Pearson Edexcel International GCSE Science Single Award Practical Skills 1: Planning, variables and controls

Pearson 4SS0 assesses experimental skills in the three written papers, not through a separate practical paper. This note develops a reusable planning contract for the official Biology, Chemistry and Physics investigations. Subject-specific methods belong to the next three notes.

Turn a prompt into a testable question

A good question names an independent variable, a dependent variable and the system studied: “How does hydrochloric acid concentration affect the initial rate of carbon dioxide production from marble chips?” is testable, while “What affects reaction rate?” is too broad.

The independent variable is deliberately changed. The dependent variable is measured. Control variables are held sufficiently constant to make the comparison valid. A control variable is not the same as a control setup. A control setup provides a comparison in which the tested factor is absent or replaced, as in a photosynthesis investigation without carbon dioxide.

Choose a sensible range with at least five values where a trend or graph is expected. Values should be safe, achievable with available apparatus and broad enough to reveal change. A pilot can identify a range that avoids results too fast to time or too small to distinguish.

Operational variables

State how each variable is changed or measured. “Control temperature” is incomplete. A stronger instruction is “place both reaction mixtures in the same thermostatically controlled water bath at $25^\circ\text{C}$, allow them to equilibrate for five minutes and verify with a thermometer.”

Some controls need subject reasoning:

• Biology may require equal organism size, prior condition or sampling effort.
• Chemistry may require equal reactant volume, mass and surface-area distribution.
• Physics may require unchanged circuit component, ray-block position or source-detector distance.

Control what could otherwise change the dependent result. Do not list irrelevant constants merely to lengthen a plan.