Variables in an experiment

The direct answer is B: duration of light exposure. An independent variable is the factor deliberately manipulated by the investigator. Here the student changes the number of light hours received each day, so that is the independent variable. Plant height is a possible dependent variable because it is a growth result that may be measured. Amount of soil and plant species are normally controlled so that they do not create extra differences; therefore C and D are not the changed factor. The reasoning is: choose different daily light durations, keep other conditions comparable, measure growth, and compare results. B is therefore correct. Exam cue: identify the experimental input, not the measured plant response.

The measured outcome is the dependent variable. Identify the result in a cause-and-effect relationship.

Sugar particle size can affect the dissolving rate so it should remain constant. In exams treat other influential factors as controlled variables.

Unequal seed numbers can affect comparison of results. Keep sample size equal in a fair experiment.

Drying time is the measured outcome so it is the dependent variable. Select the measured response as the dependent variable.

Acid concentration is changed and reaction rate is measured. The changed factor is independent and the measured outcome is dependent.

The initial angle can affect motion so it should remain constant. Keep influential factors other than the independent variable controlled.

The number of leaves is a numerically measured response. A quantitative variable is expressed as a number or measurement.

Different light exposure adds its effect on growth between the groups. Only the independent variable should differ between groups.

The sample without salt provides a baseline comparison. A control group helps identify the effect of the independent variable.

The stain type can change cleaning difficulty so the comparison is not fair. Use the same stain on all samples.

The surface type is deliberately changed by the investigator so it is the independent variable. The manipulated factor is the independent variable.

A graph usually places the independent variable on the horizontal axis and the dependent variable on the vertical axis. The independent variable is the factor that is changed or selected by the investigator. The graph then shows how the measured response changes as that factor increases or decreases. This convention also makes the direction of the relationship easy to understand.

In this experiment, light intensity is increased, while the rate of photosynthesis is measured. Thus light intensity is the independent variable and belongs on the horizontal axis. The rate of photosynthesis belongs on the vertical axis, because it is the response. The graph may rise at first and then become level, showing that the rate reaches a limiting value. Therefore, option B is correct.

Throwing force affects flight distance so it should remain constant. Only wing length should be changed.

An extraneous variable is a factor that may influence the result but is not the main variable being tested. If the researcher neither changes it deliberately nor keeps it constant, its effect can become mixed with the effect of the independent variable. This can introduce unwanted variation and make it difficult to decide what really caused the observed result. Good experimental design tries to identify and control such factors where possible.

Option A is correct because it defines an uncontrolled factor that can affect the outcome. A dependent variable is the measured result, while a constant is a condition deliberately kept the same. A control group is a comparison group, not a factor. For example, if temperature is tested but light differs between samples, light may act as an extraneous variable. Therefore, A is the appropriate term.

Enzyme amount can also affect the reaction rate. If it is not constant the true effect of temperature will be unclear.

The direct answer is C: four levels. A level means one distinct value or condition of the independent variable. The independent variable is the amount of water given to the plants. The listed values are 50 mL, 100 mL, 150 mL and 200 mL. These are four different values, so there are four levels. Option A, two, counts too few values. Option B, three, misses one of the four amounts. Option C is correct because every distinct water amount counts once. Option D, five, adds a value that was never used. Do not count the plants only; count the different settings of the variable. Even if several plants received the same amount, that would still be one level, but here each listed amount is different. Memory cue: number of levels equals number of distinct values tested.

Characteristics of one plant may make the result unrepresentative. More samples reduce the effect of biological variation.

Dim medium and bright are descriptive categories so the measurement is qualitative. A light meter could provide greater precision.

The direct answer is D: dependent variable. The dependent variable is the measured outcome that changes in response to the independent variable. In this investigation, the surface type is changed to study friction, and the force needed to pull the object is measured. Therefore the pulling force is the dependent variable. Step by step: identify the factor changed—surface type; identify the quantity measured—pulling force; connect the measured force to the surface change; choose dependent variable. Option A is wrong because a controlled variable is kept the same, such as the object’s mass or the pulling arrangement, not the measured force. Option B is wrong because the independent variable is surface type, which the experimenter changes. Option C is wrong because a control group is a comparison condition or group, not a measured quantity. Option D is correct because the required force is the response or outcome. A larger required force generally indicates greater resistance to motion in that setup, but the classification depends on the experimental roles, not on whether the force is large or small. Memory cue: the factor you change is independent; the result you measure depends on it.

Question difficulty can affect concentration scores. All participants should receive tasks of equal difficulty.

In a fair test only the independent variable changes. Other influential factors must remain constant.

Changing the measurement method creates artificial differences in height. Measure from the same starting point each time.

In the first situation selected time values are used and colour change is measured. Therefore time is the independent variable.

Water amount also affects growth so it should remain equal. This allows growth differences to be attributed to soil type.