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Ecology and Environment — Free MYP4 Biology Practice Questions
1QuestionEndangered Species and ExtinctionConcept Practice
2 marks~3 minCriterion A
The IUCN Red List classifies species into categories based on extinction risk. Five organisms and their IUCN statuses are listed below.
Giant panda: Vulnerable
Javan rhino: Critically Endangered
Monarch butterfly: Near Threatened
Blue whale: Endangered
Amur leopard: Endangered
Giant panda: Vulnerable
Javan rhino: Critically Endangered
Monarch butterfly: Near Threatened
Blue whale: Endangered
Amur leopard: Endangered
a
Identify the organism listed above that is classified as Critically Endangered by the IUCN. [1]
b
Explain why Critically Endangered represents a more severe conservation concern than Endangered, with reference to the IUCN Red List category structure. [1]
Solutions
2QuestionEndangered Species and ExtinctionConcept Practice
2 marks~3 minCriterion D
A zoo manages a captive breeding programme for the critically endangered Amur leopard. Fewer than 100 individuals survive in the wild, and the species faces ongoing habitat loss in the Russian Far East.
a
Outline how a captive breeding programme works to conserve the Amur leopard. [1]
b
Discuss one limitation that reduces the long-term effectiveness of this conservation approach. [1]
Solutions
3QuestionDeforestation, Urbanization, and Land UseConcept Practice
2 marks~3 minCriterion D
A factory in a forested region emits large quantities of . To offset these emissions, the company funds a reforestation project in a nearby degraded area, planting native tree species across 500 hectares. Critics argue that carbon offset schemes may not represent genuine environmental progress.
a
Describe one way the reforestation project acts as a carbon sink. [1]
b
Evaluate whether carbon offset projects such as this one represent a genuine solution to industrial emissions. [1]
Solutions
4QuestionDeforestation, Urbanization, and Land UseConcept Practice
2 marks~3 minCriterion A
A tropical rainforest food web contains the following organisms:
Producers: trees and shrubs
Primary consumers: insects and caterpillars
Secondary consumers: birds and frogs
Tertiary consumers: jaguars and snakes
Approximately 10% of energy is transferred between each trophic level; the remaining 90% is lost.
Producers: trees and shrubs
Primary consumers: insects and caterpillars
Secondary consumers: birds and frogs
Tertiary consumers: jaguars and snakes
Approximately 10% of energy is transferred between each trophic level; the remaining 90% is lost.
a
State the sequence of energy flow from producers to tertiary consumers, using the terms: producer, primary consumer, secondary consumer, and tertiary consumer. [1]
b
Explain why the number of jaguars in this food web is much smaller than the number of trees and shrubs. [1]
Solutions
5QuestionProducers, Consumers, and DecomposersConcept Practice
2 marks~3 minCriterion A
A pond ecosystem contains three organisms: Organism A (a cattail plant), Organism B (a dragonfly nymph), and Organism C (a crayfish). Crayfish feed on decaying plant and animal material on the pond floor, while dragonfly nymphs are active predators of small invertebrates.
a
Identify the producer in this pond ecosystem. [1]
b
The crayfish is sometimes called a "scavenger" rather than a decomposer. Explain why the crayfish can still be classified as a decomposer in this ecosystem. [1]
Solutions
6QuestionHow Biotic Factors Influence Population SizeConcept Practice
2 marks~3 minCriterion A
The diagram shows a food web in which grass is eaten by rabbits, and rabbits are eaten by foxes.
a
Identify the organism that is a predator of the rabbit. [1]
b
Explain one effect of this predator on the rabbit population size. [1]
Solutions
7QuestionConstructing and Analyzing Food WebsConcept Practice
3 marks~5 minCriterion A
A grassland ecosystem contains the following food chain:
Grass → Rabbits → Foxes → Hawks
Energy available at each trophic level:
Foxes: 100 kJ
Hawks: 10 kJ
Grass → Rabbits → Foxes → Hawks
Energy available at each trophic level:
| Grass | 10 | 000 kJ |
|---|---|---|
| Rabbits | 1 | 000 kJ |
Foxes: 100 kJ
Hawks: 10 kJ
a
State one reason why energy is lost between trophic levels. [1]
b
Using the data above, calculate the percentage of energy transferred from rabbits to foxes. Show your working. [1]
c
Explain why the pattern of energy transfer shown in this food chain means that food chains rarely exceed four or five trophic levels. [1]
Solutions
8QuestionImportance of Biodiversity in EcosystemsAssessment Practice
2 marks~3 minCriterion B
A biologist surveyed amphibian species on five islands in an archipelago.
| Island area () | 1 | 5 | 10 | 20 | 50 |
|---|---|---|---|---|---|
| Number of species | 3 | 7 | 10 | 14 | 20 |
a
Deduce the relationship between island area and amphibian species richness shown by these data. [1]
b
A conservation agency plans to protect a sixth island of 30 . Interpret the data to justify a predicted species count for this island, and explain how habitat loss on this island could affect species richness across the wider archipelago. [1]
Solutions
9QuestionEndangered Species and ExtinctionAssessment Practice
4 marks~6 minCriterion A
A conservation biologist records the following data for a critically monitored bird species:
Mature individuals: 250
Population decline over the last 10 years: 80%
Geographic range: 15,000 km²
Probability of extinction in the wild within 20 years: 25%
Mature individuals: 250
Population decline over the last 10 years: 80%
Geographic range: 15,000 km²
Probability of extinction in the wild within 20 years: 25%
a
State the IUCN population size reduction threshold that defines the Critically Endangered category. [1]
b
Using the population size reduction criterion, deduce the IUCN Red List classification for this species. [1]
c
Evaluate whether the geographic range and probability of extinction data alter the final classification of this species. [2]
Solutions
10QuestionImportance of Biodiversity in EcosystemsAssessment Practice
3 marks~5 minCriterion C
The graph "Biodiversity and Ecosystem Resistance" shows plant species richness (x-axis, 0–20 species) plotted against biomass recovery after drought (y-axis, 0%–100%). The relationship is non-linear: biomass recovery rises steeply between 1 and 8 species, then levels off toward 100% as richness approaches 20 species.
a
Describe the trend shown in the graph. [1]
b
Explain how a greater variety of plant species increases a grassland ecosystem's resistance to drought. [1]
c
Discuss the limitations of concluding from this graph alone that high plant species richness will always protect a grassland ecosystem against drought. [1]
Solutions
11QuestionThreats to Biodiversity: Habitat Loss, Pollution, Climate ChangeAssessment Practice
6 marks~9 minCriterion D
The Red Knot (Calidris canutus) is a migratory shorebird that breeds in the Arctic and winters in Australia, stopping at intertidal mudflats along the East Asian–Australasian Flyway to feed. Climate-driven sea-level rise and altered sediment patterns have caused a 70% population decline at one key stopover site over 30 years. Local communities depend on birdwatching ecotourism and traditional fishing of the same intertidal invertebrates that Red Knots consume.
a
Explain how continued mudflat loss threatens both local ecotourism revenue and traditional fishing practices. [2]
b
Describe the trophic cascade that could result if Red Knot populations collapse, and explain how this would affect intertidal ecosystem function. [2]
c
Evaluate the use of climate model predictions in planning conservation strategies for the Red Knot, including one specific limitation of these models for projections beyond 2050. [2]
Solutions
12QuestionImportance of Biodiversity in EcosystemsAssessment Practice
5 marks~8 minCriterion C
In a long-term grassland experiment, 20 plots were established with species richness ranging from 1 to 20 plant species. Biomass stability — measured as the inverse of the coefficient of variation , where higher values indicate greater stability — was recorded over five years, including two drought years. The graph shows a positive correlation: stability rises from approximately 2 at 1 species to approximately 8 at 20 species, with a best-fit line and visible scatter around it.
a
Describe the pattern shown in the graph. [1]
b
Explain one mechanism — either functional redundancy or species complementarity — that could account for this pattern. [2]
c
Evaluate whether this experimental evidence supports the hypothesis that higher biodiversity increases ecosystem resilience to drought. [2]
Solutions
13QuestionThreats to Biodiversity: Habitat Loss, Pollution, Climate ChangeAssessment Practice
2 marks~3 minCriterion A
Figure 1 shows a satellite image of the Amazon rainforest. In the foreground, a large area of forest has been cleared and replaced by cattle pasture. A jaguar (Panthera onca) is visible at the forest edge.
a
State the level of biological organisation at which habitat loss most directly reduces jaguar numbers by cutting off breeding individuals from one another. [1]
b
Explain how this isolation threatens the long-term survival of the jaguar population. [1]
Solutions
14QuestionDeforestation, Urbanization, and Land UseAssessment Practice
6 marks~9 minCriterion D
A government plans to replace a diverse natural forest with large-scale eucalyptus plantations for timber production. Eucalyptus monocultures are known to consume significantly more groundwater than natural forests and support far fewer native species. Local communities currently depend on the natural forest for food, medicinal plants, and income from sustainable harvesting.
a
Explain two ecological consequences of replacing the natural forest with a eucalyptus monoculture. [2]
b
Analyse how the loss of the natural forest disrupts the ecological relationships that previously supported stable ecosystem functioning. [2]
c
Evaluate the ethical obligations of the government towards local communities affected by this land-use change. [2]
Solutions
15QuestionSustainable Practices and Renewable EnergyAssessment Practice
6 marks~9 minCriterion B
Decomposition of organic waste under different conditions produces different quantities of methane (), a potent greenhouse gas. A controlled study compared three waste management methods over 60 days.
Decomposition rate (g waste/day): Untreated landfill = 5, Compost pile (aerobic) = 12, Anaerobic digester = 20
produced (g per kg waste): Untreated landfill = 80, Compost pile (aerobic) = 5, Anaerobic digester = 30
Decomposition rate (g waste/day): Untreated landfill = 5, Compost pile (aerobic) = 12, Anaerobic digester = 20
produced (g per kg waste): Untreated landfill = 80, Compost pile (aerobic) = 5, Anaerobic digester = 30
a
Describe the pattern in decomposition rate across the three methods. [2]
b
Deduce a general rule linking decomposition rate to production, and identify any exception in the data. [2]
c
Evaluate which method is most effective at reducing greenhouse gas emissions, using evidence from the data and your rule from (b). [2]
Solutions
16QuestionDeforestation, Urbanization, and Land UseAssessment Practice
6 marks~9 minCriterion A
The diagram below shows a tropical forest soil profile before and after deforestation. Before deforestation: a thick leaf litter layer is present, decomposer populations (fungi and bacteria) are large, and nutrient levels are high. After deforestation: leaf litter is absent, decomposer populations are greatly reduced, and nutrient levels are low.
a
State the role of leaf litter in maintaining decomposer populations in the soil. [1]
b
Explain how the loss of leaf litter leads to a decrease in soil fertility, referring to nutrient cycling in your answer. [2]
c
Analyse how decreased soil fertility affects the long-term recovery of the forest ecosystem, considering both vegetation re-establishment and ecological succession. [3]
Solutions
17QuestionSustainable Practices and Renewable EnergyAssessment Practice
7 marks~11 minCriterion C
A field trial compared two fertilizer treatments over 12 months. Plot A received traditional fertilizer; Plot B received algae-based biofuel byproduct fertilizer. Soil organic carbon (SOC) was measured monthly.
Plot A: SOC increased from 8 g/kg (month 0) to 45 g/kg (month 12).
Plot B: SOC increased from 2 g/kg (month 0) to 60 g/kg (month 12).
Plot A: SOC increased from 8 g/kg (month 0) to 45 g/kg (month 12).
Plot B: SOC increased from 2 g/kg (month 0) to 60 g/kg (month 12).
a
Describe the trend in SOC content for each plot over the 12-month period. [2]
b
Using the data, explain whether Plot B shows greater carbon sequestration than Plot A. [3]
c
Analyse one limitation of this experimental design and explain how addressing it would affect the reliability of the conclusion. [2]
Solutions
18QuestionClimate Action and Global CitizenshipAssessment Practice
6 marks~9 minCriterion C
The table below shows changes in atmospheric concentration (ppm), global average temperature anomaly (°C), and ocean surface pH from 1960 to 2020.
| Year | 1960 | 1970 | 1980 | 1990 | 2000 | 2010 | 2020 |
|---|---|---|---|---|---|---|---|
| (ppm) | 317 | 326 | 339 | 354 | 369 | 390 | 414 |
| Temperature anomaly (°C) | 0.03 | 0.02 | 0.19 | 0.37 | 0.39 | 0.65 | 0.92 |
| Ocean pH | 8.10 | 8.08 | 8.06 | 8.04 | 8.02 | 8.00 | 7.98 |
a
Describe the relationship between concentration and temperature anomaly shown in the data. [2]
b
Explain how increasing atmospheric causes ocean acidification, using the chemical reactions involved. [3]
c
A marine biologist argues that the pH change from 8.10 to 7.98 is too small to affect marine life significantly. Using the data and your knowledge of ocean chemistry, evaluate this claim. [1]
Solutions
19QuestionDeforestation, Urbanization, and Land UseAssessment Practice
8 marks~12 minCriterion D
A proposal has been made to convert a 50-year-old secondary forest in Costa Rica into a palm oil plantation. The site supports over 200 bird species, stores an estimated 300 tonnes of carbon per hectare above ground, and serves as the dry-season water source for the Indigenous Bribri community. The developer argues that satellite imagery showing canopy gaps across more than 30% of the area proves the forest is 'degraded', and that the plantation will create 500 local jobs and reduce palm oil imports from deforested regions in Southeast Asia.
a
Identify TWO environmental impacts of replacing this forest with a palm oil plantation. For each impact, refer to a specific ecological concept. [2]
b
Identify TWO societal impacts on the Bribri community, linking each impact to their specific dependence on the forest. [2]
c
Evaluate the developer's use of satellite imagery alone to classify the forest as 'degraded'. In your response, discuss at least TWO limitations of relying solely on remote-sensing data for this environmental impact assessment. [4]
Solutions
20QuestionDefinition and Components of an EcosystemAssessment Practice
2 marks~3 minCriterion B
The table below lists biotic and abiotic components for five ecosystems.
| Pond — Biotic: fish, algae, frogs, insects | Abiotic: water, sunlight, soil, rocks |
|---|---|
| Forest — Biotic: trees, deer, birds, fungi | Abiotic: sunlight, soil, air, water |
| Grassland — Biotic: grasses, rabbits, snakes, insects | Abiotic: sunlight, soil, air, water |
| Desert — Biotic: cacti, lizards, insects, snakes | Abiotic: sunlight, sand, air, water |
| Coral reef — Biotic: coral, fish, algae, sea turtles | Abiotic: sunlight, saltwater, rocks, sand |
a
Identify one pattern in how biotic and abiotic components are represented across all five ecosystems, and explain what this suggests about the completeness of the table. [1]
b
A deep-ocean hydrothermal vent is proposed as a sixth ecosystem. Deduce one biotic component and one abiotic component that would likely appear in this ecosystem's entry, justifying your choices with reference to both the ecological conditions of a hydrothermal vent and the pattern identified in part (a). [1]
Solutions
21QuestionLimiting Factors and Ecosystem StabilityAssessment Practice
5 marks~8 minCriterion D
The line graph shows population changes of wolves, elk, and vegetation in Yellowstone National Park over 20 years following wolf reintroduction in 1995. Data are recorded every two years.
| Year | 1995 | 1997 | 1999 | 2001 | 2003 | 2005 | 2007 | 2009 | 2011 | 2013 | 2015 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Wolves (individuals) | 10 | 20 | 50 | 80 | 100 | 120 | 110 | 90 | 80 | 70 | 60 |
| Elk (thousands) | 20 | 18 | 15 | 12 | 10 | 8 | 9 | 11 | 13 | 14 | 15 |
| Vegetation cover (percent) | 30 | 32 | 38 | 42 | 48 | 52 | 50 | 46 | 44 | 42 | 40 |
a
Describe the trends in elk population and vegetation cover between 1995 and 2015. [2]
b
Using the terms limiting factor, carrying capacity, and trophic cascade, explain how wolf population changes drove the patterns observed in elk and vegetation. [2]
c
By 2015, wolf numbers had stabilised at 60 individuals yet elk numbers had not returned to their 1995 level of 20,000. Evaluate one ecological explanation for why the elk carrying capacity in 2015 differed from that in 1995. [1]
Solutions
22QuestionLimiting Factors and Ecosystem StabilityAssessment Practice
4 marks~6 minCriterion A
A kelp forest ecosystem contains three organisms linked in a food chain: kelp → sea urchins → sea otters. Sea otters prey on sea urchins; sea urchins graze on kelp. A disease reduces the sea otter population by approximately 70% over two years. Kelp coverage subsequently falls to less than 10% of its original extent.
a
Deduce the sequence of population changes in sea urchins and kelp following the decline in sea otters. [2]
b
Explain how sea otters function as a biotic limiting factor for the sea urchin population, and predict what the near-disappearance of kelp reveals about the upper limit of sea urchin population growth. [2]
Solutions
23QuestionDefinition and Components of an EcosystemAssessment Practice
11 marks~17 minCriterion D
In 1995, gray wolves were reintroduced to Yellowstone National Park after a 70-year absence. Wolves preyed on elk, which had overgrazed streamside vegetation. Elk populations declined and their behaviour changed, allowing willow and aspen to recover along streams. This triggered a cascade of changes: beaver populations increased, songbird habitat improved, and soil erosion decreased. The reintroduction generated significant ecotourism revenue for local communities but caused conflict with ranchers whose livestock were occasionally killed by wolves.
a
Identify the trophic level of wolves in this ecosystem and explain how their reintroduction affected producers and primary consumers. Use evidence from the stimulus. [3]
b
Apply the concept of a trophic cascade to explain how wolf reintroduction led to increased beaver populations and reduced soil erosion. [4]
c
Evaluate whether the ecological benefits of wolf reintroduction justify the socioeconomic costs, considering the perspectives of at least two stakeholder groups. [4]
Solutions
24QuestionDefinition and Components of an EcosystemAssessment Practice
6 marks~9 minCriterion C
In 1995, wolves were reintroduced into Yellowstone National Park. Population data were recorded at five-year intervals.
Year: 1990 / 1995 / 2000 / 2005 / 2010 / 2015
Wolves: 0 / 0 / 118 / 171 / 97 / 98
Elk (thousands): 19 / 17 / 12 / 9 / 6 / 5
Aspen recruitment (stems per hectare): 0 / 0 / 2 / 5 / 8 / 10
Year: 1990 / 1995 / 2000 / 2005 / 2010 / 2015
Wolves: 0 / 0 / 118 / 171 / 97 / 98
Elk (thousands): 19 / 17 / 12 / 9 / 6 / 5
Aspen recruitment (stems per hectare): 0 / 0 / 2 / 5 / 8 / 10
a
Analyse the data to describe the population trends for wolves, elk, and aspen recruitment between 1990 and 2015. [2]
b
Explain how the removal of wolves from a currently stable ecosystem would affect elk and aspen recruitment, using the concept of trophic cascades. [2]
c
Evaluate whether the data alone are sufficient to conclude that wolves caused the observed changes in elk and aspen recruitment. [2]
Solutions
25QuestionBiomass Pyramids and Energy PyramidsAssessment Practice
2 marks~3 minCriterion C
A conservation team is restoring a wetland to support 10 bitterns (apex predators). Each bittern requires approximately 200 kg of fish per year; each kilogram of fish biomass requires approximately 10 kg of marsh plants to produce.
a
Calculate the minimum mass of marsh plants needed annually to sustain the 10 bitterns. Show your working. [1]
b
The team uses a simple energy pyramid to plan the required marsh plant area. Discuss one limitation of this model that could cause the team to underestimate or overestimate the area of marsh plants actually needed. [1]
Solutions
26QuestionDefinition and Components of an EcosystemAssessment Practice
5 marks~8 minCriterion D
The diagram below shows a simple forest ecosystem with four labelled organisms: grass, rabbit, fox, and decomposer fungi.
a
Identify the producer in this ecosystem. [1]
b
The rabbit feeds on grass, and the fox feeds on the rabbit. Deduce the trophic level occupied by the fox, and explain how energy is lost between each trophic level. [2]
c
A disease eliminates the fox population entirely. Analyse how this change would affect the populations of both rabbits and grass over time, referring to the balance of the ecosystem. [2]
Solutions
27QuestionEcosystem Changes Due to Natural and Human CausesAssessment Practice
8 marks~12 minCriterion D
Study the data below showing changes in the Amazon rainforest from 1970 to 2020.
| Year | 1970 | 1980 | 1990 | 2000 | 2010 | 2020 |
|---|---|---|---|---|---|---|
| Deforested area (million hectares) | 10 | 25 | 50 | 70 | 85 | 95 |
| Atmospheric (ppm) | 325 | 338 | 354 | 369 | 390 | 414 |
| Local annual rainfall (mm) | 2200 | 2150 | 2050 | 1950 | 1850 | 1700 |
a
Describe the overall trend shown by each of the three variables over the 50-year period. [2]
b
Explain how deforestation in the Amazon increases atmospheric concentration and contributes to global warming. [2]
c
Evaluate the use of satellite data to predict how continued deforestation might reduce local rainfall and trigger further forest loss. In your answer, identify one strength and two limitations. [4]
Solutions
28QuestionHow Biotic Factors Influence Population SizeAssessment Practice
5 marks~8 minCriterion B
A 20-year study tracked snowshoe hare and Canadian lynx populations in a boreal forest.
A biologist hypothesises that lynx population size is controlled solely by hare availability.
| Year | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hare population (thousands) | 20 | 30 | 40 | 80 | 60 | 50 | 40 | 20 | 25 | 70 | 75 | 85 | 80 | 70 | 60 | 20 | 20 | 30 | 40 | 90 |
| Lynx population (thousands) | 4 | 6 | 8 | 10 | 20 | 18 | 16 | 12 | 6 | 8 | 10 | 20 | 18 | 16 | 14 | 6 | 6 | 8 | 10 | 18 |
A biologist hypothesises that lynx population size is controlled solely by hare availability.
a
Describe the relationship between the hare and lynx populations, using specific values from the data. [2]
b
Identify the time lag in the lynx population's response to changes in hare population size, and explain what biological process this lag reflects. [1]
c
Evaluate the biologist's hypothesis using the concept of time-delayed density dependence. [2]
Solutions
29QuestionEcosystem Changes Due to Natural and Human CausesAssessment Practice
3 marks~5 minCriterion A
A graph shows plant species recovery in two forest plots over 10 years following different disturbances. In the volcanic eruption plot, species richness begins at 5 in year 1 and rises steadily to 30 by year 10. In the clear-cut plot, species richness begins at 0 in year 1 and reaches only 15 by year 10.
a
Describe the difference in recovery between the two plots. [1]
b
Explain why the volcanic eruption plot recovers more rapidly, referring to soil seed banks and surviving root systems. [1]
c
Analyse why clear-cutting results in slower and less complete recovery than volcanic eruption, despite both being severe disturbances. [1]
Solutions
30QuestionAdaptations to Environmental ConditionsAssessment Practice
2 marks~3 minCriterion D
A conservation biologist plans to reintroduce the desert kangaroo rat (Dipodomys deserti) into a restored habitat that has experienced prolonged drought. The kangaroo rat produces highly concentrated urine through elongated loops of Henle that maximise water reabsorption.
a
Outline how this kidney adaptation allows the kangaroo rat to survive in a water-scarce environment. [1]
b
Discuss one ethical issue a conservation biologist must consider before releasing kangaroo rats into a habitat where water availability remains unreliable. [1]
Solutions
31QuestionAdaptations to Environmental ConditionsAssessment Practice
4 marks~6 minCriterion C
The diagram shows a cactus with two labelled features: Feature X (spines, which are modified leaves) and Feature Y (a thick, waxy stem).
a
Explain how Feature X reduces water loss in a hot, dry environment. [1]
b
Explain how Feature Y reduces water loss in a hot, dry environment. [1]
c
A student claims that replacing the spines with broad, flat leaves would make the cactus better adapted to its desert environment because leaves carry out more photosynthesis. Evaluate this claim. [2]
Solutions
32QuestionAdaptations to Environmental ConditionsAssessment Practice
6 marks~9 minCriterion C
The diagram shows a polar bear and a fennec fox. The polar bear lives in the Arctic and has thick fur, a subcutaneous blubber layer, and small ears. The fennec fox lives in the Sahara Desert and has large ears, thin fur, and a slender body.
a
Describe how the polar bear's thick fur and blubber layer each help it survive in the Arctic. [2]
b
Explain how the fennec fox's large ears help it lose heat in the desert. [2]
c
A student claims that the polar bear's small ears and the fennec fox's large ears are both adaptations to the same underlying physiological principle. Evaluate this claim. [2]
Solutions
33QuestionAdaptations to Environmental ConditionsAssessment Practice
4 marks~6 minCriterion D
The Wollemi pine (Wollemia nobilis) is a critically endangered tree found only in a remote Australian canyon. Climate change is making its habitat warmer and drier, threatening its survival. Scientists are considering assisted migration: relocating seedlings to a cooler, wetter Tasmanian forest outside the species' natural range.
a
Explain two ecological risks of introducing the Wollemi pine to a new ecosystem in Tasmania. [2]
b
Discuss the ethical dilemma between allowing the Wollemi pine to go extinct naturally and intervening through assisted migration. In your answer, refer to both the value of biodiversity and the precautionary principle. [2]
Solutions
34QuestionConstructing and Analyzing Food WebsAssessment Practice
6 marks~9 minCriterion B
Population data for four species in a coastal ecosystem:
Year: 2019 / 2020 / 2021 / 2022 / 2023
Kelp (thousands): 120 / 90 / 60 / 80 / 110
Sea urchins (thousands): 10 / 25 / 40 / 20 / 12
Sea otters (thousands): 4 / 2 / 1 / 3 / 5
Orcas (thousands): 1 / 1 / 2 / 3 / 4
Year: 2019 / 2020 / 2021 / 2022 / 2023
Kelp (thousands): 120 / 90 / 60 / 80 / 110
Sea urchins (thousands): 10 / 25 / 40 / 20 / 12
Sea otters (thousands): 4 / 2 / 1 / 3 / 5
Orcas (thousands): 1 / 1 / 2 / 3 / 4
a
Identify the predator–prey relationships in this food web, listing each pair as predator → prey. [2]
b
Describe the relationship between sea urchin and kelp populations from 2019 to 2021, using data to support your answer. [2]
c
Analyse how the data from 2021 to 2023 support the conclusion that orcas act as a keystone predator in this ecosystem. [2]
Solutions
35QuestionDisruption of Food WebsAssessment Practice
8 marks~12 minCriterion D
In the 1950s, Nile perch (Lates niloticus) were introduced into Lake Victoria, one of Africa's largest freshwater lakes and home to hundreds of endemic cichlid species. The lake had supported thriving small-scale fisheries for generations. Following the introduction, dramatic ecological and social changes unfolded over subsequent decades, with consequences still felt today.
a
Describe the changes to Lake Victoria's food web that resulted from the establishment of Nile perch, including effects on cichlid populations and trophic structure. [3]
b
Analyse the societal and economic consequences for local fishing communities that had depended on the native cichlid fishery. [3]
c
Evaluate the decision to introduce Nile perch without prior ecosystem modelling, and assess what this case reveals about managing future species introduction proposals. [2]
Solutions
36QuestionBioaccumulation and ToxinsAssessment Practice
8 marks~12 minCriterion D
A coastal community depends on fishing for food and income. Industrial runoff has introduced mercury, a persistent toxin, into the local bay. Mercury concentrations measured across the food chain are:
Plankton: ppm
Small fish: ppm
Large fish: ppm
Sharks: ppm
The community harvests large fish and sharks as traditional food and for export.
Plankton: ppm
Small fish: ppm
Large fish: ppm
Sharks: ppm
The community harvests large fish and sharks as traditional food and for export.
a
Describe the pattern of mercury concentration across the four trophic levels and explain one direct consequence for shark populations. [2]
b
Analyse the impacts of mercury contamination on the local economy and public health. [3]
c
Evaluate the limitations of this food chain model for predicting the real-world spread of mercury in the bay. [3]
Solutions
37QuestionEnergy Loss at Each Trophic LevelAssessment Practice
4 marks~6 minCriterion A
A grassland ecosystem contains the following food chain with measured biomass values:
Grass → Grasshopper → Frog → Hawk
Biomass at each trophic level:
Frog: 100 kg
Hawk: 10 kg
Grass → Grasshopper → Frog → Hawk
Biomass at each trophic level:
| Grass | 10 | 000 kg |
|---|---|---|
| Grasshopper | 1 | 000 kg |
Frog: 100 kg
Hawk: 10 kg
a
Calculate the percentage of biomass transferred from grass to grasshopper, and from grasshopper to frog. [2]
b
Explain why only approximately 10% of biomass is transferred between trophic levels, referring to specific processes by which energy is lost. [1]
c
The hawk population in this ecosystem declines sharply due to disease. Analyse how this change would affect biomass distribution across the remaining trophic levels. [1]
Solutions
38QuestionDisruption of Food WebsAssessment Practice
3 marks~5 minCriterion C
The graph below shows the population dynamics of a native rabbit species and an introduced fox population in a grassland ecosystem over 10 years.
- x-axis: Year (0–10)
- y-axis: Population (thousands, 0–100)
- Rabbit population (solid line): starts at 80,000; declines to 20,000 by year 5; stabilises near 25,000
- Fox population (dashed line): starts at 5,000; rises to 60,000 by year 4; declines to 30,000 by year 10
- x-axis: Year (0–10)
- y-axis: Population (thousands, 0–100)
- Rabbit population (solid line): starts at 80,000; declines to 20,000 by year 5; stabilises near 25,000
- Fox population (dashed line): starts at 5,000; rises to 60,000 by year 4; declines to 30,000 by year 10
a
Describe the relationship between the rabbit and fox populations shown in the graph. [1]
b
Explain how the introduction of the fox disrupts the stability of the original food web. [1]
c
Discuss the cascading effects that the decline in rabbit population could have on other species within the grassland food web. [1]
Solutions
39QuestionConstructing and Analyzing Food WebsAssessment Practice
8 marks~12 minCriterion D
A biotechnology company proposes releasing a genetically modified (GM) mosquito into a tropical rainforest ecosystem. The GM mosquito suppresses a disease-carrying mosquito species but also competes with native insects for nectar from a keystone plant species — a primary food source for several native insect populations. The food web includes: keystone plants (producers) → native insects (primary consumers) → birds and small mammals (secondary consumers) → jaguar (apex predator).
a
Identify two feeding relationships in the food web that would be directly disrupted by the GM mosquito's competition for nectar. [2]
b
Explain how the disruption of native insect populations could trigger a trophic cascade affecting the jaguar population. [3]
c
Evaluate the reliability of laboratory-based risk assessments for predicting the long-term ecological effects of releasing the GM mosquito into the rainforest. [3]
Solutions
40QuestionDisruption of Food WebsAssessment Practice
5 marks~8 minCriterion C
In a coastal ecosystem, researchers tested whether sea otters act as a keystone species controlling sea urchin populations. Two fenced areas were established: a control area (otters present) and an experimental area (otters removed). After two years, the following data were recorded:
Control area: sea urchin density ; species richness species
Experimental area: sea urchin density ; species richness species
Control area: sea urchin density ; species richness species
Experimental area: sea urchin density ; species richness species
a
Define the term keystone species. [1]
b
Analyse the data to explain how the removal of sea otters affected species richness in the kelp forest. [2]
c
Evaluate whether the experimental evidence supports the hypothesis that sea otters are a keystone species, identifying two limitations of the experimental design that affect the strength of this conclusion. [2]
Solutions