The process through which animal cells release energy to be used for their life functions is called cellular respiration. This process involves taking a simple sugar molecule, such as glucose, C6H12O6, and oxidizing it with oxygen to produce energy, in the form of ATP (adenosine triphosphate), carbon dioxide and water, the last two being waste products. This process occurs in the mitochondrion, the bean-shaped organelle often referred to as the "power house" of the animal cell. The balanced equation for cellular respiration is shown below:
C6H12O6 + 6O2 ---> energy (ATP) + 6CO2 + 6H20
Cellular respiration is the flip equation of what occurs for plant cells, which take energy from the sun, carbon dioxide from the air, and water from the soil, combine it through the chloroplasts of the plant cell to produce glucose and give off oxygen as a waste product. It is widely speculated the oxygen content we have in the modern atmosphere was produced first as a byproduct of plants evolving and producing oxygen as a waste product. Some waste product!