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Fermentation Pathways
AP Biology · Unit 3 Cellular Energetics
Learning Objectives
Occurs in the cytosol when O₂ is absent (anaerobic)
Primary goal: Regenerate NAD⁺ so Glycolysis can continue making 2 ATP
Lactic Acid Fermentation: Pyruvate → Lactate (Muscle cells, bacteria)
Alcoholic Fermentation: Pyruvate → Ethanol + CO₂ (Yeast)
Tags
FermentationAnaerobicLactic AcidAlcoholicGlycolysis
Select Condition / Pathway
In the absence of oxygen, animal muscle cells reduce Pyruvate directly into Lactic Acid. The electrons from NADH are transferred to Pyruvate, reforming NAD⁺. This allows glycolysis to continue producing 2 ATP.
[NAD⁺] Supply
Regenerating
Net ATP/Glucose
2
Final Acceptor
Pyruvate
CO₂ Yield
0
Why Ferment?
Without NAD⁺, Stage 6 of Glycolysis halts immediately. Fermentation produces NO ATP itself; its sole purpose is to dump electrons to recycle NAD⁺ for glycolysis.