Question

Explain the structure of a mature embryo sac of a typical flowering plant.

Hint:

Remember the 3-3-2 arrangement: 3 antipodals at one end, 3 cells at the other (egg + 2 synergids), and 2 polar nuclei in the center (which often fuse). This leads to the 7-celled, 8-nucleated structure.

Answer 1

The mature embryo sac in angiosperms develops within the ovule and typically exhibits the following structure: \newline 1. Egg Apparatus (at the micropylar end): \newline \quad - Egg cell: The haploid female gamete, located at the micropylar end. \newline \quad - Synergids (two): Haploid cells flanking the egg cell, often possessing filiform apparatus to guide the pollen tube. \newline 2. Central Cell (in the center): \newline \quad - A large cell containing two haploid polar nuclei. These nuclei may fuse to form a diploid secondary nucleus before fertilization. \newline 3. Antipodal Cells (at the chalazal end): \newline \quad - Three haploid cells located at the opposite end of the embryo sac from the egg apparatus, which usually degenerate after fertilization. \newline Thus, the mature embryo sac is characterized by this specific arrangement of cells and nuclei.