How Does the Process of Fertilization Take Place in Flowers?

Fertilization in flowering plants is a crucial step in sexual reproduction, resulting in the formation of seeds. Here’s a step-by-step overview of how this process occurs:

• Pollination: The process begins when pollen grains, produced by the anther (male part of the flower), are transferred to the stigma (part of the female pistil). Transfer can happen via wind, insects, animals, or water.
• Pollen Germination and Pollen Tube Formation: Once a compatible pollen grain lands on the stigma, it absorbs moisture and germinates, producing a pollen tube. This tube grows down through the style (the stalk of the pistil) toward the ovary.
• Entry into the Ovule: The pollen tube extends until it reaches the ovary, where ovules (potential seeds) are located. The pollen tube enters the ovule through a tiny opening called the micropyle.
• Double Fertilization: Inside the ovule, the pollen tube releases two sperm cells. In a process unique to flowering plants (angiosperms), double fertilization occurs:
  • Fertilization of the Egg: One sperm cell fuses with the egg cell, forming a diploid (2n) zygote, which will develop into the embryo of the new plant.
  • Fertilization of Polar Nuclei: The second sperm cell fuses with two polar nuclei in the embryo sac, forming a triploid (3n) endosperm. The endosperm serves as a nutritive tissue supporting the developing embryo.
• Seed and Fruit Development: After fertilization, the ovule develops into a seed containing the embryo and endosperm, while the surrounding ovary often develops into a fruit that encases the seed(s).

Types of Fertilization (Based on Pollen Tube Entry into Ovule)