A student designs an experiment to test how different concentrations of salt water affect … — ACT

A student designs an experiment to test how different concentrations of salt water affect the germination rate of radish seeds. The student places 50 radish seeds in each of four petri dishes. Each dish is watered with a different concentration of salt solution ( $0\%$ , $1\%$ , $2\%$ , and $3\%$ salt). All petri dishes are kept in the same incubator at a constant temperature of $22^\circ\text{C}$ and receive 12 hours of light daily. After 5 days, the student counts the total number of germinated seeds in each dish. Match each experimental component on the left with its correct variable classification on the right.

Concentration of salt in the water ( $0\%$ , $1\%$ , $2\%$ , and $3\%$ )Independent variable
Number of germinated seeds counted after 5 daysDependent variable
Incubator temperature maintained at $22^\circ\text{C}$ Controlled variable

Answer

Concentration of salt matches the independent variable, the number of germinated seeds matches the dependent variable, and the incubator temperature matches the controlled variable.

The salt concentration is the manipulated variable (independent variable), the number of germinated seeds is the measured outcome (dependent variable), and the incubator temperature is kept constant to avoid introducing additional variables (controlled variable).

Step-by-Step Solution

Identify the factor that is altered or manipulated by the researcher.

The salt concentration of the water (

0\%

1\%

2\%

, and

3\%

) is deliberately varied, so it is the independent variable.

The independent variable is the condition that the experimenter changes to test its effects.

Identify the factor that is measured or observed as the outcome of the changes.

The number of germinated seeds is counted to see how it responds to the salt concentration, so it is the dependent variable.

The dependent variable is the response that depends on the independent variable.

Identify the factor that is kept constant to prevent it from influencing the results.

The temperature (

22^\circ\text{C}

) is held constant for all petri dishes, so it is a controlled variable.

Controlled variables are parameters that must remain constant to ensure that only the independent variable affects the outcome.

Key Concept

Identifying Independent, Dependent, and Controlled Variables

Estimated Time:1m 0s

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