2.6.2Additional lessons
Mammalian Lungs: Adaptations — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 28 of 142
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 4The Gas Exchange System
Trachea
- Trachea A wide tube reinforced by rings of cartilage that keeps the airway open as air is breathed in.
Bronchi
- Bronchi The trachea divides into two bronchi, with one leading to each lung.
Bronchioles
- Bronchioles The bronchi branch into many smaller bronchioles that carry air towards the alveoli.
Alveoli
- Alveoli Groups of tiny air sacs at the ends of the bronchioles where gas exchange occurs.
Capillary network
- Capillary network Each cluster of alveoli is surrounded by a dense network of blood capillaries.
Ciliated cells and goblet cells
- Ciliated cells and goblet cells The airway lining has goblet cells that make mucus and cilia that sweep it upward,
- so trapped dust and microbes are removed.
Part 2 of 4Adaptations of the Alveoli
Adaptations of the Alveoli
Large surface area
- Large surface area The lungs contain a very large number of small alveoli, which gives a huge total surface for diffusion.
Thin walls
- Thin walls The alveolar wall is one cell thick and the capillary wall is also one cell thick, so the diffusion distance is very short.
Rich blood supply
- Rich blood supply A dense capillary network carries blood that removes oxygen and brings in carbon dioxide,
- which keeps the concentration gradient steep.
Moist lining
- Moist lining A thin layer of fluid lets gases dissolve before they diffuse across.
Surfactant
- Surfactant Type II pneumocytes secrete a fluid that reduces surface tension, which prevents the alveoli from collapsing and sticking together.
| Cell type | Feature | Role |
|---|---|---|
| Type I pneumocyte | Very thin, flattened cell | Forms most of the alveolar wall for gas exchange |
| Type II pneumocyte | Cuboidal cell with vesicles | Secretes surfactant |
| Capillary endothelium | Single layer of cells | Short diffusion distance to the blood |
Part 3 of 4Path of a Gas Molecule
1
Air enters through the nose or mouth and passes down the trachea.
2
It flows through a bronchus and then through progressively narrower bronchioles into the alveoli.
3
Oxygen dissolves in the moist lining and diffuses across the alveolar wall and the capillary wall into the blood.
4
Carbon dioxide diffuses the opposite way, from the capillary blood into the alveolar air.
5
The carbon dioxide is then exhaled, while blood rich in oxygen returns to the heart for circulation.
Part 4 of 4Exam Checklist & Tips
2.6.2 – Key Points for the Exam
- Alveolus A tiny air sac in the lungs where gas exchange takes place.
- Surfactant A fluid that reduces surface tension in the alveoli.
- Type I pneumocyte A very thin alveolar cell that forms the exchange surface.
- Bronchiole A small airway that leads to the alveoli.
Common Mistakes
- Saying that the alveolar wall is several cells thick; it is only one cell thick.
- Writing that oxygen is carried through the alveolar wall by red blood cells, when it diffuses across.
- Forgetting that the capillary network keeps the gradient steep by moving blood.
- Confusing the trachea, which contains cartilage rings, with the alveoli, which contain none.
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