Each control answers a different question
- The idea
- Predict
- See it
- Why
- Check
The idea
“The boiled tube shows what a full reaction looks like. The controls all check the same thing.”
A rack of controls looks like one set of comparison tubes. Each one actually changes a different piece of the real test.
The short version
The mistake: The boiled tube shows what a full reaction looks like. The controls all check the same thing.
What's actually true: Each control changes one thing from the real test, so it can only tell you about that one thing.
- A negative control is built so the result shouldn't happen. Its reading is the baseline for the real test.
- Each negative control removes one piece. Boiling removes catalase's shape. Water in place of extract removes the enzyme. Water in place of H2O2 removes the substrate.
- A positive control is built so the result should happen. It shows your test can detect a yes.
On the exam: Ask what the control changed from the real test. That one change is all it can speak to.