Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation takes advantage of glycolysis, produces two ATP molecules per glucose, and reduces NAD+ to NADH. The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.

Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which NADH is oxidized to NAD+ and pyruvate is reduced to lactate.

Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.

The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt.

The baking and winemaking industries have used alcohol fermentation for thousands of years.

In Alcohol Fermentation, yeasts (single-celled fungi) oxidize NADH back to NAD+ and convert pyruvate to CO2 and ethanol.

Obligate anaerobes are poisoned by oxygen, requiring anaerobic conditions, and live in stagnant ponds and deep soils.

Facultative anaerobes include yeasts and many bacteria, and can make ATP by fermentation or oxidative phosphorylation.

Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated using carbohydrates, fats, and proteins.

Fats make excellent cellular fuel because they contain many hydrogen atoms and thus many energy-rich electrons and yield more than twice as much ATP per gram than a gram of carbohydrate or protein.

In addition to energy, cells need raw materials for growth and repair

Some raw materials are obtained directly from food

Other raw materials are made from intermediates in glycolysis and the Citric Acid cycle Biosynthesis consumes ATP