Cellular Respiration
The process of breaking down glucose to release energy as ATP — the universal energy currency used to power all cellular activities.
A. Aerobic Respiration (with oxygen)
Overview & Equation
- Requires oxygen and glucose to produce ATP
- Produces 38 ATP per glucose molecule — highly efficient
- Produces CO₂ and H₂O as by-products
- Occurs in all living eukaryotic cells with mitochondria
Overall Equation
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP)
Three Stages of Aerobic Respiration
| Stage | Location | Products | ATP yield |
|---|---|---|---|
| Glycolysis | Cytoplasm (cytosol) | 2 Pyruvate + 2 NADH | 2 ATP (net) |
| Krebs Cycle (Citric Acid Cycle) | Mitochondrial matrix | CO₂ + NADH + FADH₂ + 2 ATP | 2 ATP |
| Electron Transport Chain (ETC) | Inner mitochondrial membrane (cristae) | H₂O + 34 ATP | 34 ATP |
Glycolysis
LocationCytoplasm (cytosol)
Products2 Pyruvate + 2 NADH
ATP yield2 ATP (net)
Krebs Cycle (Citric Acid Cycle)
LocationMitochondrial matrix
ProductsCO₂ + NADH + FADH₂ + 2 ATP
ATP yield2 ATP
Electron Transport Chain (ETC)
LocationInner mitochondrial membrane (cristae)
ProductsH₂O + 34 ATP
ATP yield34 ATP
⚡ MCQ Tip Glycolysis = cytoplasm. Krebs = mitochondrial matrix. ETC = inner mitochondrial membrane. Total = 2+2+34 = 38 ATP.
B. Anaerobic Respiration (without oxygen)
Types of Fermentation
- Occurs when oxygen is unavailable (e.g. during intense exercise)
- Much less efficient — produces only 2 ATP per glucose
- Only glycolysis occurs — pyruvate is then converted rather than entering the Krebs cycle
| Type | Organisms | Products | ATP |
|---|---|---|---|
| Lactic Acid Fermentation | Animal muscles (during exercise), lactic acid bacteria | Lactic acid | 2 ATP |
| Alcoholic Fermentation | Yeast, some plant tissues | Ethanol (alcohol) + CO₂ | 2 ATP |
⚡ Clinical link Lactic acid builds up in muscles during intense exercise — causes the "burn". The liver later converts it back to glucose (Cori cycle). Alcoholic fermentation = basis of bread (CO₂ makes dough rise) and beer/wine production.
Quick MCQ Revision
| Fact | Answer |
|---|---|
| Aerobic respiration ATP yield | 38 ATP per glucose |
| Anaerobic respiration ATP yield | 2 ATP per glucose |
| Glycolysis location | Cytoplasm (cytosol) |
| Krebs cycle location | Mitochondrial matrix |
| ETC location | Inner mitochondrial membrane (cristae) |
| Products of lactic acid fermentation | Lactic acid + 2 ATP (in animal muscles) |
| Products of alcoholic fermentation | Ethanol + CO₂ + 2 ATP (in yeast) |
| Aerobic respiration equation | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP |
| ATP stands for | Adenosine Triphosphate — the energy currency of cells |