Key Idea: Most marks in topic 1.2 come from feedback loops, then stability and resilience. Learn those first, then systems and models.
1. Feedback loops (most marks)
- Negative feedback reverses a change, so the system stays stable.
- Positive feedback makes a change bigger, pushing towards a tipping point.
- Past a tipping point, the system settles in a new, different state.
- When you draw a loop, finish back where it started.
2. Stability and resilience
- Steady state: what comes in equals what goes out.
- A resilient system recovers after damage: it has large storages and many species.
- People make systems less resilient by clearing forests and overfishing.
3. Systems and models
- A transfer moves matter or energy; a transformation changes its form.
- An open system swaps energy and matter; a closed one swaps only energy.
- A model is a simple version of reality: useful, but never exact.
How it is examined:
| Question | How to score |
|---|---|
| [4] Outline a feedback loop | Show each step, and close the loop back to the start. |
| [7] How does feedback affect equilibrium? | Both negative and positive feedback, each with a named example. |
| [4] What makes a system resilient? | Say 'large' storages, many species, and a tipping point far away. |
| [9] How useful are models? | What they help us do, their limits, named models, then a conclusion. |
Key terms, one line each:
| Term | In one line |
|---|---|
| System | parts (storages) linked by flows, working as a whole |
| Transfer / transformation | a change of place / a change of form |
| Open / closed system | exchanges energy and matter / energy only |
| Negative / positive feedback | counteracts change / amplifies change |
| Steady-state equilibrium | flows continue, but inputs balance outputs |
| Tipping point / regime shift | the smallest change that tips a system / the move to a new stable state |
| Model | a simplified representation of reality |
| Emergent property | appears only when the parts interact |
| Resilience | the ability to resist, recover from or adapt to a disturbance |
Last-minute check: answer, then tap to see.
Why is the Earth treated as a closed system? Energy enters and leaves, but almost no matter does.
What holds each alternative stable state in place? Its own negative feedback.
Why do population projections for 2100 differ so much? Different assumptions, such as birth rates.
What is a time lag? A delay between a change and the system's response.
How does deforestation reduce resilience? It shrinks storages and diversity.
To what extent does the systems approach help us to understand and manage environmental change?
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Exam tips
- Use the language of systems: storages, flows, feedback, equilibrium.
- Name real examples: Daisyworld, the ice-albedo loop, Lake Taihu, Yellowstone.
- For 'to what extent', weigh what systems thinking shows against what models miss.
- One point per paragraph.