Variables and controls
Open your materials, follow the steps, then turn in your work.
Define independent, dependent, and controlled variables using teacher notes and the PLTW online task.
1. Open your materials
Use the materials named in the first step below. Open lesson resources.
2. Start the work
Take notes on variable types and experimental controls.
Show all 5 required steps
- Take notes on variable types and experimental controls.
- Define sample size and explain why it matters.
- Complete the PLTW online variables-identification activity.
- Label variables in a sample experiment description.
- Write one example of a confounding variable.
Lost your place? Lost your place? Check your notes for the three variable definitions, confirm you wrote why sample size matters, then finish the PLTW online activity and label the variables in the sample experiment.
Check your work before submitting
- All three variable types are correctly identified in the sample.
- PLTW online task is submitted complete.
3. Turn in your work
DueCheck Schoology- Hand in
- Labeled sample experiment with independent, dependent, and controlled variables identified, plus a written confounding-variable example.
How to submit and name your file
Use the submission route shown on today's today's page.
In Schoology, open your course and the assignment for this lesson. Attach your file, select Submit, and check that it appears in the submission.
PDF upload helpYou get two school days for every day you were absent, so this deadline moves with you.
Choose your Schoology section. Open only one assignment.
Check the section number beside Human Anatomy and Physiology in Schoology.
Assignment: Wk12 Lab notebook: Variables and controls
Link will not open? Open Schoology, choose your section, and find the assignment title above.
How this lesson connects
Keep using what you learned last class: Scientists use model organisms because they share conserved biology with humans, so their use always carries an ethical cost that must be weighed against the knowledge gained. Today: A controlled experiment changes one variable and holds the rest constant, so that any change in the result can be attributed to that single cause.
Unit 2 guide: what to keep and use nextOptional: listen or watch a unit review▸
Need help? Warm-up, timing, and directions▸
💡 Big idea: A controlled experiment changes one variable and holds the rest constant, so that any change in the result can be attributed to that single cause.
- 0-10Warm-up: identify what is wrong with a poorly designed experiment (projected example)
- 10-28Guided notes: independent, dependent, controlled variables, , confounding variables
- 28-45PLTW online variables-identification activity
- 45-60Label variables in a provided sample experiment description
- 60-72Write one confounding variable scenario and share with a partner
- 72-80Submit labeled experiment and PLTW activity confirmation
- • Every valid scientific experiment is built on the same logical structure: change one thing, measure one thing, control everything else.
- • Today you will master that structure using real and sample experiment descriptions.
- • Understanding variables is foundational for designing your own C. elegans investigation later this week.
- • The PLTW online activity will let you practice identifying variables in multiple scenarios.
- • The is deliberately changed; the is measured; controlled variables are held constant.
- • affects the reliability and generalizability of experimental results.
- • Confounding variables introduce alternative explanations and weaken causal conclusions.
PLTW connection and today's work
Complete the variables-identification online activity in Problem 2.3.1 Toxic Relationships in myPLTW; work through all independent, dependent, and controlled variable scenarios during the 28-45 minute window.
Today's stopping point: Monday's task is done; today the variables task should show complete in your progress bar.
PLTW activity titles identify the course connection. If your account will not open, use the posted materials for today and tell Mr. Mendoza. Do not mark an online activity complete unless you completed it.
Course connection
- Problem 2.3.1 Toxic Relationships
Use the turn-in directions at the top of this page. Do not create a second submission unless your teacher asks for one.
Show another explanation or a smaller first step
Need help? Choose a starting point
Lesson resources: reading, slides, and vocabulary▸
The deck carries the prior idea forward, lets you inspect an analogy, maps the rule to biology, and ends with the same evidence decision and exit ticket used on this page.
Generated from this lesson's canonical data with a red-team citation check.
Scientists use model organisms because they share conserved biology with humans, so their use always carries an ethical cost that must be weighed against the knowledge gained.
A controlled experiment changes one variable and holds the rest constant, so that any change in the result can be attributed to that single cause.
A research team lays out its question, variables, controls, sampling plan, measurement record, and analysis before deciding what the data support.
- Which variable is changed or compared?
- Which conditions and measurements must stay consistent?
- Which conclusion is inside the study's evidence boundary?
Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
A well-organized classroom study can still be limited by , measurement quality, confounding, and the population represented.
- • Question and variable cards map to the study design.
- • Control and measurement cards map to fair, reproducible data collection.
- • The conclusion card maps to a bounded claim supported by the analysis.
Driving question: If worms fed a high-sugar diet live shorter lives, how do we know it was the sugar and not the temperature, the crowding, or the batch of worms?
What you already know: Scientists use model organisms because they share conserved biology with humans, so their use always carries an ethical cost that must be weighed against the knowledge gained.
New idea: A controlled experiment changes one variable and holds the rest constant, so that any change in the result can be attributed to that single cause.
Visual or model: F1. F1. A lesson illustration or teaching diagram for Variables and controls. Use it with E1-E3; it is a model or context image, not experimental or patient data. What to notice: Trace the labeled structure, movement, or system relationship that connects form to function.
- Observe or measure the relevant feature in today's lesson.
- Organize the observation with a stable evidence ID.
- Apply this rule: Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
- Choose the option the evidence supports and state the limit of the conclusion.
Real biomedical example: If worms fed a high-sugar diet live shorter lives, how do we know it was the sugar and not the temperature, the crowding, or the batch of worms?
What the evidence supports: E1-E3 and F1 support the daily take-home when the response meets the stated success criteria.
What it cannot prove: The package does not support claims beyond this lesson's or any real patient diagnosis.
- • : A species, such as zebrafish or mouse, studied because its biology is similar enough to ours to teach us about human development and disease.
- • C. elegans: Use the lesson context and glossary entry to explain C. elegans in your own words.
- • : A that measures the presence, amount, or activity of a target substance such as a , , or chemical in a sample.
- • literature: The body of published research articles and reports on a topic that scientists read to learn what is already known before doing new work.
- • variable: Any factor in an experiment that can change or be changed, including what you test, what you measure, and what you hold steady.
- • control: The comparison condition that isolates the effect of the variable being tested by keeping everything else the same.
- • : The number of subjects or observations in a study; larger samples give more reliable results and reduce the role of chance.
Use it now: Choose one decision option. Cite E1 and E3, then explain how the rule connects the evidence to your choice.
Go further, optional: The source links below are optional enrichment. Every fact required for today's local evidence decision appears in this lesson package.
A planned study connects its question to defined variables, controls, sampling, measurement, and analysis so the resulting data can support a bounded and reproducible conclusion.
Limit: A statistical difference or trend does not automatically establish practical importance, causation, generalizability, or freedom from bias.
Define variables, controls, sampling, units, and the analysis plan before interpreting a result; analysis cannot repair biased or inconsistent measurement.
Limit: A well-organized classroom study can still be limited by , measurement quality, confounding, and the population represented.
All three variable types are correctly identified in the sample.
Limit: E3 defines the classroom product or success criterion. It is not independent scientific evidence and cannot justify a clinical or causal claim.
PLTW-HAP-2027-04-07 · Simulated classroom evidence scenario
Your role: anatomy and physiology consultant
Decision: Your team must decide what the evidence from today's lesson supports before submitting the notebook record named on today's page.
- • Label diet as the and lifespan as the dependent one, holding temperature and crowding steady.
- • Call the sugar diet the , since it is the condition you control in the setup.
- • Ask how lifespan was counted and how many worms each group had, since those numbers are never stated.
Response: State one choice, cite at least two evidence IDs, explain the rule that connects them, and add one limitation. Submit it as the notebook record.
Claim ceiling: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
- • The solution must address the stated need in today's lesson.
- • The decision must be supported by E1-E3.
- • The final product must make the success criteria visible.
- • Complete the work inside the 80-minute block.
- • Use only supplied or teacher-approved materials and evidence.
- • Do not trade , accessibility, or privacy for speed.
- • and evidence quality: must pass before scoring other criteria.
- • User need and effectiveness: highest scored criterion.
- • Time, cost, and ease of use: compare only after and effectiveness pass.
Test evidence: For each option, record the E1-E3 result that supports or fails each criterion. Do not assign a score without a named observation.
- Version or option tested
- Criterion met or missed
- Evidence ID and result
- Revision made
- Reason for the revision
- Need and user
- Criteria and constraints
- Chosen option and evidence
- Test result
- Revision and reason
Students often think Students often think the is "the thing you control" and mix it up with the .. The trap: Flip it and your whole experiment reads backward. The is what you change on purpose; the is what you measure in response. A quick fix: the dependent variable depends on what you did to the independent one.
Sample experiment: Testing whether a low dose of copper in the water changes how fast C. elegans worms move.
- Independent variable (what I change): the amount of copper added to the water (0, low, medium).
- Dependent variable (what I measure): the worms' movement speed (body bends per minute).
- Controlled variables (held constant): temperature, food amount, age of the worms, dish size, observation time.
Confounding variable example: if the copper dishes were also kept warmer than the control dishes, then temperature would be confounded with copper, and I could not tell whether slower movement came from the copper or the heat.
This model shows the level of evidence and organization needed to complete: A sample experiment with the independent, dependent, and controlled variables correctly identified, plus a written example of a confounding variable.
- Date and label the entry.
- Record the procedure, observation, or design decision clearly.
- End with what the evidence means and the next step.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Submit your labeled experiment on Schoology.
- CER:
- Claim, Evidence, Reasoning: make a claim, back it with evidence, explain your reasoning.
- SOP:
- Standard Operating Procedure, the exact steps to follow (especially in a lab).
- Tracker:
- Your PLTW progress log where you record completed evidence.
- myPLTW:
- The PLTW course site where you do the online activities. Find it in Clever with your Microsoft sign-in, right next to Schoology.
Tap the speaker to hear a term. Add two of these to your notebook glossary with a definition and an example in your own words.
Pick just 2 or 3 words from today and make them yours: write what each one means in your own words, name the context clue or evidence that helped, then give one example from what you actually did in Variables and controls. Try your own words first; the glossary is there if you get stuck. This is voluntary and counts as extra credit, so keep it short.
Saved on this device. Show Mr. Mendoza or add these to your notebook glossary to claim the extra credit.
Hand-picked readings, videos, and interactives for this lesson, all free and from authoritative open organizations (NIH, CDC, OpenStax, Khan Academy, PhET, HHMI, and more).
A fillable, Cornell-style notebook for Unit 2: Research Ready. Type your notes, cues, and summaries right in the PDF, or print it and write by hand. Each lesson page has a cue column, a notes column, and a summary box, plus dated lab-record pages you can turn in.
HBS Unit 2 notebook: Research Ready Fillable PDFCornell notes + lab recordsOpenVetted readings and references for this unit. Use them to prepare, to catch up if you were absent, or to go deeper on today's target.
This site may ask you to verify you are human. If it blocks you on a school device, ask for the class copy.
Practice: try a question, then check your answer▸
Claim ceiling for this check: Today's evidence supports a classroom claim about today's lesson. It cannot prove causation, diagnose a real patient, or justify action outside this room.
A student tests whether louder music makes worms move faster. They change the volume, measure worm speed, and run the test on 4 worms in a warm room and 4 in a cold room. Name the independent variable, the dependent variable, and the confounding variable.
Write an answer and pick a confidence to unlock the key.
Fast retrieval with instant answers, not the commit-then-reveal check above. Try each from memory first: write what you remember about the earlier units, then check yourself here.
Missed class or ready for more?▸
What today's skills lead to. These are real health-science careers this course builds toward. Tap one to see, on the US Department of Labor's O*NET site, what the job actually involves, what it pays, and how fast it is growing.
Why zebrafish and mice model human development, and the Atit lab's work.
Goes with: Why zebrafish and mice: animal models and the Atit lab
Use to see how IRF6's 3D shape lets it do its job.
Goes with: AlphaFold and UniProt: structure tells function
Today is individual work you can do from home: complete the same target above, then submit your Notebook check.
Go to Schoology to turn this in. Submit one PDF. Put your first and last name in the document header. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf. If you cannot get in, see Mr. Mendoza. Do not skip the work.
Class still runs. Complete the online activity above (it's self-guided). Need the concept taught without a teacher? Use this authoritative explainer:
Khan Academy: The science of biology (experimental design)You've passed Unit 2, so the optional extra-credit track is open. Complete reserved-unit work from home, including virtual labs, for extra credit. Each item shows its correct submission route.
Open the extra-credit track- CompleteEvery required part of the artifact is present, nothing left blank.
- AccurateThe science and the data are correct and match the evidence.
- Scientific reasoningYou explain your claim with evidence and reasoning (CER), not just an answer.
- Professional communicationClear, organized, labeled, and written the way a clinician or scientist would.
- SubmittedGo to Schoology to turn this in. Submit one PDF. Put your first and last name in the document header. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf. If you cannot get in, see Mr. Mendoza. Do not skip the work.
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