Respiration (breathing) is so automatic that we rarely think about it, unless we feel that enough air is not getting into our bodies. Respiration is the process that allows us to breathe in oxygen and exhale carbon dioxide. Oxygen is then used in our cells as the fuel that transforms the food we eat into energy. Use the information on this sheet to help you discuss with your students the combustion process in terms of producing energy via respiration.
The body can be described as a combustion engine. The fuel needed for this process comprises sugars and fatty acids (fat deposits in our cells), which we gain by eating food. In order to burn this fuel, oxygen is needed, as it is with any fire. The waste products from the combustion process are water and carbon dioxide. Thus, we breathe because oxygen is needed to burn the fuel (sugars and fatty acids) in our cells to produce energy The air we breathe contains about 21% oxygen. This oxygen is brought into the lungs, where it is transported by the red blood cells to the entire body. Once the red blood cells return to the lungs, the "burnt" carbon dioxide is exhaled.
To help students understand this process, correlate the combustion process to fire. You can begin by discussing how fires begin. In the Santa Monica Mountains, human actions have often been the main cause of fires. In the past, lightning from thunderstorms contributed to fires. Whatever the cause, there are three ingredients that combine to start a fire:
Fuel: “Fuel” is any combustible material. During long summer months in the Santa Monica Mountains, shrubs that become dehydrated and dead grasses provide “dry fuel” and burn more easily. When years go by without fire, dead plant material builds up, so when a fire occurs, there is ample fuel to burn.
Heat: The typical climate of an area that is susceptible to fires includes long, dry summers with little rain. These conditions increase the temperatures of the ground and “fuel,” making it easier for the “fuel” to ignite and burn. “Dry fuel” ignites easily from sources such as lightning, a burning cigarette butt, broken glass focusing sunlight by reflection or refraction, or a match.
Oxygen: Wildfires in the Santa Monica Mountains are triggered by strong winds that blow hot and dry air. This not only increases the oxygen supply and dries out the “fuel,” but also influences the spread of fire. Shrubs are more quickly ignited, as their small-sized leaves are surrounded by plenty of oxygen.