A good model answer names what the model shows, what it simplifies, and what it cannot predict. Use those three parts and most model questions become routine.
This lesson is in the health-themed science sub-cluster. A related skill appears in recognising the limits of a classroom example.
What do I say about a model?
Say what idea it shows well. Then say what it simplifies or leaves out. Finally say what question it cannot answer.
| Part | Question to ask |
|---|---|
| Shows | Which idea does this model make clear? |
| Simplifies | Which real parts are missing or replaced? |
| Cannot predict | What would you still need to find out? |
Worked example: the bell jar breathing model
A common classroom model uses a bell jar, a balloon inside as a lung, and a rubber sheet at the bottom as the diaphragm. Pulling the rubber sheet down makes the balloon inflate.
Question: State one thing the model shows and two limits. (3 marks)
Model answer. It shows that air moves into the lungs when the volume of the chest space increases, because the balloon inflates when the rubber sheet is pulled down. One limit is that the balloon represents a single lung bag, while real lungs have many tiny air sacs. A second limit is that the model has no ribs or muscles, so it cannot show how the rib cage moves.
Each point is tied to a feature of the model. A limit describes what the model covers, and it does not mean the model is bad.
The mistake that costs marks
The slip is writing that the model “is not real” or “is not accurate”. Both phrases are true of every model, so they add no information.
| Wrong | Right | |
|---|---|---|
| Limit wording | “The model is not real” | “It has no ribs, so it cannot show rib movement” |
| Shows | Nothing stated | “Air enters when volume increases” |
| Conclusion | “Model is useless” | “Useful for the pressure idea, limited for anatomy” |
Another slip is using the model to claim something about a person’s lungs. The model explains a general process only.
Check yourself
A diagram models the heart as a box with two arrows for blood flow. State one thing it shows and one limit.
Answer
It shows that blood flows in a particular direction through the heart.
One limit: a box with two arrows does not show valves, chambers or heart muscle, so it cannot explain how blood is kept moving in one direction.
What to study next
Move to identifying which claim requires a current authoritative health source. The graph evidence comparison lab provides further practice.
For a teacher to apply the three-part frame to your own diagrams, see online one-to-one Science tuition.