INTRODUCTION 

The variety of life on Earth is staggering, and humans are apart f it, so butterflies, trees, birds, mushrooms, and giraffes. The variety of living things ranges in size from bacteria, much too small to be seen by the naked eye, all the way up to giant sequoia trees that can reach heights of 100 meters (m) or more.

The diversity of life seems overwhelming, and yet all living things have certain characteristics in common. Taken together, these characteristics give us insight into the nature of life and help us distinguish living things from non-living things.