Final answer:
A negative result with a positive control is not required to validate a test; instead, a positive control must yield a positive result for test validation. Control groups allow comparison between groups that differ only by one variable and are essential for testing hypotheses.
Step-by-step explanation:
The statement that is not true of controls in experiments is 'a negative result with a positive control is required to validate the test'. In fact, a positive result in a positive control is necessary to validate the experimental test setup. A control group is crucial in experimental design because it allows comparison between two groups that differ only in a single variable. The variable in question is what the experiment aims to test, while controlled variables are kept constant throughout the experiment.
For instance, in testing the hypothesis about the role of phosphate in algae growth in freshwater ponds, the ponds with added phosphate serve as the experimental group, and those with an inert substance, like salt, serve as the control group. The growth of algae in the control group provides a baseline to compare against the growth in the phosphate-treated ponds. The control group must be identical to the test group except for the one variable of interest.