What does the following scenario describe?

a sperm nucleus joins with an egg cell after traveling down a pollen tube into the ovary.

fertilization

cephalization

segmentation

pollination

The correct answer is fertilization

Explanation:

In flowering plants when a sperm cell joins with an egg cell after traveling down through pollen tube into the ovary, this process or scenario is called fertilization.

In which out of two sperm cells one sperm cell fuse with the egg cell in the ovary and second sperm cell fuse with two nuclei forming a triple-layered cell that later develops into the endosperm.

Thus, the correct answer is fertilization.