Students are experimenting with a substance that they think can be added to soil to increase the number of flowers a certain plant will make. They set up 20 pots of soil, each planted with the same type of seed. They divide the pots into two groups and add 15 drops of the substance to pots in one group and only 10 drops to pots in the other group. After the plants grow for four weeks, the students count how many flowers each plant has made.

What does this experimental investigation lack?

a control group

an independent variable

a dependent variable

a procedure

A control group where there is no drop of substance added to the soil

Answer: a control group

Explanation:

According to the given situation a control group is absent in the given experimental investigation. The experiment includes the dependent variable that involves the growth of the seeds in the form of plants. It also includes the independent variable which includes the substance which is used for the growth of the plants. A control group should be included because it could have given indication of the fact that what will be the impact on the growth of the plants when no substance is used. A sample pot with soil and seed and kept untreated with the drop of the substance will be a control group.

A control group is the one which does not receive any kind of treatment by the experimenter. It is kept as a standard benchmark.