Pollen grain germination and growth of pollen tube

Pollination is not fertilization. To accomplish the latter, the pollen grain must germinate and grow a tube from from where it sits atop the stigma down through the style to the egg cell within the ovary. The sperm nucleus makes its way through the pollen tube, breaks from the tube to combine with the egg nucleus to accomplish fertilization. (see text) This is illustrated in the following video:

Have students consider and discuss the chemical/physical controls/interactions that must be present and active to enable this achievement.