In this topic you will learn about what organisms need to stay alive.

To live and grow, organisms need food, water, air, and a place to live. Food gives an organism energy. Energy is the ability to do work. Different organisms get food in different ways. Plants make their own food. Some animals eat only plants. Some eat only animals. Some animals eat both plants and animals. Other organisms, like mushrooms, get food from dead organisms.

Most organisms 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.

Most organisms need air because it contains oxygen. Oxygen is a gas that is in air and water. Oxygen is an important gas. You can live for a few days without food or water. However, you would die in just a few minutes without oxygen. All your body parts need oxygen to live and grow. Plants and animals also need oxygen to get the energy they need from food.

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

All organisms need a place to live. Living things respond to changes in the environment in different ways. Daylight signals some flowers to open. 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.