Learning focus
Develop transferable AO3 skills: plan, measure, record, process, interpret and evaluate biological investigations accurately and safely.
Random error
Random error causes unpredictable scatter. It may arise from biological variation, reaction-time differences or difficulty judging an endpoint. Repeats and a mean reduce its influence but do not remove it completely.
Systematic error
Systematic error shifts results consistently in one direction. A balance that reads 0.5 g too high or a thermometer with an offset produces biased data. Repeating the same biased measurement does not solve the problem.
Measurement uncertainty
Every measurement has limited certainty because instruments have finite scale divisions and endpoints may be judged. Reporting excessive decimal places creates false precision. The data should reflect instrument resolution.
Calibration and zeroing
Check zero before use and compare instruments with known standards when appropriate. A balance should be tared with the container, and a potometer should be checked for leaks. Calibration addresses systematic error.
Practical or data skill
Given examples of scattered readings, a zero error, variable potato pieces and an inconsistent colour endpoint, classify each problem and propose a suitable response.
Examination tip
Repeats address random error, not a systematic offset.
Review questions and suggested answers
Question 1
What is a systematic error?
Suggested answer
An error that shifts measurements consistently in one direction.
Question 2
How can random error be reduced?
Suggested answer
Repeat measurements and calculate a mean.
Question 3
Why should a balance be tared?
Suggested answer
To set the reading to zero with the container and avoid including its mass.
