Explanation

Your respiratory system lets oxygen be exchanged for carbon dioxide. When air that you have breathed gets into your lungs, oxygen floats into your bloodstream, which takes it to every part of your body. There are lots of other things in the air that you don't want to breathe into your lungs though, so your respiratory system keeps these out using barriers. For example, the tiny hairs inside your nose act like a fence to keep out larger particles, like dust and soot.