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IGCSE Environmental Management — Unit Exam 2 — Challenge

Unit Assessment practice — 4.2 Climate change · 5.1 Ecosystems · 5.2 Forest ecosystems — Section B is source led
90 minutes
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This paper covers only what the school unit tests: 4.2 Climate change, 5.1 Ecosystems and 5.2 Forest ecosystems. Section A (Questions 1–3, 30 marks) tests knowledge and application. Section B (Questions 4–6, 30 marks) is source led. Every question is different from Unit Exam 1, so do both.

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SECTION A — knowledge and application (Questions 1–3, 30 marks)
Question 1 — Greenhouse gases and warming
Total: 10 marks
(a)[3]
Name the three greenhouse gases listed in the syllabus.
Model Answer — 1(a)
carbon dioxide
water vapour
methane
⚠ If you missed marks here: the one everyone leaves out is water vapour, because it is not a pollutant and nobody emits it deliberately — but it absorbs and re-emits radiation, so by the definition it qualifies, and the syllabus lists it. And ozone is not on this list: writing ozone signals the ozone-layer confusion to the marker.
(b)[2]
A student writes: “Greenhouse gases trap the Sun’s heat so it cannot escape.” Explain what the gases actually do, using the correct two verbs.
Model Answer — 1(b)
the gases absorb radiation
and re-emit it (as thermal energy), in all directions — the share sent back down is what warms the surface; radiation is not sealed in, and plenty still escapes to space
⚠ If you missed marks here: "trap" describes a blanket, not a gas, and it contains neither verb the scheme wants. Absorb, then re-emit — and note the direction detail: re-emission goes in all directions, and it is the downward share that does the warming. That one clause often carries the second mark.
(c)[3]
Explain, as a chain of steps, how an increase in greenhouse gas concentration leads to climate change.
Model Answer — 1(c)
a higher concentration means more radiation is absorbed and re-emitted back to the surface — the greenhouse effect is enhanced
so the average surface temperature rises — global warming
and global warming can result in climate change: long-run shifts in rainfall, seasons and the frequency of extreme events
⚠ If you missed marks here: global warming and climate change are not synonyms, and Cambridge separates them deliberately. Warming is the rise in average temperature; climate change is what that rise does to long-run weather patterns. An answer that uses the two words interchangeably usually loses the last mark of the chain.
(d)[2]
State the difference between global warming and climate change.
Model Answer — 1(d)
global warming is the rise in average temperature of the Earth’s surface
climate change is the resulting change in long-run weather patterns — rainfall, seasons, extreme events; warming is the cause, the changed climate is the consequence
⚠ If you missed marks here: the order matters — the syllabus phrasing is that global warming can result in climate change. Writing them the other way round, or defining both as "the planet getting hotter", collapses the two ideas into one and earns one mark at most.
Question 2 — Impacts and strategies
Total: 10 marks
(a)[3]
The syllabus lists “melting of ice sheets, glaciers and permafrost, leading to a rise in sea level” as an impact of climate change. Explain why melting of this ice raises sea level, but melting of floating sea ice does not.
Model Answer — 2(a)
ice sheets, glaciers and permafrost are ice held on land — name all three
when they melt, water that was stored on land flows into the sea, adding to its volume (warmer sea water also expands)
floating sea ice is already in the sea displacing its own mass of water, so its melting does not add volume
⚠ If you missed marks here: "the ice caps melt so the sea rises" blurs the distinction the question is testing. The safe answer quotes the syllabus trio — ice sheets, glaciers, permafrost — and says the word land. Land ice adds water to the sea; floating ice was already displacing its own mass.
(b)[3]
Explain what causes ocean acidification, and why it is a different process from acid rain.
Model Answer — 2(b)
more carbon dioxide in the atmosphere means more of it dissolves in sea water
making the water more acidic
acid rain is caused by different gases — sulfur dioxide and oxides of nitrogen — and acidifies lakes, rivers and soils, not the ocean; different gases, different water bodies
⚠ If you missed marks here: "acid rain falls into the sea and makes it acidic" is the classic zero here. Ocean acidification is carbon dioxide dissolving directly into sea water; acid rain is sulfur dioxide and oxides of nitrogen, and its victims are lakes, rivers and soils. Keep the two processes in separate boxes.
(c)[4]
From the syllabus list of strategies to reduce carbon footprints, choose one strategy that reduces the amount of greenhouse gas released and one strategy that removes carbon dioxide from the atmosphere. For each, explain how it works.
Model Answer — 2(c)
reduces release: e.g. reduced use of fossil fuels, energy efficiency, reduction in livestock farming, sustainable food choices, transport policies, taxation
how it works: less combustion (or less cattle digestion and manure) means less gas released — the mechanism must match the strategy chosen
removes carbon dioxide: reforestation and afforestation, or carbon sequestration
how it works: more removal by photosynthesis; or capture and storage of carbon dioxide, for example from power station flue gases into underground stores
⚠ If you missed marks here: only two strategies on the whole list actually remove carbon dioxide — planting trees and carbon sequestration. Everything else reduces what is released. Offering "use less fossil fuel" for the removal half is the standard mix-up, and a mechanism that does not match the named strategy earns nothing.
Question 3 — Ecosystems and forest functions
Total: 10 marks
(a)[2]
Define population and community.
Model Answer — 3(a)
population: all the organisms of one species living in the same area at the same time
community: all the populations of all the species living together in one area
⚠ If you missed marks here: the ladder adds exactly one thing per rung: population = one species in one place; community = all the species in that place. Leaving out "one species" from population, or "all the species" from community, drops the distinguishing word and the mark with it.
(b)[3]
On an island, hares are eaten by lynx. Describe how the numbers of the two species change over time, and explain why the lynx peak always comes after the hare peak.
Model Answer — 3(b)
hare numbers rise, so there is more food, so lynx numbers rise; the increased lynx eat more hares, so hare numbers fall; with less food lynx numbers fall; with fewer lynx the hares recover — a repeating cycle
the two populations rise and fall in linked cycles, with the predator curve following the prey curve
the lag exists because the lynx must eat and breed before their numbers can respond — the population cannot grow the moment food appears
⚠ If you missed marks here: the time lag is the detail that separates a 2-mark answer from full marks. Saying the two cycles "mirror each other" misses it — they are offset, not mirrored, because predators must eat and breed before their numbers respond. Name the lag and say why it exists.
(c)[2]
The producers in a forest fix 200 000 kJ/m²/year. Assuming 10% of energy is transferred at each step, calculate the energy available to a tertiary consumer. Show your working.
Model Answer — 3(c)
200 000 × 0.1 × 0.1 × 0.1   M1 for three transfers of 10%
= 200 kJ/m²/year   A1
producer → primary → secondary → tertiary is three arrows, so three transfers
⚠ If you missed marks here: a tertiary consumer is three arrows from the producer, so 10% applies three times: 20 000, then 2 000, then 200. Applying it twice gives 2 000 — the always-by-one miscount. Write each line of the chain; the method mark survives a slip in the arithmetic.
(d)[3]
Describe the role of a forest in the water cycle, and state what happens to surface run-off when the forest is present.
Model Answer — 3(d)
leaves intercept rain, so it reaches the ground slowly
roots take up water from the soil, and leaves return it to the air by transpiration
all of this reduces surface run-off — interception, uptake, transpiration, run-off are the syllabus’s four words; use them
⚠ If you missed marks here: four technical words carry this answer — interception, uptake, transpiration, run-off — and vague substitutes ("the trees soak up the rain") do not earn their marks. Note the direction of the last one: with the forest present, run-off decreases. It is removing the forest that speeds it up.
SECTION B — source led (Questions 4–6, 30 marks). Quote figures from the sources.
Question 4 — Source A, global temperature anomaly
Total: 10 marks
SOURCE A — Global mean surface temperature anomaly, by decade, 1900s–2020s
-0.4 -0.2 0.0 +0.2 +0.4 +0.6 +0.8 +1.0 -0.30 1900s -0.20 1920s -0.10 1940s -0.05 1960s +0.15 1980s +0.45 2000s +0.85 2020s temperature anomaly / degrees C decade
Each bar is the average for one decade. The anomaly is the difference between that decade’s mean temperature and the mean for a fixed reference period, in degrees Celsius. A negative bar means the decade was cooler than the reference period; a positive bar means warmer.
(a)(i)[1]
Using Source A, identify the decade with the lowest anomaly, and state its value.
Model Answer — 4(a)(i)
the 1900s, at −0.30 °C
the decade and the value, with its sign, are both needed
⚠ If you missed marks here: the lowest value on this chart is the most negative one, not the shortest bar. And the minus sign is part of the answer: 0.30 and −0.30 are different temperatures. Read the sign off the axis, not off the bar’s length.
(a)(ii)[3]
Calculate the difference between the anomaly for the 2020s and the anomaly for the 1900s. Then calculate the average rate of change per year between the 1980s bar and the 2020s bar, taking the bars to be 40 years apart. Show your working.
Model Answer — 4(a)(ii)
0.85 − (−0.30) = 1.15 °C   M1 A1 — subtracting a negative adds
(0.85 − 0.15) ÷ 40 = 0.0175 °C per year   A1
⚠ If you missed marks here: the trap is the negative sign: 0.85 − (−0.30) is 1.15, not 0.55. Subtracting a value below zero adds the two distances from zero. For the rate, the difference is 0.70 °C over 40 years — dividing by the number of bars instead of the number of years is the other common slip.
(b)[3]
Describe the pattern shown in Source A. Use figures from the chart in your answer.
Model Answer — 4(b)
the first four decades shown are all below the reference period — from −0.30 °C in the 1900s to −0.05 °C in the 1960s
from the 1980s the anomalies are positive and rising: +0.15, then +0.45, then +0.85 °C
the rise is accelerating: +0.30 between the 1980s and 2000s bars, +0.40 between the 2000s and 2020s bars (or: every decade shown is warmer than the one before)
1 mark per point, maximum 3; a point with no figure attached caps the answer at 1
⚠ If you missed marks here: the chart has two halves and a good describe names both: below the reference line early, above it late, with the crossover between the 1960s and 1980s. "It gets warmer" with no figures is one mark. Quote a pair of values so the marker can see the comparison you are making.
(c)[2]
The chart shows anomalies rather than actual temperatures. Suggest one advantage of presenting the data this way, and state whether this chart on its own proves that human activity caused the change. Justify your answer.
Model Answer — 4(c)
advantage: an anomaly shows the change directly — small differences are visible against a fixed baseline, and places with different actual temperatures can be combined or compared fairly
no — the chart shows temperature only; it contains no data about greenhouse gases or human activity, so by itself it shows a warming pattern, not its cause; linking cause needs other evidence, such as gas concentration records
⚠ If you missed marks here: this is the AO3 discipline of saying what a source can and cannot support. One variable cannot prove a cause — the chart has no greenhouse gas data in it, so "yes, it proves it" overclaims. The strong answer says what extra evidence would be needed. That sentence is where the mark lives.
(d)[1]
State one other thing that Source A does not tell you.
Model Answer — 4(d)
it does not show how temperature varied within each decade, or between different regions
it does not show any impact — sea level, ice, rainfall, extreme events
it does not state which reference period was used, or how the measurements were made
any one of these scores
⚠ If you missed marks here: averages hide variation — a decade bar says nothing about the years inside it or the places behind it. That single idea generates a valid answer for almost any averaged chart. Do not repeat the cause point if you already used it in (c); the question says other.
Question 5 — Source B, forest loss in Region Z
Total: 10 marks
SOURCE B — Forest area in Region Z, 1990–2020, and the causes of clearance in 2020
Year1990200020102020
Forest area / million hectares62.058.554.650.8
Cause of clearance, 2020Share of area cleared
commercial farming (cattle ranching and cash crops)55%
subsistence farming20%
logging and timber extraction15%
roads and settlements6%
rock, ore and mineral extraction4%
Region Z is mostly tropical forest. Figures are from satellite surveys; the causes table shows the share of the area cleared in 2020 attributed to each activity.
(a)(i)[1]
Using Source B, identify the decade in which forest was lost fastest, and state the area lost in that decade.
Model Answer — 5(a)(i)
2000–2010, a loss of 3.9 million hectares (58.5 to 54.6)
the losses by decade are 3.5, 3.9 and 3.8 — the middle decade is fastest
⚠ If you missed marks here: the table gives areas, not losses — you have to subtract each pair before you can compare. Guessing the most recent decade because "it must be getting worse" fails here: 3.8 is less than 3.9. Do the three subtractions; they take ten seconds and make the mark certain.
(a)(ii)[3]
Calculate the total loss of forest area between 1990 and 2020, and express it as a percentage of the 1990 area. Give the percentage to 3 significant figures. Show your working.
Model Answer — 5(a)(ii)
62.0 − 50.8 = 11.2 million hectares   M1 A1
11.2 ÷ 62.0 × 100 = 18.1%   A1 (18.064… to 3 significant figures; the divisor is the 1990 value)
⚠ If you missed marks here: percentage change divides by the starting value, 62.0 — dividing by 50.8 gives 22.0%, which is wrong. And 18.064… to 3 significant figures is 18.1, not 18.06: significant figures are counted from the first non-zero digit, so 1, 8 and the 0 are the three.
(b)[2]
Describe the trend in forest area shown in the first table. Use figures in your answer.
Model Answer — 5(b)
forest area falls in every decade, from 62.0 to 50.8 million hectares over the thirty years
the rate is roughly steady — 3.5, 3.9 and 3.8 million hectares per decade (about 0.37 million hectares a year); it is not slowing down
⚠ If you missed marks here: direction and rate, always. "It falls" is the direction; the second mark is for what the rate does, and here the honest word is steady — the three decade losses are within 0.4 of each other. Claiming the loss is accelerating misreads 3.8 as bigger than 3.9.
(c)[4]
Using the second table, identify the largest cause of clearance in Region Z, explain why that activity clears such large areas, and explain one impact of the clearance on the soil of the cleared land. Use the chain of causes, not just the label.
Model Answer — 5(c)
largest cause: commercial farming, at 55% of the area cleared — more than all the other causes combined
it clears large areas because cattle ranching and cash crops such as soya and oil palm are grown for sale, so the scale is set by markets, not by a family’s needs — unlike subsistence plots
soil impact: without the canopy, rain strikes bare soil directly and washes it away; without roots, nothing binds the soil in place
so the fertile topsoil is eroded, the ground supports fewer plants, and in dry regions the land can degrade towards desert
⚠ If you missed marks here: "soil erosion" as a bare label is worth one of the two soil marks at most — the explain marks are on the links: no canopy, so rain hits bare soil; no roots, so nothing holds it. And keep subsistence and commercial farming apart: they are different causes with different scales, and the table separates them for exactly that reason.
Question 6 — Using Source A and Source B together
Total: 10 marks
(a)[4]
Climate change appears in the syllabus both as a cause of deforestation and as an impact of it. Using the two sources as illustration, explain how this works as a feedback loop.
Model Answer — 6(a)
as an impact: forest loss (Source B, 11.2 million hectares in Region Z) means less removal of carbon dioxide by photosynthesis, and burning or rotting the felled timber releases stored carbon — both push warming upwards, as in Source A’s rising anomalies
as a cause: rising temperatures and changing rainfall dry forests out, so trees die and fires spread more easily and burn larger areas — forest is lost without anyone clearing it
each process strengthens the other: warming kills forest, and the lost forest adds to the warming — that closed circle is the feedback loop
uses a figure from each source to anchor the two halves (e.g. +0.85 °C in the 2020s; 50.8 million hectares left by 2020)
⚠ If you missed marks here: a feedback answer needs both directions and the join. Most answers give only one arrow — forest loss causes warming — and stop. The syllabus put climate change on both lists deliberately; say the loop out loud: warming kills forest, lost forest feeds warming, so each cycle reinforces the next.
(b)[6]
The government of Region Z proposes a law restricting commercial farming in the remaining forest, arguing this will slow both deforestation and climate change. Using both sources and your own knowledge, discuss the benefits and limitations of this proposal. Reach a judgement.
Model Answer — 6(b)
benefit — targeting: commercial farming is 55% of clearance, the largest single cause, so restricting it addresses more area than any other measure could
benefit — the forest kept: the remaining 50.8 million hectares keeps working as a carbon sink and store, and its water-cycle, soil and biodiversity functions continue
limitation — the other 45%: subsistence farming, logging, roads and mining continue, and the law does nothing about them — at the recent rate a substantial loss would continue
limitation — enforcement and people: a law needs monitoring and enforcement across a huge area; ranchers and farm workers lose income, so without alternatives the clearing may move elsewhere or continue illegally
limitation — scale of the climate claim: Region Z is one region and the warming in Source A is global, driven mostly by fossil fuel combustion; the law can slow the region’s contribution, not the global trend by itself
judgement: a reasoned conclusion that follows, e.g. worth doing because it attacks the largest cause and keeps the sink standing, but its climate effect is regional at best, and it needs enforcement plus support for displaced farming to work at all
⚠ If you missed marks here: the top band asks who bears the cost and over what timescale — here the cost falls on ranchers and farm workers, and that is exactly why enforcement is hard. An answer that treats "pass a law" as the end of the story, or claims one region’s law will change the global curve in Source A, has overclaimed on both counts.

Self-Assessment

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IGCSE Environmental Management 0680 — Unit Exam 2 — 4.2 Climate change, 5.1 Ecosystems, 5.2 Forest ecosystems — Challenge
For examination preparation only. Not an official Cambridge Assessment paper.