Have you ever traveled in a plane?Have you ever felt that your ears pop up when you are on a high altitude? This happens due to atmospheric pressure.As you go up ,air pressure outside your ears becomes lower than the air pressure inside your body! Your ears pop to equalize that gap. Do you know that the air around us has weight, and it presses against everything it touches. This pressure is called atmospheric pressure or air pressure.This is helpful in several areas for living organisms like respiration.Air pressure drops as we move to higher altitudes as explained in above example.As the air pressure decreases,the amount of oxygen also decreases that is why mountaineers carry oxygen cylinders with them to breathe on higher altitudes.