What is Anaerobic Respiration?
Anaerobic respiration, also called fermentation, is how cells break down glucose for energy without oxygen. It happens in muscle cells during intense exercise and in yeast fermenting bread or beer. Because it skips the oxygen-dependent steps of respiration, it produces far less ATP than aerobic respiration.
Anaerobic respiration is the breakdown of glucose without oxygen; glycolysis yields a net 2 ATP, and pyruvate is converted to lactic acid or ethanol to regenerate the NAD+ that glycolysis needs to keep running.
- •Occurs in muscle cells & some bacteria (e.g., yogurt)
- •Pyruvate is reduced directly to lactic acid
- •No CO2 released
- •Causes the burning/fatigue feeling in muscles
- •Occurs in yeast & some plant cells
- •Pyruvate → acetaldehyde → ethanol
- •Releases CO2 gas
- •Used in baking (bread rising) and brewing
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Step-by-step worked examples
A muscle cell ferments 5 molecules of glucose anaerobically during a sprint. How much net ATP is produced?
Net ATP = 2 × number of glucose molecules Net ATP = 2 × 5 = 10 ATP Also produces 10 molecules of lactic acid
A yeast culture ferments 3 molecules of glucose via alcohol fermentation. How many CO2 molecules are released?
Alcohol fermentation releases 2 CO2 per glucose fermented CO2 released = 2 × 3 = 6 molecules Also produces 6 ethanol molecules and 6 net ATP (2 × 3)
During a 60-second all-out sprint, a runner's leg muscles ferment about 12 glucose molecules due to oxygen debt. Calculate the net ATP produced.
Net ATP = 2 × number of glucose molecules Net ATP = 2 × 12 = 24 ATP This is far less than the ~36 ATP per glucose available with oxygen, so the muscle fatigues quickly
Flashcards
Quick quiz
Q1.What is the net ATP yield from glycolysis alone (before fermentation)?
Q2.Which fermentation pathway produces ethanol and CO2?
Q3.Why does anaerobic respiration produce far less ATP than aerobic respiration?
Q4.What causes the burning feeling in muscles during intense exercise?
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Common mistakes
Anaerobic respiration produces the same amount of ATP as aerobic respiration. — Correct: It produces far less — only 2 net ATP per glucose vs. up to ~36 in aerobic respiration.
Fermentation is just glycolysis without oxygen. — Correct: Fermentation is glycolysis PLUS an extra step that regenerates NAD+ (converting pyruvate to lactic acid or ethanol) so glycolysis can keep running.
Yeast and muscle cells use the same fermentation pathway. — Correct: Muscle cells (and some bacteria) use lactic acid fermentation; yeast (and some plants) use alcohol fermentation, releasing CO2.
Anaerobic respiration means 'no respiration happens'. — Correct: It means respiration without oxygen — cells still break down glucose for energy, just far less efficiently.
FAQ
What is anaerobic respiration?
Anaerobic respiration (fermentation) is how cells break down glucose for energy without oxygen, producing a net 2 ATP per glucose plus lactic acid or ethanol and CO2.
What is the fermentation formula?
Glucose → 2 lactic acid + 2 ATP (lactic acid fermentation), or Glucose → 2 ethanol + 2 CO2 + 2 ATP (alcohol fermentation).
What are examples of anaerobic respiration?
Muscle cells during intense exercise, yeast making bread rise and beer/wine brewing, and some bacteria producing yogurt are all examples.
How do you calculate ATP from anaerobic respiration?
Multiply the number of glucose molecules fermented by 2, since fermentation yields a net 2 ATP per glucose molecule.