14Class 11 Biology
Breathing and Exchange of Gases short notes
Short notes on breathing, gas exchange and transport, with lung volumes. It's numbers-heavy, so learn the values.
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Breathing
- Air passes through nostrils, pharynx, larynx, trachea, bronchi and bronchioles to the alveoli.
- Inspiration: the diaphragm contracts and the chest volume rises, lowering lung pressure.
- Expiration is usually passive.
- Rate is about 12 to 16 breaths a minute.
Lung volumes
- Tidal volume: about 500 mL.
- Inspiratory reserve volume: 2500 to 3000 mL.
- Expiratory reserve volume: 1000 to 1100 mL.
- Residual volume: 1100 to 1200 mL.
- Vital capacity = TV + IRV + ERV.
- Total lung capacity = vital capacity + residual volume.
Gas exchange and transport
- In alveoli, pO₂ is about 104 mmHg and pCO₂ about 40 mmHg.
- About 97% of O₂ travels as oxyhaemoglobin, and 3% dissolved in plasma.
- CO₂: about 70% as bicarbonate, 20 to 25% as carbaminohaemoglobin, and 7% dissolved.
- The oxygen dissociation curve is sigmoid. High pCO₂, high H⁺ and high temperature shift it right.
- The rhythm centre is in the medulla, and the pneumotaxic centre in the pons moderates it.
Disorders
- Asthma: bronchi and bronchioles become inflamed.
- Emphysema: alveolar walls are damaged, often due to smoking.
- Occupational disorders come from long exposure to dust.
Where students slip up
- Thinking vital capacity includes residual volume. It doesn't.
- Saying most CO₂ is carried bound to haemoglobin. Most is carried as bicarbonate.
- Reversing the shift of the dissociation curve.
Try it on your weakest chapter.
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