IB DP Environmental Systems and Societies – Climate, biomes, zonation and succession 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 climate, biomes, zonation and succession for IB Diploma Programme Environmental Systems and Societies. It is aligned to the IB Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026, syllabus subtopics 2.4 (Climate and biomes) and 2.5 (Zonation, succession and change in ecosystems). All questions are core content for 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.

The brief gives Topic 2 Ecology 22 teaching hours at SL and 35 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.

The brief describes Paper 2 as short-answer and data-based questions plus structured essays; questions 1–11 practise the first style and question 12 the second. All data are fictional.

Learn the content first in the study guide and revision notes. The IB DP ESS course hub and printable checklist show where this unit sits. For broader Topic 2 practice, try the Topic 2 Ecology practice set.

Questions

1. Distinguish between weather and climate. [2]

2. Define the term biome. [2]

3. Explain why insolation per unit area of the Earth’s surface decreases from the equator towards the poles. [3]

4. Using the tricellular model, explain why the equator receives high rainfall while a belt of hot deserts is found at about 30° N and S. [5]

5. The table shows climate data for two fictional stations.

Month	J	F	M	A	M	J	J	A	S	O	N	D
X temp (°C)	−24	−25	−21	−13	−3	5	9	7	1	−9	−17	−22
X precip (mm)	8	7	8	9	12	20	32	30	22	15	10	9
Y temp (°C)	14	16	20	25	30	34	35	34	31	25	19	15
Y precip (mm)	5	4	3	1	0	0	0	0	0	1	3	5

(a) Calculate the annual precipitation at station X. [1] (b) Calculate the annual temperature range at station X. [1] (c) Identify the biome at each station, using data to support your answers. [4] (d) Suggest two reasons why net primary productivity is low at station X. [2]

6. Distinguish between primary and secondary succession, giving one example of each. [4]

7. A student ran a transect inland from the strandline across a sand dune system.

Distance from strandline (m)	0	20	40	80	150	300
Species richness	2	4	7	12	18	22
Bare sand (%)	85	60	30	10	2	0
Soil organic matter (%)	0.2	0.5	1.4	3.0	5.5	8.0
Soil pH	8.6	8.2	7.6	6.8	5.9	5.2

(a) Calculate the percentage increase in soil organic matter from 40 m to 300 m. [2] (b) Describe the trend in species richness along the transect. [2] (c) Explain how changes in the soil could account for this trend. [3] (d) Explain why this transect can be used as evidence of succession as well as zonation. [2]

8. Fictional productivity data for four seral stages of a secondary succession (kJ m⁻² yr⁻¹):

Stage (age)	GPP	R
A (2 years)	2,400	1,000
B (15 years)	8,800	4,400
C (60 years)	14,400	10,800
D (200 years)	18,000	17,100

(a) Calculate the NPP and the P:R ratio for stage C. [2] (b) The P:R ratio is 2.4 at stage A and 1.05 at stage D. Explain this change. [3]

9. Compare r-strategist and K-strategist species, and relate each to a stage of succession. [4]

10. On a fictional mountain, the upper tree line rose from 1,850 m in 1960 to 1,910 m in 2020.

(a) Calculate the mean rate at which the tree line rose. [1] (b) Explain two possible consequences of this change for alpine tundra species above the tree line. [4]

11. Explain what is meant by a plagioclimax, using an example, and what would happen if the human activity maintaining it stopped. [4]

12. To what extent is a climax community a fixed end point of succession? [8]

Answers

1. Weather is the state of the atmosphere at a place over a short period (hours or days) [1]; climate is the average weather pattern over a long period, usually 30 years or more [1]. [2] Examiner insight: “Distinguish” needs the contrast (short-term state vs long-term average) made explicit; two unrelated definitions may not earn both marks.

2. A collection of ecosystems sharing similar climatic conditions [1], which therefore have similar communities/vegetation even in different parts of the world [1]. [2] Examiner insight: A biome is defined by climate, not by location; “a large area such as the Amazon” names an example, not a definition.

3. Near the poles the Sun’s rays strike at a lower angle [1], so the same energy is spread over a larger surface area [1]; low-angle rays also pass through more atmosphere, so more energy is absorbed, scattered or reflected before reaching the surface [1]. [3] Examiner insight: Each mark needs a mechanism, so “the poles are further from the Sun” earns nothing and is incorrect.

4. At the equator intense insolation heats the surface and air rises, forming low pressure [1]. Rising air cools, water vapour condenses and heavy convectional rain falls (ITCZ) [1]. The air moves poleward at altitude and sinks at about 30° N and S (Hadley cell) [1]. Sinking air warms and dries, so relative humidity falls [1]; high pressure prevents cloud formation, so rainfall is very low and deserts form [1]. [5] Examiner insight: The desert marks depend on “sinking air warms/dries” and “high pressure”; saying it is simply “hot” at 30° does not score.

5. (a) 8 + 7 + 8 + 9 + 12 + 20 + 32 + 30 + 22 + 15 + 10 + 9 = 182 mm [1] (b) 9 − (−25) = 34 °C [1] (c) X is tundra [1]: eight months below 0 °C, warmest month only 9 °C and low precipitation (182 mm) [1]. Y is hot desert [1]: annual precipitation only 22 mm with five months at 0 mm, and summer means of 34–35 °C [1]. (d) Low temperatures limit enzyme activity and photosynthesis for most of the year / short growing season [1]; low precipitation or frozen soil (permafrost) limits water available to plants, and low insolation limits light [1]. Examiner insight: In (c) the evidence mark needs actual figures from the table; “cold and dry” alone usually gains only the identification mark.

6. Primary succession begins on bare ground with no soil [1], e.g. newly cooled lava or rock exposed by a retreating glacier [1]. Secondary succession begins where soil is already present but the community has been removed [1], e.g. after a forest fire or on abandoned farmland [1]. [4] Examiner insight: The deciding feature is soil presence; an example placed in the wrong category loses its mark even if the definition is right.

7. (a) (8.0 − 1.4) ÷ 1.4 × 100 [1] = 471% [1] (b) Species richness increases with distance inland [1], from 2 at the strandline to 22 at 300 m, rising most steeply over the first 80 m and levelling off further inland [1]. (c) Organic matter rises (0.2% to 8.0%), so the soil holds more water and nutrients [1]; less bare sand means a more stable surface [1]; pH falls (8.6 to 5.2) as humus builds, so species intolerant of dry, alkaline sand can establish [1]. (d) Dunes further inland formed earlier, so they are older [1]; moving inland therefore shows the sequence of seral stages over time, even though the data were collected at one time along a spatial gradient [1]. Examiner insight: In (b), quoting figures from the table earns the second mark; in (a), dividing by the final value instead of the starting value loses the accuracy mark.

8. (a) NPP = 14,400 − 10,800 = 3,600 kJ m⁻² yr⁻¹ [1]; P:R = 14,400 ÷ 10,800 = 1.33 [1] (b) At stage A, GPP is well above R, so NPP is positive and biomass accumulates [1]. As biomass grows, its respiration rises faster than GPP [1]. By stage D, R nearly equals GPP, so P:R approaches 1 with little net biomass gain, typical of climax [1]. Examiner insight: An answer that says “productivity falls” is wrong here — GPP rises from A to D; the mark is for explaining that respiration catches up.

9. r-strategists produce many small offspring, grow and mature fast and disperse well [1]; they dominate early/pioneer stages where conditions are unstable [1]. K-strategists produce fewer, larger offspring with long lifespans and strong competitive ability [1]; they dominate late stages and the climax, where conditions are stable [1]. [4] Examiner insight: “Compare” needs matched features of both types, each linked to a seral stage; unlinked lists lose marks.

10. (a) (1910 − 1850) ÷ (2020 − 1960) = 60 ÷ 60 = 1.0 m per year [1] (b) Trees and shrubs invade the alpine zone, shading and outcompeting low-growing tundra plants [1], so the area of tundra habitat shrinks [1]. Species cannot move above the summit, so populations become smaller and isolated [1], raising the risk of local extinction [1]. Examiner insight: “Explain two” needs two consequences, each developed with a reason; four one-word effects score less.

11. A plagioclimax is a community prevented from reaching climax by human activity [1], e.g. heather moorland burned in rotation, or grazed pasture [1]. The activity (burning/grazing) removes woody seedlings, so succession is arrested [1]. If it stopped, secondary succession would resume, with shrubs and then trees colonising towards a woodland climax [1]. [4] Examiner insight: The example must name the human activity; “a grassland” alone does not.

12. Indicative points (in the real exam, extended responses are marked holistically against the IB’s assessment criteria, not point by point; your teacher will share the criteria):

• Classical view: succession leads to a stable climax in equilibrium with climate and soil, with P:R ≈ 1 [1].
• Support: undisturbed seres follow a predictable sequence, e.g. dunes to woodland [1].
• But the climax depends on local soil, drainage and topography, so one region can hold several different stable communities [1].
• Natural disturbance (fire, storms, floods) regularly resets succession, so many ecosystems are rarely at climax [1].
• Grazing or burning holds communities at a plagioclimax [1].
• Climate change shifts the conditions that set the climax, so the “end point” itself moves, e.g. biomes shifting poleward and upslope [1].
• Crossing a tipping point can push an ecosystem into an alternative stable state that does not return to the original climax, linked to resilience [1].
• Judgement: the climax is better seen as a dynamic equilibrium that is stable only while conditions stay the same — so only to a limited extent a fixed end point [1]. [8] Examiner insight: “To what extent” needs a supported conclusion; an answer that lists arguments on both sides but never weighs them is weaker than one that ends with a judgement backed by examples.

Where marks are usually lost

• Explaining the fall in insolation with distance from the Sun rather than angle and atmospheric path.
• Giving “hot” as the reason for deserts at 30° instead of sinking, warming, drying air.
• Identifying a biome from data without quoting any figures.
• Missing units on NPP (kJ m⁻² yr⁻¹) or rates (m per year).
• Saying productivity falls late in succession when GPP rises and only NPP falls.
• Naming a plagioclimax without the human activity that maintains it.
• Ending a “to what extent” answer without a clear judgement.

Next steps

• Revision notes for this unit
• Study guide for this unit
• IB DP ESS course hub
• Printable ESS checklist
• 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.