Describe temperature effects from enzyme-activity data
Find the fastest tested condition without assuming every enzyme has the same optimum.
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-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.
Before you begin
- Recall protein building blocks and the distinction between a molecule and a living cell.
- Use the supplied observations, quantities and units rather than assuming an optimum for every enzyme.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
On an activity graph, which tested point is fastest?
What you will learn
- Find the fastest tested condition without assuming every enzyme has the same optimum.
- Apply the explanation to the stated evidence and recognise the limits of the model.
Read the measured pattern
In a typical enzyme investigation, activity rises as temperature increases toward an optimum, then falls at sufficiently high temperatures as denaturation reduces activity. The optimum is the temperature at which activity is greatest under the stated conditions.
Different enzymes and conditions can have different optima. Do not assume 37 °C is correct for every enzyme, or that the fastest measured point is the exact optimum when only widely spaced temperatures were tested.
Use supplied points honestly
The supplied model has rates 1, 2, 4, 6, 2 and 0.2 units/min at 10, 20, 30, 40, 50 and 60 °C. The greatest measured rate is at 40 °C. Additional nearby temperatures would help locate the optimum more precisely.
Compare like measurements and hold pH, substrate and enzyme quantities constant. A fall in a graph is evidence of reduced measured activity; the shape alone does not establish every possible cause or prove complete inactivity.
Sources for this lesson
Pause and explain
How could a tested peak near 40 °C be located more precisely?
Worked example
Using the supplied data, identify the fastest tested temperature and compare rates at 30 and 40 °C.
Show the worked solution
- The maximum supplied rate is 6 units/min at 40 °C.
- The 30 °C rate is 4 units/min.
- 6 ÷ 4 = 1.5, under these test conditions.
Answer 40 °C is fastest tested; its measured rate is 1.5 times the 30 °C rate.
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.
At 10, 20 and 30 °C, supplied rates are 1, 2 and 4 units/min. Which tested temperature is fastest?
Give me a hint
Choose the largest rate.
Compare my reasoning
- 4 is the greatest supplied rate.
- It occurs at 30 °C.
30 °C is fastest among these tested temperatures.
Look for these in your work
- Use rate rather than temperature alone.
- Limit the conclusion to tested conditions.
The full model gives 6 units/min at 40 °C and 2 units/min at 50 °C. Compare the measured rates.
Give me a hint
Divide rates, not temperatures.
Compare my reasoning
- 6 ÷ 2 = 3.
The measured rate at 40 °C is three times that at 50 °C.
Look for these in your work
- Divide the relevant measurements.
- Avoid a universal rate multiplier.
A student claims every enzyme has optimum 40 °C because this model peaks there. Evaluate the claim.
Give me a hint
Separate this enzyme’s sampled data from a universal statement.
Compare my reasoning
- The model describes one enzyme under stated conditions.
- Different enzymes may have different optima.
- Nearby untested temperatures could alter the estimated peak.
The data support 40 °C as fastest tested here, not an exact optimum for all enzymes.
Look for these in your work
- State what the data support.
- Identify both generalisation and sampling limits.
Common mistakes
- The fastest tested point is not an exact universal optimum.
- A low nonzero rate is not complete inactivity.
What can you explain now?
How could a tested peak near 40 °C be located more precisely?
Compare with the explanation
Test additional temperatures near that region with matched conditions.
Closer sampling can refine the estimate.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Sketch an activity-temperature pattern and label fastest tested versus exact optimum.
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.