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B3.1.4—Mammalian lung adaptations

Mammalian lungs use many thin, moist and vascular alveoli, with pneumocytes, surfactant and elastic tissue supporting rapid gas exchange during ventilation.

Syllabus
First assessment 2025
Objective
B3.1.4
Level
SL

Exam analysis

Chance of appearing7%of analysed past papers
Latest appearanceNovember 2025
Most common paperPaper2
Typical marks1–4

Common command terms

  • Describe
  • Explain
  • Outline
  • Identify
  • Predict

Scoring notes

Common mistake
Treating alveoli as muscular structures rather than thin exchange surfaces supported by ventilation and elastic recoil.

Recent exam appearances

November 2025Paper2 ["SL"] · TZ34(c)[ 2 ]B3.1.4—Mammalian lung adaptations
May 2024Paper3 ["SL"] · TZ23(c)[ 2 ]B3.1.4—Mammalian lung adaptations
November 2023Paper2 ["SL"] · TZ17(c)[ 4 ]B3.1.4—Mammalian lung adaptations
May 2021Paper1 ["SL"] · TZ227[ 1 ]B3.1.4—Mammalian lung adaptations
November 2019Paper2 ["SL"] · TZ06(c)[ 7 ]B3.1.4—Mammalian lung adaptations
Practice this objective

Coverage 2010–2025 · Updated 15 Jul 2026

Mammalian Lungs Build a Short, Well-Supplied Path

Mammalian lungs use branching airways, many alveoli, thin epithelium and dense capillaries to maximize gas exchange.

Branching distributes air, alveoli create area, the thin alveolar-capillary barrier shortens diffusion distance and blood flow carries gases away. Elastic tissue and surfactant support repeated ventilation.

Link adaptation to function: bronchioles distribute; alveoli add area; thin walls shorten distance; capillaries maintain gradients.

A red blood cell passing through an alveolar capillary encounters oxygen-rich air across a very thin moist barrier.

Lung adaptations work together; naming one feature without its mechanism does not explain efficient exchange.

Mammalian lung adaptations

Assessment in practice

1–4 marks
How it is assessed

This objective is assessed through structured response, commonly using Describe / Explain / Outline.

Command terms

Describe / Explain / Outline / Identify / Predict

What earns marks

Build the answer around this relationship: Many alveoli create a large surface area for diffusion.

Watch for

Treating alveoli as muscular structures rather than thin exchange surfaces supported by ventilation and elastic recoil.

Representative question

Question 1

[Maximum number: 6]

A supply of oxygen is needed for aerobic respiration in mitochondria. Describe the features of alveoli in human lungs that adapt them for efficient absorption of oxygen.

Gas Exchange Across Animals And Leaves

Core gas-exchange answers link exchange surfaces to diffusion gradients. For animals, exchange surfaces are explained by diffusion properties, ventilation, and blood flow. For plants, leaves allow carbon dioxide entry and oxygen/water vapour exit while controlling water loss through stomata. Spirometry, transpiration, and stomatal density data provide evidence of gradient and surface-area effects.

  • Core animal answer: large, thin, moist, permeable surface plus ventilation and blood flow.
  • Core plant answer: stomata, guard cells, mesophyll air spaces, cuticle, and transpiration factors.
  • Data questions usually test rate, gradient, volume, or density per area.

Concept essentials

  • Many alveoli create a large surface area for diffusion.
  • Type I pneumocytes and capillary walls provide a short diffusion distance.
  • Type II pneumocytes secrete surfactant that reduces surface tension.
  • Emphysema reduces gas exchange by destroying alveolar surface area and elasticity.