Final answer:
The student's research project is not accurately described as one experiment due to the use of two different independent variables simultaneously; hence, it comprises two experiments. An experiment should test the effect of one independent variable on a dependent variable while controlling for all other potential variables that might affect it.
Step-by-step explanation:
The description of the student's research project as one experiment is not entirely accurate. Considering that an experiment generally tests how one variable (the independent variable) affects another (the dependent variable), and in this scenario, the student is using two different independent variables (detergent presence and sunlight exposure), it is more appropriate to describe the setup as two different experiments being conducted simultaneously. The correct option in relation to the student's description would be C, as the student is using the same control (pots without detergent) but two different independent variables affecting the dependent variable (plant growth).
To control an experiment effectively, factors such as the amount of water, type of soil, and environmental conditions like temperature should be constant, except for the independent variable being tested. If the student intended to study the effect of detergent in the soil on plant growth, then having one group in the sun and the other in the shade introduces an additional independent variable – the amount of sunlight – which could confound the results. Therefore, a better experimental design would involve all pots receiving the same light exposure, with only the presence of detergent being different between the control and the experimental groups.
In Gary's experiment, factors such as container size and water amount are controlled to ensure that these do not affect the outcome, which in this scenario is likely the amount of sunshine received by plants.