AP Syllabus focus:
‘Fermentation allows glycolysis to continue without oxygen, regenerating NAD+ and producing organic products like alcohol or lactic acid.’
Fermentation is a set of anaerobic reactions that keep cells making a small but vital supply of ATP when oxygen is unavailable by recycling key electron carriers.
Core idea: why fermentation happens
Cells rely on glycolysis to generate ATP quickly. Glycolysis requires a steady supply of NAD+ to accept electrons. When oxygen is absent, the electron transport chain cannot oxidise NADH back to NAD+, so glycolysis would stop unless NAD+ is regenerated another way.
Practice Questions
FAQ
If ATP demand briefly exceeds oxygen delivery, fermentation can supply ATP faster per unit time, despite low efficiency.
It depends on enzymes present in the organism/tissue. Different enzyme sets channel pyruvate into different reduction pathways.
Lactate can be transported to other tissues and converted back to useful metabolites when oxygen availability improves.
Production and export of acidic or charged end products can alter ion balance and contribute indirectly to pH changes.
Glycolysis requires NAD$^+$ as an electron acceptor; without recycling NAD$^+$, key oxidation steps halt and ATP output stops.
