Question

3
Select the correct answer.
You are conducting an experiment on the effects of fertilizer on the growth of three types of plants, all grown from seed. Multiple plants for each type will be grown. Which action must be done to aid your experiment?

A.
Give fertilizer to all the plants of one type, and don’t give fertilizer to any plants of the other two types.

B.
Give fertilizer to all the plants of two types, and don’t add fertilizer to any plants of the third type.

C.
For each plant type, either add fertilizer to all the plants or don’t add fertilizer to any of the plants.

D.
For each plant type, add fertilizer to some of the plants and don’t add fertilizer to some of the plants.

Answer 1

D

You must apply the treatment (fertilizer) and include controls within each plant type so you can separate the effect of fertilizer from differences among plant types. Answers A–C would confound fertilizer with plant type.