To interpret respiration data, describe the trend with numbers, explain it with biology, and conclude in answer to the aim. Keep each step in its own sentence.
This lesson follows relating substrates, products and energy in the SPM Biology cellular respiration chapter.
What is the routine?
- Describe: quote the pattern with at least two values.
- Explain: give the biological reason for the pattern.
- Conclude: answer the aim, using only what the data show.
- Check the control: say what the control tells you.
Worked example: germinating seeds at different temperatures
Some germinating seeds are placed in a respirometer, a sealed flask with a coloured-liquid tube. Soda lime absorbs the carbon dioxide, so the liquid moves as the seeds use oxygen. The distance moved in 10 minutes at each temperature is:
| Temperature (°C) | 10 | 20 | 30 | 40 | 50 |
|---|---|---|---|---|---|
| Distance moved (mm) | 2 | 5 | 11 | 14 | 3 |
Describe. The distance rises from 2 mm at 10 °C to 14 mm at 40 °C. It then falls to 3 mm at 50 °C.
Explain. A higher temperature gives molecules more energy, so the enzymes in respiration work faster. At 50 °C the enzymes lose their shape, so the rate falls.
Conclude. The rate of respiration is highest near 40 °C among the temperatures tested.
A boiled-seed control should show no movement. That shows the liquid moved because the living seeds were respiring.
The mistake that costs marks
The common slip is to say “respiration stops at 50 °C”. The data show 3 mm, not 0, so the rate fell but did not stop.
| Wrong | Right | |
|---|---|---|
| At 50 °C | Respiration stops | Rate falls to 3 mm |
| Best temperature | 40 °C is the optimum for all seeds | Highest among those tested |
| Order | Explain before describing | Describe with numbers, then explain |
Conclusions should only reach as far as the tested range.
Check yourself
A student places germinating seeds and boiled seeds in separate flasks with limewater. After 30 minutes, the limewater with germinating seeds is cloudy, and the limewater with boiled seeds is clear. What does the boiled-seed flask show?
Answer
The boiled seeds are dead, so they do not respire and produce no carbon dioxide. The limewater stays clear.
The boiled-seed flask is the control. It shows the cloudiness in the other flask comes from the living seeds respiring and releasing carbon dioxide.
What to study next
Finish the chapter with distinguishing breathing from cellular respiration. The graph evidence and fair-comparison lab lets you compare sets of results, and the mistake log and paper-error review records slips.
If you would like a teacher to go through your conclusions, see online one-to-one Biology tuition.