Plan a controlled yeast temperature investigation
Measure a gas-production proxy with matched conditions.
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cell processes, enzymes and the distinction between gas exchange and breathing.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the intended independent variable here?
What you will learn
- Change temperature deliberately
- Control measurement and conditions
Plan a controlled yeast temperature investigation
| Feature | Meaning |
|---|---|
| Change | Measured mixture temperature |
| Measure | Collected gas volume in fixed time |
| Match | Yeast · glucose · pH · oxygen conditions |
| Practical status | Teacher-supervised work remains pending |
Change temperature deliberately
Yeast is a living microorganism that can release carbon dioxide while breaking down glucose. A teacher-supervised investigation can compare collected gas volume in a fixed time at different temperatures. Temperature is the independent variable; the measured gas volume or calculated gas-production rate is the dependent variable. This is a proxy for respiratory activity, not a direct measurement of energy released.
Use a water bath to hold each yeast and glucose mixture at its selected temperature, checking the actual mixture temperature rather than relying only on the bath label. Allow consistent equilibration before the timed measurement and use the same approved starting procedure. Record the measurement interval and units, for example cubic centimetres collected in four minutes.
Control measurement and conditions
Keep yeast amount, glucose concentration and volume, total mixture volume, pH, apparatus and timing comparable. Keep the intended oxygen conditions consistent as well: gas production alone does not establish that a sample is anaerobic. Use equivalent gas collection with a checked, unobstructed outlet and leak-tight connections according to the supervised apparatus method.
Gas can dissolve in the liquid, and temperature affects gas behaviour and collection. These are limitations when interpreting collected volume as a biological rate proxy. Repeat independent trials and compare results under the same method; do not claim every difference is caused by respiration if apparatus, oxygen access or quantities also changed. Use supplied data unless performing an approved supervised practical.
Pause and explain
Which comparison best isolates temperature?
Worked example
Trial A has twice as much yeast as B at different temperatures. Is this a fair temperature comparison?
Show the worked solution
- Both temperature and yeast amount changed.
- The amount of respiring cells is a confounder.
Answer No; match yeast amount so temperature is the intended changed variable.
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.
Identify the independent variable and a dependent measurement in this investigation.
Give me a hint
Separate the changed condition from the recorded outcome.
Compare my reasoning
- The selected temperatures are changed.
- Gas volume over a fixed time is measured.
Independent: temperature. Dependent: collected carbon-dioxide gas volume in a fixed time, or its calculated rate.
Look for these in your work
- Identify both roles
- Include the timed measurement
List four controls and explain why equal timing matters.
Give me a hint
Use quantities and measurement conditions.
Compare my reasoning
- Match yeast, glucose concentration/volume, pH and apparatus.
- Longer collection can increase volume even at the same rate.
Match yeast amount, glucose concentration and volume, pH and apparatus; use equal collection times so volume differences are comparable.
Look for these in your work
- Name four relevant controls
- Explain the timing confounder
A student changes temperature and removes the gas outlet to stop gas escaping. Improve the plan.
Give me a hint
Collection needs a controlled route, not an unvented vessel.
Compare my reasoning
- Use the teacher-approved gas-collection outlet and checked connections.
- Match conditions and measure gas through that route.
Retain the approved unobstructed gas-collection route and supervision; compare temperatures with matched mixtures, apparatus and timing.
Look for these in your work
- Correct the collection route
- Retain the fair comparison
Common mistakes
- Calling gas volume a direct energy measurement.
- Sealing an active gas-producing vessel without an approved outlet.
What can you explain now?
Which comparison best isolates temperature?
Compare with the explanation
Matched yeast, glucose, pH, timing, oxygen conditions and apparatus at different temperatures
Other influential conditions are controlled.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Name the variables, controls and proxy limitation in a yeast 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.