Pearson Edexcel International GCSE Human Biology Practical Skills 6: Planning, analysis and evaluation

This chapter consolidates the experimental-skills contract in Pearson Edexcel International GCSE Human Biology (4HB1), Issue 2, pages 21 to 22. Pearson assesses practical skills through written examinations: solving practical problems, planning, safe method selection, precise observation, variables, analysis, communication, reliability, accuracy and validity. This is a cross-cutting skills chapter, not a sixth numbered Pearson investigation.

1. Start with a testable question

A testable question names the system, independent variable and measurable dependent variable. “How does temperature affect amylase?” is incomplete until activity is operationalized, for example as reciprocal time for starch disappearance under specified conditions.

A hypothesis predicts a direction or pattern and gives biological reasoning. It is not a conclusion written before data. A null hypothesis states no association or difference where statistical testing is relevant, but Pearson questions may focus on ordinary evidence-based predictions.

Define the population or material and the conditions to which the conclusion will apply. A study on one food extract or one participant cannot justify a universal claim.

2. Variables

The independent variable is deliberately changed or used to form comparison groups. The dependent variable is measured. Control variables are factors kept sufficiently constant so the independent variable provides the most plausible explanation for change.

List how each variable is changed, measured or controlled. “Keep temperature the same” is weaker than “maintain all tubes at 30 °C in a thermostatically controlled water bath and verify with a thermometer”.

Some biological variables cannot be fixed, such as participant physiology. Restrict, match, randomize, block or use within-participant designs, then acknowledge remaining variation.

3. Range and intervals

Choose an independent-variable range wide enough to reveal a trend but safe and biologically relevant. Include enough levels to distinguish a curve from a straight line. Intervals can be narrower around a suspected threshold or optimum.

A pilot study checks whether the range, method, endpoint and timing are workable. It can prevent ceiling effects, where all values hit the maximum, or floor effects, where none is detectable.

Do not choose a range simply because apparatus labels are convenient. Justify it using biology and safety.

4. Controls and comparisons

A negative control lacks the factor expected to cause the result and reveals background change or contamination. A positive control contains a factor known to produce the expected response and checks that the method can detect it. A solvent control separates an active substance from its carrier.