Life is everywhere. You know that plants and animals are living things, but so are mushrooms, seaweed, and tiny, invisible creatures like bacteria. Living things come in all shapes, colors, and sizes.
Now consider some non-living things that you see in daily life, such as rocks, mountains, and oceans. What makes these things different from the living creatures? How do you know that something is alive?
Look at the two photos shown in Figure 1. One of the hippos is an animatronic machine, while the other is a living hippo. Can you tell one from the other? What characteristics do living things have that make them “alive”?