AP BIOLOGY

Detailed explanation-1: -One of the male gametes fertilizes the egg resulting in the formation of a zygote and the other unites with 2 polar nuclei for the formation of an endosperm.

Detailed explanation-2: -The pollen grain represents the male gametophyte generation; it contains two male nuclei: a generative nucleus and a tube nucleus.

Detailed explanation-3: -Two sperm cells fertilize two female gametophytic cells: the egg cell and the central cell (Fig. 1; Appendix). After fertilization, the embryo develops from the fertilized egg cell and the central cell gives rise to the endosperm, which nourishes the embryo for its development.

Detailed explanation-4: -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-5: -One of the male gametes fuses with the egg to form diploid zygote. The other male gamete fuses with the central cell (containing two nuclei) to form triploid endosperm. Hence, a total of five nuclei take part in double fertilisation. Q.