Notes: Sexual Reproduction in Flowering Plants

Introduction

• Presented by Dr. Vepan Kumar Sharma
• Beginning of the 12th-grade syllabus
• Detailed description in NCERT
• Use of flowcharts for revision

Structure of the Flower

• Four parts in a flower:
  • Anther (male part)
  • Style
  • Ovary (female part)
  • Pistil (carpel)
• Anther has two lobes and four theca (tetrasporangiate)
• Sporocytes in microsporangium

Formation of Male Gamete

• Four microspores formed in anther
• Four haploid cells formed through meiosis
• Two cells in pollen grain:
  • Vegetative cell
  • Generative cell (produces two male gametes)

Formation of Female Gamete

• Ovary, style, and stigma in pistil
• Megaspore mother cell in ovule
• Four megaspores formed by meiosis, three degenerate (monosporic development)
• One megaspore progresses and forms the embryo sac

Fertilization

• Pollen grain falls on stigma, formation of pollen tube
• Double fertilization:
  • One male gamete + one female gamete = zygote
  • Two polar nuclei + one male gamete = primary endosperm nucleus

Development of Embryo

• Importance of zygote and endosperm
• Endosperm:
  • Precedes embryo development
  • Example of coconut
• Formation of embryo:
  • Differences in monocots and dicots

Formation of Fruits

• Fruits:
  • True fruits (formed from ovary)
  • False fruits (formed from other parts)
  • Examples of parthenocarpy and apomixis

Types of Pollination

• Autonomy (within a flower)
• Geitonogamy (within a tree)
• Cross-pollination (between different trees)

Pollination Agents

• Biotic:
  • Insects, birds
• Abiotic:
  • Wind, water

Important Points

• Effects of in-breeding and out-breeding
• Methods of out-breeding:
  • Unisexual flowers
  • Non-synchrony
  • Difference in position
  • Self-incompatibility

Conclusion

• Summarization of key points in this chapter
• Next session: Principles of Inheritance and Variation