AP BIOLOGY

Detailed explanation-1: -Pollen consists of one or more vegetative cells and a reproductive cell. A pollen grain itself is not the male gamete. In angiosperms and certain gymnosperms, the vegetative cell forms the pollen tube that grows to meet the unfertilized ovules, and the reproductive cell is the source of the sperm.

Detailed explanation-2: -Flowering plants have evolved two pollination methods: 1) pollination without the involvement of organisms (abiotic), and 2) pollination mediated by animals (biotic). About 80% of all plant pollination is by animals. The remaining 20% of abiotically pollinated species is 98% by wind and 2% by water.

Detailed explanation-3: -Mature pollen grains contain two cells: a generative cell and a pollen tube cell. The generative cell is contained within the larger pollen tube cell. Upon germination, the tube cell forms the pollen tube through which the generative cell migrates to enter the ovary.