IB Biology Quiz: Understand Climate Change
20 questions · exam conditions
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Understand Climate ChangeQuestion 1 of 20

[HL only] A butterfly species has evolved to lay its eggs on a specific host plant just as its leaves emerge in spring. Due to climate change, the plant's leaves are now emerging two weeks earlier on average, but the butterfly's egg-laying cue, day length, has not changed. This situation is best described as:

a phenological mismatch leading to synchrony disruption.
competitive exclusion between the butterfly and another insect.
a geographical range shift of the butterfly population.
an example of stabilizing selection acting on the host plant.
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IB Biology Quiz

IB Biology Quiz: Understand Climate Change

Practice Understand Climate Change in IB Biology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

What this quiz covers

This quiz focuses on Understand Climate Change, giving you a quick way to practice the rules, question types, and explanations that matter most for IB Biology.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

[HL only] A butterfly species has evolved to lay its eggs on a specific host plant just as its leaves emerge in spring. Due to climate change, the plant's leaves are now emerging two weeks earlier on average, but the butterfly's egg-laying cue, day length, has not changed. This situation is best described as:

  1. a phenological mismatch leading to synchrony disruption. (correct answer)
  2. competitive exclusion between the butterfly and another insect.
  3. a geographical range shift of the butterfly population.
  4. an example of stabilizing selection acting on the host plant.
Explanation: The correct answer is A. Phenology is the study of the timing of recurring biological events. The plant's leaf emergence and the butterfly's egg-laying are phenological events. Because the plant's timing has shifted in response to temperature cues while the butterfly's has not (being cued by day length), their interaction is now out of sync. This is termed synchrony disruption. B is incorrect as there is no mention of competition. C describes a change in location, not timing. D describes a mode of natural selection, which is not what the scenario is directly illustrating.

Question 2

Long-term data show a strong positive correlation between atmospheric CO₂ concentrations and average global temperatures. From a scientific perspective, what is the most appropriate conclusion to draw from this correlation alone?

  1. The correlation proves that rising CO₂ concentrations are the sole cause of the observed increase in global temperatures.
  2. The relationship is purely coincidental, and another unknown factor must be responsible for both increases.
  3. The correlation suggests a strong association, which is supported by a known physical mechanism (the greenhouse effect), making a causal link highly probable. (correct answer)
  4. The correlation demonstrates that rising global temperatures cause an increase in atmospheric CO₂ concentrations through outgassing from oceans.
Explanation: The correct answer is C. This reflects proper scientific reasoning (Nature of Science). Correlation does not, by itself, prove causation. However, when a strong correlation is coupled with a well-understood physical mechanism (the greenhouse effect), the evidence for a causal relationship becomes very strong. A is too strong a statement; correlation alone does not prove causation, and other factors can influence climate. B is incorrect because dismissing the correlation is unwarranted given the known physics. D describes a feedback mechanism that does exist (warmer oceans hold less CO₂), but it is not the primary driver of the current rapid increase in CO₂; anthropogenic emissions are.

Question 3

Which of the following describes a scenario of carbon sequestration?

  1. The burning of fossil fuels in a power plant, which converts solid carbon into gaseous carbon dioxide.
  2. The growth of a large forest, where trees incorporate atmospheric carbon dioxide into their biomass through photosynthesis. (correct answer)
  3. The decomposition of organic matter by methanogenic archaea in a landfill, releasing methane into the atmosphere.
  4. The cultivation of rice in paddies, which releases significant quantities of methane due to anaerobic conditions in the soil.
Explanation: The correct answer is B. Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. Photosynthesis by plants, especially in a growing forest, removes CO₂ from the atmosphere and stores it as organic carbon in wood, leaves, and roots. A, C, and D all describe processes that release carbon compounds (CO₂ or CH₄) into the atmosphere, which are sources of carbon, not sequestration sinks.

Question 4

[HL only] The timing of flowering in a certain plant species is determined by the accumulation of 'growing degree days' (a measure of heat). In response to a warmer climate, the species begins to flower earlier in the spring. This is an example of:

  1. directional selection for genes that cause early flowering.
  2. sympatric speciation driven by changes in reproductive timing.
  3. a genetic bottleneck caused by high temperatures killing late-flowering individuals.
  4. phenotypic plasticity, as the flowering time changes in response to environmental cues without genetic change. (correct answer)
Explanation: The correct answer is B. Phenotypic plasticity is the ability of one genotype to produce more than one phenotype when exposed to different environments. In this case, the plants' genetic makeup for flowering is not changing, but the environmental cue (heat accumulation) is being met earlier in the year, causing the phenotype (flowering time) to change. A describes an evolutionary change, which might happen over many generations, but the immediate response described is plasticity. C is a mechanism of genetic drift, not the direct explanation for the shift in timing. D is a mode of speciation, which is a much larger-scale outcome than the shift in flowering time for a single species.

Question 5

[HL only] Asynchronous phenological shifts between species can disrupt ecological interactions. Which is the most likely consequence if a flowering plant shifts its flowering time earlier due to warming, but its specialist insect pollinator does not?

  1. Both the plant and pollinator populations will likely decline due to reproductive failure. (correct answer)
  2. The pollinator will switch to a different food source, and the plant will evolve to self-pollinate.
  3. The plant will benefit from a longer growing season, and the pollinator will be unaffected as it can enter diapause.
  4. Both species will exhibit phenotypic plasticity, allowing them to rapidly re-synchronize their life cycles within a single season.
Explanation: The correct answer is A. This describes a classic case of synchrony disruption. The plant may not be pollinated, leading to reduced seed set and reproductive failure. The specialist pollinator, emerging after the flowers have faded, will have lost its primary food source, leading to starvation and its own reproductive failure. B is too speculative; switching food sources may not be possible for a specialist, and evolving self-pollination is a slow process. C is incorrect as the plant's potential benefit is negated by pollination failure, and the pollinator is directly and negatively affected. D is unlikely; if the species are cued by different things (e.g., temperature for the plant, day length for the insect), they cannot simply choose to re-synchronize.

Question 6

Rewilding is an approach to conservation that aims to restore ecosystem processes. How can the reintroduction of a keystone species, such as the wolf, contribute to mitigating climate change effects at a local level?

  1. Wolves directly consume atmospheric CO₂ as part of their metabolic processes, reducing greenhouse gas levels.
  2. Wolves are a major source of methane, and their reintroduction increases greenhouse gas emissions, worsening climate change.
  3. The presence of wolves increases the albedo of the landscape, reflecting more solar radiation back into space.
  4. By controlling herbivore populations, wolves can prevent overgrazing, allowing forests to regenerate and sequester more carbon. (correct answer)
Explanation: The correct answer is B. This describes a trophic cascade. By preying on large herbivores like deer or elk, wolves can reduce grazing pressure on young trees. This allows forests to grow and regenerate more effectively. Healthy, growing forests are significant carbon sinks, sequestering atmospheric CO₂ in their biomass. A is biologically impossible. C is incorrect; wolves do not significantly change the landscape's albedo. D is incorrect; while animals produce some methane, it is negligible compared to the positive effect on carbon sequestration from forest regeneration.

Question 7

Some proposals for climate change mitigation involve 'carbon capture and storage' (CCS), where CO₂ from industrial sources is captured and injected into deep geological formations. What is a primary environmental concern associated with this technology?

  1. The process requires large amounts of water, potentially straining local freshwater resources.
  2. The underground reservoirs of CO₂ will spontaneously combust, causing widespread fires and explosions.
  3. The injection process releases other, more potent greenhouse gases, such as sulfur hexafluoride.
  4. The captured CO₂ could potentially leak back into the atmosphere over long timescales or through seismic activity. (correct answer)
Explanation: The correct answer is B. A major challenge and concern for geological sequestration is ensuring the long-term permanence of the storage. There is a risk that geological instability, fractures, or improperly sealed injection sites could allow the stored CO₂ to leak back into the atmosphere, negating the climate benefit. A is a potential issue, but the primary environmental concern is the integrity of the storage. C is incorrect; the process is designed to store CO₂, not release other gases. D is incorrect; CO₂ is not flammable and will not combust.

Question 8

The thawing of Arctic permafrost is a major concern in climate science as it can initiate a positive feedback loop. Which statement accurately describes the mechanism of this loop?

  1. Thawing permafrost releases trapped methane, a greenhouse gas, which causes further atmospheric warming, leading to more permafrost thawing. (correct answer)
  2. Increased atmospheric CO₂ causes warming, which melts permafrost, allowing for the growth of tundra vegetation that absorbs atmospheric CO₂, thus cooling the planet.
  3. Melting permafrost increases local water vapour, which acts as a greenhouse gas, but this effect is localized and does not contribute to global feedback.
  4. The decomposition of organic matter in thawing permafrost consumes oxygen, which depletes atmospheric ozone and enhances incoming solar radiation.
Explanation: The correct answer is A. This describes the complete positive feedback cycle: warming -> thawing -> release of greenhouse gases (methane and CO₂) -> more warming -> more thawing. B describes a negative feedback loop, which may occur but is not the primary concern associated with permafrost thaw. C is incorrect because the effect is not merely localized; methane and CO₂ mix globally, contributing to overall warming. D is incorrect as it misidentifies the gases involved and their effects; decomposition does not significantly impact ozone.

Question 9

A species of alpine plant is adapted to a narrow range of cool temperatures. As the regional climate warms, what is the most likely long-term change in the distribution of this species?

  1. Its range will shift to lower altitudes and further from the poles to find more nutrient-rich soils.
  2. Its range will shift to higher altitudes on mountains and its overall habitable area will likely contract. (correct answer)
  3. It will expand its range both to higher and lower altitudes due to the fertilizing effect of increased atmospheric CO₂.
  4. It will adapt rapidly to warmer temperatures through physiological acclimatization, maintaining its current range without shifting.
Explanation: The correct answer is B. Organisms adapted to cool temperatures will need to track their preferred climate. On a mountain, this means moving to higher altitudes where it is cooler. This is an example of a range shift. As the species moves up the mountain, the total available land area typically decreases, leading to range contraction. A suggests a shift to warmer areas, which is incorrect. C incorrectly assumes the CO₂ fertilization effect will override the negative impact of thermal stress. D describes acclimatization, a short-term physiological response of an individual, not a long-term distributional shift of a population or species, and may not be sufficient to cope with significant warming.

Question 10

Increased frequency and intensity of forest fires in boreal regions is an observed effect of climate change that also contributes to it. How does this phenomenon represent a positive feedback cycle?

  1. Forest fires release large amounts of stored carbon as CO₂, which enhances the greenhouse effect and leads to warmer, drier conditions conducive to more fires. (correct answer)
  2. The ash from forest fires darkens the surface of nearby glaciers, lowering their albedo and causing them to melt faster.
  3. After a fire, new plant growth is stimulated, which draws down large amounts of atmospheric CO₂, creating a stabilizing negative feedback.
  4. Smoke particles from fires act as cloud condensation nuclei, increasing cloud cover that reflects sunlight and causes regional cooling.
Explanation: The correct answer is A. This correctly identifies the positive feedback loop: warming leads to conditions for more fires, the fires release CO₂ (a greenhouse gas), the increased CO₂ leads to more warming, creating a self-reinforcing cycle. B describes a real effect but is a separate feedback loop (ice-albedo), not the primary one involving the fire and atmospheric CO₂. C describes a potential negative feedback, but on the timescale of the fire event and its immediate aftermath, the carbon release far outweighs the subsequent slow uptake. D describes a potential negative feedback (aerosol effect), but the warming effect of the released CO₂ is the dominant long-term climatic impact.

Question 11

What is the specific role of greenhouse gases in the Earth's energy balance that leads to the greenhouse effect?

  1. They absorb incoming short-wave ultraviolet radiation from the sun, trapping it in the upper atmosphere.
  2. They reflect incoming short-wave solar radiation back into space, preventing it from reaching the Earth's surface.
  3. They are transparent to incoming short-wave solar radiation but absorb and re-radiate outgoing long-wave infrared radiation. (correct answer)
  4. They catalyze chemical reactions in the troposphere that generate heat, directly increasing the atmosphere's temperature.
Explanation: The correct answer is C. This accurately describes the mechanism of the greenhouse effect. The sun's energy arrives primarily as short-wave radiation (visible light and UV), which passes through the atmosphere. The Earth's surface absorbs this energy and re-radiates it as long-wave (infrared) radiation. Greenhouse gases absorb this outgoing infrared radiation and re-radiate it in all directions, including back towards the surface, trapping heat. A is incorrect; ozone absorbs UV, but this is not the primary mechanism of the greenhouse effect. B describes the effect of aerosols or clouds, which increase albedo, but not the action of greenhouse gases. D is incorrect; the warming is due to radiative properties, not catalysis of heat-generating reactions.

Question 12

Climate change poses two distinct threats to coral reefs: coral bleaching and ocean acidification. What is the direct physiological cause of coral bleaching?

  1. A decrease in ocean pH reduces the availability of carbonate ions, causing the coral's calcium carbonate skeleton to dissolve.
  2. Elevated sea temperatures cause coral polyps to expel their symbiotic zooxanthellae algae, leading to a loss of colour and energy source. (correct answer)
  3. Increased dissolved CO₂ in the water directly poisons the coral polyps, causing them to die and turn white.
  4. Sea level rise increases water depth above the reef, reducing the amount of sunlight available for the symbiotic algae to perform photosynthesis.
Explanation: The correct answer is B. Coral bleaching is a specific stress response where prolonged elevated water temperatures cause the breakdown of the symbiosis between corals and their zooxanthellae. The algae are expelled, and the white calcium carbonate skeleton becomes visible. A describes the mechanism of ocean acidification's impact on skeleton formation, which is a different issue. C is incorrect; CO₂ is not directly toxic to the polyps in this manner. D is a potential stressor but is not the direct mechanism of bleaching, which is primarily temperature-driven.

Question 13

The ice-albedo feedback is a significant positive feedback mechanism in the climate system. Which statement correctly explains this process?

  1. Warmer temperatures melt ice, which has a low albedo, exposing darker ocean or land, which has a high albedo, leading to further cooling.
  2. Warmer temperatures melt ice, which is highly reflective, exposing darker ocean or land, which absorbs more solar radiation, leading to further warming. (correct answer)
  3. Increased solar radiation melts ice, releasing large amounts of fresh water, which changes ocean salinity and disrupts currents, causing regional cooling.
  4. Ice absorbs a large amount of long-wave radiation, so its removal allows more of this radiation to escape into space, creating a cooling effect.
Explanation: The correct answer is B. Albedo is a measure of reflectivity. Ice and snow have a high albedo (they are very reflective). As temperatures rise and ice melts, it exposes darker surfaces like open ocean or land, which have a low albedo. These darker surfaces absorb more solar radiation, leading to further warming, which in turn melts more ice. This is a classic positive feedback loop. A incorrectly swaps the albedo properties of ice and ocean/land. C describes a different process related to ocean circulation, not the albedo feedback. D is incorrect; ice reflects short-wave radiation, and its removal does not cause a cooling effect in this manner.

Question 14

Biomagnification of pollutants like mercury can be exacerbated by climate change. What is a plausible mechanism for this interaction?

  1. Warmer temperatures cause pollutants to become more toxic, increasing their effect at each trophic level.
  2. Increased rainfall due to climate change dilutes the concentration of pollutants in aquatic ecosystems, reducing biomagnification.
  3. Changes in food web structure, such as the loss of certain prey species due to warming, can force predators to consume prey from higher trophic levels with greater pollutant loads. (correct answer)
  4. Higher atmospheric CO₂ directly binds to mercury, creating a more stable compound that is easily absorbed by primary producers.
Explanation: The correct answer is C. Climate change can alter species distribution and abundance, thus changing the structure of food webs. If a predator's usual prey becomes scarce, it might switch to consuming other predators, effectively feeding at a higher trophic level. Since persistent pollutants biomagnify up the food chain, this change in diet would lead to the predator accumulating a higher concentration of the pollutant. A is possible but less of a direct link to biomagnification itself. B describes the opposite of what is generally expected. D describes a nonexistent chemical interaction.

Question 15

[HL only] How is rapid climate change expected to act as a powerful selective pressure on populations of organisms?

  1. It causes all individuals within a population to physiologically acclimatize, shifting the entire population's traits without genetic change.
  2. It induces new, favourable mutations in individuals that allow them to survive in the changing environment.
  3. It favours the survival and reproduction of individuals with pre-existing genetic traits that are better suited to the new conditions. (correct answer)
  4. It forces populations to undergo large-scale migration, which is a form of selection for mobility rather than for climatic tolerance.
Explanation: The correct answer is C. This is the core principle of natural selection. Environmental change does not create new traits on demand. Instead, it acts upon the existing variation within a population. Individuals whose inherited traits (e.g., higher heat tolerance, different breeding times) happen to be advantageous in the new climate are more likely to survive and reproduce, passing those traits to the next generation. A describes phenotypic plasticity, not evolution. B is incorrect; mutations are random, not directed by environmental needs. D describes one possible outcome (migration), but the fundamental selective pressure acts on heritable traits related to tolerance of the new climate.

Question 16

The increase in atmospheric CO₂ concentration leads to ocean acidification. Which chemical change is the primary reason this is detrimental to marine calcifying organisms like corals and molluscs?

  1. Dissolved CO₂ combines with water to form carbonic acid, which directly corrodes existing calcium carbonate skeletons.
  2. Increased hydrogen ion concentration (lower pH) leads to a reduction in the concentration of available carbonate ions (CO₃²⁻). (correct answer)
  3. Higher CO₂ levels in the water reduce the amount of dissolved oxygen, leading to hypoxic conditions for marine organisms.
  4. The ocean becomes supersaturated with bicarbonate ions (HCO₃⁻), which are toxic to the metabolic processes of calcifying organisms.
Explanation: The correct answer is B. When CO₂ dissolves in seawater, it forms carbonic acid (H₂CO₃), which dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻). The excess H⁺ ions react with available carbonate ions (CO₃²⁻) to form more bicarbonate. This reduces the concentration of carbonate ions, which calcifying organisms need to build their calcium carbonate (CaCO₃) shells and skeletons. A is an oversimplification; while corrosion can occur in very acidic conditions, the main problem is the inhibition of new skeleton formation. C describes deoxygenation, a separate issue related to warming, not the chemical mechanism of acidification. D is incorrect; bicarbonate ions are not toxic and are a key part of the buffering system.

Question 17

Which statement accurately distinguishes between the causes of sea level rise in a warming world?

  1. The primary cause is the melting of floating sea ice, such as the Arctic ice cap, which displaces a large volume of water.
  2. Thermal expansion is the only significant factor; the contribution from melting ice is negligible in comparison.
  3. Sea level rise is mainly due to increased precipitation over the oceans, which adds a greater volume of water to the basins.
  4. The two main causes are the thermal expansion of ocean water as it warms and the melting of land-based ice sheets and glaciers. (correct answer)
Explanation: The correct answer is B. The two dominant, roughly equal contributors to modern sea level rise are the thermal expansion of water (as water warms, its volume increases) and the addition of new water to the oceans from the melting of land-based ice (e.g., Greenland and Antarctic ice sheets, mountain glaciers). A is a common misconception; the melting of floating sea ice does not significantly change sea level, as the ice was already displacing its own weight in water (Archimedes' principle). C is incorrect; changes in precipitation patterns do not contribute to sea level rise in this way. D is incorrect as it dismisses the very significant contribution from melting land ice.

Question 18

Which of the following scenarios best illustrates the concept of an ecological tipping point resulting from climate change?

  1. The gradual northward shift of the geographic range of a temperate tree species by 50 km over a century.
  2. A 15% decrease in the population of a specific seabird species due to more frequent extreme weather events.
  3. After years of gradual warming and reduced rainfall, a large portion of a rainforest ecosystem rapidly converts to savanna following a single severe drought. (correct answer)
  4. The annual sea ice in the Arctic melts completely each summer but refreezes each winter, following a predictable seasonal pattern.
Explanation: The correct answer is C. A tipping point is a threshold beyond which a system undergoes a rapid, often irreversible shift to a new state. The sudden conversion of a rainforest to savanna after a period of gradual stress is a classic example. A describes a gradual change, not a rapid shift. B describes a population decline, which may be reversible and is not a system-state change. D describes a seasonal, cyclical, and currently reversible process, not a tipping point.

Question 19

The Earth's climate has changed naturally in the past. What key feature distinguishes current, anthropogenic climate change from most past natural climate fluctuations, such as ice age cycles?

  1. The current warming is caused by changes in the Earth's orbital parameters, known as Milankovitch cycles.
  2. The magnitude of the current temperature change is far greater than any change that has occurred in the geological past.
  3. The rate of increase in both greenhouse gas concentrations and global temperature is exceptionally rapid. (correct answer)
  4. Past climate changes were driven by geological processes, whereas the current change is driven by solar activity.
Explanation: The correct answer is C. While the Earth's climate has always changed, the defining characteristic of the current event is the unprecedented speed. The rate at which CO₂ is being added to the atmosphere and the resulting rate of temperature increase are much faster than the changes seen in the ice core records of past glacial-interglacial cycles. This rapid rate poses significant challenges for ecosystems and species to adapt. A describes a cause of past ice ages, not current warming. B is incorrect; the Earth has been much warmer in its deep past, but the rate of change is the key issue. D is incorrect; current change is not driven by solar activity, and past changes had multiple drivers, including GHGs.

Question 20

Both methane (CH₄) and carbon dioxide (CO₂) are significant anthropogenic greenhouse gases. Which statement best evaluates their respective contributions to global climate change?

  1. Methane is the dominant driver of climate change because its global warming potential per molecule is much higher than that of carbon dioxide.
  2. Carbon dioxide is the dominant driver of climate change because its atmospheric concentration and persistence are much greater than methane's, despite its lower warming potential per molecule. (correct answer)
  3. Their contributions are approximately equal, as methane's high warming potential is balanced by carbon dioxide's high concentration.
  4. Neither is the dominant anthropogenic driver; water vapour released from industrial processes has a greater overall effect on the greenhouse effect.
Explanation: The correct answer is B. While methane is more potent on a per-molecule basis, carbon dioxide's vastly higher atmospheric concentration and its long residence time (hundreds of years) make it the primary contributor to anthropogenic global warming. A is incorrect because it ignores the crucial role of concentration and persistence. C is incorrect because the balance is not equal; CO₂'s effect is significantly larger. D is incorrect because while water vapour is a powerful greenhouse gas, its atmospheric concentration is primarily a function of temperature (a feedback), not direct anthropogenic emissions, making it a response to, rather than a primary driver of, long-term climate change.