NEET BIOLOGY

Detailed explanation-1: -A mature embryo sac consists of two synergids, one egg cell and three antipodal cells with one nucleus each. Then there is one large central cell that has two nuclei. Hence, a mature embryo sac consists of 7 cells and 8 nuclei.

Detailed explanation-2: -A typical embryo sac has 7 cells and 8 nuclei. There are 3 antipodal cells at the chalazal end, one central cell and 3 cells in the egg apparatus (one egg and two synergids). Hence, the cellular arrangement is 3+1+3.

Detailed explanation-3: -Three cells present at the chalazal end of embryo sac are called as antipodals. The large central cell has two polar nuclei. This makes embryo sac 7 celled and 8 nucleate structure.

Detailed explanation-4: -The two haploid nuclei migrate to the opposite poles of the embryo sac and then undergo two rounds of mitosis generating four haploid nuclei at each pole. One nucleus from each set of four migrates to the center of the cell. Cellularization occurs, resulting in an eight-nucleate seven-celled structure.

Detailed explanation-5: -Thus, a typical angiosperm embryo sac at maturity is 7-celled but 8-nucleated as the central cell has 2-nuclei.