Module 3: Measuring Oxygen Uptake in Mammals
These free OCR A Level Biology Measuring Oxygen Uptake in Mammals revision notes have been written for specification point 3.1.1(e).
Measuring oxygen uptake: Respirometer vs Spirometer
A respirometer is a device that can be used to measure oxygen uptake.
A spirometer measures breathing patterns, and produces a trace on graph paper as the test subject breaths; the graph produced is a reflection of the subject’s tidal volume and breathing rate.
The diagram below presents a typical spirometer set-up and accompanying spirometer trace.
The table below outlines the key components needed to set up a spirometer and their function:
| Component | Purpose |
|---|---|
| Soda lime (KOH) | Absorbs carbon dioxide, so that the volume changes reflect oxygen uptake only |
| Spirometer chamber | A sealed air tank that moves up and down with each breath |
| Kymograph/data logger | Records breathing patterns (tidal volume, breathing rate, etc.) |
| Water bath/heater | Maintains a constant temperature for the spirometer chamber, preventing volume changes due to thermal expansion |
| Nose clip | Ensures all air is breathed through the mouthpiece |
Spirometer interpretation
A spirometer trace allows you to calculate:
- Tidal Volume: Height of each wave
- Breathing Rate: Number of waves per minute
- Oxygen Uptake: Overall volume change over time
These measurements can be used to assess respiratory health, athletic performance, and how someone is affected by conditions like asthma or emphysema.
The table below outlines how you determine these values:
| Measurement | What to Measure | How to Calculate |
|---|---|---|
| Tidal Volume (TV) | Height between the peak of inhalation and the trough of exhalation. | The value gives the volume of air per breath (usually in dm³ or ml). |
| Breathing Rate (BR) | The number of complete breathing waves in a set time period. | Divide the number of breaths by the time interval (in minutes) to get breaths per minute. |
| Oxygen Uptake (VO₂) | The overall drop in baseline volume is due to oxygen absorption over time. | Measure volume change over time (e.g. per minute) to calculate oxygen uptake rate in dm³ min⁻¹. |