Biology / Unit 3: Cellular Energy
3.5 Fermentation
Notes
When oxygen is not available, cells can use fermentation (anaerobic) to keep glycolysis going.
- Fermentation recycles NAD+ so glycolysis can keep making 2 ATP per glucose.
- Lactic acid fermentation: happens in muscle cells during hard exercise and in bacteria used to make yogurt.
- Alcoholic fermentation: yeast make ethanol and $\text{CO}_2$; used in bread and brewing.
- Aerobic means with oxygen; anaerobic means without oxygen.
Practice
A sprinter's leg muscles burn after a fast 400 m race. Which process caused this?
Short on oxygen, muscle cells switch to lactic acid fermentation.
Bread dough rises because yeast produce:
Alcoholic fermentation releases CO2 gas, which forms bubbles in the dough.
Why does fermentation produce much less ATP than aerobic respiration?
Without oxygen, the Krebs cycle and electron transport chain cannot run.
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