Molecular model and stack of books in classroom
Jupiterimages/Comstock/Getty Images

Aerobic respiration occurs when your cells produce energy in the presence of oxygen. The three key steps of aerobic respiration are glycolysis where the sugar glucose is broken down, the Kreb's cycle where products from glycolysis are converted to other molecules and cellular energy and the electron-transport chain where molecules from the Kreb's cycle split apart to fuel the cell. Throughout this process, molecules are produced as others are broken down. Some of these end products are waste that the cell must get rid of, while other products provide energy for cellular activity.


Although some water is necessary to complete the processes of aerobic respiration, it is ultimately a waste product. During glycolysis, two water molecules are produced when glucose is broken down. Another water molecule is given off during the early stages of the Kreb's cycle. Additional water molecules are given off during the electron-transport stage of aerobic respiration. Breathing, urinating and sweating are some of the ways your body gets rid of this excess cellular water.

Carbon Dioxide

Carbon dioxide is a waste product of aerobic respiration. The first carbon dioxide production occurs when the products created from glucose during glycolysis are converted into the initial molecule needed to begin the Kreb's cycle. During the middle stages of the Kreb's cycle, two more carbon dioxide molecules are given off. When you breathe, you release some of this carbon dioxide.

Adenosine Triphosphate

The molecule adenosine triphosphate, more commonly known as ATP, is held together by certain chemical bonds called phosphate bonds. When split, these phosphate bonds give off energy that fuels cellular reactions. The production of ATP occurs in the middle stage of the Kreb's cycle and also during the electron-transport stage of aerobic respiration.

Electron Transporters

In the Kreb's cycle, two energy-carrying molecules are formed: NADH and FADH2. NADH is produced in three different stages of the Kreb's cycle, while FADH2 is produced during the middle stages of the cycle. Once released from the Kreb's cycle, these molecules move on to the third step of aerobic respiration -- the electron-transport chain. This chain is a group of molecules in the cell where a series of energy-producing steps occur when NADH and FADH2 are split apart from their hydrogen atoms. This splitting releases energy for the cell to create more ATP.