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Unit 1: Reproduction
Chapter 1.1: Sexual Reproduction in Flowering Plants
Flower Structure
Definition:
The reproductive organ of angiosperms.
Main Parts:
Calyx (Sepals):
Protects the bud.
Corolla (Petals):
Attracts pollinators.
Androecium (Stamens):
Male reproductive part.
Gynoecium (Pistil/Carpel):
Female reproductive part.
Androecium (Male)
Composed of
stamens
.
Each stamen has:
Filament:
The stalk.
Anther:
Produces pollen.
Gynoecium (Female)
Composed of
carpels
.
Each carpel has:
Ovary:
Contains ovules.
Style:
Connects ovary to stigma.
Stigma:
Receptive tip for pollen.
Male Gametophyte
Microsporangium (Pollen Sac):
Located in the anther.
Contains sporogenous tissue.
Microsporogenesis:
Formation of microspores from microspore mother cells (MMCs) via meiosis.
Pollen Grain:
Represents the male gametophyte.
Pollen Grain Structure
Exine:
Hard outer layer (sporopollenin).
Intine:
Thin inner layer (pectocellulose).
Two Cells:
Vegetative Cell:
Forms pollen tube.
Generative Cell:
Forms two male gametes.
Female Gametophyte
Ovule (Megasporangium):
Develops into a seed after fertilization.
Anatropous Ovule:
Most common, inverted type.
Megasporogenesis:
Formation of megaspores from a megaspore mother cell (MMC) via meiosis.
Embryo Sac:
The female gametophyte.
Embryo Sac Development
Develops from a single functional megaspore.
7-celled, 8-nucleate structure:
Egg apparatus:
1 egg cell, 2 synergids.
Central cell:
2 polar nuclei.
Antipodal cells:
3 cells at the chalazal end.
Pollination
Definition:
Transfer of pollen from anther to stigma.
Types:
Autogamy:
Self-pollination (same flower).
Geitonogamy:
Same plant, different flower.
Xenogamy:
Cross-pollination (different plant).
Agents of Pollination
Abiotic:
Wind (Anemophily):
Grasses, corn.
Water (Hydrophily):
Vallisneria
,
Zostera
.
Biotic:
Insects (Entomophily):
Bees, butterflies.
Animals (Zoophily):
Birds, bats.
Outbreeding Devices
Mechanisms to encourage cross-pollination.
Dichogamy:
Anthers and stigma mature at different times.
Herkogamy:
Physical barrier between anther and stigma.
Heterostyly:
Different lengths of styles and stamens.
Self-incompatibility:
Genetic mechanism to prevent self-pollen germination.
Unisexuality:
Male and female flowers on different plants.
Pollen-Pistil Interaction
The sequence of events from pollen deposition to pollen tube entry into the ovule.
Recognition:
Pistil recognizes compatible pollen.
Germination:
Pollen tube grows.
Entry into Ovule:
Pollen tube enters the ovule, usually through the micropyle.
Artificial Hybridization
A crop improvement program.
Steps:
Emasculation:
Removal of anthers.
Bagging:
Covering the flower to prevent unwanted pollination.
Pollination:
Dusting with desired pollen.
Rebagging:
Until fruit develops.
Double Fertilization
A unique event in flowering plants.
Syngamy:
One male gamete + egg cell ->
Zygote (2n)
.
Triple Fusion:
Other male gamete + two polar nuclei ->
Primary Endosperm Nucleus (PEN) (3n)
.
Post-Fertilization Events
Ovary
->
Fruit
Ovules
->
Seeds
Zygote
->
Embryo
PEN
->
Endosperm
Seed and Fruit
Seed:
Albuminous:
Retains endosperm (e.g., wheat, maize).
Non-Albuminous:
No residual endosperm (e.g., pea, groundnut).
Fruit:
True Fruit:
Develops only from the ovary.
False Fruit:
Develops from the ovary and other floral parts.
Special Modes of Reproduction
Apomixis:
Seed formation without fertilization.
Parthenocarpy:
Fruit development without fertilization (seedless fruits).
Polyembryony:
Occurrence of more than one embryo in a seed.
Seed and Fruit Dispersal
Significance:
Prevents overcrowding.
Colonization of new areas.
Promotes genetic diversity.
Agents:
Wind, water, animals, explosive mechanisms.