IB Diploma · Biology D4.2
IB Biology D4.2: Stab. & Change — Practice Questions & Answers
IB Biology D4.2 Stability and change study notes: ecosystem stability, keystone species, tipping points, biodiversity and human impact.
Here are 10 practice questions with full answers and explanations.
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Practice questions with answers
1
Multiple choice
What is a key property of natural ecosystems that allows them to persist over long periods?
- Stability
- Rapid change
- Constant disturbance
- Low biodiversity
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WhyStability lets natural ecosystems maintain their structure and function over long periods despite disturbances.
2
Multiple choice
What are essential requirements for ecosystem stability?
- Supply of energy, nutrient recycling, genetic diversity
- Rapid species turnover, constant disturbance
- Low energy input, limited nutrient cycling
- Low genetic diversity, extreme climatic variation
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WhyEcosystem stability requires a continuous energy supply, nutrient recycling, and genetic diversity among species.
3
Multiple choice
What is a potential consequence of deforestation of the Amazon rainforest?
- Tipping point in ecosystem stability
- Increased biodiversity
- Enhanced water vapor generation
- Decreased air flows
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WhyAmazon deforestation can push the ecosystem past a tipping point into an irreversible, degraded state.
4
Multiple choice
What type of model can be used to investigate the effect of variables on ecosystem stability?
- Mesocosm
- Microcosm
- Simulation
- Statistical model
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WhyA mesocosm is a small experimental enclosure used to test how variables affect ecosystem stability under controlled conditions.
5
Multiple choice
What type of ecosystem is preferable for mesocosm experiments?
- Aquatic or microbial ecosystems
- Terrestrial ecosystems
- Large-scale ecosystems
- Highly complex ecosystems
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WhyAquatic or microbial ecosystems are preferred for mesocosms because they are small, self-contained, and quick to respond.
6
Multiple choice
What is the disproportionate impact of a species on community structure called?
- Keystone species role
- Dominant species role
- Indicator species role
- Pioneer species role
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WhyA keystone species has a disproportionately large effect on community structure relative to its abundance.
7
Multiple choice
What is the sustainability of resource harvesting dependent on?
- Harvesting rate being lower than replacement rate
- Harvesting rate exceeding replacement rate
- Harvesting rate being independent of replacement rate
- Maximum harvesting rate
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WhyHarvesting is sustainable only when the removal rate stays below the population's natural replacement rate.
8
Multiple choice
What factors affect the sustainability of agriculture?
- Soil erosion, nutrient leaching, pollution
- Increased biodiversity, minimal input
- Rapid resource depletion, high yields
- Low carbon footprint, minimal fertilizer use
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WhyAgricultural sustainability is undermined by soil erosion, nutrient leaching, and pollution from farming practices.
9
Multiple choice
What is the process of nutrient enrichment in aquatic ecosystems due to leaching called?
- Eutrophication
- Biomagnification
- Biodegradation
- Bioaccumulation
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WhyEutrophication is the enrichment of water bodies with leached nutrients, triggering excessive algal growth.
10
Multiple choice
What is a consequence of eutrophication?
- Increased biochemical oxygen demand (BOD)
- Decreased BOD
- Increased water clarity
- Decreased algal blooms
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WhyEutrophication raises biochemical oxygen demand as decomposing algae consume dissolved oxygen, harming aquatic life.
Key terms in Stab. & Change
Stability: The ability of an ecosystem to maintain its structure and function over time and to recover after disturbance.
Biodiversity: The variety of life in an ecosystem, including genetic, species and habitat diversity; generally linked to greater stability.
Keystone species: A species whose effect on its community is far larger than its abundance suggests, so its removal greatly alters the ecosystem.
Tipping point: A threshold beyond which an ecosystem shifts abruptly and often irreversibly into a different stable state.
Resilience: The capacity of an ecosystem to absorb disturbance and return to its original state.
Invasive species: A non-native species that spreads rapidly in a new environment, often harming native species and reducing stability.
Eutrophication: Enrichment of water with nutrients, causing algal blooms that deplete oxygen and damage aquatic ecosystems.
Mesocosm: An enclosed, experimental model ecosystem used to study the conditions required for stability and sustainability.
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