Carlo is wondering what causes plants to grow at different rates. Carlo’s hypothesis is “Plants will grow more when the day is longer.” To test his hypothesis, Carlo sets up an investigation that includes an experimental and control group. What factor would remain constant in the control group, but would change in the experimental group?

The factor Carlo is testing is day length, which changes how long plants are exposed to sunlight. The experimental group should receive a different amount of sunlight, while the control group keeps its usual exposure. Soil type, plant type, and the way growth is measured should stay the same in both groups so they do not affect the results. Therefore, the factor that changes is exposure to sunlight.

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