We all need the energy to function, and we get this energy from the foods we eat. The most efficient way for cells to harvest energy stored in food is through cellular respiration; which requires a cell to exchange two gases with its surroundings. The cell takes in oxygen in the form of the gas. It then throws away the waste in the form of the gas carbon dioxide. Oxygen present in the air you inhale disperses across the outline of your lungs and into your bloodstream. And the carbon dioxide in your bloodstream diffuses into your lungs and exits when you exhale. Every molecule of carbon dioxide that you exhale was originally formed in one of the mitochondria of your body's cells. (Chapter 6 pg. 91)
             Let's start with the stage of cellular respiration; glycolysis means "splitting sugars." Glucose, a six-carbon sugar, it is split into two molecules of three-carbon sugar. During the process, two molecules of ATP and two molecules of pyruvic acid and two high-energy electron carrying molecules of nicotinamide adenine dinucleotide are produced. Glycolysis can occur with or without oxygen. In the company of oxygen, glycolysis is the first stage of cellular respiration. Without oxygen, glycolysis allows cells to make small amounts of ATP; this process is called fermentation. Fermentation is the breakdown of sugar into an acid or alcohol. According to www.khanacademy.org, these are the steps of glycolysis step one the enzyme hexokinase phosphorylates adds a phosphate group to glucose in the cell's cytoplasm. In the process, a phosphate group from ATP is transferred to glucose producing glucose phosphate. Step two, the enzyme phosphoglucoisomerase converts glucose phosphate into its isomer fructose phosphate. Isomers have the same molecular formula, but the atoms of each molecule are arranged differently. Step three, the enzyme phosphofructokinase uses another ATP molecule to transfer a phosphate group to fructose phosphate to form fructose, bi...