Systems you can play with.
Change an input and watch the system respond, so the idea lands before the vocabulary does. Each one goes with a lesson.
Environmental Systems & Societies
Systems, feedback and the human–environment interactions behind the ESS guide.
A tree as a system
Sort the 35 components of a tree system — inputs, stores, outputs, flows and processes — then get your own whiteboard copy of the tree and draw the links between them (IB ESS 1.2.1–1.2.4).
A pond as a system
Nineteen measured components of a pond, sorted into storages, inputs, outputs and the flows within. The diagram draws itself to scale as you go, so the sediment really is 400 times the carnivores, and the pond turns out to be quietly filling itself in (IB ESS 1.2.3–1.2.8, 1.2.17).
Open, closed and isolated systems
Matter drawn as particles, energy as flowing arrows, and a counter that stops moving the moment you close the boundary. Switch between open, closed and isolated, then try a tree, a drainage basin, Biosphere 2 and the Earth, and watch the same stuff change category as the boundary moves (IB ESS 1.2.5).
Feedback loops
Toggle between a balancing loop (fox & rabbit) and a reinforcing loop (ice, albedo & temperature) to see how systems self-regulate or amplify change.
Daisyworld
Watson and Lovelock's planet of black and white daisies, beside the same planet with no life. Brighten its sun and watch the daisies hold the temperature steady while the lifeless planet heats by over 50 °C, knock them back and watch it return, then push the sun until the regulation collapses (IB ESS 1.2.8 to 1.2.11).
A British temperate woodland food web
Oak to caterpillar to blue tit to sparrowhawk: the woodland's producers, primary, secondary and tertiary consumers, saprotrophs and parasites drawn as one annotated food web, with every arrow pointing the way energy and carbon compounds flow (IB ESS 2.2.5, 2.2.9–2.2.11, 2.2.15).
Will it mix?
Cool the surface of Lake Geneva and watch how deep the water turns over. Mixing depth holds up, then collapses. Find the point where the answer changes, then press Ocean and watch the carbon sink fail the same way.
Hold, stir or sink?
Set the temperature and salinity of a surface layer and the deep water under it, add wind, and find out which of three things happens: the layers hold, the wind stirs them, or the surface has become denser and sinks. The densities are real ones from TEOS-10, so fresh water turns out to be densest at 4 °C and salt water never gets the chance (IB ESS 4.1.10 to 4.1.12).
Protected area design
Sketch a reserve network for a rare predator — toggle buffer zones, surrounding land use and wildlife corridors, then assemble a Paper 2 answer from the linked brainstorm cards.
Soil texture and productivity
Mix sand, silt, clay and humus and watch the four properties that decide how well plants grow. The clay that holds the nutrients is the clay that stops the soil draining, so every soil is a trade-off and one weak property drags the whole thing down (IB ESS 5.1.12–5.1.13).
Sink, store or source: a soil carbon model
A soil gains carbon from dead organic matter and loses it through decomposition, and only the balance of those two rates decides which of the three it is. Plough a grassland, drain a peat bog, and watch the same model change state (IB ESS 5.1.14).
A population as a system
Births and immigration in, deaths and emigration out, and fifty years of the storage in between. Set the three rates and watch natural increase, growth rate and doubling time recalculate, then load Switzerland and find the country whose population is shrinking naturally and growing anyway (IB ESS 8.1.1–8.1.3).
Eutrophication: a systems model
Nutrients in, phytoplankton bloom, decomposition strips the dissolved oxygen and aquatic life suffocates — the positive feedback loop drawn as a stock-and-flow diagram, with green/red arrows for the polarity of each link (IB ESS 4.4.5–4.4.6).