AP 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: -One cell of the nucellus undergoes meiosis to produce four megaspores. One megaspore survives and undergoes three rounds of free nuclear division followed by cellularization to produce an embryo sac consisting of 8 nuclei in 7 cells (Evans & Grossniklaus, 2009; Serbes et al., 2019).

Detailed explanation-3: -The nucleus at the micopylar end divides mitotically. The nucleus at the chalazal end divides mitotically. This results in 2 nuclei at each end and four-nucleate embryo-sac forms. This results in 4 nuclei at each end and thus forms eight-nucleate embryo-sac.

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.