In an experiment, we have different variables that we can control and measure. The independent variable is the factor that we deliberately manipulate or change. In this case, the independent variable is the type of fertilizer used.
The dependent variable, on the other hand, is the factor that is being measured or observed in response to the changes in the independent variable. In this case, the dependent variable is the growth rate of the plants.
By using different fertilizer brands, we are testing the effect of the different fertilizers on the growth rate of the plants. This allows us to determine which fertilizer brand leads to a higher or faster growth rate.
So, to summarize, the growth rate is the dependent variable because it depends on the independent variable, which is the type of fertilizer used.