Investigate temperature and water uptake
Compare supplied repeated results at controlled temperatures without declaring a universal optimum.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall means and experimental variables.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Why allow stabilisation after changing a condition?
What you will learn
- Design a matched temperature comparison
- Calculate means and compare tested conditions
Supplied temperature repeats
| Temperature | Trial 1 | Trial 2 | Trial 3 | Mean (mm/min) |
|---|---|---|---|---|
| 15 °C | 2 | 3 | 4 | 3 |
| 25 °C | 5 | 6 | 7 | 6 |
Match the rest of the environment
Compare a teacher-prepared potometer shoot at controlled measured temperatures after allowing stabilisation. Keep wind speed, humidity, light, leaf area, capillary and shoot condition comparable. Record temperature near the leaves rather than relying only on a heater setting.
If a lamp provides heating, it may also change light. Use the laboratory’s controlled heating method and check other environmental readings. Keep the shoot hydrated and use supervised procedures for glass and sharp preparation tools.
Read repeated results
Supplied equal-duration displacement rates at 15 °C are 2, 3 and 4 mm/min; at 25 °C they are 5, 6 and 7 mm/min. Their means are 3 and 6 mm/min. The mean uptake rate doubles across these tested conditions.
The comparison does not locate an optimum temperature or show an unlimited rise. Only two temperatures were tested. Plants can close stomata or become stressed, so conclusions must remain tied to the measured range and controlled conditions.
Sources for this lesson
Pause and explain
What do the two-temperature data establish?
Worked example
Calculate both mean rates and their ratio from the supplied repeats.
Show the worked solution
- (2 + 3 + 4) / 3 = 3 mm/min.
- (5 + 6 + 7) / 3 = 6 mm/min; 6 / 3 = 2.
Answer Means: 3 and 6 mm/min. The tested mean rate doubles.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
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.
Find the mean of 2, 3 and 4 mm/min.
Give me a hint
Add the rates and divide by the number of repeats.
Compare my reasoning
- The total is 9 mm/min.
- Divide by 3.
Mean = 3 mm/min.
Look for these in your work
- Sum correctly
- Divide by three
Find the mean of 5, 6 and 7 mm/min and compare it with 3 mm/min.
Give me a hint
Calculate the mean before the ratio.
Compare my reasoning
- The total is 18; 18 / 3 = 6 mm/min.
- 6 / 3 = 2.
Mean = 6 mm/min, twice the lower-temperature mean.
Look for these in your work
- Calculate 6 mm/min
- Give the twofold ratio
How would you improve the claim “25 °C is optimal” using further measurements?
Give me a hint
An optimum needs results either side of a peak.
Compare my reasoning
- Test additional temperatures below and above the candidate value with matched conditions.
- Repeat and compare rates and plant condition.
Add repeated, controlled measurements around and beyond 25 °C; the existing pair alone does not establish an optimum.
Look for these in your work
- Add relevant temperatures
- Retain controls/repeats and the bounded conclusion
Common mistakes
- Calling the higher of two tested temperatures an established optimum.
- Ignoring light changes when using a heating lamp.
What can you explain now?
What do the two-temperature data establish?
Compare with the explanation
Higher mean uptake at 25 °C than 15 °C in this setup
The measured comparison supports this bounded result.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Write the strongest conclusion justified by the two-temperature data.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.