IB DP Environmental Systems and Societies – Human populations, urban systems and urban air pollution Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

This practice set covers Topic 8, Human populations and urban systems, of IB Diploma Programme Environmental Systems and Societies. It is aligned to the International Baccalaureate Diploma Programme Subject Brief: Environmental systems and societies, first assessment 2026, syllabus sections 8.1–8.3, and suits both SL and HL. It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions. All data are fictional.

The brief gives Topic 8 Human populations and urban systems 9 teaching hours at SL and 15 at HL. It does not list the subtopics or learning outcomes for this topic, so the numbered subtopics and outcomes on this page follow the syllabus numbering used in the printable ESS checklist, not the brief itself.

Learn the content first in the study guide and the revision notes. The IB DP ESS course hub and the printable syllabus checklist show where this topic sits. Extended answers list indicative points; real exam essays may be judged holistically against IB criteria, which your teacher will share.

Questions

1. Define crude birth rate and total fertility rate. [2]

2. Country K has a population of 24.0 million. In one year it records 432,000 births and 144,000 deaths.

(a) Calculate the crude birth rate and crude death rate. [2] (b) Calculate the natural increase rate. [2] (c) Estimate the doubling time and state one assumption you have made. [3]

3. The table shows the age structure of two fictional countries.

Age group	Country A (%)	Country B (%)
0–14	42	13
15–64	55	63
65+	3	24

(a) Calculate the dependency ratio for each country. [2] (b) Suggest the stage of the demographic transition model for each country, giving a reason. [2] (c) Outline one environmental or resource implication of each age structure. [2]

4.

(a) Explain why a population may keep growing in stage 3 of the demographic transition model even though the birth rate is falling. [2] (b) Outline two limitations of the demographic transition model. [2]

5. Distinguish between pro-natalist and anti-natalist policies, giving one measure of each. [3]

6. Outline why a city is described as an open system. Identify two inputs and two outputs in your answer. [4]

7. The table shows population data for a fictional country.

Year	Total population (millions)	Urban population (%)
1990	30	28
2010	40	41
2030 (projected)	48	55

(a) Calculate the urban population in 1990 and in 2030. [2] (b) Calculate the percentage increase in urban population from 1990 to 2030. [2] (c) The rural population is the same in 1990 and 2030. Explain what this suggests about rural–urban migration and suggest two push factors. [3]

8. Mean night-time temperatures in July were 24.6 °C in a city centre, 22.1 °C in its suburbs and 20.3 °C in the nearby countryside.

(a) Calculate the urban heat island intensity between the city centre and the countryside. [1] (b) Explain two causes of the urban heat island. [4]

9. Hourly roadside readings (µg/m³) on a sunny, calm day in a fictional city:

Time	06:00	09:00	12:00	15:00	18:00	21:00
NO₂	40	95	60	45	80	50
O₃	20	35	90	130	70	30

(a) Describe the daily pattern of each pollutant. [2] (b) Explain why ozone peaks later in the day than nitrogen dioxide. [3] (c) Calculate the percentage increase in ozone from 06:00 to its peak. [2]

10. Explain how a thermal inversion can lead to a serious urban air pollution episode. [4]

11. A fictional city introduced a low-emission zone that charges older, more polluting vehicles to enter the centre. Mean annual NO₂ fell from 52 to 39 µg/m³ and mean PM2.5 fell from 30 to 27 µg/m³.

(a) Calculate the percentage change in each pollutant. [2] (b) Evaluate the low-emission zone as a strategy for managing urban air pollution. [8]

12. “Urban planning is the most effective way to reduce the environmental impact of a growing urban population.” To what extent do you agree? [9]

Answers

1. Crude birth rate: number of live births per 1,000 people per year. [1] Total fertility rate: average number of children a woman would have in her lifetime at current age-specific birth rates. [1] Examiner insight: “Per 1,000 per year” is part of the definition; leaving out either the 1,000 or the time period loses the mark.

2. (a) CBR = 432,000 ÷ 24,000,000 × 1,000 = 18.0 per 1,000 [1]; CDR = 144,000 ÷ 24,000,000 × 1,000 = 6.0 per 1,000 [1] (b) NIR = (18.0 − 6.0) ÷ 10 [1] = 1.2% [1] (c) Doubling time ≈ 70 ÷ 1.2 [1] = 58.3 ≈ 58 years [1]. Assumes the growth rate stays constant and there is no net migration. [1] Examiner insight: Show the rule-of-70 working; the assumption mark is separate and often missed.

3. (a) A: (42 + 3) ÷ 55 × 100 = 81.8 [1]; B: (13 + 24) ÷ 63 × 100 = 58.7 [1] (b) A: stage 2 or early 3, because 42% are under 15 (high birth rate) and only 3% are over 65. [1] B: stage 4 or 5, because only 13% are under 15 and 24% are over 65 (low fertility, long lives). [1] (c) A: population momentum raises future demand for food, water, land and housing. [1] B: slow growth limits rising resource demand, but consumption per person may be high and fewer workers support many elderly people. [1] Examiner insight: Back each stage with a figure from the table.

4. (a) The birth rate is still above the death rate, so natural increase is positive. [1] A large, young population is entering child-bearing age (population momentum), so the number of births stays high. [1] (b) It is based on European history, so it may not fit countries developing today. [1] It ignores migration / gives no timescale / assumes birth rates will fall once death rates fall. [1] Examiner insight: “Outline” needs a brief reason with each limitation, not one word.

5. Pro-natalist policies aim to raise the birth rate; anti-natalist policies aim to lower it. [1] Pro-natalist: child benefit payments, paid parental leave or subsidised childcare. [1] Anti-natalist: free contraception, family planning services or education for women. [1] Examiner insight: “Distinguish” needs both sides made explicit; defining only one type caps the answer.

6. An open system exchanges both energy and matter with its surroundings. [1] Inputs: any two of food, water, fuel/electricity, building materials, migrants. [1] Outputs: any two of solid waste, sewage, air pollutants, waste heat, manufactured goods. [1] The city depends on land and ecosystems far beyond its boundary, so its ecological footprint is much larger than its own area. [1] Examiner insight: Include matter flows as well as energy, or the “open” point is not shown.

7. (a) 1990: 30 × 0.28 = 8.4 million [1]; 2030: 48 × 0.55 = 26.4 million [1] (b) (26.4 − 8.4) ÷ 8.4 × 100 [1] = 214% (214.3) [1] (c) Rural population is 21.6 million in both years (30 − 8.4 and 48 − 26.4). [1] Rural natural increase is still positive, so the extra people must be moving to towns. [1] Push factors: any two of lack of jobs, farm mechanisation, low incomes, poor services, drought or land degradation. [1] Examiner insight: Support “suggest” answers with a figure calculated from the data.

8. (a) 24.6 − 20.3 = 4.3 °C [1] (b) Dark surfaces such as asphalt and concrete [1] absorb solar radiation by day and release it slowly at night. [1] Less vegetation and more impermeable surfaces [1] mean less evapotranspiration, so less energy is used to evaporate water and cool the air. [1] (Waste heat or reduced wind speed also credited.) Examiner insight: Each cause needs a named feature and its mechanism for both marks.

9. (a) NO₂ has two peaks, 95 at 09:00 and 80 at 18:00, matching rush hours. [1] O₃ rises from 20 to a single peak of 130 at 15:00, then falls to 30 by 21:00. [1] (b) Ozone is a secondary pollutant formed from NO₂, so NO₂ must build up first. [1] Sunlight splits NO₂ into NO and an oxygen atom, which joins O₂ to form O₃. [1] Sunlight is strongest around midday and early afternoon, so ozone formation is greatest then. [1] (c) (130 − 20) ÷ 20 × 100 [1] = 550% [1] Examiner insight: “Describe” answers must quote values and times from the table.

10. Normally air cools with height, so warm polluted surface air rises and disperses. [1] In an inversion a layer of warmer air lies above cooler air near the surface. [1] The cool, dense air cannot rise through the warm layer, so pollutants build up near the ground. [1] Inversions are likely on calm, clear nights and in valleys or basins, and can last days. [1] Examiner insight: The mechanism mark needs warm air above cool air.

11. (a) NO₂: (39 − 52) ÷ 52 × 100 = −25.0% [1]; PM2.5: (27 − 30) ÷ 30 × 100 = −10.0% [1] (b) Indicative points:

• It works at the “control release” level (and partly “alter human activity”) of pollution management. [1]
• NO₂ fell by 25%, a large benefit for respiratory health in the centre. [1]
• PM2.5 fell only 10%: particulates also come from tyres, road dust and heating. [1]
• Traffic may divert to roads outside the zone, moving pollution rather than removing it. [1]
• One year’s change may reflect weather, so a longer data series is needed. [1]
• Ozone, a secondary pollutant, may not fall in step with NO₂. [1]
• Charges fall hardest on lower-income drivers with older vehicles, while residents with breathing problems benefit. [1]
• Judgement: effective for NO₂ in the centre, but best combined with public transport that cuts car use overall. [1] Examiner insight: Use the given data and end with a judgement; a plain list of pros and cons scores lower.

12. Indicative points:

• Planning shapes land use for decades, acting at the level of altering human activity. [1]
• Compact, mixed-use design and public transport cut car use, energy demand and air pollution. [1]
• Brownfield development limits sprawl onto farmland and habitats. [1]
• Green infrastructure reduces the heat island, flood risk and some particulates. [1]
• Plans are slow to take effect, and informal settlements can grow faster than planners act. [1]
• Much of a city’s footprint comes from consumption of imported food and energy, which planning does not control. [1]
• Other approaches matter too: technology (catalytic converters, renewable energy), pricing (congestion charges) and population policy. [1]
• Perspectives: developers may favour greenfield sites; low-income residents may lose out if compact housing raises prices. [1]
• Judgement: planning is necessary but not sufficient; it works best combined with technology and lower consumption. [1] Examiner insight: “To what extent” needs a stated position weighed against an alternative.

Where marks are usually lost

• NIR written as 12 instead of 1.2% because the ÷ 10 step was missed.
• Doubling times with no assumption stated.
• Percentage changes divided by the new value instead of the original.
• DTM stages suggested without a figure from the data.
• Ozone called a primary pollutant, or smog explained without sunlight.
• Inversions described without saying that warm air lies above cool air.
• Heat island causes named without the mechanism.
• Evaluations with no judgement, or that ignore the data in the question.

Next steps

• Recap the key facts in the revision notes.
• Re-learn any weak area in the study guide.
• See the rest of the course on the IB DP ESS course hub and tick off the printable syllabus checklist.
• Plan your revision with the ESS exam preparation guide.
• Try all free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026. The brief lists subtopics for Topic 1 only; the subtopic numbering on this page follows the printable ESS checklist.