It is true that the Earth's atmosphere consists of approximately 78% nitrogen, 21% oxygen, and small amounts of other gases. So, in terms of the overall composition, we do breathe in more nitrogen than oxygen. However, when people say that we breathe in oxygen, they are referring to the fact that oxygen is the gas that our bodies specifically need for respiration.
In the process of respiration, our bodies use oxygen to convert food into energy through a series of chemical reactions. Oxygen is vital for this energy-producing process, and without it, our cells would not be able to function properly. Oxygen is transported from the lungs to the bloodstream and delivered to the body's tissues to support cellular respiration.
Although we do inhale a significant amount of nitrogen along with other gases present in the atmosphere, nitrogen does not play a direct role in respiration. Nitrogen is relatively inert and does not undergo significant chemical reactions within the body. It mainly acts as a diluent, helping to balance the concentrations of other gases in the air we breathe.
So, while the atmosphere contains a higher percentage of nitrogen, it is the oxygen that our bodies specifically require for respiration and energy production. Therefore, it is accurate to say that we breathe in oxygen, even though we also inhale nitrogen and other gases in smaller quantities.