Fermentation (College Board AP® Biology): Study Guide

Alcohol & lactic acid fermentation

• Fermentation allows cells to continue to produce ATP when oxygen is absent

  • It is also known as anaerobic respiration

  • It produces less ATP than cellular respiration

• The ATP produced during fermentation comes from glycolysis, which can occur without oxygen

• Depending on cell type, the products of fermentation can include either:

  • alcohol or

  • lactic acid

Alcohol fermentation

• Fermentation in yeast cells produces alcohol

• Hydrogen is removed from NADH to form ethanol (alcohol) as follows:

  • pyruvate from glycolysis is converted to ethanal, releasing carbon dioxide

  • hydrogen from NADH is transferred to ethanal, producing ethanol

    • Ethanal is the hydrogen acceptor

• The removal of hydrogen from NADH produces NAD which can re-enter glycolysis, allowing glycolysis to continue

  • This is essential because glycolysis is the process that produces ATP during fermentation

Lactic acid fermentation

• Fermentation in muscle cells produces lactic acid

  • This occurs when the blood cannot supply oxygen to muscles quickly enough to supply their energy needs

• Hydrogen is removed from NADH and transferred to pyruvate, converting it to lactic acid, or lactate

  • Pyruvate is the hydrogen acceptor

• This process regenerates NAD, allowing glycolysis to continue and meaning that muscle cells can keep on producing ATP for a short period