IB MYP 4-5 Biology-Aerobic and Anaerobic- Study Notes - New Syllabus
IB MYP 4-5 Biology-Aerobic and Anaerobic- Study Notes – New syllabus
IB MYP 4-5 Biology-Aerobic and Anaerobic- Study Notes – IB MYP 4-5 Biology – per latest IB MYP Biology Syllabus.
Key Concepts:
- Comparison of energy output
- Oxygen debt in anaerobic respiration
- Fermentation in yeast and muscles
Comparison of Energy Output: Aerobic vs. Anaerobic Respiration
Aerobic Respiration
Definition: Complete breakdown of glucose in the presence of oxygen.
Steps Involved:- Glycolysis (cytoplasm)
- Link reaction
- Krebs cycle
- Electron transport chain (mitochondria)
- ATP Yield: 36 to 38 ATP per glucose molecule
Most ATP is produced in the electron transport chain - End Products: Carbon dioxide, Water
- Energy Output: High ATP yield
Anaerobic Respiration
Definition: Partial breakdown of glucose without oxygen.
- Steps Involved: Glycolysis only (in cytoplasm)
- ATP Yield: 2 ATP per glucose molecule
- End Products:
- In animals: Lactic acid
- In yeast: Ethanol + Carbon dioxide
- Limitations:
- Very low energy output
- Can lead to fatigue and acidity (in animals)
- Only used when oxygen is scarce
Comparison Table: Aerobic vs. Anaerobic Energy Output
| Feature | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Oxygen Required | Yes | No |
| Location in Cell | Mitochondria (mostly) | Cytoplasm only |
| Number of ATP Molecules | 36–38 per glucose | 2 per glucose |
| Efficiency | High (around 40%) | Low (around 2%) |
| End Products | CO₂ and H₂O | Lactic acid or ethanol + CO₂ |
| Duration | Sustained over long periods | Short-term only |
| Example Organisms | Most animals, plants, aerobic microbes | Yeast, some bacteria, muscle cells |
Key Takeaway
Aerobic respiration is much more efficient and preferred under normal conditions. Anaerobic respiration serves as a backup mechanism during oxygen shortage, but it yields far less energy and leads to by-products that must be cleared.
Oxygen Debt in Anaerobic Respiration
What is Oxygen Debt?
Why Does It Occur?
During vigorous exercise, when the demand for energy exceeds the oxygen supply, muscle cells switch to anaerobic respiration.
Anaerobic respiration allows short-term energy production without oxygen, but it leads to the buildup of lactic acid, which the body needs to break down later using oxygen.
Thus, after exercise, the body continues to breathe heavily to:
- Oxidize lactic acid into carbon dioxide and water
- Restore ATP and creatine phosphate levels
- Reoxygenate myoglobin in muscle cells
Process of Paying Back the Oxygen Debt
After anaerobic activity:
- The breathing rate and heart rate remain high for some time
- This ensures more oxygen is delivered to tissues
- Lactic acid is transported to the liver, where it is either:
- Converted back to glucose
- Broken down in the Krebs cycle (aerobic process)
Consequences of Oxygen Debt
- Muscle fatigue
- Soreness or cramping due to lactic acid buildup
- Increased need for recovery time after intense activity
Key Biological Roles
| Component | Role During Recovery |
|---|---|
| Oxygen | Used to oxidize lactic acid and restore energy stores |
| Liver | Converts lactic acid back to glucose |
| Muscles | Regain normal pH and energy levels |
| ATP | Rebuilt through aerobic respiration |
Summary
- Oxygen debt is a temporary physiological state where the body needs additional oxygen after anaerobic activity.
- This oxygen is essential to remove lactic acid and restore normal muscle conditions.
- Regular training improves how efficiently the body handles oxygen debt and lactic acid clearance.
Fermentation in Yeast and Muscles
What is Fermentation?
Fermentation is a type of anaerobic respiration that occurs without oxygen. It allows cells to continue producing ATP when oxygen is unavailable by converting pyruvate (from glycolysis) into other end products.
Fermentation yields less energy than aerobic respiration but is essential in short-term oxygen-limited conditions.
1. Fermentation in Yeast (Alcoholic Fermentation)
Organism: Yeast (unicellular fungi)
Process:
- Glucose is broken down by glycolysis into pyruvate
- Pyruvate is converted into ethanol and carbon dioxide
Overall Equation:
Glucose → Ethanol + CO₂ + Energy (2 ATP)
Features:
- Occurs in anaerobic conditions
- Produces ethanol, used in brewing and biofuel industries
- Carbon dioxide causes dough to rise in baking
2. Fermentation in Muscles (Lactic Acid Fermentation)
Organism: Human muscle cells (temporarily during vigorous activity)
Process:
- Glucose is broken down by glycolysis into pyruvate
- Pyruvate is converted into lactic acid
Overall Equation:
Glucose → Lactic Acid + Energy (2 ATP)
Features:
- Occurs during intense exercise when oxygen is insufficient
- Lactic acid builds up, causing muscle fatigue and pain
- Oxygen is required later to break it down (oxygen debt)
Comparison: Yeast vs. Muscle Fermentation
| Feature | Alcoholic Fermentation | Lactic Acid Fermentation |
|---|---|---|
| End Product | Ethanol and CO₂ | Lactic acid |
| ATP Yield | 2 ATP | 2 ATP |
| Organism | Yeast (fungi) | Animal cells (e.g., human muscle) |
| Industrial Application | Baking, brewing, biofuels | No industrial use, but biologically important |
| Reversible? | Yes, ethanol is stable | Yes, lactic acid is later oxidized |
Importance of Fermentation
- Maintains ATP supply when oxygen is limited
- Allows glycolysis to continue by regenerating NAD+
- Plays a key role in various industries (yeast fermentation)
Acts as a temporary solution in muscle tissue under stress
Summary
- Fermentation is an anaerobic pathway that helps organisms generate ATP without oxygen.
- In yeast, it leads to ethanol and carbon dioxide.
- In muscles, it leads to lactic acid buildup.
- While not as efficient as aerobic respiration, fermentation is crucial for survival under oxygen-deficient conditions.