Double Fertilization in Angiosperms

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.

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Process of Double Fertilization

1. 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).

2. 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.

3. First Fertilization (Syngamy)

   • One male gamete (n) fuses with the egg cell (n).

   • This forms the zygote (2n), which develops into the embryo.

4. 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.)

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Importance of Double Fertilization

1. Formation of the Zygote – Ensures the development of a new plant embryo.

2. Endosperm Formation – Provides nutrients for embryo development, essential for seed germination.

3. Efficient Resource Use – Endosperm forms only if fertilization occurs, preventing wastage of energy.

4. Unique to Angiosperms – This process is absent in gymnosperms, making angiosperms more advanced.

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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.