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Respiration

Aerobic, anaerobic, gas exchange, breathing

Aerobic Respiration

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)

Happens in mitochondria (in two stages: glycolysis in cytoplasm, Krebs cycle + ETC in mitochondria)

Requires oxygen. Produces large amount of ATP (~38 ATP per glucose). Most efficient.

Energy used for: movement, maintaining temperature, active transport, growth, protein synthesis

Anaerobic Respiration — In Animals

C₆H₁₂O₆ → 2C₃H₆O₃ (lactic acid) + energy (2 ATP)

No oxygen needed. Happens in cytoplasm. Much less ATP (only 2 per glucose).

Lactic acid builds up: Muscle fatigue, soreness. Must be removed (converted back to glucose in liver).

Used during intense exercise when O₂ delivery < demand

Anaerobic Respiration — In Yeast

C₆H₁₂O₆ → 2C₂H₅OH (ethanol) + 2CO₂ + energy (2 ATP)

Fermentation: No oxygen. Produces ethanol (alcohol) & CO₂. Only 2 ATP.

Used in: Brewing (beer/wine), baking (bread rises from CO₂)

Yeast prefers aerobic (more ATP) but survives anaerobically

Comparison: Aerobic vs Anaerobic

Feature	Aerobic	Anaerobic
Oxygen needed	Yes	No
Location	Mitochondria	Cytoplasm
ATP produced	~38 per glucose	2 per glucose
Products	CO₂ + H₂O	Lactic acid (animals) or ethanol + CO₂ (yeast)
Efficiency	Very high	Very low

Gas Exchange — Alveoli (Lung Structure)

Alveoli: Tiny air sacs in lungs. Site of gas exchange between air and blood.

Four adaptations:
• Large surface area: Millions of alveoli
• Thin walls: One cell thick (diffusion distance short)
• Moist lining: Dissolves gases for diffusion
• Rich blood supply: Dense capillary network

O₂ diffuses IN (blood gets oxygenated); CO₂ diffuses OUT (removed from blood)

Breathing — Ventilation of Lungs

Inspiration (breathing in): Diaphragm contracts (flattens). External intercostal muscles pull ribs UP. Chest cavity volume increases → pressure decreases → air flows IN

Expiration (breathing out): Diaphragm relaxes (domes up). Intercostal muscles relax, ribs fall. Volume decreases → pressure increases → air flows OUT

Note: Breathing brings fresh air to alveoli. Exchange happens passively (diffusion).

Oxygen & Carbon Dioxide Transport

O₂: Binds to haemoglobin in RBCs. Transported from lungs to tissues.

CO₂ (from cellular respiration): Transported to lungs in three ways:
• 85%: converted to bicarbonate ions (HCO₃⁻) in plasma
• 15%: binds to haemoglobin
• Trace: dissolved in plasma

CO₂ is converted back to CO₂ in lungs → exhaled

Exam Tips

✓ Aerobic equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

✓ Anaerobic (animals): glucose → lactic acid + 2 ATP

✓ Anaerobic (yeast): glucose → ethanol + CO₂ + 2 ATP

✓ Alveoli: large SA, thin walls, moist, blood supply

✓ Diaphragm contracts → volume increases → air IN

Key Takeaways

✅ Aerobic: glucose + O₂ → CO₂ + H₂O + ~38 ATP (mitochondria)

✅ Anaerobic (animals): glucose → lactic acid + 2 ATP

✅ Anaerobic (yeast): glucose → ethanol + CO₂ + 2 ATP

✅ Alveoli: large SA, thin walls, moist, rich blood supply

✅ Breathing: diaphragm changes volume, changes pressure, moves air

✅ O₂ in RBCs; CO₂ mostly as bicarbonate in plasma

Breathing powers your life! 💨✓