The food we eat was change into tiny molecules of nutrients. This is done through the process of digestion in which the mouth, the stomach and the small intestine breaks and digest the food. The nutrients, like the red blood cells passes through the blood and float into the plasma. After, this nutrients get into the cells just like the oxygen and go through the walls of the capillaries.

Many nutrients comes in the form of sugars. The cells now use oxygen to break down this sugars into carbon dioxide and water. In the times that the cells break down sugars, the cells release energy from the sugars. Then, the cells now store the energy so that it can be used in the future. All the energy that our body uses everyday is made  in this way.

The cells in our body uses oxygen to get energy from the food. In order to keep us warm, the cells use this energy. When we get cold our cells releases extra energy which makes us warm.

The cells make use of this energy in order for them to grow, to divide to fix damage and to do special jobs.