The Earth is surrounded by air. Air is a group of many gases (oxygen, carbondioxide, nitrogen etc). We breathe in oxygen and breathe out carbondioxide.
When we breathe in oxygen, the oxygen is carried by the blood to every cell in our body (The blood also carries food in liquid form). In every cell the oxygen combines with a substance in the food called Glucose (a kind of sugar). When Glucose and oxygen combine, carbon dioxide, water vapour and energy are produced. The carbon dioxide passes through the wall of the cell and goes into the blood. The blood carries the gas to our lungs, where we breathe it out. Thus, the extra carbon dioxide we breathe out comes from the cells' use of oxygen and food. Because the cells use some of the oxygen, we breathe out less oxygen than we breathe in.
Energy is produce when glucose and oxygen combine in the cells. With this energy, the cells can grow and repair themselves. 05 October 2010Comment