Final answer:
In the scientific question 'How does fertilizer affect a plant's ability to grow?', the growth of the plant represents the dependent variable.
Step-by-step explanation:
The dependent variable in the scientific question 'How does fertilizer affect a plant's ability to grow?' represents the growth of the plant. The dependent variable is the variable that is being measured or observed in an experiment. In this case, the growth of the plant is being measured to determine how it is affected by the fertilizer.
The independent variable, on the other hand, is the variable that is being manipulated or changed by the researcher. In this experiment, the independent variable would be the amount or presence of fertilizer given to the plants.
The controlled variables are any other factors that might influence the dependent variable and need to be kept constant in the experiment. For example, factors like the amount of water, the amount of soil, the amount of sunshine, and the type of soil should be controlled to ensure that the only variable affecting plant growth is the fertilizer.