To live and grow, animals need food, water, air, and a place to live. Food gives an animal energy. Energy is the ability to do work. Different animals get food in different ways. Some animals eat only plants. Some eat only animals. Some animals eat both plants and animals. Most animals' bodies are made up mostly of water. Water has several important jobs. It helps the body use food as fuel. It helps some animals stay cool. It helps get rid of body wastes.

All animals need air because it contains oxygen. Oxygen is a gas that is in air and water. Oxygen is an important gas. Animals can live for a few days without food or water. However, they would die in just a few minutes without oxygen. All body parts need oxygen to live and grow.

Some needs, like the need for food, are inner needs. Signals inside an animlal's body tell it what to do to respond to an inner need. When you are hungry your brain tells you to eat.

All animals need a place to live. Animals respond to changes in the environment in different ways. Bats return to their caves to sleep. When the weather gets colder and the days get shorter, some animals gather food for the winter. Geese and butterflies migrate. To migrate means to move to another place. Bears and other animals find places to hibernate. To hibernate means to rest or sleep through the cold winter.