Why does the amount of oxygen change when you exhale?

The amount of oxygen changes when you exhale because the body uses oxygen during cellular respiration. Cellular respiration is the process by which cells convert glucose into energy. When you inhale, you bring oxygen into your lungs. This oxygen is then transported to your cells through your bloodstream. Once in your cells, the oxygen is used to break down glucose and release energy. The waste products of cellular respiration are carbon dioxide and water. Carbon dioxide is transported back to your lungs through your bloodstream and is then exhaled.

The amount of oxygen you exhale is therefore less than the amount of oxygen you inhale. This is because some of the oxygen you inhale is used to fuel cellular respiration. The amount of oxygen you exhale also varies depending on your activity level. When you are at rest, you exhale less oxygen than when you are exercising. This is because your body uses more oxygen during exercise.