Which of the following descriptions constitutes a controlled experiment?
A)using a microscope to observe organisms present in a sample of pond water and recording the number of each type of organism observed
B)setting up a bird feeder and compiling a list of all of the bird species seen at the feeder over a period of several weeks
C)growing one set of 10 seedlings under white light and one set of the same type of seedlings under red light and measuring their growth over a period of two weeks
D)growing one set of 10 seedlings under white light at 30°C and one set of a different type of seedlings under red light at 25°C and measuring their growth over a period of two weeks

Question

Quizplus · Accepted Answer

A controlled experiment involves manipulating one variable while keeping all other variables constant. In choice C, the type of light is the manipulated variable while all other factors such as the type of seedlings and the length of time the seedlings are grown are held constant. This allows for a direct comparison of the effect of the different light types on the growth of the seedlings.

Which of the Following Descriptions Constitutes a Controlled Experiment