🌺 CHAPTER 1
SEXUAL REPRODUCTION IN FLOWERING PLANTS
(Summary & Quick Revision Notes)
🔹 1. Parts of a Flower
(Reproductive Organs)
Flower – The reproductive unit of
angiosperms.
Four whorls:
1.
Calyx
(Sepals): Protection
in bud stage.
2.
Corolla
(Petals): Brightly
colored for attracting pollinators.
3.
Androecium
(Stamens): Male
reproductive organ → anther + filament.
4.
Gynoecium
(Carpels/Pistil):
Female organ → stigma, style, ovary.
Types:
- Bisexual – Both androecium and gynoecium
present (e.g., hibiscus).
- Unisexual – Either male or female organ
present (e.g., papaya).
🔹 2. Structure of the Stamen
(Male Reproductive Part)
- Each stamen = filament +
anther.
- Anther – bilobed; each lobe has two
microsporangia → total four pollen sacs.
- Inside: Epidermis,
Endothecium, Middle layers, Tapetum.
- Tapetum – nourishes developing pollen.
🔹 3. Microsporogenesis
(Formation of Pollen Grains)
- Microspore Mother Cell (MMC) → meiosis → microspore
tetrad.
- Each microspore → pollen
grain (male gametophyte).
- Pollen wall:
- Exine: Made of sporopollenin,
very tough.
- Intine: Made of cellulose and pectin.
- 2-celled stage: Vegetative cell + Generative
cell.
- 3-celled stage (in tube): 2 male gametes + vegetative
cell.
🔹 4. Structure of the Ovule
(Female Reproductive Part)
- Funicle: Stalk attaching ovule to ovary
wall.
- Nucellus: Tissue inside ovule.
- Integuments: Protective layers.
- Micropyle: Opening for pollen tube entry.
- Chalaza: Opposite end of micropyle.
- Contains Megaspore Mother
Cell (MMC) → gives rise to embryo sac.
🔹 5. Megasporogenesis
(Formation of Female Gametophyte)
- MMC (2n) → meiosis → 4
haploid megaspores.
- 3 degenerate, 1 functional.
- Functional megaspore → embryo
sac (female gametophyte).
Embryo
Sac Structure (Polygonum type):
- 7 cells, 8 nuclei:
- 1 egg cell + 2 synergids
(micropylar end)
- 3 antipodals (chalazal end)
- 1 central cell (2 polar
nuclei)
🔹 6. Pollination
Definition: Transfer of pollen from anther →
stigma.
Types:
1.
Autogamy
(Self-pollination)
– Same flower.
2.
Geitonogamy – Different flower, same plant.
3.
Xenogamy – Different plant
(cross-pollination).
Agents:
- Wind (Anemophily): Light pollen, feathery stigma
(e.g., maize).
- Water (Hydrophily): Pollen floats (e.g.,
Vallisneria).
- Insects (Entomophily): Bright colors, nectar (e.g.,
sunflower).
- Birds (Ornithophily): Tubular flowers (e.g.,
hibiscus).
🔹 7. Outbreeding Devices
(Prevention of Self-Pollination)
1.
Dichogamy: Anther & stigma mature at
different times.
2.
Herkogamy: Physical separation (hibiscus).
3.
Unisexuality: Male & female flowers separate
(papaya).
4.
Self-Incompatibility: Chemical barrier rejects self
pollen.
5.
Heterostyly: Different stigma & anther
heights.
🔹 8. Artificial
Hybridization (Plant Breeding Technique)
Steps:
1.
Selection
of parents
2.
Emasculation: Removal of anthers before dehiscence.
3.
Bagging: Covering flower to avoid
contamination.
4.
Pollination: Manually apply desired pollen.
5.
Re-bagging: Protect till fruit formation.
🔹 9. Pollen-Pistil
Interaction
- Pollen lands on stigma,
germinates → pollen tube grows through style → enters ovule
through micropyle.
- Guided by synergids
(filiform apparatus).
- Pollen tube carries 2 male
gametes.
🔹 10. Double Fertilization
(Unique to Angiosperms)
- One male gamete + egg → Zygote
(Syngamy)
- Other male gamete + 2 polar
nuclei → Primary Endosperm Nucleus (Triple Fusion)
Hence, Double Fertilization = Syngamy + Triple Fusion
Significance:
- Ensures simultaneous formation
of zygote and endosperm.
🔹 11. Post-Fertilization
Changes
|
Structure |
After Fertilization |
|
Ovary |
Fruit |
|
Ovule |
Seed |
|
Zygote |
Embryo |
|
Integuments |
Seed coat |
|
Endosperm nucleus |
Endosperm |
🔹 12. Endosperm Formation
- Develops from primary
endosperm nucleus (3n)
Types:
1.
Nuclear – Free nuclei, e.g., coconut water
2.
Cellular – With cell walls, e.g., Datura
3.
Helobial – Partial cellular, e.g., monocots
Function: Nourishes developing embryo.
🔹 13. Embryo Development
- Zygote → pro-embryo → globular
→ heart-shaped → mature embryo.
Dicot embryo: 2 cotyledons, plumule, radicle, embryonal axis.
Monocot embryo: 1 cotyledon (scutellum), coleoptile, coleorhiza.
🔹 14. Seed
Parts:
- Seed coat (testa + tegmen)
- Embryo (radicle, plumule,
cotyledon)
- Endosperm (in some)
Types:
- Endospermic: Food in endosperm (maize).
- Non-endospermic: Food in cotyledons (bean).
🔹 15. Fruit Formation
- Ovary → fruit; ovule → seeds.
Types: - True fruit: From ovary only (mango).
- False fruit: From ovary + other parts
(apple).
- Parthenocarpic fruit: Without fertilization
(banana).
🔹 16. Apomixis
Definition: Seed formation without
fertilization.
Types:
- From diploid cells of ovule
(asexual).
Examples: Citrus, mango.
Importance: - Maintains hybrid vigour.
- Cost-effective for farmers.
🔹 17. Polyembryony
Definition: More than one embryo in a seed.
Causes:
- Multiple fertilizations.
- Embryos from nucellus or
integuments.
Example: Citrus.
Benefit: Multiple seedlings from one seed.
🔹 18. Seed Dispersal
Agents:
1.
Wind: Light, hairy (cotton).
2.
Water: Floating (coconut).
3.
Animals: Sticky or edible (mango).
4.
Explosion: Bursting pods (balsam).
Importance:
- Prevents competition.
- Spreads species to new areas.
🔹 19. Seed Germination
Process:
1.
Imbibition: Absorption of water.
2.
Enzyme
activation.
3.
Radicle
emergence.
4.
Plumule
growth.
Conditions: Water, oxygen, temperature, viable
seed.
🔹 20. Important Diagrams
(Must Practice)
✅
Structure of Anther
✅ Pollen Grain (2-celled & 3-celled stage)
✅ Structure of Ovule
✅ Embryo Sac (7-celled, 8-nucleate)
✅ Double Fertilization (Syngamy + Triple Fusion)
✅ Structure of Dicot & Monocot Seeds
📒 Important Terms
(One-Liners for Quick Revision)
|
Term |
Meaning |
|
Syngamy |
Fusion of male and female gametes |
|
Triple Fusion |
Fusion of male gamete with two polar nuclei |
|
Double Fertilization |
Combination of syngamy + triple fusion |
|
Parthenocarpy |
Fruit formation without fertilization |
|
Apomixis |
Seed formation without fertilization |
|
Endosperm |
Triploid nutritive tissue |
|
Tapetum |
Nourishing layer in anther |
|
Micropyle |
Opening for pollen tube entry |
|
Funicle |
Stalk attaching ovule to ovary |
|
Nucellus |
Tissue enclosing embryo sac |
|
Antipodals |
Cells at chalazal end of embryo sac |
💡 Quick Recap
(One-Word/Concept Questions)
1.
Unique
feature of angiosperm fertilization → Double Fertilization
2.
Layer
nourishing microspores → Tapetum
3.
Pollen
tube entry through micropyle → Porogamy
4.
Outer
wall of pollen → Exine (Sporopollenin)
5.
Type
of embryo sac → Polygonum type (most common)
6.
Functional
megaspore → Haploid
7.
Endosperm
ploidy → Triploid (3n)
8.
Apomixis
example → Citrus
9.
Non-endospermic
seed → Bean
10.Endospermic seed → Maize
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