Respiration

• Cellular respiration — breakdown of glucose for ATP energy.
• Aerobic — with O₂: complete breakdown → CO₂ + H₂O + more ATP.
• Anaerobic — without O₂: partial breakdown (yeast → ethanol + CO₂; muscles → lactic acid).
• Human respiratory system — nose, trachea, bronchi, lungs, alveoli.
• Gas exchange — O₂ in, CO₂ out at alveoli; haemoglobin transport.

1. Aerobic equation — C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (38 ATP approx.).
2. Anaerobic in yeast — glucose → ethanol + CO₂ + little energy (fermentation).
3. Anaerobic in muscles — during heavy exercise: lactic acid + energy (cramp).
4. Alveoli — thin wall, large surface, rich blood supply — efficient gas exchange.
5. Diaphragm & ribs — breathing movements; inhalation: diaphragm flattens, chest expands.
6. Haemoglobin — carries O₂ as oxyhaemoglobin in RBCs.
7. CO₂ transport — dissolved, as bicarbonate, carbamino compounds.
8. Plants respire too — stomata exchange gases day and night.
9. ATP — usable energy currency for cell processes.
10. NCERT comparison — aerobic yields far more ATP than anaerobic.

Compare aerobic and anaerobic respiration in yeast

Aerobic (with O₂): complete oxidation of glucose → CO₂ + H₂O + ~38 ATP
Anaerobic (without O₂): fermentation → C₂H₅OH + CO₂ + 2 ATP
Yeast used in bread (CO₂ rises dough) and alcohol industry.
Conclusion: anaerobic incomplete but useful commercially.

• Confusing respiration with breathing (breathing = ventilation only).
• Misconception: plants don't respire (they photosynthesise AND respire).
• Thinking anaerobic always in yeast (yeast can respire aerobically too).
• Forgetting lactic acid cause of muscle fatigue.
• Reversing inhalation vs exhalation rib movements.

• Write word equation for aerobic respiration.
• What is produced during anaerobic respiration in muscles?
• Where does gas exchange occur in lungs?
• Why is ATP called energy currency?

Open the Practice tab for graded questions on Respiration.