Final answer:
The factor that affected the tomato plants growth is the independent variable, which in this case is the amount of sunlight hitting each side of the house. The dependent variable, the growth of the tomato plants, was observed to be better on the north side which received more sunlight.
Step-by-step explanation:
The factor in the observation that affected the tomato plants growth is the independent variable.
The independent variable is the variable that is intentionally changed or manipulated in an experiment. In this case, the amount of sunlight hitting each side of the house is the independent variable because it was deliberately measured and determined to be different on the north side and west side of the house.
The dependent variable is the variable that is observed or measured and is expected to be influenced by the independent variable. In this case, the growth of the tomato plants is the dependent variable as it was found to be better on the north side which received more sunlight.