Ultimately, all life on Earth depends on plants to provide food, shelter, and oxygen for other living things. Consequently, plant reproduction is crucial to all other life on this planet. The first step in plant reproduction is the intricate process called pollination, which occurs when pollen grains, the male germ cell of a plant, reach the stigma, the female reproductive part of the same species of plant. Depending on the plant species, a flower can produce male, female, or both structures. Pollination can also occur within the same flower.

Most flowering plants (90 percent) depend on animals to make the vital pollen-grain delivery. The remaining flowering plants rely on wind and some-times splashing raindrops to ferry pollen, but this is a less precise method. Pollinating animals do the job for a reward: food, usually in the form of nectar. The lessons in this online unit explore the theme of the National Zoo's Pollinarium exhibition: how plant and animal partners interact to accomplish pollination.