Plant Reproduction and Reproduction in Flowering Plants

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Plant Reproduction — Key Facts for Sri Lanka A/L Examination

Asexual Reproduction:

• No gamete fusion
• Offspring genetically identical to parent (clones)
• Methods: Binary fission, budding, fragmentation, spore formation, vegetative propagation

Sexual Reproduction in Plants:

• Fusion of male and female gametes
• Requires pollination (pollen to stigma)
• Double fertilization (unique to angiosperms)

Flower Structure:

Part	Function	Type
Sepals	Protect bud	Calyx (all sepals)
Petals	Attract pollinators	Corolla (all petals)
Stamens	Male organs	Anther + Filament
Carpels	Female organs	Stigma + Style + Ovary

Pollination Types:

Type	Agent	Example
Self-pollination	Same flower	Wheat, rice
Cross-pollination	Wind, insects, animals	Apple, mango

⚡ A/L Exam Tip: Double fertilization is unique to angiosperms - one sperm fertilizes egg, other fertilizes central cell!

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Plant Reproduction — Detailed Study Guide

Sexual Reproduction in Flowering Plants

Microsporogenesis (Male gametophyte formation):

1. Diploid microspore mother cell in anther
2. Meiosis → 4 haploid microspores
3. Each microspore → pollen grain (male gametophyte)
4. Pollen grain: 2 cells (tube cell + generative cell)

Megasporogenesis (Female gametophyte formation):

1. One megaspore mother cell in ovule
2. Meiosis → 4 haploid megaspores
3. 3 degenerate, 1 survives
4. Surviving megaspore → embryo sac (female gametophyte)
5. 7-celled, 8-nucleate structure

Embryo Sac Structure:

Cell	Location	Function
Egg cell	Micropylar	Fertilization
Synergids	Micropylar	Guide pollen tube
Central cell	Center	2 polar nuclei, becomes endosperm
Antipodals	Chalazal	Function unclear

Double Fertilization

Process:

1. Pollen lands on stigma
2. Pollen tube grows down style
3. Pollen tube enters micropyle
4. Pollen tube releases 2 sperm cells
5. Sperm 1 + Egg cell → Zygote (2n) → Embryo
6. Sperm 2 + Central cell (2 polar nuclei) → Primary endosperm (3n)
7. Triple fusion complete

Endosperm:

• Nourishes developing embryo
• 3n (triploid) tissue
• In monocots: Starchy endosperm persistent
• In dicots: May be consumed during development

Seed Development:

Structure	Formation
Ovule	Seed
Ovary	Fruit
Outer integument	Seed coat
Zygote	Embryo
Primary endosperm	Endosperm

⚡ A/L PYQ: “Why is double fertilization important in angiosperms?” Answer: It ensures the development of endosperm only when fertilization occurs, preventing wasted resources. It also increases genetic diversity.

Asexual/Vegetative Reproduction

Natural Methods:

Method	Description	Example
Runners/Stolons	Horizontal stems	Strawberry
Rhizomes	Underground stems	Ginger, turmeric
Tubers	Underground storage	Potato
Bulbs	Underground buds	Onion, garlic
Corms	Solid underground stems	Yam, crocus
Offsets	Side shoots	Coconut

Artificial Propagation:

Method	Description	Example
Cuttings	Stem pieces root	Rose, hibiscus
Layering	Stem bent to soil	Mango
Grafting	Bud/scion on rootstock	Fruit trees
Tissue culture	Micropropagation	Orchids

Advantages of Vegetative Propagation:

• Rapid multiplication
• Preserves desirable traits
• No pollination required
• Can reproduce when seed production fails

⚡ A/L Important: Coconut palms in Sri Lanka are commonly propagated by removing and planting the whole nut (seed propagation). This maintains genetic characteristics of superior palms.

Pollination Mechanisms

Wind Pollination (Anemophily):

• Light, non-sticky pollen
• Large, feathery stigmas
• No showy flowers (no petals)
• Examples: Grasses, rice, coconut

Insect Pollination (Entomophily):

• Sticky pollen
• Brightly colored flowers
• Nectar and scent
• Examples: Mango, papaya, many fruit trees

Sri Lankan Examples:

• Coconut: Wind-pollinated (monoecious)
• Mango: Insect-pollinated
• Rice: Wind-pollinated
• Rubber: Insect-pollinated

Agents of Cross-Pollination:

• Wind (anemophily)
• Insects (entomophily)
• Birds (ornithophily)
• Animals (zoophily)
• Water (hydrophily)

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Plant Reproduction — Complete Notes for A/L Sri Lanka

Pollination and Fertilization Adaptations

Flower Adaptations for Pollinators:

Pollinator	Flower Adaptations
Bees	Blue/purple petals, UV patterns, sweet nectar
Butterflies	Bright colors, narrow tubes
Moths	White petals, night-scented
Birds	Red flowers, no landing platform
Bats	Large, nocturnal, strong scent

Pollen-Pistil Interaction:

1. Pollination: Pollen on stigma
2. Pollen recognition: Compatible pollen germinates
3. Pollen tube growth: Through style
4. Guidance: Synergid cells guide tube
5. Fertilization: Discharge of sperm cells

Self-Incompatibility Mechanisms:

• Prevents self-fertilization (inbreeding)
• Gametophytic: S allele of pollen matches style
• Sporophytic: S allele of pollen parent controls

Fruit and Seed Development

Fruit Types:

Type	Fleshy/Dry	Example
Berry	Fleshy	Tomato, grape, papaya
Drupe	Fleshy with stone	Mango, coconut
Capsule	Dry, opens	Cotton, okra
Legume	Dry, splits	Pea, bean
Grain	Dry, fused to fruit	Rice, wheat
Nut	Dry, hard	Cashew

Fruit Development:

Ovary → Fruit (true fruit if from ovary)
Other parts → Accessory fruit (e.g., apple receptacle)

Sri Lankan Examples:

• True fruit: Mango, papaya, chili
• False fruit (accessory): Apple (fleshy receptacle), strawberry (fleshy receptacle)

Seed Dispersal Mechanisms:

Mechanism	Agent	Examples
Anemochory	Wind	Coconut (buoyant), dandelion
Hydrochory	Water	Coconut (water-dispersed), mangrove
Zoochory	Animals	Mango (eaten), guava (eaten)
Autochory	Explosive dehiscence	Okra, rubber

Seed Dormancy:

• Types:
  • Physical dormancy (hard seed coat)
  • Physiological dormancy (hormones)
  • Morphological dormancy (embryo immature)
• Breaking Dormancy:
  • Scarification (scratching seed coat)
  • Stratification (cold treatment)
  • Light exposure

GCE A/L Sri Lanka Past Paper Tips

Common Diagram Questions:

1. Draw and label LS of anther (6 marks)
2. Draw and label TS of an ovule (6 marks)
3. Draw LS of a flower showing fertilization (10 marks)
4. Draw and label stages of embryo development (8 marks)

Structured Questions:

1. “Describe the process of double fertilization in a flowering plant” (10 marks)
2. “Explain three methods of natural vegetative propagation, with named examples” (12 marks)
3. “Describe the adaptations of wind-pollinated flowers” (8 marks)
4. “Explain the development of a dicotyledonous embryo” (10 marks)

Practical Work:

• Examine floral structure (dissect Hibiscus rosa-sinensis)
• Study pollen grain morphology
• Observe pollen tube growth on agar medium
• Identify fruit types in local flora

⚡ A/L Strategy: For flower dissection practicals in Sri Lanka, Hibiscus is commonly used - know its structure (superior ovary, numerous stamens, large showy petals)!

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