In this lesson, you explored the following essential questions:

• How far can cellular respiration go without the presence of oxygen?
• How does anaerobic respiration release potential energy from organic compounds?

Principles of anaerobic respiration have been utilized by industry to create food and fuels. Scientists have learned the value of single-celled organisms to the production of foods like bread and yogurt and fuels such as biogas. In order for this technology to provide people with mass-produced food and fuels that exist today, researchers need a solid understanding of the chemical reactions that occur to transfer energy and matter among cells.

The initial step of all respiration begins with glycolysis. Oxygen is not required for glycolysis to occur. When oxygen is not available to normally aerobic cells, the process of lactate fermentation occurs. Glucose becomes oxidized and forms pyruvate and ATP.

Pyruvate is reduced by NADH to form lactic acid. It is a lactic acid buildup that causes muscles to become sore during strenuous exercise. Fortunately, the production of lactic acid is reversible once an oxygen debt is repaid.

Many cells, such as bacteria and yeast, do not require oxygen to survive, so they function through the process of alcohol fermentation. When you leave a lunch container sealed in your bag for a few weeks, this type of fermentation occurs. Glycolysis breaks down glucose, provides energy for the cells to do work, and produces ethanol and carbon dioxide. The container may bulge with the production of the gas, and you will come to know what fermentation smells like!

Both lactate fermentation and alcohol fermentation produce two ATP molecules from the oxidation of glucose. As you saw in Lesson 5, aerobic respiration is much more efficient at producing ATP from the breakdown of glucose molecules than anaerobic respiration is.

Lesson Glossary

biofuel: ethanol produced during the fermentation of biomass

biogas: methane captured from animal waste that is used as fuel

glycolysis: a metabolic pathway in which one glucose molecule is broken down to form two, 3-carbon molecules and a small amount of ATP

Glycolysis is the first step in both anaerobic and aerobic respiration.

phosphorylation: the process of adding a phosphate to a molecule; occurs in cellular respiration to activate glucose and enable its breakdown

pyruvate: three carbon molecules produced by glycolysis