Gathering Data & Making Measurements (AQA A-Level Biology): Revision Notes
Gathering Data & Making Measurements
Estimating results
Before performing calculations, make a sensible estimate of your expected result. This helps identify obvious errors, particularly when using calculators where incorrect data entry can produce unrealistic answers.
Estimation involves making an educated guess based on your understanding of typical biological measurements. Practice this skill during practical work to develop confidence with realistic ranges for different biological structures.
Developing good estimation skills during practical work will help you identify unrealistic results and catch calculation errors before they affect your conclusions.
Uncertainties in measurements
Every measurement contains some degree of uncertainty due to instrument limitations and human error. Even high-quality rulers and thermometers have inherent precision limits.
The uncertainty of measurement represents the maximum likely error. For example, measurements using a standard mm ruler typically have an uncertainty of ±0.5 mm when measured carefully.
Calculating percentage error
Percentage error quantifies measurement uncertainty relative to the measured value:
Worked Example: Calculating Percentage Error
For a 6 mm object measured with a ±0.5 mm uncertainty ruler:
For an 87 mm object measured with the same ruler:
Larger objects have smaller percentage errors because the fixed instrument uncertainty becomes a smaller proportion of the total measurement.
Different instruments have different uncertainty values. Digital balances might specify ±0.01 g, while thermometers may have ±0.5°C uncertainty when read by eye.
Key Points to Remember:
- Estimate results before calculating to catch obvious errors and develop an understanding of realistic biological measurements
- Percentage error = (maximum error ÷ measured value) × 100 - larger objects have smaller percentage errors