Why do our bodies rearrange the food we eat and the oxygen we breathe (O2) into carbon dioxide (CO2) and water (H2O)?

a
In order to release the energy found in food.
b
In order to eliminate the calories found in food.
c
In order to remove excess water in the body.
d
In order to release the matter found in food.

Every cell in your body needs oxygen to function. You get the oxygen your cells need from the air you breathe. The air you breathe is made up of 20 percent oxygen. The rest of the air is mostly nitrogen (79%). Your body cells use the oxygen you breathe to get energy from the food you eat. This process is called cellular respiration. During cellular respiration the cell uses oxygen to break down sugar. Breaking down sugar produces the energy your body needs. This is very similar to wood burning in a fire. As the wood burns, it combines with oxygen and releases heat energy and carbon dioxide. When the cell uses oxygen to break down sugar, oxygen is used, carbon dioxide is produced, and energy is released. But instead of heat energy, much of the energy produced in cellular respiration is stored chemically for the cell to use later. Carbon dioxide is the waste product of cellular respiration that you breathe out each time you breathe. Blood picks up oxygen and releases carbon dioxide in the lungs. The opposite takes place in the cells where the blood releases oxygen and picks up carbon dioxide.