Concepts and formula to Remember

Development of Embryo Sac in Angiosperms:

Megasporogenesis: Begins with the formation of megaspores from the megasporocyte within the ovule.

Functional Megaspore: One out of four megaspores becomes the functional megaspore, while the others degenerate.

Female Gametophyte: The functional megaspore undergoes mitotic divisions, forming the female gametophyte or embryo sac.

Components of Embryo Sac: The embryo sac typically consists of seven cells and eight nuclei:

• Three Antipodal Cells
• Two Synergid Cells
• One Egg Cell (Oosphere)
• Two Polar Nuclei

Pollen Tube Guidance: Synergid cells guide the pollen tube toward the egg cell for fertilization.

Fertilization: The pollen tube delivers sperm cells. One sperm cell fuses with the egg cell to form a zygote, while the other fuses with polar nuclei to initiate endosperm formation.

Embryo Development: The zygote within the embryo sac develops into the future plant embryo. Synergids are pair of haploid cells present at the micropylar end of embryo sac. Zygote which is a diploid structure undergoes divisions to form an embryo. Antipodal and polar nuclei are also haploid in nature. Primary endosperm nucleus is triploid in nature. In a fertilized embryo sac the haploid, diploid and triploid structures are synergid, zygote and primary endosperm respectively.

Seed Formation: The mature embryo sac, with the embryo and endosperm, leads to seed formation within the ovule.