2.6.2Inquiry Process
Mammalian Lungs- Adaptations — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 64 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 4Structure of the Gas Exchange System
Air travels along a branching tube network before reaching the exchange surface.
1
Air enters through the nose or mouth and passes down the trachea, which is held open by C-shaped rings of cartilage.
2
The trachea divides into two bronchi, one to each lung, and these branch repeatedly into smaller bronchioles.
3
Each bronchiole ends in a cluster of tiny air sacs called alveoli, where gas exchange with the blood takes place.
4
The airways are lined with ciliated epithelium and goblet cells, which trap dust and microbes in mucus and sweep it away.
5
Lungs sit inside the thorax protected by the rib cage and are covered by moist pleural membranes that reduce friction.
Part 2 of 4Adaptations of the Alveolus
Huge surface area
- Huge surface area Hundreds of millions of alveoli give the lungs a combined exchange area of tens of square metres inside a compact organ.
Thin wall
- Thin wall Alveolar walls are made of flattened type I pneumocytes only one cell thick,
- so oxygen and carbon dioxide diffuse over a very short distance.
Dense capillary network
- Dense capillary network Each alveolus is wrapped in capillaries with walls one cell thick, bringing blood extremely close to the air.
Surfactant
- Surfactant Type II pneumocytes secrete a detergent-like fluid that reduces surface tension in the water film,
- so alveoli do not collapse or stick together on exhaling.
Steep gradients
- Steep gradients Ventilation brings fresh air high in oxygen while blood flow carries oxygenated blood away, so concentration gradients are maintained.
| Feature | How it speeds exchange |
|---|---|
| Thin walls | Shorter diffusion distance |
| Many alveoli | Larger surface area |
| Capillary flow | Removes oxygen, keeps gradient steep |
Part 3 of 4Linking Structure to Function
Linking Structure to Function
Moisture
- Moisture A thin film of fluid lining the alveoli lets gases dissolve before diffusing across the membranes.
Elastic fibres
- Elastic fibres Elastic tissue in alveolar walls stretches on inhalation and recoils on exhalation, helping to push air out.
Pressure difference
- Pressure difference Oxygen has a higher partial pressure in alveolar air than in arriving blood,
- so it diffuses into the blood; carbon dioxide moves the other way.
Short transit
- Short transit Red blood cells are squeezed through narrow capillaries, which slows them and holds them close to the alveolar wall.
Part 4 of 4Exam Checklist & Tips
2.6.2 – Key Points for the Exam
- Alveolus A microscopic air sac in the lung that is the site of gas exchange.
- Surfactant A mixture of phospholipids and proteins that lowers surface tension inside alveoli.
- Bronchiole A small airway without cartilage that carries air to the alveoli.
- Pneumocyte
- A cell lining the alveolus;
- type I cells form the thin wall and type II cells make surfactant.
- A cell lining the alveolus;
- Ciliated epithelium A lining whose cilia move mucus and trapped particles out of the airway.
Common Mistakes
- Saying that gas exchange happens in the bronchi or trachea;
- only the alveoli (and thin-walled bronchioles at the ends) exchange gases.
- Stating that surfactant helps oxygen dissolve;
- its main role is reducing surface tension to keep alveoli open.
- Writing that alveoli have one cell layer in total;
- the exchange barrier is two thin layers, alveolar wall and capillary wall.
- Forgetting that ventilation and blood flow are needed to keep the gradient steep.
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