📝 Independent vs dependent variable (7 MCQs)
📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 7 questions available
What is Independent vs dependent variable?
Definition:
The independent variable is the variable that is manipulated or changed by the researcher in an experiment, and it is the presumed cause, while the dependent variable is the variable that is measured or observed to assess the effect of the independent variable, and it is the presumed outcome, and the relationship between them is the focus of hypothesis testing.
Working:
In an experiment, the independent variable is deliberately altered (e.g., different doses of a drug), and the dependent variable is measured (e.g., blood pressure) to see if it changes in response; the values of the dependent variable depend on the independent variable, and the relationship is often expressed as , where is the independent variable and is the dependent variable, and statistical analysis is used to determine if the changes in are significant and attributable to .
Example:
A simple example is an experiment testing the effect of light intensity on photosynthesis: light intensity is the independent variable (controlled by the researcher), and the rate of oxygen production is the dependent variable (measured); if light intensity is increased, the oxygen production may increase, demonstrating a relationship, and this helps test the hypothesis that light affects photosynthesis.
Reason:
Understanding independent and dependent variables is essential for designing experiments, interpreting data, and understanding cause-and-effect relationships in biology, making it a core concept in scientific methodology and a crucial skill for all biology students.
📝 All Independent vs dependent variable MCQs
Q1. A researcher changes the amount of sunlight received by identical plants and records their average height after four weeks. Which identification best describes the variables?
📖 Explanation: The independent variable is the factor deliberately changed by the researcher, while the dependent variable is the measured outcome. Here, sunlight is manipulated and plant height is measured to determine whether it responds.
Q2. Students test whether temperature affects bacterial growth. They use identical cultures at different temperatures and measure colony size after 48 hours. A student says colony size is the independent variable because it changes between groups. What is the best correction?
📖 Explanation: A variable does not become independent merely because its values differ among groups. Temperature is intentionally manipulated, making it the independent variable, while colony size is the measured response and therefore dependent.
Q3. A scientist compares two fertilizers by applying different fertilizer amounts to otherwise similar plants and measuring leaf number. Which redesign would most clearly preserve the distinction between independent and dependent variables?
📖 Explanation: The independent variable must be the factor intentionally manipulated, whereas the dependent variable must be the response measured. Changing fertilizer amount while measuring leaf number maintains this causal structure.
Q4. A graph shows that as daily exercise time increases from 10 to 50 minutes, average resting heart rate decreases. Which interpretation correctly identifies the variables represented by the axes?
📖 Explanation: In an experimental relationship, the manipulated or explanatory factor is the independent variable and the measured response is the dependent variable. Exercise time is varied, while resting heart rate is observed.
Q5. A researcher wants to determine whether water salinity affects seed germination. She changes salinity levels but also uses different seed species at each level. She then records germination percentage. What is the major problem with identifying salinity as the sole independent variable?
📖 Explanation: Salinity can be the intended independent variable, but changing seed species simultaneously introduces a confounding variable. Because species may independently affect germination, differences cannot confidently be attributed only to salinity.
Q6. Two groups of seedlings receive different light intensities. Their mean heights are measured weekly. At week 1 the difference is small, but by week 4 the high-light group is substantially taller. Which conclusion best follows from the graph pattern?
📖 Explanation: The changing separation in height indicates a response developing over time after light intensity was varied. Thus, light intensity functions as the independent variable and seedling height as the dependent measurement.
Q7. A researcher investigates whether increasing nutrient concentration improves plant growth. She predicts growth will increase, but after testing several concentrations, growth initially rises and then declines at the highest concentration. Which statement best identifies the variables and interprets the result?
📖 Explanation: Nutrient concentration is deliberately varied, so it is the independent variable; plant growth is measured, so it is dependent. The rise followed by decline suggests a non-linear response rather than a simple continuously increasing relationship.