Design An Evidence Test
Design a fair evidence test with a sample, positive control, negative control, and clear result rule.
- Read a data table: Students need to find values, labels, and units before calculating or graphing.
- Fair-test logic: Variables and controls make comparisons meaningful.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Design a fair evidence test with a sample, positive control, negative control, and clear result rule.
| Test plan part | Example |
|---|---|
| Question | Is starch present? |
| Positive control | Known starch solution |
| Negative control | Water |
| Sample | Unknown food extract |
Use the evidence test table. Why include water as a negative control in a starch test?
Reviewed| Test plan part | Example |
|---|---|
| Question | Is starch present? |
| Positive control | Known starch solution |
| Negative control | Water |
| Sample | Unknown food extract |
- A.It should stay negative, so any positive comes from the food
- B.It should turn positive, showing the iodine reagent still works
- C.It sets the color that every positive result must match
- D.It stands in for the unknown food if there is not enough
Show the worked solution ▾
Answer: A. It should stay negative, so any positive comes from the food
- Step 1: Read the table: Water is listed as negative control.
- Step 2: Explain its job: It should not show the target, so it checks background signal.
Why it's right: A negative control checks for false positive signal.
- B: That is the positive control's job; a negative control must stay negative.
- C: The positive control sets the color to match; water shows what negative looks like.
- D: A control is a known sample run beside the unknown, not a substitute for it.
Aligned to Biotechnology Research and Experiments · reading level ~grade 9
In a Benedict test for reducing sugar, the known sugar standard stays blue after heating while the unknown turns orange. What does that blue standard tell you?
Reviewed- A.Benedict solution works only on unknown samples, never on known standards
- B.The unknown is definitely positive, since only its tube changed color at all
- C.The standard was supposed to stay blue, so the whole run counts as valid
- D.The reagent or the heating failed, so the orange reading cannot be trusted
Show the worked solution ▾
Answer: D. The reagent or the heating failed, so the orange reading cannot be trusted
- Step 1: Say what the standard is for: A known sugar sample is a positive control: it must turn color if the test is working.
- Step 2: Read the failure: It stayed blue, so either the reagent or the heating did not work, and every reading in that run is in doubt.
Why it's right: A positive control that fails to turn color shows the run itself did not work, so no result from that run can be reported.
- A: Standards are run on purpose so the test can be checked against a known answer.
- B: A color change means nothing when the control proves the test was not running properly.
- C: A positive control is meant to CHANGE color; staying blue is the failure signal.
Aligned to Biotechnology Research and Experiments · reading level ~grade 9
- In Unit 1.1 to 1.2 Evidence & Biomolecules, this skill turns class evidence into a result another person can check.
Fill these in as you work through the lesson.
- Positive control (known sample that should test positive):
- Negative control (known sample that should test negative):
- Result rule (how to decide positive or negative):
- Sample (unknown being tested):
A good evidence test includes a control, a negative control, the unknown , and a clear result .
- What should the positive control do?
- What should the negative control do?
- What color or signal counts as positive?
Design a test for glucose in an unknown drink using controls and a result rule.