Hypothesis

In the syllabus and the exam

Hypothesis-writing is one of the science process skills tested throughout Paper 2's structured questions and in Paper 3's planning stage, wherever a candidate is given an experimental scenario and asked to state what is expected to happen before any reading is taken. A complete hypothesis names the manipulated variable and the responding variable and links them with a clear direction, following a pattern such as 'the higher/lower the manipulated variable, the higher/lower the responding variable'. Examiners award marks only when both variables appear and the relationship's direction is explicit; a sentence that mentions just one variable, or states a relationship without direction, is marked incomplete. A frequent error is submitting the aim of the investigation (for example, 'to study the effect of temperature on the rate of transpiration') in place of a hypothesis, which does not predict an outcome and earns no credit. Another common confusion is treating a hypothesis as the same thing as an inference: an inference is written after an observation has already occurred, to explain what was seen, while a hypothesis comes before the experiment and must still be tested by collecting data. Some candidates also weaken an otherwise correct hypothesis by leaving out units or by using vague comparative words instead of naming the actual variable. Higher-order questions sometimes ask candidates to evaluate whether a given hypothesis is testable at all, expecting them to check that both variables are measurable and that the predicted relationship could, in principle, be shown false by the results, which is what separates a scientific hypothesis from a mere opinion. This same requirement carries over into Paper 3, where a poorly worded hypothesis at the planning stage can cost marks even before any practical work begins.

Example

Before testing how pH affects enzyme activity, a candidate writes: 'The higher the pH above 7, the lower the rate of reaction, because the enzyme's shape changes.'

Related terms

Manipulated variableResponding variableInference

Source:SRC-DSKP-EN