Question

Write an essay on Sexual Reproduction in Flowering Plants

Answer 1

Introduction

Sexual reproduction in flowering plants (angiosperms) is the process by which male and female gametes fuse to form a zygote that develops into a new plant. It involves the production of flowers, formation of gametes, fertilization, and development of fruits and seeds. This process ensures genetic variation and evolution in plants.

Structure of a Flower

A flower is the reproductive organ of a flowering plant. It has four main parts:

• 
  Calyx (sepals) — protects the flower in its bud stage.
• 
  Corolla (petals) — brightly coloured to attract pollinators.
• 
  Androecium — the male reproductive part consisting of stamens (anther and filament).
• 
  Gynoecium — the female reproductive part consisting of pistil (stigma, style, and ovary).

Formation of Gametes

The male gametes are produced inside the
anthers through a process called
microsporogenesis, which results in the formation of pollen grains (male gametophytes). The female gametes (eggs) are formed inside the
ovule through
megasporogenesis, producing an embryo sac (female gametophyte) that contains the egg cell.

Pollination

Pollination is the transfer of pollen grains from the anther to the stigma of a flower. It can occur in two ways:

• 
  Self-pollination — pollen is transferred within the same flower or to another flower on the same plant.
• 
  Cross-pollination — pollen is transferred to the stigma of a flower on a different plant of the same species. It is often aided by wind, insects, water, or animals.

Fertilization

After pollination, the pollen grain germinates on the stigma and forms a pollen tube that carries two male gametes to the ovule through the style. Inside the embryo sac:

• One male gamete fuses with the egg cell to form a
  zygote (syngamy).
• The other male gamete fuses with two polar nuclei to form a
  triploid endosperm nucleus (triple fusion).

This process, unique to angiosperms, is called
double fertilization.

Formation of Fruit and Seed

After fertilization:

• The
  zygote develops into an
  embryo.
• The
  ovule becomes a
  seed.
• The
  ovary develops into a
  fruit that protects the seeds and helps in their dispersal.

Seed Germination

When a mature seed is dispersed and lands in a favorable environment (moisture, air, warmth), it germinates. The embryo grows into a new plant, completing the life cycle.

Conclusion

Sexual reproduction in flowering plants is a highly organized process that ensures the continuation of species and introduces genetic variation. It is fundamental to plant evolution, biodiversity, and agricultural productivity.