Final answer:
To accurately measure the impact of fertilizer on plant growth, control for all variables except the one being tested, such as by having a control group of plants grown without fertilizer under otherwise identical conditions. A control group is crucial in an experiment to ensure that the results are due to the independent variable alone and not other factors.
Step-by-step explanation:
When conducting an experiment on the effects of fertilizer on the growth of grown plants, it is imperative to control extraneous variables to ensure accurate results. The independent variable in this scenario is the presence or absence of fertilizer, while the dependent variable is the growth of the plants. To adequately explore the effects of fertilizer on plant growth, a control group is necessary. This control group should be given every aspect of care as the experimental group, such as the same amount of water, light, and similar environmental conditions, but without the addition of fertilizer. In the given scenarios, the control would be the corn plants grown without fertilizer while other conditions remain consistent.
The student experiment that involved pots with or without detergent in the soil made a critical mistake by placing the test pots in the sun and the control pots in the shade. This introduces a second variable—the amount of sunlight—which would make it impossible to determine if the growth differences were due to detergent or sunlight exposure. All factors that could influence growth, such as water, sunlight, and soil quality, should be controlled to isolate the effect of the independent variable being tested—in this case, the presence of fertilizer or detergent.
In any experiment, including those in a laboratory setting studying plant growth, it is essential to maintain consistency across all control and experimental groups, except for the independent variable being investigated. This ensures that the data collected can accurately be attributed to the changes made to the independent variable.