The shape of the lesson
By the end of the lesson, learners can
- A constant internal environment: Press Eat a sugary meal and watch the graph of blood glucose.
- Insulin, glucagon and the liver: Extended.
- Body temperature: Extended.
- Homeostasis: maintenance of a constant internal environment. Insulin lowers blood glucose.
- Negative feedback (Extended): a change from the set point triggers a response that reverses it.
- Glucose (Extended): high: insulin, glucose to glycogen in the liver. Low: glucagon, glycogen to glucose.
- Temperature (Extended): hot: vasodilation, sweating. Cold: vasoconstriction, shivering, hairs up, insulation.
One picture every idea returns to
Homeostasis is the maintenance of a constant internal environment. Insulin decreases blood glucose concentration. Extended: homeostatic control works by negative feedback: when a condition moves away from its set point, the body responds in a way that brings it back. The pancreas secretes insulin or glucagon and the liver stores or releases glucose; the brain controls sweating, shivering and the arterioles of the skin to keep core temperature close to 37 °C.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Keeping the inside constant.. Outside, the weather swings and meals come and go. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: A constant internal environment | Press Eat a sugary meal and watch the graph of blood glucose. Project tab 4 of the lab (Controlling blood glucose) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Insulin, glucagon and the liver | Extended. | Pairs |
| 21 to 30 min | Teach and check: Body temperature | Extended. Project tab 5 of the lab (The skin and body temperature) and let a student drive it while the class predicts. | Mix-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 23 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Body temperature, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Mix-Pair-Share
Students mix around the room until you call pair; they pair with the nearest classmate, discuss the prompt, then mix again. Three prompts of rising difficulty, three different partners.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Negative feedback does not mean the response is bad or stops something. | It means the response acts in the opposite direction to the change, so the level returns towards the set point. |
| Glycogen and glucagon sound alike. | Glycogen is the storage carbohydrate in the liver; glucagon is the hormone that makes the liver break glycogen down. |
| In vasodilation the arterioles supplying the skin capillaries widen. | Capillaries do not move up or down through the skin, and they cannot constrict: they have no muscle in their walls. |
Homeostasis: worksheet
6 questions, 23 marks. Written in the style of the papers; no past paper question is reproduced.
Define homeostasis and state the effect of insulin on blood glucose concentration.
Extended. Explain how blood glucose concentration is returned to normal after a meal rich in carbohydrate, using the idea of negative feedback.
Extended. Two people each drank a glucose solution at time 0. Their blood glucose was measured.
| Time / min | 0 | 30 | 60 | 120 |
|---|---|---|---|---|
| Person A / mmol dm−3 | 5.0 | 7.8 | 6.1 | 5.1 |
| Person B / mmol dm−3 | 7.5 | 13.9 | 15.2 | 12.8 |
(a) Which person is likely to have Type 1 diabetes? Give two pieces of evidence. (b) Outline how this condition is treated.
Extended. A diagram of a section through human skin is labelled A to G. State the function of: (a) sweat glands, (b) hair erector muscles, (c) fatty tissue, (d) receptors.
Extended. A person sits outdoors on a cold winter day. Explain how their body keeps its core temperature close to 37 °C. Refer to vasoconstriction in your answer.
Extended. Explain why sweating cools the body less effectively in very humid air, and why the skin of a person looks red after exercise.
Answer key and marking notes
- Homeostasis is the maintenance of a constant internal environment.
- Insulin decreases (lowers) the blood glucose concentration.
- Blood glucose rises above the set point after the meal.
- The pancreas detects the rise and secretes insulin into the blood.
- Insulin causes the liver to convert glucose into glycogen and store it (and other cells take up more glucose).
- Blood glucose falls back towards the set point.
- This is negative feedback: the change causes a response that reverses it; as glucose falls, less insulin is secreted.
- (a) Person B.
- Their glucose is higher even before the drink (7.5 compared with 5.0), and it keeps rising to 60 min and is still high (12.8) at 120 min, while person A returns to about 5.0.
- (b) Insulin injections (or an insulin pump), with regular measurement of blood glucose.
- Control of diet, especially carbohydrate intake, and planning exercise to keep glucose within the normal range.
- (a) Sweat glands secrete sweat on to the skin surface; its evaporation cools the body.
- (b) Hair erector muscles contract to raise the hairs, trapping a layer of insulating air.
- (c) Fatty tissue insulates the body, reducing heat loss.
- (d) Receptors detect changes in temperature and send impulses along sensory neurones.
- The brain detects the fall in blood temperature (and receives impulses from cold receptors in the skin).
- Vasoconstriction: arterioles supplying the skin surface capillaries narrow, so less blood flows near the surface and less heat is lost by radiation.
- Shivering: muscles contract rapidly, and the respiration releases heat.
- Sweating stops, so no heat is lost by evaporation of sweat; hairs are raised to trap air.
- The layer of fatty tissue insulates the body; together these return the temperature towards the set point (negative feedback).
- Sweat cools the body only when its water evaporates, transferring heat away from the skin.
- In humid air the air is already nearly saturated with water vapour, so less sweat evaporates and less heat is lost.
- After exercise vasodilation widens the arterioles to the skin capillaries, so more blood flows near the surface, making the skin look red and losing more heat.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which is the best definition of homeostasis?
- AThe maintenance of a constant internal environment
- BThe removal of waste products of metabolism
- CThe detection of changes in the surroundings
- DThe control of growth by hormones
What is the effect of insulin on blood glucose concentration?
- AIt decreases it
- BIt increases it
- CIt has no effect on it
- DIt keeps it above normal
The graph shows blood glucose in two people after the same meal. How long does person 1 take to return to their starting value after the peak?
- A60 minutes
- B30 minutes
- C90 minutes
- D120 minutes
Extended: using the same graph, which explanation best fits person 2?
- AThey have Type 1 diabetes and make little or no insulin
- BThey secrete too much insulin after the meal
- CTheir liver converts glucose to glycogen too quickly
- DThey secrete too much glucagon only when fasting
Body temperature, blood glucose and blood water content are all kept nearly constant. Why is this important?
- ACells and their enzymes work best in steady conditions
- BIt stops the body needing to eat or drink
- CIt means receptors are no longer needed
- DIt lets the body grow as fast as possible
Extended: when blood glucose falls below the set point, which pair of events restores it?
- APancreas secretes glucagon; liver converts glycogen to glucose
- BPancreas secretes insulin; liver converts glucose to glycogen
- CLiver secretes glucagon; pancreas converts glycogen to glucose
- DPancreas secretes glycogen; liver converts glucagon to glucose
Extended: on a hot day, why does the skin of the face look redder?
- AArterioles to the skin capillaries widen, so more blood flows near the surface
- BCapillaries move up through the skin towards the surface
- CArterioles to the skin capillaries narrow, trapping blood in the skin
- DSweat glands release red blood cells on to the skin
Extended: a swimmer is in cold water. Which set of responses helps keep the core temperature near 37 °C?
- AShivering, vasoconstriction, sweating stops
- BShivering, vasodilation, sweating increases
- CNo shivering, vasoconstriction, sweating increases
- DNo shivering, vasodilation, sweating stops
Quiz key
Homeostasis is the maintenance of a constant internal environment, such as blood glucose and body temperature. Removing metabolic waste is excretion, which helps homeostasis but is not its definition. Detecting changes is the job of receptors. Hormonal control of growth is a different process.
Insulin decreases blood glucose concentration, for example after a meal. Glucagon and adrenaline are the hormones that increase it. Insulin clearly has an effect, which is why people without it develop very high blood glucose, and it brings glucose down towards the normal range, not above it.
Person 1 peaks at 30 min and first returns to the starting value of 5.0 mmol/dm3 at 90 min, so 90 − 30 = 60 minutes. 30 minutes is the time to reach the peak. 90 minutes is the time from the meal, not from the peak. 120 minutes is a time when the level had already been back at 5.0 for half an hour.
Person 2's glucose rises to 14 mmol/dm3 and stays far above the normal range, showing that glucose is not being lowered: insulin is missing, as in Type 1 diabetes. Too much insulin would make glucose fall too low. Fast conversion to glycogen would lower glucose quickly. Glucagon secreted only during fasting would not explain a high level after a meal.
Keeping the internal environment constant gives cells and enzymes steady conditions so metabolism runs reliably. The body still needs food and water to replace what is used. Receptors are essential to detect any change that needs correcting. Homeostasis is about stability, not maximum growth.
Low glucose is detected by the pancreas, which secretes glucagon; glucagon makes the liver break down glycogen to glucose and release it. Insulin with glucose-to-glycogen is the response to high glucose. The liver does not secrete glucagon. Glycogen is a stored carbohydrate, not a hormone, and glucagon is not converted into glucose.
In vasodilation the arterioles supplying the skin surface capillaries widen, so more blood flows close to the surface, the skin looks red and more heat is lost. Capillaries do not move through the skin. Narrowing arterioles is vasoconstriction, the cold response, which makes skin paler. Sweat is mainly water and salts; it contains no blood cells.
In the cold, shivering releases heat from respiration in the muscles, vasoconstriction reduces blood flow to the skin surface so less heat is lost, and sweating stops so no heat is lost by evaporation. Vasodilation and increased sweating are responses to overheating and would cool the swimmer further. Without shivering less heat would be produced.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.