--- title: "How does your body stay at 37 °C?" subtitle: "Year 9 Biology · Coordination and control · Lesson 5" --- # How does your body stay at 37 °C? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** 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. :::teacher-note **In one sentence:** 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). **Students should be able to say:** 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. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **You walk from air-conditioning into a 42 °C day. What happens to your body temperature?** ☐ It stays exactly 37 °C because that's your temperature ☐ It starts to rise, the body detects it and responds, and it comes back near 37 °C ☐ It rises to 42 °C ☐ It drops My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** It starts to rise, receptors detect it, the hypothalamus switches on sweating and sends more blood to the skin, and it comes back near 37 °C. It is corrected, not fixed. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: negative feedback :::keep-together ### Hot or cold **Too hot or too cold: which responses switch on?** Groups: Too hot, Too cold - Sweating: {{field-15}} - Shivering: {{field-15}} - Blood vessels near the skin widen (skin flushes): {{field-15}} - Blood vessels near the skin narrow (skin goes pale): {{field-15}} - Hairs stand up (goosebumps): {{field-15}} ::: :::teacher-note **Answer:** Sweating → Too hot; Shivering → Too cold; Blood vessels near the skin widen (skin flushes) → Too hot; Blood vessels near the skin narrow (skin goes pale) → Too cold; Hairs stand up (goosebumps) → Too cold ::: :::keep-together ### Negative **Why is it called negative feedback?** ☐ The receptors stop working ☐ It makes the temperature go down only ☐ It is bad for the body ☐ The response reverses the change: a rise causes a fall, a fall causes a rise ::: :::teacher-note **Answer:** The response reverses the change: a rise causes a fall, a fall causes a rise ::: :::keep-together ### Switching off **On the board, what happens to sweating once body temperature is back at 37 °C?** ☐ It turns into shivering ☐ It keeps going all day ☐ It gets stronger ☐ It switches off, because the stimulus (too hot) has gone ::: :::teacher-note **Answer:** It switches off, because the stimulus (too hot) has gone ::: :::keep-together ### Four parts **Match each part of a negative feedback loop to what it is in body temperature control.** A. What the effectors do to reverse the change, such as sweating B. A change away from the set point, such as body temperature rising on a hot day C. Receptors sense the temperature is back near 37 °C, so the response switches off D. The value the body keeps conditions near: about 37 °C {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `Set point` | | | `Deviation` | | | `Corrective response` | | | `Return detection` | | ::: :::teacher-note **Answer:** Set point → D. The value the body keeps conditions near: about 37 °C; Deviation → B. A change away from the set point, such as body temperature rising on a hot day; Corrective response → A. What the effectors do to reverse the change, such as sweating; Return detection → C. Receptors sense the temperature is back near 37 °C, so the response switches off ::: :::typical ## Elaborate: blood sugar :::keep-together **Order the steps when blood sugar rises after lunch.** Groups: 1st, 2nd, 3rd, 4th - Blood sugar rises above the set point: {{field-15}} - Cells in the pancreas detect it and release insulin: {{field-15}} - Liver and muscle cells take up glucose: {{field-15}} - Blood sugar falls, so the pancreas releases less insulin: {{field-15}} ::: :::teacher-note **Answer:** Blood sugar rises above the set point → 1st; Cells in the pancreas detect it and release insulin → 2nd; Liver and muscle cells take up glucose → 3rd; Blood sugar falls, so the pancreas releases less insulin → 4th ::: ::: :::wider ## Elaborate: break the loop :::keep-together ### Real failure **If the sweat glands couldn't work (as in some burns patients), what would happen on a hot day?** ☐ The body couldn't cool down enough and could overheat, even though the brain detects the rise ☐ Nothing: the brain would fix it ☐ The body would get cold ::: :::teacher-note **Answer:** The body couldn't cool down enough and could overheat, even though the brain detects the rise ::: ::: ## 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. ## Exit ticket :::keep-together **Describe what happens when your body temperature rises above 37 °C.** {{lines-3}} ::: :::teacher-note **Answer:** Temperature receptors detect it; the hypothalamus sends impulses to the sweat glands and skin blood vessels; sweating and widened vessels cool the body; once it is back near 37 °C, they switch off. :::