Measure temperature effects with a simple respirometer
Describe a controlled respirometer investigation of temperature and respiration rate, including gas-volume measurements and limitations.
A Level; Cambridge International Biology 9700, 2028–2030. Written practice is self-checked; practical investigations need supervised work and human subject-teacher review remains pending.
Before you begin
- ATP transfers energy for cellular work, and enzymes control metabolic reactions.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why is carbon dioxide absorbed when a respirometer is used to estimate oxygen uptake?
What you will learn
- Plan a respirometer comparison across temperatures
- Control gas-volume, organism and apparatus variables
Build the explanation
A simple respirometer can compare oxygen uptake by a known mass of yeast or another suitable respiring sample over a fixed time. A carbon-dioxide absorbent is held separately from the organisms so a fall in gas volume estimates oxygen consumption. Measure at several controlled temperatures, allow samples to equilibrate, keep mass and other conditions constant, and calculate a rate such as volume of oxygen consumed per minute per gram. Repeat trials and use an appropriate control.
Apply it carefully
Temperature affects both respiration and gas volume, so equilibration and constant pressure conditions matter. Check the apparatus for leaks, ensure the absorbent does not contact organisms, and do not infer an exact optimum beyond the tested range. State whether the apparatus measures oxygen uptake or total gas exchange; these are not interchangeable.
Pause and explain
Which variable must be controlled besides temperature when comparing equal-time respirometer trials?
Worked example
A sample uses 0.6 cm³ oxygen in 3 minutes. What is the mean oxygen-uptake rate?
Show the worked solution
- Divide volume consumed by elapsed time.
- 0.6 ÷ 3 = 0.2 cm³ per minute.
Answer 0.20 cm³ min⁻¹.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline how to measure the effect of temperature on respiration rate with a simple respirometer.
Give me a hint
Include equilibrating, gas absorption, rate and repeats.
Compare my reasoning
- Use equal masses of respiring sample, controlled temperatures, fixed time and separate CO₂ absorbent.
- After equilibration, measure volume change, calculate oxygen uptake per time per mass and repeat.
Place equal masses of respiring sample in a leak-checked respirometer with a separate carbon-dioxide absorbent. Equilibrate each setup at a controlled temperature, record volume change over the same fixed time, and calculate oxygen uptake per minute per gram. Repeat each temperature and include an appropriate control; use supervised apparatus handling.
Look for these in your work
- Equal sample amount
- Temperature and time controlled
- CO₂ absorbent role
- Rate and repeats included
A sample takes up 1.2 cm³ oxygen in 4 minutes and has mass 0.30 g. Calculate oxygen-uptake rate per gram.
Give me a hint
First calculate per minute, then divide by sample mass.
Compare my reasoning
- Rate = 1.2 ÷ 4 = 0.30 cm³ min⁻¹.
- Per gram = 0.30 ÷ 0.30 = 1.0 cm³ min⁻¹ g⁻¹.
Oxygen uptake per minute is 1.2/4 = 0.30 cm³ min⁻¹. Per gram, 0.30/0.30 = 1.0 cm³ min⁻¹ g⁻¹.
Look for these in your work
- Per-minute rate correct
- Mass normalisation correct
- Units included
A respirometer reading falls after the room warms, but the sample's respiration may also change. Explain how to improve the comparison.
Give me a hint
Separate biological temperature effects from physical gas-volume effects.
Compare my reasoning
- Equilibrate apparatus and sample at each set temperature.
- Use a control, fixed pressure conditions and repeats; check for leaks.
Equilibrate the apparatus and sample at each measured temperature, use matched trials and a suitable control, maintain consistent pressure conditions, and check that the apparatus is airtight. Repeat readings so biological changes can be distinguished from physical gas-volume effects as far as the method allows.
Look for these in your work
- Equilibration included
- Control and repeats included
- Pressure/leak limits considered
Common mistakes
- Using total gas change as oxygen uptake when CO₂ is not absorbed
- Ignoring temperature-related gas-volume changes
- Comparing samples with different mass or duration
What can you explain now?
Why is carbon dioxide absorbed when a respirometer is used to estimate oxygen uptake?
Compare with the explanation
To prevent CO₂ production masking the volume change caused by oxygen consumption
Then the change in gas volume more directly estimates O₂ uptake.
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Make it stick
What must be controlled when using a respirometer to compare temperature effects?
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