Embryo Sac Structure in Angiosperms

The embryo sac, also known as the female gametophyte, is a specialized structure in the ovule of flowering plants (angiosperms) where the female gametes are produced and fertilization occurs. It has a specific organization and structure, consisting of several cells and nuclei arranged in a precise manner. The typical structure of an angiosperm embryo sac includes the following components:

• Egg Cell (Oosphere): This is the central cell located at the micropylar end of the embryo sac, closest to the entrance where pollen tubes enter. The egg cell is involved in fertilization and gives rise to the future embryo upon fertilization.

• Central Cell: Located in the central region of the embryo sac, the central cell contains two polar nuclei. These polar nuclei are essential for the formation of endosperm after fertilization, as they fuse with a sperm cell to produce triploid endosperm.

• Synergid Cells: There are typically two synergid cells located at the micropylar end, flanking the egg cell. Synergid cells play a critical role in guiding the pollen tube toward the egg cell during fertilization. They release chemical signals to attract the pollen tube.

• Antipodal Cells: Three antipodal cells are located at the chalazal end of the embryo sac, opposite the micropylar end. The function of antipodal cells is not entirely clear, but they may be involved in nourishing the developing embryo or embryo sac.

• Polar Nuclei: As mentioned earlier, the central cell contains two polar nuclei. These nuclei will fuse with one of the sperm cells from the pollen tube during double fertilization, resulting in the formation of the triploid endosperm.