DSE Biology - Hormones and Blood Glucose Prep Guide (for tutors) | Three-step negative feedback, glycogen versus insulin dose, HbA1c conversion

DSE Biology – Hormones and Blood Glucose Prep Guide (for tutors) | Three-step negative feedback, glycogen versus insulin dose, HbA1c conversion

2026-11-05

Tutor lesson-prep guides · Secondary Biology

Students can write that insulin lowers blood glucose, then fail to draw the arrow that points backwards. This lesson fixes sense, secrete, respond and restore with one glucose reading and one HbA1c figure.

Objectives — Students can: (1) draw the negative feedback loop between insulin and glucagon and label sensor, coordinator and effector; (2) show that 3 litres of plasma at 5.0 mmol per litre holds only 2,700.0 mg of glucose, and explain why the level cannot swing; (3) combine a carbohydrate ratio with a correction factor for a 8 unit dose, and convert an HbA1c of 7 percent to an average of 8.57 mmol per litre.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Normal range	What is a normal fasting blood glucose?	About four to six millimoles per litre
Liver function	What happens to surplus glucose after a meal?	It becomes glycogen in liver and muscle
Negative feedback	Does negative feedback amplify or oppose the original change?	It opposes it, narrowing the swing

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Prior knowledge check	Ask the three prior questions and write the normal range on the board	Answer orally and copy any wrong item once
5-17 min	Act one: two hormones on a seesaw	Draw the loop and label sensor, islets and effector	Copy it and add the backward arrow themselves
17-30 min	Act two: the whole body holds a few grams	Compute 3 litres times 5.0 to get 2,700.0 mg	Compute once, then compute the impact of fifty grams
30-40 min	Act three: from dose to HbA1c	Combine 60 g of carbohydrate and 2 correction units into 8 units	Compute once, then convert seven percent to an average
40-43 min	One-sentence summary	Ask for one sentence on how insulin and glucagon relate	Answer orally; tutor corrects only wording
43-45 min	Exit check	Hand out three items and collect them	Work alone with books closed

03 Teaching script (read it out)

Scene 1: Act one: negative feedback is an arrow pointing back

Glucose rises, beta cells in the islets sense it, insulin is secreted, liver and muscle convert glucose to glycogen and fat cells take it up, so glucose falls.
Glucose falls, alpha cells sense it, glucagon is secreted, liver glycogen is broken down and glucose enters the blood, so glucose rises.
The decisive step is the last one: the result suppresses the secretion that caused it. Without that backward arrow it is influence, not regulation.
Adrenaline is a third player that raises glucose under stress as a short-term response, not part of daily homeostasis.

Ask students to repeat: insulin lowers, glucagon raises, each suppresses the other, and the backward arrow must be drawn.

Scene 2: Act two: the whole body holds two or three grams

3 litres at 5.0 millimoles per litre is 15 millimoles; at 180 grams per mole that is 2,700.0 mg, about 2.7 grams, less than a teaspoon.
A 50 g glucose load is 278 millimoles; if it all stayed in plasma the concentration would reach 93 millimoles per litre, which is fatal. The real rise is about 2.5, so under 2.7 percent stays in plasma and the rest is taken up by liver, muscle and fat or lost in urine.
That calculation is the best answer to why hormones exist: not for tidiness, but to avoid a 93 millimole swing.

Ask students to repeat: the body holds only two or three grams, so a fifty gram load must be cleared at once.

Scene 3: Act three: dose and long-term index are both multiplications

Meal dose is carbohydrate divided by grams per unit: 60 divided by 10 gives 6 units.
Correction dose is (current minus target) divided by the sensitivity factor: (11.0 minus 6.0) divided by 2.5 gives 2 units, so 8 units in total.
For the long-term index, an HbA1c of 7 percent maps to an average glucose of 28.7 times the percentage minus 46.7, which is 154.2 mg per decilitre, and dividing by 18 gives 8.57 millimoles per litre.
Remember the diagnostic lines: fasting at or above 7.0, and two-hour oral tolerance at or above 11.1 millimoles per litre.

Ask students to repeat: carbohydrate over coverage, difference over sensitivity, and A1c times 28.7 minus 46.7 then divided by 18.

04 Question types and worked steps

Type	Example	Steps	Answer
Feedback diagram	Glucose rises to nine millimoles per litre	Draw sensor to effector, then add the backward arrow	Insulin rises, glycogen synthesis rises, glucose falls
Storage calculation	3 litres at 5.0 millimoles per litre	Multiply millimoles by 180 mg	2,700.0 mg
Dose calculation	60 g carbohydrate, 10 g per unit, current 11.0	Two formulas, then add	8 units
Long-term index	HbA1c of 7 percent	Times 28.7, minus 46.7, divide by 18	8.57 millimoles per litre

Sanity check (teach this): Three read-backs: (1) glucose in millimoles per litre times volume gives millimoles, and only then multiply by 180 for milligrams; (2) the whole body holds 2.7 grams, so any answer in hundreds of grams lost the volume; (3) 7 percent maps to 8.57, and a teens figure means the division by 18 was skipped.

05 Independent practice (3 questions)

Question	Answer	What to watch
Four litres at five millimoles per litre: how many milligrams?	3,600 mg	Check volume first, then 180
45 g of carbohydrate at 15 g per unit: how many units?	3 units	Check division rather than a ratio guess
Why does glucagon rise during exercise?	Muscle uses glucose, liver glycogen replaces it, which is negative feedback	Check that sensing and suppression are named

06 Common mistakes and what to say

Mistake	Student writes	Say this
Backward arrow missing	Glucose rises so insulin rises, and the diagram stops	Show insulin lowering glucose, which then suppresses secretion.
Units confused	Five millimoles means five grams	Five is a concentration; multiply by volume for an amount.
Cell types swapped	Insulin comes from alpha cells	Beta cells make insulin, alpha cells make glucagon.
HbA1c read as today	An HbA1c of seven means today glucose is seven	It reflects a two to three month average.

07 Homework (paper, section and question numbers)

Redo this chapter — Redo the three items, units first
Nervous coordination — Compare nervous and hormonal signalling in three points
Biology chapter index — Pick one more chapter and draw the flowchart only

08 Exit check (last 5 minutes)

Question	Answer	Decision
3 litres at 5.0 millimoles per litre: how many grams?	About 2.7 grams	Error: treating concentration as amount
What is the decisive step in negative feedback?	The result suppresses the secretion that produced it	Error: writing only that glucose falls
HbA1c of seven percent: average glucose?	About 8.57 millimoles per litre	Error: answering seven

09 Tutor FAQ

Which year is this for?

Mainly S5, and a summary for S6 homeostasis and diabetes.

Is 45 minutes enough for two systems?

Yes, because only insulin and glucagon are drawn in full and the same feedback language covers the rest.

Is there a companion worksheet?

Three practice items with answers on the page, plus the nervous coordination chapter.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.