--- marp: true theme: default html: true --- # How does your body stay at 37 °C? Year 9 Biology · Coordination and control --- ## Today **We are learning to** 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. - 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. --- ## Why it matters > 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. --- 💬 Discussion ## Engage: predict **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 --- ✍️ Activity ## Explore it {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-9%2Ffeedback%2Fstep-2&code=widget%3A+coordination%0Amode%3A+feedback%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-9/feedback/?full=step-2#step-2) --- ✅ Check ## What happened? * 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. --- ✅ Check ## Hot or cold **Too hot or too cold: which responses switch on?** Groups: Too hot · Too cold Sweating · Shivering · Blood vessels near the skin widen (skin flushes) · Blood vessels near the skin narrow (skin goes pale) · Hairs stand up (goosebumps) * 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 --- ✅ Check ## 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 * Answer: The response reverses the change: a rise causes a fall, a fall causes a rise --- ✅ Check ## 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 * Answer: It switches off, because the stimulus (too hot) has gone --- ✅ Check ## Four parts **Match each part of a negative feedback loop to what it is in body temperature control.** | | | |---|---| | `Set point` | A. What the effectors do to reverse the change, such as sweating | | `Deviation` | B. A change away from the set point, such as body temperature rising on a hot day | | `Corrective response` | C. Receptors sense the temperature is back near 37 °C, so the response switches off | | `Return detection` | D. The value the body keeps conditions near: about 37 °C | * 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 --- ✅ Check ## Elaborate: blood sugar **Order the steps when blood sugar rises after lunch.** Groups: 1st · 2nd · 3rd · 4th 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 * 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 --- ✍️ Activity ## Elaborate: break the loop {{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fbiology-9%2Ffeedback%2Fstep-5&code=widget%3A+coordination%0Amode%3A+feedback%0Abreak%3A+on%0A&fresh=1}} [Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/biology-9/feedback/?full=step-5#step-5) --- ✅ Check ## 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 * 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. --- ✅ Check ## Exit ticket **Describe what happens when your body temperature rises above 37 °C.** * 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.