Biology isn't just a "subject" in school. Biology is the science of life itself. Biology is the study of what makes an eagle fly, a flower bloom, or a caterpillar turn into a butterfly. It's the study of ourselves--of how our bodies grow and change and respond to the outside world, and it's the study of our planet, a world transformed by the actions of living things. All organisms interact with one another and with the environment in ways that create our planet's web of life. Organisms make tropical rain forests and coral reefs, prairies and swamps--and farms and cities. Our interactions involve not only each other--but also the winds and ocean currents that tie our planet together. Human activity can change, and is changing, local and global environments in ways that alter our ability to produce food and protect ourselves from diseases. We are one on the global ecological level.