AP BIOLOGY

Detailed explanation-1: -Synergids play some role in guiding the entry of pollen tube into the embryo sac in close vicinity of an egg cell. The two polar nuclei fuse to form a secondary nucleus or definitive nucleus which after an act of double fertilization forms triploid nutritive tissue called endosperm.

Detailed explanation-2: -Final answer: Growth of pollen tube towards embryo sac is Chemotropic.

Detailed explanation-3: -Entry of pollen tube into embryo sac is under the guidance of chemotropism.

Detailed explanation-4: -The generative nucleus divides in the pollen tube to form the two male gametes. The tube nucleus disintegrates. One of the male gametes that reach the ovary through the pollen tube fuses with the egg to form the zygote.

Detailed explanation-5: -The pollen tube in a flowering plant grows in a direction that is influenced by the mechanical properties of the stigma papillae and the organization of structures called cortical microtubules inside these cells.