Double Fertilization in Angiosperms
Double fertilization is a unique process in flowering plants (angiosperms) where two male gametes from a pollen grain fertilize two different cells in the embryo sac. This results in the formation of both the zygote and the endosperm.
Process of Double Fertilization
Pollen Germination & Pollen Tube Formation
After pollination, the pollen grain lands on the stigma and forms a pollen tube.
The pollen tube grows through the style toward the ovary.
Inside the pollen tube, the generative cell divides to form two male gametes (sperm cells, n).
Entry into the Ovule
The pollen tube enters the ovule through the micropyle.
It reaches the embryo sac, which contains the egg cell, two synergids, three antipodal cells, and a central cell with two polar nuclei.
First Fertilization (Syngamy)
One male gamete (n) fuses with the egg cell (n).
This forms the zygote (2n), which develops into the embryo.
Second Fertilization (Triple Fusion)
The second male gamete (n) fuses with the two polar nuclei (n + n) in the central cell.
This forms the triploid endosperm (3n), which acts as a nutrient storage tissue for the developing embryo.
Diagram: Double Fertilization Process in Flowering Plants
(A labeled diagram showing pollen tube entry, male gamete fusion with the egg cell, and triploid endosperm formation.)
Importance of Double Fertilization
Formation of the Zygote – Ensures the development of a new plant embryo.
Endosperm Formation – Provides nutrients for embryo development, essential for seed germination.
Efficient Resource Use – Endosperm forms only if fertilization occurs, preventing wastage of energy.
Unique to Angiosperms – This process is absent in gymnosperms, making angiosperms more advanced.
Conclusion
Double fertilization is a distinctive and efficient reproductive mechanism in angiosperms. It ensures both the formation of the next generation (zygote) and nutrient supply (endosperm), leading to successful seed development and plant growth.