5.1 Plant Reproduction

Key Concepts: Sexual Reproduction

• Involves production and fusion of male and female gametes.
• Primary organ in flowering plants: Flower.
• Flower Structure: Male (stamen - anther, filament), Female (pistil/carpel - stigma, style, ovary, ovules).

Pollination

• Transfer of pollen grains from anther to stigma.
• Self-Pollination: Pollen transferred within same flower/plant.
• Cross-Pollination: Pollen transferred between different plants of same species (promotes genetic diversity).
• Pollinating Agents: Wind, water, insects, animals.

Fertilization

• Fusion of male and female gametes.
• Pollen grain lands on stigma, germinates, grows pollen tube to ovule.
• Double Fertilization (Unique to Flowering Plants):
  • One sperm + egg → diploid zygote (embryo).
  • Other sperm + two polar nuclei → triploid endosperm (nutritive tissue).

Seed and Fruit Formation

• Following fertilization:
  • Ovule develops into a seed (contains embryo and endosperm).
  • Ovary matures into a fruit (encloses and protects seeds).

Vegetative Reproduction Methods (Asexual)

• New plants generated from vegetative parts (stems, roots, leaves) without seeds/spores.
• Offspring are genetically identical clones.

Natural Vegetative Propagation

• Runners (Stolons): Horizontal stems along ground (e.g., Strawberry).
• Rhizomes: Underground stems (e.g., Ginger, Bamboo).
• Tubers: Swollen underground stems/roots (e.g., Potato, Sweet potato).
• Bulbs: Short, underground stems with fleshy leaves (e.g., Onion, Garlic).
• Corms: Swollen, solid underground stem bases (e.g., Gladiolus).
• Plantlets: Miniature plants on leaves/stems (e.g., Kalanchoe).
• Suckers: New shoots from roots/base of stem (e.g., Banana).

Artificial Vegetative Propagation (Horticultural)

• Cutting: Section of plant (stem, leaf, root) planted to form new plant (e.g., Rose).
• Layering: Stem/branch induced to root while attached to parent (e.g., Jasmine).
• Grafting: Joining parts of two plants to grow as one (scion + rootstock) (e.g., Apple trees).
• Tissue Culture (Micropropagation): Growing plants from small tissue pieces in sterile medium (large number of identical plants).

Seed Dispersal Methods

• Movement of seeds away from parent plant.
• Wind Dispersal (Anemochory): Lightweight seeds, feathery/winged structures (e.g., Dandelion, Maple).
• Water Dispersal (Hydrochory): Buoyant, waterproof seeds (e.g., Coconut, Water Lily).
• Animal Dispersal (Zoochory): External attachment (hooks), internal dispersal (edible fruits), caching (burying nuts), ant dispersal.
• Gravity Dispersal (Barochory): Heavy fruits/seeds fall (e.g., Apple, Coconut).
• Explosive Dispersal (Autochory): Fruits burst open to scatter seeds (e.g., Pea pods, Okra).

Importance of Seed Dispersal

• Reduces Competition: For resources near parent plant.
• Colonization of New Areas: Expands geographical range.
• Promotes Genetic Diversity: Facilitates cross-pollination and genetic mixing.
• Avoids Predation and Disease: Seeds escape density-dependent mortality.
• Maintains Ecosystem Health and Biodiversity.