Hypothesis and experimentation

The direct answer is B. The dependent variable is the result that is measured in an investigation; it may change because the independent variable is changed. If a plant experiment changes a factor such as water or light and measures plant growth, growth is the dependent variable. Option A is wrong because changing the water amount describes the independent variable, not the measured result. Option B is correct: plant growth is measured and is therefore dependent. Option C is wrong because keeping soil the same describes a controlled variable, not the dependent variable. Option D is also wrong because keeping pot size the same is another controlled condition. A useful chain is: change one factor, keep other conditions controlled, measure the outcome. Memory cue: dependent means the measured result that depends on the test factor.

A data table presents results clearly and systematically. In exams include headings and units.

A scientific conclusion is based on evidence collected from the experiment. In exams connect the conclusion with data.

Data may support a hypothesis but testing continues with new evidence. In exams distinguish support from absolute proof.

An unsupported hypothesis may be revised according to evidence. In exams remember that scientific thinking is flexible.

More samples can reduce the effect of individual variation. In exams connect sample size with reliability.

A guess cannot replace an actual measurement and may make data unreliable. In exams measure using an instrument.

Similar results obtained by different students show reproducibility. In exams identify independent repetition.

Broken apparatus may cause injury so the teacher should be informed immediately. In exams prioritise safety.

An unknown chemical may be toxic, corrosive, or harmful in another way. Tasting it can allow the substance to enter the body and cause injury, so option C is correct. Rapid evaporation is not the main reason for never tasting a chemical. Exam tip: Never taste or directly smell an unknown substance in the laboratory.

Washing hands removes residues of chemicals or microorganisms. In exams remember cleaning after experiments.

This hypothesis gives a testable comparison between fertiliser and growth. In exams choose statements with a clear comparison.

The independent variable is the factor deliberately changed by the investigator. If temperature is the factor being changed, temperature is the independent variable.

Direct answer: Option C, dependent variable. The independent variable is the factor deliberately changed; here it is temperature. The dependent variable is the outcome measured to see the effect of that change; here it is germination time. The reasoning is: change temperature, observe when germination occurs, record the time, and compare the times. Because the time is measured and may depend on temperature, it is the dependent variable. Option A is wrong because a controlled variable is kept constant, not the measured time. Option B is wrong because temperature is the changed factor, so it is independent. Option C is correct because germination time is the measured outcome. Option D is wrong because a safety rule is an instruction, not an experimental variable. Memory cue: “changed cause = independent; measured effect = dependent.”

Direct answer: D, seeds of similar size reduce initial differences. In a fair experiment, the tested factor should be the main reason for any later difference. Seed size can influence stored food, germination, and early growth. Step by step: select seeds that are alike, place them under the same conditions, change only the intended variable, observe growth, and compare results. D is correct because similar starting seeds make the comparison fairer. A is wrong because seed selection does not change the hypothesis. B is wrong because it does not improve colour. C is wrong because seed size is not the independent variable being removed; it is a starting condition to control. Memory cue: similar beginnings make a fair test.

During data analysis results are compared and interpreted. In exams place analysis before the conclusion.

An average gives a representative value and reduces the effect of small variations. In exams average comparable values.

A suitable title states which relationship between variables is being tested. In exams choose a clear and concise title.

A clear method allows another person to repeat the same experiment. In exams write a stepwise procedure.

A scientific investigation begins with a question and moves through hypothesis and experiment to a conclusion. In exams remember the logical order.

A good experiment provides a fair test under controlled conditions and can be repeated. In exams remember these three qualities.

The independent variable is the factor that a researcher deliberately changes to test its effect. The dependent variable is the result that is measured, while other important conditions should be kept controlled. Identifying the action in the hypothesis often makes the independent variable easy to find: the stated cause is changed and the stated effect is observed.

In this investigation, different amounts of salt are added to water. The amount of salt is therefore deliberately changed, so it is the independent variable. The boiling point is measured as the possible response, making it the dependent variable. Container size should be controlled, and a thermometer reading is a measurement rather than the changed factor. Hence option A is correct.

Water and soil kept the same are controlled variables. In exams treat constant conditions as controlled variables.

Repeating the experiment is useful when results differ greatly. In exams choose repetition for inconsistent data.

Choosing precautions according to the hazard reduces the chance of an accident. In exams match risks with safety measures.