Homeostasis keeps internal conditions near a set point by negative feedback: a change away from the set point is detected, and the response reverses it. Body temperature is controlled by the hypothalamus through sweating, shivering and blood flow.
On a 45 °C day in Marble Bar or a frosty morning in Canberra, your body stays within about half a degree of 37 °C. Something is constantly correcting it.
Responses follow a pathway. This lesson: a pathway whose response feeds back to switch off its own stimulus.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: what keeps it steady?
ExploreTry it on the board and compare what happens with your prediction.
Explore: push it and watch it recover
Drag the Air slider far up or down. Watch the body temperature on the graph, and the message under the loop saying which corrective response is on. When the body has recovered, push it the other way.
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Push the body temperature away from 37 °C and let it recover, twice (once hot, once cold).
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: negative feedback
In your book: draw the feedback loop for body temperature with the receptors, the hypothalamus and the effectors, and arrows showing what happens when you get too hot. Label the set point, the deviation, the corrective response and the return detection.
Too hot or too cold: which responses switch on?
Sweating
Shivering
Blood vessels near the skin widen (skin flushes)
Blood vessels near the skin narrow (skin goes pale)
Hairs stand up (goosebumps)
Match each part of a negative feedback loop to what it is in body temperature control.
Set point
Deviation
Corrective response
Return detection
Elaborate TypicalUse the same idea in a new context.
Elaborate: blood sugar
Order the steps when blood sugar rises after lunch.
Blood sugar rises above the set point
Cells in the pancreas detect it and release insulin
Liver and muscle cells take up glucose
Blood sugar falls, so the pancreas releases less insulin
Elaborate WiderUse the same idea in a new context.
Elaborate: break the loop
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Break one part of the loop, then push the temperature off 37 °C.
Use the board. This ticks when you get there.
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
Homeostasis: keeping internal conditions (temperature, blood sugar, water) near a set point.
Negative feedback has four parts around a set point: a deviation (a change away from it) is detected; a corrective response reverses it; return detection (receptors sensing it is back near the set point) switches the response off. "Negative" means it opposes the change.
Too hot: sweating, skin blood vessels widen. Too cold: shivering, skin blood vessels narrow, goosebumps. The hypothalamus is the control centre.
For teachers
Students operate a body-temperature negative feedback loop, explain why it is negative, and apply the pattern to blood sugar (AC9S9U01, node 5, a hinge node). About 22 minutes.
I can explain homeostasis as keeping conditions near a set point.
I can describe how negative feedback corrects body temperature in both directions.
I can apply the same loop to blood sugar.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider.
The hinge misconceptions are that body temperature is simply constant, and that "negative" means harmful.
Board notes: a toy model. Body temperature drifts towards the air temperature and the body's own heat; the effectors respond to how far it is from 37 °C, with a short lag, so it wobbles and settles. A recovery counts once the body comes back within 0.3 °C after being more than 0.6 °C away. The numbers are not a real body's: real core temperature moves much less. The wider tier's break buttons switch off the receptors, the control centre or the effectors.
Running the lesson
Engage: count how many chose 'exactly 37'.
Explore: ask students to describe what the effectors do as the temperature comes back.
Explain: 'why negative' is the checkpoint.
The hard part (on purpose)
Seeing feedback as constant correction that reverses a change, in both directions. When a student says the body is just at 37 °C, ask what happened on the board when the air got very cold.
When students get stuck
A student can't get a recovery. Ask: Have you left the slider somewhere and waited? Fix: Push it far, then leave it: the body recovers even while the air stays hot or cold.
A student says negative feedback only cools you down. Ask: What happened when you made the air very cold? Fix: It warmed back up: negative means it opposes the change, either way.
Stretch and support
Stretch: Why would positive feedback (a rise causing more rise) be dangerous for body temperature?
Support: Give a loop diagram with blanks for the stimulus, receptor, control centre, effector and response.
Where it leads
Next unit: reproduction (AC9S9U02). Later: blood sugar and diabetes as a context in Health.
In class: measure skin temperature before and after exercise; a thermostat as a model (and where it breaks: the body has many effectors working together).
What each step is for
Engage: what keeps it steady?: Students who think the body is simply 'at 37' don't expect constant correction; the board shows temperature wobble and recover.
Explore: push it and watch it recover: Driving the temperature off the set point twice and watching the effectors switch on and off makes negative feedback a loop students have operated.
Explain: negative feedback: Naming each part of the loop and why it is 'negative' is the hinge.
Elaborate: blood sugar: The same loop with a hormone as the message shows negative feedback is a pattern.
Elaborate: break the loop: Breaking one part of the loop and watching control fail shows every part is needed.
Now you can
Explain homeostasis as keeping conditions near a set point.
Describe how negative feedback corrects body temperature in both directions.