Investigate wind speed and water uptake
Plan a controlled potometer comparison and interpret supplied displacement data.
Section B8.3 · Transpiration
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 controls, rate and the uptake proxy.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which variable is deliberately changed in this comparison?
What you will learn
- Identify wind speed as the independent variable
- Compare uptake rates under matched conditions
Supplied airflow comparison
| Airflow | Travel (mm) | Time (min) | Rate (mm/min) |
|---|---|---|---|
| Still | 6 | 2 | 3 |
| Low | 10 | 2 | 5 |
| Higher | 14 | 2 | 7 |
Change one environmental factor
A teacher-prepared, airtight potometer can measure water uptake by a leafy cut shoot using bubble displacement in a uniform capillary. After stabilisation, compare still air with measured airflow from a fan. Keep leaf area, light, temperature, humidity, shoot condition and duration comparable.
A fan can also alter temperature or humidity. Record those conditions rather than assuming that changing fan setting changes only wind speed. Position the fan consistently and use an anemometer or the stated measured airflow levels when available.
Use the same interval and apparatus
Supplied 2-minute displacements are 6, 10 and 14 mm for still, low and higher airflow. The displacement rates are 3, 5 and 7 mm/min. In the same uniform capillary, greater displacement rate corresponds to greater water-uptake rate.
Repeat trials, reset the bubble using the teacher’s procedure and allow the shoot to stabilise after a condition change. These measurements are uptake proxies. They support a trend over the tested airflow levels, not a universal claim that wind always increases loss indefinitely.
Sources for this lesson
Pause and explain
What does greater bubble displacement per minute indicate here?
Worked example
Compare 6 mm and 14 mm movement in 2 min in the same capillary.
Show the worked solution
- Divide each distance by 2 min: 3 and 7 mm/min.
- The second rate is higher; both measure water uptake.
Answer 3 and 7 mm/min: uptake is faster in the tested higher-airflow condition.
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.
Calculate displacement rates for 6, 10 and 14 mm in 2 min.
Give me a hint
Rate is distance divided by time.
Compare my reasoning
- Divide each distance by 2.
- Keep the mm/min unit.
3, 5 and 7 mm/min respectively.
Look for these in your work
- Calculate all three rates
- Use mm/min
Give three conditions to control in the wind comparison and explain one.
Give me a hint
Keep another possible cause of uptake change constant.
Compare my reasoning
- Choose temperature, humidity and light, for example.
- Changing temperature could alter water loss independently of airflow.
Control temperature, humidity and light; temperature changes could otherwise provide an alternative cause of uptake differences.
Look for these in your work
- Name three valid controls
- Explain one causal reason
The fan condition is also warmer. What additional comparison is needed before attributing the full increase to wind?
Give me a hint
Separate airflow from temperature.
Compare my reasoning
- Match temperature across wind conditions.
- Repeat the airflow comparison with other conditions controlled.
Compare airflow levels at matched temperature; the existing result confounds wind and temperature.
Look for these in your work
- Identify the confound
- Describe a controlled follow-up
Common mistakes
- Comparing raw distances from unequal times.
- Assuming a fan leaves temperature and humidity unchanged.
What can you explain now?
What does greater bubble displacement per minute indicate here?
Compare with the explanation
Greater water uptake in the same capillary
Displacement tracks uptake with a fixed cross-sectional area.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
State the changed variable, measured proxy and two controls in a wind investigation.
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.