In an automobile, various systems are designed to supply the car's engine with fuel and remove the waste gases it produces.

Oxygen, taken in from the air, is mixed with fuel in the engine’s carburetor before the mixture passes into the combustion chamber. Inside the combustion chamber, the mixture is compressed and ignited, producing a chemical reaction. The waste products of this reaction—carbon dioxide, carbon monoxide, and water—pass through the exhaust system and exit through the car's tailpipe.

Animal cells also have “engines.” Cellular engines are the mitochondria. Mitochondria receive fuel, in the form of chemical nutrients, and they produce waste products when they convert this fuel into usable energy. Like car engines, mitochondria also need oxygen to “burn” this fuel for energy. For cells, the process of cellular respiration is like the process of internal combustion for cars.

Although animals don't have carburetors or exhaust systems, they do have ways to transfer oxygen from the atmosphere into every body cell. Animals also produce carbon dioxide and water, and have ways to dispose of these wastes.

This process, called gas exchange, is the main function of the respiratory system.

In this activity, we’ll study the ways animals obtain oxygen and dispose of carbon dioxide. We’ll see that gas exchange involves both the respiratory system and the circulatory system.

First, we’ll look at the variety of respiratory systems found in animals, beginning with the simplest of multicellular organisms.

Next, we’ll focus on the human respiratory system, and see how the lungs and circulatory system work together in mammals.

Then we’ll look at the biochemistry of gas exchange in the lungs and body tissues.

Finally, we'll see how blood transports oxygen and carbon dioxide around the body.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education