HS-LS1-3: Feedback Loops and Homeostasis
Also called NGSS HS-LS1-3 · Topic: Structure and Function · Life Science
The Official Wording
Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis.
Clarification statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.
Assessment boundary: Assessment does not include the cellular processes involved in the feedback mechanism.
NGSS Lead States, 2013 · Read it on nextgenscience.org · checked October 15, 2026
What HS-LS1-3 Means in Plain English
Students plan and run their own investigation into how the body or a plant keeps conditions steady. They change something, like exercise level or soil moisture, measure the response, such as heart rate or leaf pores closing, and show how the response pushes conditions back toward normal.
The evidence comes from what students can measure in the whole organism, not the chemistry of hormones or receptors inside cells. It builds on the body systems in HS-LS1-2 and prepares students for how populations and ecosystems stay in balance in HS-LS2-6.
HS-LS1-3 I Can Statements
- I can explain how a negative feedback loop keeps a condition steady.
- I can plan a fair test of how the body responds to exercise.
- I can use measured data as evidence that homeostasis is happening.
HS-LS1-3 Worked Example
A step test the whole class can run with a sturdy bench, a stopwatch and their own pulse.
How does heart rate respond to exercise, and how fast does it return to resting?
Set It Up: A sturdy step or bench about 30 cm high, a stopwatch or phone timer, and a data table for each pair.
- Sit quietly for two minutes, count your pulse at the wrist for 15 seconds and multiply by 4.Resting: about 72 beats per minute
- Step up and down at a steady pace for three minutes while your partner keeps time.Breathing faster, face warmer
- Take your pulse right after stopping.About 130 beats per minute
- Keep taking it once a minute while sitting.112, 94, 80, 74
- Graph heart rate against time for the whole class.Sharp rise, then a curve back down
Heart rate nearly doubled during exercise and fell back close to resting within about four minutes.
Why it works: Working muscles need more oxygen, so the body speeds the heart to supply it and slows it again once demand falls, a negative feedback loop that holds conditions steady.
Common Mistakes with HS-LS1-3
Calling any change a failure of homeostasis
“Heart rate went up, so homeostasis broke”
Try this: The rise is the response that keeps blood oxygen steady. Homeostasis is the steadiness of internal conditions, not an unchanging heart rate.
Mixing up negative and positive feedback
“Negative feedback is bad for the body”
Try this: Negative feedback reverses a change and brings a condition back toward its set point. Positive feedback amplifies a change, as in labor contractions.
No baseline or repeats
One student's single trial used as the class conclusion
Try this: Measure a resting baseline first, keep the step height and pace the same, and pool several students' trials before drawing a conclusion.
Where HS-LS1-3 Fits
Practice HS-LS1-3
Quick Check
- Why does breathing speed up during exercise?
- Is sweating on a hot day negative or positive feedback?
- Why measure resting heart rate before the step test?