Products of Anaerobic Respiration

There are two types of anaerobic respiration depending on what is formed at the end:

a. Alcoholic Fermentation

  • Happens in yeast and some bacteria.
  • Pyruvic acid is converted into:
    • Alcohol (ethanol – C₂H₅OH)
    • Carbon dioxide (CO₂) – which causes the dough to rise in bread.

🧁 Example: Yeast is used in baking. The CO₂ gas forms bubbles and makes the dough rise. That’s alcoholic fermentation at work!

b. Lactic Acid Fermentation

  • Happens in muscle cells during heavy exercise.
  • Also happens in some bacteria.
  • Pyruvic acid is changed into lactic acid (C₃H₆O₃).

🏃‍♂️ Example: When you run fast and breathe heavily, your muscles may not get enough oxygen. So they switch to lactic acid fermentation. That’s why your muscles feel sore – lactic acid builds up.

Aerobic Respiration Explained

Now let’s move to aerobic respiration — the complete and most efficient way of getting energy.

Where It Happens

  • Takes place in almost all cells of plants, animals, and other organisms.
  • After glycolysis, the remaining steps happen in a special part of the cell called the mitochondrion. This is known as the “powerhouse” of the cell.

What Happens in Aerobic Respiration?

  1. Glucose is broken into pyruvic acid (glycolysis – no oxygen needed).
  2. Then, pyruvic acid is fully broken down into CO₂ and water – with the help of oxygen.
  3. This process releases all the energy stored in the original glucose.

Aerobic Respiration – Four Stages

Let’s divide the whole process into four steps:

1. Glycolysis

  • Happens in the cytoplasm.
  • Glucose → Pyruvic Acid.
  • No oxygen needed.
  • Produces a small amount of energy (2 ATPs).

2. Pyruvic Acid Oxidation

  • Pyruvic acid enters the mitochondria.
  • It is prepared for the next step by converting it into another compound called acetyl-CoA.

3. Krebs Cycle (also called Citric Acid Cycle)

  • Happens in the mitochondria.
  • Acetyl-CoA is broken down.
  • Produces CO₂, NADH, FADH₂ (molecules that carry energy).
  • Produces 2 ATPs.

4. Electron Transport Chain (ETC) & Chemiosmosis

  • Also happens in mitochondria.
  • Electrons from NADH and FADH₂ are passed through a series of proteins.
  • This movement creates energy that is used to produce a large amount of ATP (about 34 ATPs).
  • Oxygen is the final acceptor of the electrons and combines with hydrogen to make water.

⚡ In total, aerobic respiration produces 36 to 38 ATPs from one molecule of glucose — much more than anaerobic respiration.

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