Final answer:
To test if fertilizer aids tomato plant growth, Mary needs to design an experiment with a control group of plants without fertilizer, an independent variable (type and amount of fertilizer), and a dependent variable (plant growth rate), while keeping all other growth conditions constant.
Step-by-step explanation:
To conduct a controlled experiment on whether fertilizer helps tomato plants grow faster, Mary could follow these steps:
- Question: Does fertilizer help tomato plants grow faster?
- Hypothesis: The hypothesis is that using fertilizer will increase the growth rate of tomato plants.
- Independent Variable (IV): The independent variable would be the amount and type of fertilizer applied, as this is what Mary is testing the effects of.
- Dependent Variable (DV): The dependent variable is the growth rate of the tomato plants, which includes measurable factors such as height, biomass, or fruit yield.
- Control Group: The control group would consist of tomato plants that are not given any fertilizer.
- Constant Variables: Constants should include the type of soil, amount of sunlight, water quantity, and any other factors that could influence plant growth, to ensure that any differences in growth rate are due to the fertilizer alone.
In this experiment, the control group is critical since it provides a comparison against the tomato plants receiving the fertilizer. All other conditions must be kept constant to ensure a fair test of the hypothesis. By regularly measuring the growth of the plants in both groups under the controlled conditions, Mary can determine if the addition of fertilizer has a significant effect on the growth rate of the tomato plants.