Hypothesis and experimentation

After testing the data is analysed and an evidence-based conclusion is drawn. In exams place analysis after the experiment.

The direct answer is B: the factors kept the same are controlled variables. In a fair experiment, usually one factor is deliberately changed, the response is measured, and other important conditions are kept constant. For example, when testing the effect of fertiliser on plant growth, the fertiliser may be changed, height may be measured, and pot size, soil type, water and light should remain the same. Option B is correct because these fixed conditions prevent an unfair comparison. Option A, observations, are things noticed or measured; they are not necessarily kept constant. Option C, conclusions, are statements made after studying results. Option D, hypotheses, are testable predictions made before or during an investigation. Thus a controlled variable is a condition held steady, not a record, final statement or prediction. Exam cue: changed factor is independent, measured result is dependent, and held-constant factor is controlled.

This statement gives a testable relationship between light and growth. Identify testable if-then statements.

Changing one main variable allows its effect to be tested clearly. Remember the principle of a fair test.

The direct answer is A: a control group provides a basis for comparison. To understand it, imagine two similar groups. The treatment group receives the factor being tested, while the control group does not receive that treatment or remains under the normal condition. Comparing their results helps us decide whether the treatment caused the observed change. Option A is correct because the control group acts as a reference or baseline. Option B is wrong: a control group is not created to make an experiment longer. Option C is wrong: changing all variables would make the investigation unfair and would prevent us from identifying the cause. Option D is wrong: a control group is not used to hide results; good science records and reports results honestly. For example, when testing fertiliser, untreated plants can be the control group and fertilised plants the treatment group. The groups should otherwise be as similar as possible. Memory cue: control means comparison, not secrecy or total change.

Writing the hypothesis and method beforehand makes the investigation clear and organised. Understand the importance of planning.

The experimenter changes the amount of water so it is the independent variable. Identify the deliberately changed factor.

A dependent variable is the result that is measured in an experiment. Its value may change in response to the independent variable. In a plant investigation, the researcher might change water amount, light, or fertilizer, and then measure plant height to see what effect the chosen condition has. The dependent variable must be recorded using a clear and consistent method.

Option D is correct because plant height is the measured outcome. It depends on the experimental conditions and may increase differently when the independent variable changes. A controlled variable is deliberately kept the same, an independent variable is deliberately changed, and a constant refers to something that remains unchanged. The key clue is the word “measured”: the measured response is the dependent variable.

Recorded data provide evidence of the observations and measurements made during an experiment. The data are analysed to draw a conclusion that supports or rejects the hypothesis, so option A is correct. Merely remembering results is not enough because a written record can be checked and used when repeating the experiment. Exam tip: Always link a conclusion to the observed data or measurements.

The direct answer is B: the reliability of the result increases. Repeating an experiment means performing the same investigation more than once, while keeping the method and important conditions as similar as possible. First record the result of trial 1, then repeat the procedure and record trial 2 and further trials. If the results are similar, we have stronger reason to trust that the finding is real and not just caused by chance or a small accidental mistake. Repetition does not guarantee that every error disappears. Option A is therefore wrong because some systematic errors can remain. Option B is correct because consistent repeated results increase confidence and reliability. Option C is wrong because a hypothesis does not automatically become a law merely because an experiment is repeated; it must be supported by much wider evidence and is still not the same as a law. Option D is wrong because controlled variables are kept the same, not changed, during a fair repeat. Memory cue: repeat, compare, and trust consistent results more.

The method of an experiment is the practical plan that tells a person how to perform the investigation. It normally lists the materials or important conditions and then presents the actions in an order that another learner can follow. A clear method helps make the experiment fair, repeatable and easier to check. It is different from the question, the prediction or the final conclusion.

Option D is correct because it refers to the steps for carrying out the experiment. A guess belongs to a hypothesis, the question states what is being investigated, and the final result is recorded after the procedure is completed. For example, measuring a liquid, adding another substance and recording the change would be method steps. Therefore, the method is not limited to one type of statement; it describes the organised procedure.

Using similar plants reduces differences in factors such as their size, age, and initial health. Therefore, if one plant is given a treatment, the results can be compared more fairly. Similar plants do not guarantee exactly identical results every time because other factors may still affect growth. Exam tip: In a fair test, change only the factor being investigated and keep the other conditions the same.

Direct answer: Option B, maintaining a controlled variable. A fair experiment changes one main factor and keeps other relevant factors constant. If temperature is kept the same while another factor is tested, temperature cannot produce a hidden difference between groups. This makes any observed change more confidently linked to the independent variable. Option A is wrong because changing the independent variable means deliberately varying the test factor, not holding temperature constant. Option B is correct because temperature is being kept fixed as a controlled variable. Option C is wrong because writing a conclusion happens after examining results. Option D is wrong because a hypothesis is a testable prediction and is not removed merely by keeping a condition constant. Memory cue: controlled variables are “kept constant for a fair comparison.”

The direct answer is C: the seedling was eight centimetres long. Quantitative data are data expressed through numbers and measurements. A number becomes especially useful when it is joined to a suitable unit, such as centimetres, grams, seconds, or degrees Celsius. Step by step: inspect each statement; ask whether it gives a measurable number; check whether a unit or numerical scale is present; choose the numerical measurement. Option A, “looked healthy,” is qualitative because it describes an appearance or condition in words. Option B, “the liquid was dark,” is also qualitative because it describes colour without a numerical measurement. Option C is quantitative because length is measured as 8 centimetres, written as a number plus unit. Option D, “felt moist,” is qualitative because it gives a descriptive judgement about moisture rather than a measured amount. The correct answer does not depend on whether the observation is useful; it depends on how the information is expressed. Memory cue: quantitative means quantity—look for a number and a unit; qualitative means quality or description.

Safety instructions are part of good scientific practice because experiments may involve heat, glassware, chemicals, electricity, sharp tools, or moving equipment. Following the rules reduces the chance of burns, cuts, spills, harmful exposure, breakage, and other injuries. Safety also includes using equipment correctly, wearing suitable protection, keeping the workspace orderly, and reporting accidents promptly.

The purpose of a safety rule is not to make an activity difficult or to change its scientific result. It is also not to decorate instruments. Its main purpose is to protect the learner, nearby people, and the equipment while the investigation is carried out. Therefore “to prevent accidents and harm” gives the correct reason, so option D follows.

A beaker is a laboratory container used to hold and mix liquids, and it may also be used for gentle heating when appropriate. Therefore, option A is correct. A stopwatch measures time, a balance measures mass, and a thermometer measures temperature. Exam tip: match each laboratory apparatus with its main function.

A stopwatch is suitable for accurately measuring the time interval between the start and end of an event. A balance measures mass, while a thermometer measures temperature. Exam tip: Match the instrument with the physical quantity to be measured.

Direct answer: C, plants receiving more light showed greater average growth. A conclusion is a statement that explains what the collected data indicate. First, an experiment is planned; then materials are used and measurements are taken; finally, the results are interpreted. C reports a comparison based on measured growth, so it can be a conclusion, provided the data support it. A is only a material or action. B describes measurement during the method, not the finding. D describes writing a hypothesis, which happens before testing and is not a result. Memory cue: method tells what was done; conclusion tells what the data mean.

The direct answer is D: safety goggles. In an experiment, liquid chemicals, hot drops, glass fragments, dust, or small particles may unexpectedly move toward the face. Safety goggles are designed to cover and protect the eyes from the front and, depending on their design, from the sides. Therefore they are the proper protective equipment. Option A, a cotton cap, may cover hair but does not protect the eyes. Option B, a wristwatch, tells time and may even be unsuitable near chemicals or water; it gives no eye protection. Option C, ordinary spectacles, are made mainly for vision correction and usually do not seal or cover the eyes sufficiently against splashes and flying particles. They are not a substitute for laboratory goggles. Option D is correct because goggles are specifically made for laboratory eye safety. A careful student should put them on before beginning the practical work, follow the teacher’s instructions, and never look directly into a reaction. Exam cue: eye protection in a laboratory means safety goggles, not ordinary glasses.

An average summarises several measurements into a representative value. Recognise averages of repeated measurements.

All actual measurements and observations obtained during an experiment should be recorded honestly, as they form the basis for an unbiased scientific conclusion. An unusual value should be checked by reviewing the instrument, method, and measurement rather than being removed at once. Changing data to fit a hypothesis violates the scientific method. Exam tip: In questions on data recording, words such as “actual” and “honestly” usually indicate correct scientific practice.

The direct answer is C, the time taken for sugar to dissolve. In an experiment, the independent variable is the factor deliberately changed, while the dependent variable is the result observed or measured. Here the student wants to compare warm water with another temperature, so temperature is changed. The student then measures how long the sugar takes to disappear into the water; therefore dissolving time is dependent on the changed temperature. Option A, water colour, is not the stated result. Option B, type of sugar, is a possible controlled or independent factor, but it is not the measured outcome here. Option C is correct because time is measured. Option D, beaker size, is a condition that should normally be kept the same. Exam cue: ask, “What result is being measured?” That is usually the dependent variable.

Water temperature is deliberately changed so it is the independent variable. Identify the changed factor.

Keeping sugar amount constant allows a fair comparison of temperature effects. Identify controlled variables.

A prediction states the expected result if the hypothesis is correct. Treat it as an expectation made before testing.