We inhale oxygen when we breathe and exhale carbon dioxide. What is the oxygen used for and where does the carbon dioxide come from?

When we breathe, we inhale oxygen (O2) from the air and exhale carbon dioxide (CO2) back into the environment. This process is called respiration. The oxygen we inhale is essential for our bodies to function, while the carbon dioxide we exhale is a waste product formed during cellular processes.

The main purpose of inhaling oxygen is so that it can be used in a process called cellular respiration. This process takes place in the cells' mitochondria, the powerhouses of cells. During cellular respiration, glucose (C6H12O6), a sugar molecule obtained from the food we eat, reacts with oxygen to produce energy, water (H2O), and carbon dioxide. The overall chemical equation for cellular respiration is: C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP) As seen in the equation, oxygen is used to break down glucose and produce energy, which is stored in molecules called ATP (adenosine triphosphate). ATP molecules provide the energy needed for various biochemical reactions and cellular functions like muscle contraction, neural function, and cell division.

As mentioned earlier, carbon dioxide is produced as a by-product of cellular respiration. During the breakdown of glucose, carbon atoms from glucose combine with oxygen atoms to form carbon dioxide molecules. As CO2 is not used by our body and can be acidic, it needs to be removed to maintain a stable internal environment, or homeostasis. Hence, CO2 diffuses from the cells into the bloodstream, where it is carried to the lungs. When we exhale, the carbon dioxide is expelled from our lungs back into the atmosphere.