37 exam-style questions on Systems and models — topic T4 of Skills in the study of ESS in the IB Environmental Systems and Societies syllabus — with answers and explanations. Samples below; the full set is free with an account.
Two research groups run climate models for the same emissions scenario and obtain different amounts of warming by 2100. The main reason for the difference is that
Answer: the models represent processes such as cloud formation differently
A model is a simplification, and small-scale processes such as cloud formation and feedbacks have to be approximated in different ways. The spread between models is a measure of that structural uncertainty, which is why results are reported as a range.
A student draws a systems diagram of a lake. Nitrate dissolved in the water and nitrogen held in the fish are drawn as rectangles, and the arrow between them is drawn twice as wide as the arrow leaving the lake. In standard systems notation the width of an arrow shows
Answer: the rate of the flow the arrow represents
In a systems diagram rectangles are storages and arrows are flows, with arrow width drawn proportional to the rate of that flow. A wide arrow therefore says the transfer is fast, not that the storage it comes from is large.
A team models the nitrogen budget of a single arable field. If the boundary of the modelled system is redrawn to enclose the whole farm, including its livestock sheds, then manure spread on the field becomes
Answer: an internal transfer rather than an input
Where the boundary is drawn decides what counts as an input or output; the flow of manure itself has not changed at all. This is why any nutrient budget must state the boundary before its figures can be compared with another study.
A simple climate model treats the area of Arctic sea ice as a fixed value rather than letting it shrink as temperature rises. Compared with the real system, this model is most likely to
Answer: underestimate warming, because a positive feedback has been left out
Melting ice lowers the albedo, so more solar radiation is absorbed and more ice melts: the ice-albedo loop is positive feedback that amplifies the original warming. Freezing the ice area as a constant removes that amplifier, so the model runs too cool.
A team runs its catchment model many times, changing one input value at a time by plus or minus 10 % and recording how far the predicted peak discharge moves. This procedure is best described as
Answer: sensitivity analysis, showing which input the output depends on most
Sensitivity analysis varies inputs to find which ones the output responds to most, so it tells the modeller where better data would be worth collecting. Calibration and validation both compare the model against observations; a sensitivity analysis needs no observations at all.
A rainfall-runoff model of a small catchment works out one value of river discharge for each calendar month. Compared with the real catchment, this model will
Answer: miss the short flood peaks produced by individual storms
Nothing that happens faster than the time step of a model can appear in its output, so a monthly step averages a two-day storm away completely. Choosing the time step is therefore a decision about which processes the model is allowed to show at all.
That was 6 of 37 Systems and models questions.
Practise all 37 freeOutlineAO2 · 1–4 marks
A brief account or summary: the main points in two or three sentences, no evaluation.
DrawAO1 · 1–2 marks
A labelled, accurate drawing with a ruler where lines are straight; axes and units on a graph.
DistinguishAO2 · 1–4 marks
Make the difference clear for BOTH terms — a definition of one of them is only half an answer.
37 Systems and models questions — free with an account. Spaced repetition, streaks and full exam simulations included.
Practise them freeThis platform is independently developed and is not endorsed by, affiliated with, or sponsored by the International Baccalaureate Organization. “International Baccalaureate” and “IB” are registered trademarks of the IBO.