CourseCourseQuestionQuestionDocumentDocument

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

Coverage 2010–2025 · Updated 15 Jul 2026

Alveoli Combine Area, Thinness and Gradient Maintenance

Millions of alveoli create a very large moist surface. Type I pneumocytes and capillary endothelium form a short diffusion path; elastic fibres support recoil and surfactant limits collapse.

airway branching → alveolar air → type I pneumocyte → basement membrane region → capillary endothelium → plasma → erythrocyte haemoglobin

SL Summary: One Diffusion Model

Feature Lung Leaf
area many alveoli broad blade + mesophyll walls
path thin barrier thin leaf + air spaces
gradient air + blood flow CO₂ use + stomata

Spirometry measures ventilation; a potometer estimates water uptake; a leaf cast measures stomatal density. Match each method to its direct measurement.

Mammalian lung adaptations

[ 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.

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.