Final answer:
Gary is conducting a plant growth experiment with the independent variable being the amount of water. He controls for container size but must also control for other factors affecting plant growth. In a similar experiment, the control is the row of plants not receiving the independent variable, such as fertilizer.
Step-by-step explanation:
In experimental design for a plant growth experiment, it's crucial to control for variables that are not the focus of the study to ensure accurate results. In Gary's experiment, the independent variable is the amount of water, as he is testing its effect on plant growth. The dependent variable is the growth of the plants themselves, which is measured and statistically analyzed.
For control variables, Gary should be considering the size of the containers, which he does, ensuring they do not affect the dependent variable. However, many aspects like soil characteristics, temperature, amount of sunlight, and possible interference by insects should also be controlled. There is a scientific reason for having the same amount of water for each plant every day—to ensure that water is not a confounding variable when evaluating the effect of other variables, such as the amount of sunlight or the use of fertilizer.
When a scientist applies fertilizer to one row of corn and not the other while keeping sun and water conditions constant, the control in the experiment is the row without the fertilizer. It serves to show the growth of corn plants without the independent variable (fertilizer) and is crucial for comparing the effects of the fertilizer on the tested row.