Oxygen is vital for cellular respiration, which produces ATP

ATP powers cell processes; it’s made by adding a phosphate to ADP

Aerobic respiration (with oxygen) is the most efficient way to make ATP

When oxygen is unavailable, cells can still make ATP using fermentation

Fermentation allows glycolysis to continue by regenerating NAD

Glycolysis breaks glucose into pyruvate, yielding 2 ATP and 2 NADH

Without oxygen, NADH can’t go through the electron transport chain

Fermentation recycles NADH back to NAD+ by transferring electrons to pyruvate or its derivatives

This keeps glycolysis running and ensures some ATP is produced

Fermentation is less efficient than aerobic respiration but essential in low-oxygen conditions