Anaerobic Respiration

What Happens to Pyruvate Without Oxygen?

After glycolysis, if there's no oxygen, cells can’t go into the Krebs cycle or ETC.
So instead, they use anaerobic respiration (fermentation) to recycle NAD⁺ so glycolysis can keep going.

Lactic Acid Fermentation (Used in animals like humans)

Step	What Happens
1⃣	Glycolysis produces pyruvate and NADH
2⃣	Pyruvate is converted into lactic acid (lactate)
3⃣	NADH is oxidized back to NAD⁺, which allows glycolysis to continue
4⃣	No ATP is made in this step (ATP comes from glycolysis only)

🧠 Analogy:
Pyruvate is like dirty laundry. You need to "dump" your electrons somewhere (NADH → NAD⁺), so you use pyruvate as the basket and throw it out as lactic acid or ethanol.

Anaerobic Respiration in Prokaryotes (Bacteria)

• Bacteria don’t always need oxygen!

• They still use an ETC, but it’s in their plasma membrane (not mitochondria)

Final Electron Acceptors:

Instead of oxygen, they use:
Sulfate (SO₄²⁻)
Nitrate (NO₃⁻)
Iron ions (Fe³⁺)

✅ This still lets them make some ATP, just less than aerobic respiration.

➡ The electron is passed through the Electron Transport Chain
➡ Then it’s handed off to something (like oxygen OR sulfate/nitrate/iron)
➡ This handoff lets the bacteria keep making ATP

🔁 Summary Table:

Type	Used By	Final Product	Purpose
Lactic acid fermentation	Animals, humans	Lactate	Recycle NAD⁺ for glycolysis
Alcohol fermentation	Yeast, fungi, plants	Ethanol + CO₂	Recycle NAD⁺ for glycolysis
Anaerobic respiration	Bacteria	Varies (Sulfate, etc.)	Generate ATP without O₂

What is fermentation?

Fermentation is an anaerobic process that allows glycolysis to continue by recycling NAD⁺ through the conversion of pyruvate into another product (lactic acid or ethanol).

What’s the difference between lactic acid and alcohol fermentation?

• Lactic acid fermentation: Pyruvate → Lactate (no CO₂ made)

• Alcohol fermentation: Pyruvate → Acetaldehyde → Ethanol + CO₂
  Used by different organisms and make different products.