Characteristics of Living Things

The science background gives teachers more detailed explanations of the scientific phenomena that students will explore in this unit. In this particular lesson, students deepen their understanding of living versus nonliving, and also once-living things.

Living things need water. Water has many important functions, including helping to transport food through the body and eliminate waste. And all living things exchange gasses with the environment. Animals such as bats and humans breathe in oxygen and breathe out carbon dioxide. Plants take in carbon dioxide and release oxygen. This exchange of gasses between life forms and the environment is called the oxygen cycle.

All living things respond to their environment. To respond means to react to something that happens. Most animals respond to their environment in ways we can observe, such as jumping when they hear loud noises or moving away when they feel threatened. Plants respond to their environment in less obvious ways, such as by growing toward the sun or reaching their roots downwards or sideways to find water.

All living things also eventually die. Some have very short lives before they die. Mosquitoes generally live for about two weeks before dying. Some sharks can live for 200 years, while scientists have found several Great Basin bristlecone pine trees that are around 5,000 years old. When an organism dies, it decomposes, returning its nutrients to the soil. It is no longer alive, but it was once alive. Dead animals, leaves, and logs are all once-living things.