What should be varied?
- Vary temperature between otherwise comparable respirometer treatments.
- Use progressively narrower capillary tubing at higher temperatures.
- Increase the mass of respiring material with each higher temperature.
Respiration reasoning; AQA RP9 connection, not its identical protocol · practical reasoning
Respiration: correct a displacement measurement
Investigate temperature and gas-displacement readings for comparable respiring material over five minutes.
The model apparatus has carbon dioxide absorbed, so a corrected displacement can indicate oxygen uptake under its stated conditions. A matched blank is supplied at each temperature. Displacement in mm is not oxygen volume without apparatus geometry, and is not ATP production. This is a data exercise, not a laboratory protocol.
Questions only · Matched example · 3 readings per condition.
Plan the comparison
Which processing method supports the stated temperature comparison?
- Multiply corrected displacement by capillary diameter to obtain oxygen volume.
- Use live displacement over five minutes without subtracting the matched blank.
- Subtract matched-blank displacement from live displacement over the same five minutes.
Which control approach is useful?
- Match temperature and apparatus, but use a different mass of live material in each condition.
- Use equal live mass, comparable apparatus and matched temperature blanks.
- Use the blank measured at the lowest temperature to correct every temperature condition.
Calculate from evidence
Live mass and apparatus geometry are comparable; matched blanks are supplied.
| Temperature / °C | Reading 1 | Reading 2 | Reading 3 | Matched blank / mm |
|---|---|---|---|---|
| 10 | 1.1 | 1.2 | 1.3 | 0.2 |
| 15 | 1.9 | 2 | 2.1 | 0.4 |
| 20 | 2.9 | 3 | 3.1 | 0.5 |
| 25 | 3.9 | 4 | 4.1 | 0.6 |
| 30 | 4.9 | 5 | 5.1 | 0.8 |
Corrected displacement = mean live displacement − matched blank. Corrected rate = corrected displacement ÷ 5 min. Give numerical answers to about three significant figures.
Calculate the blank-corrected mean displacement at 20 °C, in mm.
Calculate the corrected displacement rate at 20 °C, in mm min⁻¹.
Evaluate the comparison
Explain what the matched blank corrects and why it cannot remove the unequal-live-mass confound. State an improvement and the limit of reporting displacement as a measure of respiration.
Use the alternate example below alongside the data above.
| Temperature / °C | Reading 1 | Reading 2 | Reading 3 | Matched blank / mm |
|---|---|---|---|---|
| 10 | 1.1 | 1.2 | 1.3 | 0.2 |
| 15 | 2.4 | 2.5 | 2.6 | 0.4 |
| 20 | 4.4 | 4.5 | 4.6 | 0.5 |
| 25 | 6.9 | 7 | 7.1 | 0.6 |
| 30 | 9.9 | 10 | 10.1 | 0.8 |
Original authored examples, not real experimental predictions, official marks or a laboratory protocol.