Human Anatomy & Physiology (Human Body Systems)

Unit 2: Unit 2: Communication (Nervous & Endocrine)HBS 2.2Human Body Systems: research methods

Control variables

Change one thing on purpose, hold everything else steady, and keep a group that gets no change.

Builds on (2 levels back)inferred · high confidence

Cause and effect: Controlling variables is how you show that one thing caused a change, not just happened near it.
Measuring an outcome: You must be able to measure the dependent variable to tell whether changing the independent variable did anything.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

A fair test changes one independent variable, holds the controlled variables constant, measures the dependent variable, and includes a control group that gets no change.

Step 1: Change one thing

Change only the independent variable. If you change two things at once, you cannot tell which one caused the result.

Step 2: Hold the rest constant

Controlled variables are everything you deliberately keep the same for every group: temperature, food, age, timing: so they cannot explain the difference.

Step 3: Add a control group

The control group gets no treatment (or a fake one). You compare the treated group to it to see whether the change actually did anything.

Practice

A team tests whether a drug speeds nerve signaling in worms. Group A gets the drug; Group B is kept identical but gets none. What is the role of Group B?

Reviewed

Group	Drug?	Temperature	Worm type
A (treated)	Yes	20 C	C. elegans
B (comparison)	No	20 C	C. elegans

A.It is a second independent variable
B.It is the control group, used to compare against the treated group
C.It is the dependent variable
D.It makes the test unfair

Show the worked solution ▾

Answer: B. It is the control group, used to compare against the treated group

Step 1: See what is held the same: Both groups have the same temperature and worm type; only the drug differs.
Step 2: Name the no-change group: Group B gets no drug, so it is the control group you compare the treated group against.

Why it's right: Group B is identical except it gets no drug, so it is the control group that shows what happens without the treatment.

Why the others miss:

A: Group B is not a variable; it is a comparison group.
C: The dependent variable is the measured signaling speed, not a group.
D: A control group makes the test more fair, not less.

Aligned to HBS 2.2: control group and controlled variables · reading level ~grade 9

Where you'd see this

A drug trial gives one group the real pill and a control group a sugar pill, keeping everything else the same, so any difference points to the drug.

Careers that use this

Clinical Research Coordinator: Keeps treatment and control groups identical except for the one factor under study so the result is trustworthy.

Video library

Watch: Control variables

Nature of Science

Amoeba Sisters · 8 min

Guided notes

Fill these in as you work through the lesson.

Big idea: To learn what one thing does, change only that one thing, keep everything else the same, and compare against a group that did not get the change.

Key terms: write the meaning

Independent variable (the one thing you change on purpose):
Dependent variable (the result you measure):
Controlled variable (a factor you keep the same for everyone):
Control group (the group that gets no change, for comparison):

The rule

Change one variable (the variable), keep the other factors the for everyone, and compare your treated group to a group that got no change.

Check yourself

In a study, which variable do you change on purpose?
Why keep the controlled variables the same for every group?
What is the job of the control group?

Work one example

A class tests whether caffeine speeds up reaction time. Name the independent variable, the dependent variable, two variables they should control, and what the control group gets.