BIOLOGY WITH HAMZA · MDCAT REVISION
Respiration
Name: ____________________ Date: ______________
Recall first. Check second. Return to the ideas you missed.
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Learning targets
- Distinguish ventilation, gas exchange, transport and cellular respiration.
- Explain breathing through volume and pressure changes.
- Predict changes using ventilation and diffusion calculations.
Core notes
- Ventilation, exchange, transport and cellular respiration are distinct and connected.
- Volume changes create the pressure differences driving airflow.
- Dead space makes breathing depth important even at equal minute ventilation.
- Area, thickness, gradients and perfusion all matter.
Read, cover and redraw
Air moves along pressure differences.
Gases diffuse across thin barriers.
Blood connects lungs with tissues.
Oxygen supports aerobic electron transport.
Written recall
1. 600 mL breaths, 150 mL dead space and ten breaths/minute: alveolar ventilation?
2. Area halves and thickness doubles: relative diffusion rate?
3. Why does diaphragm contraction cause inward airflow?
4. Can oxygen and carbon dioxide diffuse in opposite directions?
5. Why is ventilation alone insufficient?
Apply the idea
1. Tidal volume is 500 mL, anatomical dead space is 150 mL and breathing frequency is 12 min⁻¹. What is alveolar ventilation?
- 4.2 L min⁻¹
- 1.8 L min⁻¹
- 6.0 L min⁻¹
- 7.8 L min⁻¹
My answer: _____ Reason: ____________________________________
2. Both patterns move 6 L of air per minute. Which provides greater alveolar ventilation if anatomical dead space is 150 mL per breath?
| Pattern | Tidal volume / mL | Breaths / min |
|---|---|---|
| P | 500 | 12 |
| Q | 250 | 24 |
- Q, because faster breathing always exchanges more gas
- P, because fewer breaths waste less volume in dead space
- They must provide identical alveolar ventilation
- Neither moves air beyond the trachea
My answer: _____ Reason: ____________________________________
3. Alveolar wall thickness doubles while surface area and the oxygen partial-pressure difference remain constant. In a simple diffusion model, oxygen transfer rate should:
- Quadruple
- Approximately double
- Approximately halve
- Become independent of wall thickness
My answer: _____ Reason: ____________________________________
Answer key
Cover this section while attempting the questions.
Written recall
1. (600 − 150) × 10 = 4,500 mL/min = 4.5 L/min.
2. One quarter, assuming other factors remain constant.
3. Volume increases, alveolar pressure falls below atmosphere and air flows down that pressure difference.
4. Yes. Each follows its own partial-pressure gradient.
5. Gas must cross the barrier and be transported by adequate blood flow to tissues.
Applied questions
1. A — Alveolar ventilation = (tidal volume − dead space) × frequency = (500 − 150) × 12 = 4,200 mL min⁻¹. Total minute ventilation would be 6 L min⁻¹.
2. B — P gives (500−150)×12 = 4,200 mL min⁻¹; Q gives (250−150)×24 = 2,400 mL min⁻¹. Equal total ventilation does not imply equal alveolar ventilation.
3. C — Diffusion rate is inversely related to barrier thickness when area, diffusion coefficient and the driving difference remain constant.