Hypothesis and experimentation

Correct answer: A. The instrument resolution is insufficient

A ruler divided only into centimetres cannot accurately resolve small millimetre differences. Choose an instrument with finer divisions.

Correct answer: A. When the observer is not told which sample belongs to the treatment group

Not knowing group identity can reduce expectation based observation bias. Apply the same measurement rules to both groups.

Correct answer: A. Treatment and control averages are nearly equal and differences are inconsistent across trials

A small inconsistent difference may indicate a weak effect or natural variation. Use more samples and repetitions to strengthen the test.

Correct answer: B. Revise the hypothesis using the new explanation and test again

Scientific hypotheses can change according to evidence. Test the revised hypothesis with a new experiment.

Correct answer: A. Systematic differences between instruments may affect group comparison

Different instruments may produce different readings. Use the same calibrated instrument or verified equivalent instruments.

Correct answer: A. The same student immediately repeats the test using the same instrument

Repetition by the same student shows repeatability but not independent reproducibility. Testing by another person or group is needed.

Correct answer: A. Establish clear, measurable criteria

Terms such as ‘good’ and ‘poor’ can mean different things to different observers, so they do not provide objective data. The dependent variable should be recorded using clear measurable criteria, such as plant height in centimetres, percentage germination, or reaction time. Changing ‘good’ to ‘very good’ is still subjective. Exam tip: Record experimental outcomes with numbers, units, or pre-decided observation criteria.

Correct answer: A. The true difference between groups may become smaller or unclear

The control group should remain free from the treatment. Exposure contaminates the baseline for comparison.

Correct answer: A. If temperature increases then the average melting time of equal sized ice pieces will decrease

The first statement can be contradicted by experimental results so it is falsifiable. A scientific hypothesis must be testable.

Correct answer: A. When samples have different initial values

With different initial values percentage change can show relative growth. Keep both original values and calculations.

Correct answer: A. Transparent and complete data recording

A procedural change may affect the result and must be recorded. Scientific records should be complete and honest.

Correct answer: A. Testing the effect of different water amounts on seed germination

Direct answer: Option A, testing different water amounts on seed germination, most needs a large sample size. Individual seeds naturally differ in viability, age, genetics, and health. If only a few seeds are used, one unusually weak or strong seed can strongly affect the result. Using many seeds in each water group reduces the influence of individual differences, makes averages more stable, and helps reveal the general effect of water amount. Option A is correct because germination is a biological process with natural variation. Option B is wrong: calibrating one thermometer concerns one instrument, not a variable population of living subjects. Option C is wrong for the same reason; checking one ruler does not require many specimens. Option D is wrong because measuring one container is a single-object measurement, not a sample-based biological comparison. The groups should also be similar, randomly assigned, and given equal light and temperature. Memory cue: biological variation calls for replication and larger samples.

Correct answer: A. Light condition also changed

The direct answer is A, the light condition also changed. In a fair fertiliser experiment, fertiliser should be the only important difference between treatment and control groups. Light affects photosynthesis and plant growth, so placing one group near a window and the other in darkness introduces a second cause. Step by step: the treatment is fertiliser; the measured result may be plant growth; both groups must receive comparable water, soil, temperature, pot size and light; here light differs; if the groups grow differently, we cannot know whether fertiliser or light caused it. A is correct. B is wrong because fertiliser is the independent variable being tested, not a controlled variable. C is wrong because height is usually a measured result or starting condition, not the deliberately changed factor here. D is wrong because a dark control group is not automatically more reliable; unequal light makes comparison unfair. Memory cue: one experiment should change one main variable at a time.

Correct answer: B. The difference cannot be considered reliably measured

A difference smaller than instrument capability cannot be distinguished accurately. Measure again with a finer instrument.

Correct answer: A. The observer knows which group is expected to perform better and personally classifies vague outcomes

Prior expectation can influence vague classification. Blind testing and clear criteria reduce bias.

Correct answer: A. Available evidence supports the hypothesis but further testing remains possible

Several supportive trials increase confidence but do not establish permanent final truth. Science remains open to new evidence.

Correct answer: A. Separate columns for light duration and average height gain

Clear columns for both variables help comparison and trend identification. Include headings and units.

Correct answer: A. Repeatability

Direct answer: Option A, repeatability, will decrease first. Repeatability means obtaining comparable results when the same method is performed again under the same conditions. If the method changes slightly between trials, then a difference in results may come from the changed method rather than from the factor being studied. The trials are no longer directly comparable, so confidence in repeated performance falls. Option A is correct. Option B is irrelevant because colour purity is not a general quality of experimental procedure. Option C is wrong because changing the method does not automatically change how many samples were used. Option D is wrong because the length of a hypothesis is unrelated to procedural consistency. To protect repeatability, write a precise method, use the same equipment and quantities, keep conditions constant, and follow the same sequence each time. Memory cue: same method, repeatable result.

Correct answer: A. Testing an intervention where the control group receives no active treatment

A negative control shows the normal outcome without active treatment. It provides comparison for changes caused by the treatment.

Correct answer: A. Test the revised hypothesis with a new independent experiment

A new hypothesis formed from existing data is not independently supported by the same data. It requires a new test.

Correct answer: A. Group sizes are unbalanced and the control group cannot represent natural variation well

A one plant control group may be strongly affected by an unusual individual. Use adequate and comparable sample sizes in both groups.

Correct answer: A. The test uses only one plant species in one environment

A result from one species and environment may not apply elsewhere. Test under different conditions before making broad conclusions.

Correct answer: A. Changing light duration will produce no difference in average plant height gain

A null hypothesis usually states that there is no effect or difference. It is tested using data.

Correct answer: A. A hypothesis gives a measurable prediction and a controlled experiment tests it using fair data

A hypothesis offers a possible explanation while an experiment gathers evidence for or against it. The conclusion should use all data.

Correct answer: B. Repeat the experiment with more samples and analyse the variation

With large variation a difference in averages alone may not be sufficient evidence. More samples and repetitions help clarify the reliability of the result.