Hypothesis and experimentation

The independent variable is the factor deliberately changed during an experiment. Here, the student changes the temperature of the water to observe its effect on how quickly sugar dissolves, so water temperature is the independent variable. Dissolving time is the dependent variable because it changes in response to temperature. Exam tip: Identify the factor that the experimenter changes intentionally.

A dependent variable is the outcome that is observed or measured in an experiment. Here, the time taken for sugar to dissolve is being measured, so it is the dependent variable. The type of sugar may be changed, so it can be an independent variable rather than the outcome. Exam tip: Look for the “measured result”; it is usually the dependent variable.

Keeping the plant type the same makes the effect of water amount clear. Water amount will be the independent variable.

The direct answer is C: at the time of observation or measurement. Data should be written immediately, or as close as safely possible to the moment when the observation is made. This preserves the actual reading and reduces memory mistakes, accidental changes, and confusion between trials. Step by step: perform one observation or measurement; read the instrument carefully; write the value at once; include the unit and, when useful, the trial number and conditions; repeat for the next reading. Option A is wrong because waiting until the next day may cause the researcher to forget or mix up values. Option B is wrong because data are evidence used to form a conclusion, so they must exist before the conclusion. Option C is correct because recording during observation gives the most reliable primary record. Option D is wrong because relying on memory is not a dependable scientific method. A value without a unit may also be unclear, so units should be recorded. Memory cue: observe, measure, record—then analyse. Never create or rewrite data merely to make a pattern look better.

A control group shows the condition without the independent variable being applied. It provides a basis for comparison.

A control group is the comparison group that does not receive the experimental treatment, while other important conditions are kept as similar as possible. It shows what happens under ordinary conditions. Comparing the treated group with this baseline helps the investigator decide whether a difference is caused by the treatment rather than by unrelated conditions.

In a fertiliser experiment, the treatment is the addition of fertiliser. The plant receiving no fertiliser is therefore the control group, so option B is correct. The tallest plant is a result, not a comparison group, and the largest pot is merely a condition that could affect growth. For a fair test, the plants should also have similar light, water, soil, pot size, and starting conditions.

A hypothesis being unsupported also provides scientific knowledge. It may be revised according to the data.

A useful hypothesis makes a prediction that can be tested by an investigation. It normally connects a condition or cause with an expected effect, often in an “if...then...” form. The cause should be something that can be changed or compared, and the result should be observable or measurable. This makes the hypothesis more precise than a general opinion or description.

Option A is correct because it states both parts clearly: increasing water temperature is the proposed cause, and faster salt dissolving is the predicted result. A suitable experiment could compare the dissolving time at different temperatures while controlling other conditions. “Salt is white” is a description, while the other statements are vague and do not specify a measurable cause-and-effect relationship.

To study the effect of light its duration or amount is changed. Other factors should be kept the same.

A unit gives physical meaning to a measured number. For example, writing only 5 does not tell whether it means 5 cm, 5 m, or 5 s. Thus, a unit makes the type and magnitude of a measurement clear. Changing a hypothesis is not the purpose of writing units. Exam tip: Record every observation with a number and an appropriate SI unit.

The direct answer is D: record the unusual value and repeat the experiment. An unusual result may be caused by a reading error, a faulty instrument, a mistake in procedure, an unusual sample, or a real scientific effect. The correct scientific response is not to remove data simply because it looks inconvenient. First record it honestly, then check the instrument, materials, units and method, and repeat the measurement or experiment when possible. Option D is correct because it protects the reliability and transparency of the investigation. Option A is wrong because immediate deletion hides evidence. Option B is wrong because replacing a real value with a “normal” value invents data. Option C is wrong because hiding it is dishonest and prevents others from checking the work. If repetition shows the same unusual result, it may be an important finding; if it disappears, an error may have occurred. Memory cue: unusual does not mean useless—record, check and repeat.

Direct answer: Option A, changing one factor while keeping the other relevant factors the same, describes a fair experiment. A fair test is designed so that any important difference in the result can reasonably be linked to the one factor being tested. First decide the independent factor, change only that factor, keep temperature, time, amount, equipment, and other relevant conditions constant, and measure the dependent result in the same way. Option A works because it gives a valid comparison. Option B is unfair because different soil and water introduce several changes at once, so the cause of a result is unclear. Option C is poor science because recording only preferred results hides evidence and creates bias. Option D is unreliable because unchecked instruments may give inaccurate or incomparable measurements. Memory cue: one change, all other important conditions the same.

Placing identical wet cloths in sunlight and shade allows drying times to be compared. Keep other conditions the same.

Plant height is recorded with a number and a unit, such as 12 cm or 15 cm. Therefore, it is quantitative data. Qualitative data describe features such as colour or healthy/unhealthy rather than giving a numerical measurement. Exam tip: Data that can be counted or measured are generally quantitative.

Direct answer: Option A, allowing another person to repeat the experiment, is the benefit of writing a procedure. A procedure is a clear record of materials, quantities, conditions, sequence, timing, and measurement steps. Another learner can follow those instructions without guessing, perform the same investigation, and check whether similar results are obtained. Option A is correct because repeatability helps test reliability and makes the work scientifically useful. Option B is wrong: detailed steps cannot make an incorrect result automatically correct; results still need careful measurements and analysis. Option C is wrong: variables do not disappear when a procedure is written; they must be identified and controlled or changed deliberately. Option D is wrong: a procedure may test a hypothesis, but it cannot prove it in advance. Evidence can support or fail to support a hypothesis. Exam cue: a written method makes an investigation repeatable.

Measurements taken at equal time intervals can be compared easily. This makes the trend of change clear.

The direct answer is C: the plant is twenty centimetres tall. An observation is information obtained directly by seeing, measuring, counting, or otherwise recording what happens. Saying that the plant is twenty centimetres tall reports a present measurement; it does not claim why the plant has that height or what will happen next. Option A is a hypothesis because it predicts that increasing light will cause greater plant height, and this can be tested. Option B is also a testable prediction linking higher temperature with faster melting, so it is a hypothesis rather than a direct observation here. Option C is correct because the plant’s height is a measured fact. Option D is another hypothesis because it predicts that less water will make soil dry faster. A hypothesis is a possible explanation or prediction that can be tested by changing one factor and measuring another. Keep observations separate from predictions and explanations. Memory cue: measured or directly seen fact is observation; an if-then prediction is usually a hypothesis.

Support means the available evidence agrees with the hypothesis. New evidence may change the conclusion.

By giving different amounts of water, the number of seeds that germinate can be counted and compared. It is therefore a suitable measurable outcome (dependent variable) for seed germination. Time taken for germination can also be measured in some investigations, but the number of germinated seeds most directly shows germination success in this question. Exam tip: Change only the amount of water and keep the seed type, light, and temperature the same.

Different-sized pots can hold different amounts of soil and water and provide different space for roots. Therefore, pot size may influence an outcome such as plant growth, making it an uncontrolled variable. Option C is incorrect because different pots do not make plants identical. Exam tip: For a fair test, keep all conditions the same except the factor being investigated.

Widely different results may show error or natural variation. Repetition helps produce a reliable conclusion.

Recording only results that support the hypothesis creates selective bias because contrary or different results are deliberately left out. This makes the conclusion unreliable. Repeating a procedure and recording all data generally improve reliability, while using the same instrument can reduce unnecessary variation between measurements. Exam tip: In an unbiased experiment, record both supporting and non-supporting results.

The direct answer is A. Temperature is the independent variable when the experimenter deliberately changes temperature and observes its effect on another measurement. In option A, ice is placed at different temperatures, and the time needed to melt is measured. Thus temperature is changed, while melting time is the dependent variable; other conditions such as ice amount should be controlled. Option B changes ice mass but only observes colour, so mass—not temperature—is the changed factor. Option C changes container shape while temperature stays the same, so container shape is independent and temperature is controlled. Option D, comparing beauty, is subjective and does not clearly define a measurable scientific variable. Therefore A is the only option in which temperature is intentionally varied. Remember: the factor changed by the investigator is independent; the response measured is dependent.

In this experiment, the time taken by sugar to dissolve is measured, so time is the dependent variable. Temperature is the factor changed by the experimenter, making it the independent variable. Measuring only the mass of a container does not measure time as a response to a changed factor. Exam tip: The result that is measured or observed is usually the dependent variable.

The direct answer is C: to organise data. During an experiment, observations and measurements can include numbers, times, temperatures, masses, or descriptions. A table places related information in rows and columns, usually with a clear heading and the correct unit. This makes values easier to read, compare, check, and use when finding a pattern or drawing a graph. Option A is wrong because a table is not mainly decoration; scientific recording should be clear and useful. Option B is wrong because equipment is stored in cupboards, trays, or suitable places, not in a data table. Option C is correct because tables organise experimental data systematically and allow fair comparison between trials or conditions. Option D is wrong because a table should display relevant information openly, not hide the hypothesis. For example, columns might show water volume in millilitres and plant height in centimetres. Always include headings and units. Exam cue: when the question asks where results are arranged for easy comparison, choose the data table.