In this topic you will learn about how to tell living things from nonliving things.

An organism is a living thing. How can you tell an organism from a nonliving thing? A living thing grows. It starts out small. Then it gets bigger. Organisms also change as they grow.

The way a living thing changes during its life is called development. An oak tree begins as an acorn. Then it grows to a young tree. Its branches and trunk become thicker and stronger. The oak tree changes shape and color as it develops.

Another feature of living things is that they make more of their own kind. Reproduction is the way living things make more of their own kind. Plants grow from seeds. Chicks hatch from eggs. Some animals, like puppies, are born live.

All organisms live in an environment. An environment is made up of everything that surrounds an organism, including the air, water, soil, and even other organisms. An organism responds to its environment. To respond means the way a living thing reacts to changes in its environment. The leaves on trees respond to a change in environment by turning color in autumn. Bears respond by sleeping in a cave in the winter.

Living things use their senses to gather information about their environment. When living things share information by sending, receiving, and responding to signals, they communicate. They use their senses of sight, smell, hearing, and touch to collect information. Living things communicate in different ways. Some birds sing to mark their territory or area. Skunks sometimes spray a strong-smelling liquid to communicate.