Which of the following 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 ten 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 ten 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 this case, the variable being manipulated is the type of light the seedlings are exposed to. The control group in this experiment is the set of seedlings grown under white light, which allows for a comparison with the experimental group grown under red light. Other variables such as the type of seedling and the duration of the experiment are kept constant, making this a controlled experiment. Option A is an observational study, Option B is a survey, and Option D involves two different types of seedlings which makes it difficult to draw conclusions about the effect of the light on growth.

Which of the Following Constitutes a Controlled Experiment