Correct Response: D. During angiosperm fertilization, each pollen grain divides and forms two sperm cells. One sperm cell fertilizes the ovum (egg) to produce the zygote. The other sperm cell combines with the two polar nuclei within the embryo sac and forms a triploid cell. This triploid cell develops into the food storage tissue (endosperm) of the seed. Polyploidy (having several complete sets of chromosomes) and hybridization (the combination of nuclei from different species of organisms) (A) occur more frequently in plants but are not the result of double fertilization. Only one sperm cell derived from a single grain of pollen is required to fertilize each ovum (B). Zygotes form during the sporophyte stage (C) of the angiosperm life cycle.
