Carlo is wondering what causes plants to grow at different rates. Carlo's hypothesis is "Plants will grow more when the day is longer." What would be the difference between the test group and the control group in this experiment?

The difference between the test group and the control group in this experiment would be exposure to sunlight.

Explanation:

According to the scientific method, experiments are done to prove a hypothesis right or wrong. A scientific experiment usually contains a control group and an experimental group.

To prove the above hypothesis, Carlo should have a control group which shall be given equal amounts of sunlight. Let's say 4 hours per day.

In the experimental group, the plants should be given a varied amount of sunlight, let's say one of the experimental group is given 3 hours exposure to light, the second group is given 5 hours exposure, thrid group is given 6 hours exposure.