Reproduction - Sexual Reproduction In Flowering Plants [Detailed Notes]

1. Structure of a flower:

• Parts of a flower (petals, sepals, stamens, pistil):

• Each part performs specific functions in reproduction.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Floral diagram:

• Pictorial representation of flower’s structure.

• Helps understand variations and relationships between flowers.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Types of inflorescence:

• Arrangement of flowers on the peduncle.

• Racemose, cymose, and capitate inflorescences.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

2. Stamen:

• Structure of anther and filament:

• Filament: Stalk that supports the anther.

• Anther: Contains pollen grains.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Microsporogenesis (process of pollen formation):

• In anther’s microsporangia, diploid microspore mother cell undergo meiosis.

• 4 haploid microspores form tetrads.

• Microspores mature into pollen grains.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

3. Pistil:

• Structure of ovary, style, and stigma:

• Ovary: Swollen basal part of pistil, containing ovules.

• Style: Slender stalk connects ovary to stigma.

• Stigma: Uppermost receptive part of pistil receives pollen.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Megasporogenesis and formation of embryo sac (development of female gametophyte):

• Inside ovary’s ovule, a diploid cell undergoes meiosis.

• 4 haploid megaspores form. 3 degenerate, leaving one megaspore.

• Megaspore undergoes mitosis to form embryo sac (female gametophyte). -8 nuclei in embryo sac: one egg cell, two synergids, two polar nuclei, three antipodals. -Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

4. Pollination:

• Types of pollination (self-pollination, cross-pollination):

• Self-pollination: Pollen from same flower or same plant reaches the stigma.

• Cross-pollination: Pollen from one flower reaches stigma of another flower on a different plant.

• Agents responsible, ecological significance.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Agents of pollination (wind, insects, birds, mammals):

• Wind, butterflies, bees, birds, bats, lizards, snails.

• Adaptations for attracting specific pollinators.

• Co-evolution between plants and pollinators.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Pollination syndromes:

• Combinations of floral traits, rewards, attract specific pollinator type.

• Examples: Nectar guides, fragrant flowers, showy petals.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

5. Fertilization:

• Germination of pollen grains and growth of pollen tube:

• Pollen on stigma absorbs water, germinates.

• Pollen tube grows through style to ovary, carrying sperm cells.

• Requires compatible pollination for germination and growth.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Transfer of male gametes (sperm cells) to the embryo sac:

• Pollen tube enters the embryo sac through the micropyle.

• Releases 2 sperm cells. One fuses with egg cell (syngamy), forming a zygote.

• Other sperm fuses with 2 polar nuclei (triple fusion), forming a triploid primary endosperm nucleus (PEN).

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Double fertilization (fusion of one sperm cell with the egg cell and another with the polar nuclei):

• The process of fertilization involves two fusions.

• Syngamy: fusion of sperm and egg, resulting in diploid zygote.

• Triple fusion: fusion of other sperm and two polar nuclei, resulting in triploid endosperm nucleus.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

6. Post-fertilization changes:

• Development of endosperm (storage tissue):

• Primary endosperm nucleus divides repeatedly to form endosperm tissue.

• Provides nutrition to the developing embryo and seedling.

• Types of endosperm: cellular and nuclear.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Development of embryo (formation of zygote, proembryo, and mature embryo):

• Zygote undergoes mitosis, forming proembryo.

• Proembryo further differentiates into embryo with a radicle, plumule, and one or two cotyledons.

• Development varies in monocotyledons and dicotyledons.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

7. Fruit and seed development:

• Structure of a fruit:

• Mature ovary along with enclosed seeds.

• Function: protect, disperse seeds, attract animals for dispersal.

• Types: simple, aggregate, multiple (collective), parthenocarpic.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Fruit types (simple, aggregate, multiple):

• Simple fruits develop from a single pistil.

• Aggregate fruits develop from several pistils of the same flower.

• Multiple fruits develop from several flowers that unite.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Seed structure (testa, tegmen, nucellus, and embryo):

• Testa: Seed coat.

• Tegmen: Inner protective layer.

• Nucellus: Tissue surrounding embryo sac before fertilization.

• Embryo: Plant in the early stage of development.

• Refer to NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

• Seed coat features:

• Adaptations for survival, dispersal, protection.

• Hardness, wings, spines, hairs, water-resistant, etc.

• NCERT Biology Class 11, Chapter 5 “Morphology of Flowering Plants”.

8. Reproductive structures in some other angiosperms:

• Asteraceae (Compositae):

• Composite flowers.

• Head inflorescence bearing florets.

• Inferior ovary.

• Example: Sunflower.

• NCERT Biology Class 12, Chapter 2 “Sexual Reproduction in Flowering Plants”.

• Liliaceae:

• Flowers arranged in a racemose inflorescence.

• Superior ovary.

• Example: Lily.

• NCERT Biology Class 12, Chapter 2 “Sexual Reproduction in Flowering Plants”.

• Papilionaceae/Leguminosae:

• Flowers usually papilionaceous.

• Monothecous anther.

• Pod (legume) fruit.

• Example: Bean, pea.

• NCERT Biology Class 12, Chapter 2 “Sexual Reproduction in Flowering Plants”.

9. Parthenocarpy and apomixis:

• Definition and significance of parthenocarpy and apomixis:
• Parthenocarpy: Fruit development without fertilization.
• Apomixis: Seeds develop without fertilization.
• Applications in agriculture and plant breeding.
• NCERT Biology Class 12, Chapter 2 “Sexual Reproduction in Flowering Plants”.

10. Applications of sexual reproduction in flowering plants:

• Plant breeding and crop improvement:

• Introduction, hybridization, and selection to develop new varieties.

• NCERT Biology Class 12, Chapter 5 “Principles of Inheritance and Variation”.

• Ornamental plants:

• Hybridization to produce desirable flower shapes and colors.

• NCERT Biology Class 11, Chapter 7 “Structural Organisation in Animals”.

• Medicinal plants:

• Production of valuable secondary metabolites used in medicines.

• Plants contain different bioactive molecules that can be used for medicinal purposes.

• NCERT Biology Class 11, Chapter 4 “Animal Kingdom”.

• Conservation of plant species:

• Understanding reproductive biology aids conservation efforts.

• Conservation of endangered plant species using seed banks and tissue culture techniques.

• NCERT Biology Class 12, Chapter 15 “Biodiversity and Conservation”.