Hypothesis and experimentation

Measuring leaf area directly represents the outcome in the hypothesis. In exams choose a direct measure of the dependent variable.

Light intensity is changed while the number of bubbles is measured. In exams distinguish the changed factor from the measured result.

Wire material and thickness affect resistance so they must be kept constant. In exams control additional influencing variables.

Applying the result from one species to all plants is an unjustified generalisation. In exams keep conclusions within the sample limits.

Repeated measurements at each temperature show both the trend and reliability. In exams choose sufficient and repeated data.

This hypothesis clearly states the independent variable and a measurable dependent variable. In exams look for both a time period and a measurement.

The amount of water may also affect germination so the effect of temperature alone will be unclear. In exams identify confounding variables.

A control group represents the normal condition for comparison with the treated group. In exams understand it as the baseline group.

A consistent deviation in one direction indicates systematic error. In exams connect it with a problem in the instrument or method.

Inconsistent results may indicate a problem with the method or apparatus. In exams investigate the cause before retesting.

Boiling point is the measured outcome and therefore the dependent variable. In exams choose the factor measured as the effect.

Selecting only favourable results is confirmation bias. In exams record all trials objectively.

An automatic sensor reduces dependence on human reaction time. In exams choose automated measurement for rapid events.

Consistent reliable contrary evidence is a valid reason to revise a hypothesis. In exams base decisions on evidence.

Growth is correctly measured by the difference between final and initial height. In exams record the starting value when measuring change.

The volume of gas produced in a fixed time is a measurable indicator of reaction rate. In exams choose a time-based measure for rate.

A one-millimetre division supports a reading to one decimal place in centimetres. In exams do not report more decimals than the instrument permits.

Different initial conditions may affect the outcome and obscure the true treatment effect. In exams keep starting conditions similar.

This conclusion is limited to the tested range and available data. In exams avoid overgeneralisation.

The values are precise because they are close together but inaccurate because they are far from the accepted value. In exams distinguish the two qualities.

Greater water loss in the same time is direct evidence of faster evaporation. In exams link the result directly to the hypothesis.

The direct answer is B, asking only science club students about interest in science. A sample should represent the population being studied. If the question concerns students’ general interest, students from the whole school should have a fair chance of selection. Science club members have already chosen to join a science-related group, so they are more likely than average to be interested. Step by step: population is the school students; selected sample is only science club students; membership is related to the topic being measured; answers will probably overestimate general interest; this is sampling bias. A is better because random selection from all classes can represent the school. C is also fair because every plant is numbered before random selection. D is sensible because samples from different locations cover variation rather than excluding locations. Thus A, C and D describe more representative procedures, while B deliberately limits the sample. Exam cue: when the chosen people already have a special connection with the question, suspect sampling bias.

An outlier may result from error or real variation so it must be investigated. In exams do not remove a value without evidence.

Calibration helps check instrument accuracy and reduce systematic error. In exams connect calibration with accuracy.

Keeping sugar and water amounts the same ensures that only temperature is tested. In exams change only one independent variable.