Ivy Tech Microbiology Lab Test 2 Practice 2026 - Free Microbiology Lab Practice Questions and Study Guide

A negative control provides a baseline so you can tell whether any signal you see comes from the organism’s metabolism or from other, non-biological factors. By running the assay without the biological activity of interest (for example, without the organism or without the substrate), you establish what the test looks like when nothing biologically meaningful is happening. If the negative control remains unchanged, you can attribute a positive signal in the actual test to the organism’s metabolism rather than background changes, reagents, or contamination. If the control showed a signal, you’d know the result could be due to non-biological factors rather than the metabolic activity you’re trying to measure. That’s why the correct choice is that the negative control confirms that a positive result is due to the organism’s metabolism, ruling out background changes. It does not accelerate metabolism, nor does it guarantee a dye color change—the control’s job is to reveal background effects, not to drive the test outcome.