A scientist sets up an experiment to see if plants grow faster under only ultraviolet light. Which setup has the correct use of an experimental control?

A. All of the plants are outside

B. some plants are outside, some plants are inside under an ultraviolet lamp

C. All the plants are under an ultraviolet lamp

D. An equal number of plants are placed outside and inside under an ultraviolet lamp

An equal number of plants are placed outside and inside under an ultraviolet lamp

To determine which setup has the correct use of an experimental control, let's first understand what a control is in an experiment.

An experimental control is a group or condition in an experiment that is not exposed to the independent variable, which is the factor being tested. It serves as a baseline reference for comparison, allowing the researcher to determine the effects of the independent variable by comparing the experimental group to the control group.

Now, let's look at the options given:

A. All of the plants are outside: This setup does not have an experimental control because all of the plants are exposed to the same conditions, including ultraviolet light. Without a control group that is not exposed to ultraviolet light, it is difficult to determine the specific influence of ultraviolet light on plant growth.

B. Some plants are outside, some plants are inside under an ultraviolet lamp: This setup does not have a clear control group either. Although some plants are outside and not exposed to the ultraviolet lamp, there is no specific group that serves as the control to compare the effects of ultraviolet light on plant growth.

C. All the plants are under an ultraviolet lamp: This setup does not have a control group either because all the plants are exposed to the same condition. Similar to option A, without a group that is not exposed to ultraviolet light, it is challenging to determine the specific impact of ultraviolet light on plant growth.

D. An equal number of plants are placed outside and inside under an ultraviolet lamp: This setup has the correct use of an experimental control. By placing an equal number of plants outside, where they are not exposed to ultraviolet light, and inside under the ultraviolet lamp, there is a clear control group. This allows the scientist to compare the growth of plants under ultraviolet light with those not exposed to ultraviolet light, which helps determine the influence of ultraviolet light on plant growth.

Therefore, option D is the correct answer because it incorporates a control group.