01442234892 info@hemelprivatetuition.co.uk

Hemel Private Tuition

Name: Philip M Russell Ltd
Address: 53 Hilldown Road, Hertfordshire, HP1 3JD, GB
Telephone: 01442234892

Learning Biology

An experiment for Teaching Immunity with a Classroom Epidemic Simulation

Immunity is one of those biology topics that can feel a bit abstract to students. We talk about pathogens, antigens, and antibodies, but unless they’ve actually been ill (or recently jabbed), the concepts don’t always stick. That’s where a classroom epidemic simulation comes in — a hands-on way to show how infections spread and how immunity protects us.

Extension Experiment: “Tokens in Spheres” – How Immunity Ends an Outbreak

This tabletop simulation models how an infectious disease grows, peaks, and fades as natural immunity builds in a population.
Materials
26 opaque plastic spheres/capsules (or ping-pong balls with stickers).
26 small plastic counters (“tokens”), one per sphere.
1 cloth bag (opaque).
Whiteboard or grid paper to draw a bar chart by round.
Marker and simple results table.
Meaning: each sphere = one person. A token inside = still susceptible. Removing the token = infected then immune.

Setup
Put one token inside each sphere and all 26 spheres into the bag.
Draw a results table with columns:
Round | Draws | New Cases | Cumulative Cases | Susceptible Left | Immune.
Rules of Play Round 1: Draw 1 sphere from the bag. If it contains a token (it will, at the start), that’s 1 new case. Remove the token (the person becomes immune) and return the sphere to the bag.
Plot the bar for Round 1 (height = new cases).

Next rounds: The number of draws = 2 × (new cases from the previous round). For each sphere you draw: if it still has a token, that’s a new case; remove the token and return the sphere. If it has no token, they’re already immune—no new case—return it.
Tally new cases, update the table, and plot the bar.

Continue until a round produces 0 new cases (the outbreak has died out). The multiplier “2” is your classroom R (each case seeds two exposure attempts next round). You can change it to explore different R values.

What Students See
Early rounds: bars rise (exponential-like growth).
Middle: the peak—lots of draws are “wasted” on people who’ve already become immune.
Late: bars fall to zero—herd effects emerge as the susceptible pool shrinks.

Debrief Questions
Why do new cases peak even though we keep drawing more spheres at first?
What does removing tokens represent biologically?
How does changing the multiplier from 2 to 1.5 or 3 alter the curve?
Where would you place the herd immunity threshold in this model?
GCSE Links Communicable disease, immune response, vaccination, herd immunity (qualitative).
Reading simple bar charts; relating shape to mechanism.
A-Level Links S-I-R ideas (Susceptible → Infected → Removed/Immune).
R₀ and effective reproduction number Rₜ = R₀ × (S/N).
As S falls, Rₜ < 1, so cases decline.
Stochastic effects: different runs give slightly different peaks.

Debrief Questions
Why do new cases peak even though we keep drawing more spheres at first?
What does removing tokens represent biologically?
How does changing the multiplier from 2 to 1.5 or 3 alter the curve?
Where would you place the herd immunity threshold in this model?
GCSE Links Communicable disease, immune response, vaccination, herd immunity (qualitative).
Reading simple bar charts; relating shape to mechanism.
A-Level Links S-I-R ideas (Susceptible → Infected → Removed/Immune).
R₀ and effective reproduction number Rₜ = R₀ × (S/N).
As S falls, Rₜ < 1, so cases decline.
Stochastic effects: different runs give slightly different peaks.

Learning Biology

An experiment for Teaching Immunity with a Classroom Epidemic Simulation

Extension Experiment: “Tokens in Spheres” – How Immunity Ends an Outbreak

Download the free Worksheet