Introduction

All living things need air to stay alive. The air you breathe is a mixture of different gases in the atmosphere. These gases include nitrogen, oxygen, and carbon dioxide. Of these gases, oxygen is the main gas needed by your body.

Oxygen combines with glucose, a kind of carbohydrate from food, in each cell in your body through the process called respiration. During respiration, energy is released and carbon dioxide is produced as a waste product. Your body uses this energy in performing its different activities. Carbon dioxide, on the other hand, is taken back to your lungs and is released from your body when you exhale or breathe out.