principles And Processes Study Guide
Chapter 12 Biotechnology and Its Application
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Chapter 13 Organisms and Populations
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Chapter 14 Ecosystem
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Chapter 15 Biodiversity and Conservation
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Chapter 16 Environmental Issues
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