A biology student is studying ways to grow crops in soils that are high in salts and other dissolved solids. To determine whether corn plants can tolerate salty soil conditions, she grows 50 corn plants in typical garden soil and the same amount of corn plants in garden soil plus varying amounts of salt: 0.01 kg, 0.1 kg, and 1 kg of salt. After 6 weeks of growth, there was an inverse relationship between the amount of salt in the soil and plant height: the more salt present, the shorter the plants. The student concluded that salt did have an effect on the growth of corn.

What was the control in the experiment?

Select one:

a. The varying amounts of salt added to the soil

b. Plants grown in typical soil

c. The length of time the plants were grown

d. 50 plants per trial

The experimental control is one that controls for the condition you have changed. The student was changing the salt concentration. But she has to also grow plants in typical conditions to make sure that the plants are able to grow typically. It ensures that any changes made are the result of the changing experimental conditions, not some other factor.

This controls for unforeseen circumstances, such as that none of the plants grow (maybe the seeds were faulty, maybe the weather was poor). It allows you to make conclusions based on what would have happened if you changed nothing. It is vital for ALL scientific experiments!