In a controlled scientific experiment designed to test the effect of nitrogen fertilizer concentration on tomato plant growth rate, which variable must be held constant across all experimental groups?
Answer and explanation
Correct answer: A. Daily sunlight exposure and volume of water supplied
- Step 1: In experimental methodology, control variables are all factors that could potentially influence the dependent variable (plant growth) other than the independent variable being tested (fertilizer concentration).
- Step 2: Water volume, sunlight, temperature, and soil type must be kept identical across all test groups.
Answer
Daily sunlight exposure and volume of water supplied.
Why not the others: 'Concentration of fertilizer' is the independent variable that is deliberately varied; 'Height at conclusion' is the dependent outcome variable measured; 'Genetic mutation rate' is not a controllable laboratory variable.
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