Biology: Sexual Reproduction in Flowering Plants

Sexual Reproduction in Flowering Plants

Self-Incompatibility Mechanisms

• Self-incompatibility: the inability of a flower to fertilize itself with its own pollen
• Mechanisms to prevent self-fertilization:
  • Genetic incompatibility: genes that control pollen growth and pistil recognition prevent self-pollination
  • Physical barriers: structures in the flower that prevent self-pollination (e.g., stamen and pistil arrangement)
  • Chemical barriers: chemical signals that prevent self-pollen from germinating or growing on the stigma

Fruit and Seed Formation

• Fruit formation:
  • Ovary development: after fertilization, the ovary grows and matures into a fruit
  • Pericarp differentiation: the ovary wall differentiates into exocarp, mesocarp, and endocarp
• Seed formation:
  • Embryo development: the zygote develops into an embryo
  • Endosperm development: the fertilized central cell develops into the endosperm, providing nutrients to the embryo

Embryo Development

• Stages of embryo development:
  1. Zygote formation: fusion of sperm and egg nuclei
  2. Embryo formation: series of cell divisions and differentiation
  3. Organogenesis: formation of root, stem, and leaf primordia
• Embryo structure:
  • Radicle (primary root)
  • Hypocotyl (stem)
  • Cotyledon (seed leaf)

Pollination

• Types of pollination:
  • Self-pollination: pollination within the same flower
  • Cross-pollination: pollination between different flowers
• Agents of pollination:
  • Biotic agents: insects, birds, bats, and other animals
  • Abiotic agents: wind, water, and gravity

Fertilization

• Process of fertilization:
  1. Pollen germination: pollen grain grows a pollen tube
  2. Sperm delivery: sperm nuclei are released into the pollen tube
  3. Fertilization: sperm nuclei fuse with the egg nucleus and central cell nucleus
• Double fertilization:
  • Fertilization of the egg nucleus: forms the zygote
  • Fertilization of the central cell nucleus: forms the endosperm

Sexual Reproduction in Flowering Plants

Self-Incompatibility Mechanisms

• Self-incompatibility prevents a flower from fertilizing itself with its own pollen
• Genetic incompatibility prevents self-pollination through genes controlling pollen growth and pistil recognition
• Physical barriers, such as stamen and pistil arrangement, prevent self-pollination
• Chemical barriers, such as chemical signals, prevent self-pollen from germinating or growing on the stigma

Fruit and Seed Formation

• Fruit formation occurs after fertilization, where the ovary grows and matures
• Ovary wall differentiates into exocarp, mesocarp, and endocarp
• Seed formation involves embryo development from the zygote
• Endosperm development provides nutrients to the embryo, formed from the fertilized central cell

Embryo Development

• Embryo development involves three stages: zygote formation, embryo formation, and organogenesis
• The radicle develops into the primary root
• The hypocotyl develops into the stem
• The cotyledon develops into the seed leaf

Pollination

• Self-pollination occurs within the same flower
• Cross-pollination occurs between different flowers
• Biotic agents, such as insects, birds, and bats, facilitate pollination
• Abiotic agents, such as wind, water, and gravity, also facilitate pollination

Fertilization

• Fertilization involves pollen germination, sperm delivery, and fertilization of the egg nucleus and central cell nucleus
• Double fertilization results in the formation of the zygote and endosperm
• The zygote develops into the embryo, while the endosperm provides nutrients to the embryo