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B3.1.6—Lung volume measurements

Lung volume measurements use spirometer traces and breathing calculations to quantify tidal volume, ventilation rate, minute ventilation and vital capacity.

Syllabus
First assessment 2025
Objective
B3.1.6
Level
SL

Exam analysis

Chance of appearing8%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper3
Typical marks1–2

Common command terms

  • Define
  • State
  • Calculate
  • Compare
  • Describe
  • Outline

Scoring notes

Common mistake
Giving a ventilation-rate number without breaths per minute or another valid time unit.

Recent exam appearances

May 2025Paper1A ["SL"] · TZ114[ 1 ]B3.1.6—Lung volume measurements
November 2024Paper2 ["SL"] · TZ15(a)(ii)[ 1 ]B3.1.6—Lung volume measurements
November 2024Paper2 ["SL"] · TZ15(a)(i)[ 1 ]B3.1.6—Lung volume measurements
November 2023Paper3 ["SL"] · TZ13(c)[ 3 ]B3.1.6—Lung volume measurements
November 2023Paper3 ["SL"] · TZ13(b)[ 1 ]B3.1.6—Lung volume measurements
Practice this objective

Coverage 2010–2025 · Updated 15 Jul 2026

Spirometry Measures Air Volumes, Not Every Lung Volume

A spirometer records air volume moved over time. Tidal volume is the air moved in a normal breath; inspiratory and expiratory reserve volumes are the additional amounts moved by maximal inspiration or expiration.

On a trace, vertical differences represent volume and the horizontal axis represents time. Identify the normal peak-to-trough change for tidal volume, then measure from a normal limit to the corresponding maximal limit for each reserve.

Vitalcapacity=inspiratoryreservevolume+tidalvolume+expiratoryreservevolume.Useoneconsistentvolumeunit,suchasdm3orL.Vital capacity = inspiratory reserve volume + tidal volume + expiratory reserve volume. Use one consistent volume unit, such as dm³ or L.

Measure the vertical distance from maximal inspiration to maximal expiration to obtain vital capacity; it should equal the sum of the three component volumes measured from the same calibrated trace.

Simple spirometry cannot directly measure residual volume because that air never leaves the lungs. Do not confuse a spirometer with a respirometer, which measures aspects of respiration rather than lung ventilation.

Lung volume measurements

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, commonly using Define / State / Calculate.

Command terms

Define / State / Calculate / Compare / Describe / Outline

What earns marks

Build the answer around this relationship: Tidal volume is the volume of air moved during one normal breath.

Watch for

Giving a ventilation-rate number without breaths per minute or another valid time unit.

Representative question

Question 1

[Maximum number: 2]

Outline how ventilation rate could have been monitored in this study.

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

  • Tidal volume is the volume of air moved during one normal breath.
  • Ventilation rate is calculated from the number of breaths per unit time.
  • Minute ventilation is tidal volume multiplied by ventilation rate.
  • Spirometer traces can show breath volume, breathing frequency and oxygen consumption patterns.
  • Vital capacity is the largest usable change in lung volume during forced breathing.