Final answer:
A controlled experiment is a scientific investigation performed under controlled conditions where variables are manipulated to see their effect on the outcome. It involves having controlled variables that do not change and also includes a control group that does not receive the experimental treatment.
Step-by-step explanation:
An experiment is a special type of scientific investigation that is performed under controlled conditions. It involves manipulating some factors in a system to see how they affect the outcome. A controlled experiment has one or more variables that can change during the experiment, as well as controlled variables that do not change. The experiment may also include a control group, which is a group that does not receive the experimental treatment.
For example, in a study testing the effect of phosphate on algae growth in freshwater ponds, half of the ponds are treated with phosphate while the other half are treated with a non-nutritional mineral. The presence/absence of phosphate is the experimental variable, while the volume of water in each pond is a controlled variable. The control group consists of ponds that receive the non-nutritional mineral instead of phosphate. By comparing the growth of algae in the treated and control ponds, we can determine if phosphate promotes algae growth.