Chapter 45: Plant Reproduction and Development

Overview

• Focus on how plants reproduce.
• Examine the structures and functions of flowers, specifically angiosperms.
• Explore fruits, seeds, germination, pollination, and seed dispersal.

Plant Reproduction

• Asexual Reproduction

  • Example: "Mother of thousands" plant; new plants grow from the parent plant's edges, genetically identical.
  • Other examples include strawberry runners.

• Sexual Reproduction

  • Alternation of generations:
    • Sporophyte: Diploid stage, large visible plant.
    • Gametophyte: Haploid stage, produces gametes (eggs and sperm).
    • Fertilization leads to a new diploid zygote.
  • Example: Ferns have free-living gametophytes.

Flower Structure and Function

• Focus on angiosperms (flowering plants).
• Dominance of animal pollination (insects, birds, bats).
• Wind pollination is less common (10% of angiosperms).
• Parts of a Flower:
  • Sepals: Protect the bud.
  • Petals: Attract pollinators.
  • Carpel: Contains ovary and ovules (female reproductive parts).
  • Stamen: Anthers produce pollen (male reproductive parts).
  • Stigma: Pollen landing spot for fertilization.

Incomplete and Complete Flowers

• Complete flowers have all reproductive parts.
• Incomplete flowers (e.g., grass) may lack petals or sepals.
• Some plants separate male and female flowers (e.g., pumpkins, zucchini).

Development of Male and Female Gametophytes

• Male Gametophyte (Pollen Grain):
  • Develops from microspore mother cell.
  • Consists of two sperm cells and a tube cell.
• Female Gametophyte:
  • Develops from megaspore mother cell.
  • Produces one egg cell.

Double Fertilization

• Unique to angiosperms.
• Two sperm per pollen grain:
  • One fertilizes the egg to form an embryo.
  • Other forms endosperm for seed nourishment.

Fruits and Seeds

• Fruits: Mature ripened ovary containing seeds.
  • Can be edible or non-edible.
• Seed Development:
  • Parts: Seed coat, endosperm, cotyledons.
• Germination:
  • Dormancy period prevents early sprouting.
  • Environmental cues for germination (drying, cold, seed coat disruption).

Seed Germination Structures

• Apical and hypocotyl hooks protect seedlings during soil emergence.

Plant-Pollinator Interactions

• Co-evolution examples:
  • Orchids mimicking female wasps.
  • Yucka plants/nurseries for moths.
  • Figs pollinated by wasps.

Seed Dispersal by Fruits

• Evolution favors wide seed dispersal for survival.
• Methods include:
  • Animal Dispersal: Seeds stick to fur or are eaten.
  • Explosive Dispersal: Jewelweed seed pods burst open.
  • Wind Dispersal: Maple seeds.
  • Water Dispersal: Coconuts.

These notes provide a comprehensive overview of the major topics covered in the chapter on plant reproduction and development.