IB Biology Quiz: Understand Sustainability And Change
19 questions · exam conditions
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Understand Sustainability And ChangeQuestion 1 of 19

[HL] An area of temperate forest is cleared for agriculture but is then abandoned. Over the next century, the area undergoes ecological succession. Which feature most clearly indicates that this is secondary, not primary, succession?

The first macroscopic organisms to colonize are hardy grasses and weeds.
The biodiversity of the area increases over time.
The process is initiated in an environment that already contains soil and organic matter.
The final community is likely to be a stable forest ecosystem.
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IB Biology Quiz

IB Biology Quiz: Understand Sustainability And Change

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

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

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Question 1

[HL] An area of temperate forest is cleared for agriculture but is then abandoned. Over the next century, the area undergoes ecological succession. Which feature most clearly indicates that this is secondary, not primary, succession?

  1. The first macroscopic organisms to colonize are hardy grasses and weeds.
  2. The biodiversity of the area increases over time.
  3. The process is initiated in an environment that already contains soil and organic matter. (correct answer)
  4. The final community is likely to be a stable forest ecosystem.
Explanation: The defining difference between primary and secondary succession is the starting condition. Primary succession begins on a substrate devoid of life and soil (e.g., bare rock after a volcanic eruption). Secondary succession occurs where an existing community has been disturbed, but the soil remains intact (e.g., an abandoned field). The presence of soil allows the process to happen much faster.

Question 2

A fish stock is managed based on the principle of Maximum Sustainable Yield (MSY), aiming to maintain the population at a size that produces the highest catch rate. Why might a management strategy strictly adhering to MSY fail to be ecologically sustainable in the long term?

  1. It ignores the economic viability of the fishing industry, leading to over-investment in fishing fleets.
  2. It fails to account for natural fluctuations in population size and changing environmental conditions. (correct answer)
  3. It prioritizes the conservation of the target fish species over the economic needs of the human population.
  4. It is based on harvesting only the oldest individuals, which disrupts the population's reproductive potential.
Explanation: MSY models often assume a stable carrying capacity and predictable population growth, which is rarely the case in real ecosystems. Natural environmental fluctuations (e.g., changes in water temperature, food availability) can cause the population's carrying capacity and reproductive rate to vary. Harvesting at a fixed MSY level during a period of natural population decline can lead to over-exploitation and stock collapse, thus it is not truly sustainable.

Question 3

In a coastal marine ecosystem, sea otters are a keystone species that prey on sea urchins. Sea urchins graze on kelp, which forms large underwater forests. If a disease significantly reduces the sea otter population, what is the most likely long-term consequence for fish populations that use the kelp forest as a nursery?

  1. Fish populations would increase, as their main predators, the sea otters, have been removed.
  2. Fish populations would decrease due to the loss of habitat and shelter provided by the kelp forests. (correct answer)
  3. Fish populations would remain stable as the food web change does not directly involve them.
  4. Fish populations would increase as their main competitors for resources, the sea urchins, also decline.
Explanation: The removal of the keystone predator (sea otters) would lead to an increase in their prey (sea urchins). Increased sea urchin populations would lead to overgrazing and the destruction of the kelp forests. Since the fish populations use the kelp as a nursery, the loss of this critical habitat would cause a decline in fish populations. This is an example of a trophic cascade.

Question 4

A persistent organic pollutant (POP) is found in a lake. Analysis reveals its concentration in zooplankton is 0.05 ppm, in small fish that eat zooplankton it is 1.0 ppm, and in predatory birds that eat the fish it is 25 ppm. Which statement best explains these observations?

  1. Bioaccumulation has occurred within each organism, and biomagnification has occurred across trophic levels. (correct answer)
  2. Biomagnification has occurred within each individual organism, leading to high concentrations in the birds.
  3. Bioaccumulation has occurred across the food chain, causing the pollutant to become more concentrated.
  4. The pollutant is water-soluble, allowing it to be easily passed up the food chain to high concentrations.
Explanation: Bioaccumulation is the build-up of a substance in an individual organism's tissues over its lifetime. Biomagnification (or bioamplification) is the increasing concentration of that substance in organisms at successively higher levels in a food chain. The data shows increasing concentration at each trophic level (biomagnification), which is a result of each organism bioaccumulating the pollutant from its food.

Question 5

In an alpine meadow, a single species of grass accounts for 80% of the total biomass. In a nearby coral reef, a species of sea star with a very low total biomass prevents mussels from monopolizing all available rock space. Which statement correctly identifies the roles of the grass and the sea star?

  1. Both are keystone species because they have a disproportionately large impact on their ecosystems.
  2. The grass is a dominant species due to its high biomass, while the sea star is a keystone species. (correct answer)
  3. The sea star is a dominant species because of its control over the community, while the grass is a keystone species.
  4. Both are dominant species because they are critical to the structure of their respective communities.
Explanation: A dominant species is one that is most abundant or has the highest biomass in a community (the grass). A keystone species has a disproportionately large effect on its ecosystem relative to its abundance or biomass (the sea star). The sea star's removal would lead to a drastic decrease in diversity, a classic indicator of a keystone species.

Question 6

A pesticide is applied to a field and has a concentration of 0.003 ppm in the soil. Earthworms bioaccumulate this to a concentration 10 times that of the soil. Shrews eat the earthworms, leading to a magnification factor of 20. Owls eat the shrews, resulting in a further magnification factor of 10. What is the approximate concentration of the pesticide in the owls?

  1. 0.6 ppm
  2. 60.0 ppm
  3. 0.06 ppm
  4. 6.0 ppm (correct answer)
Explanation: This requires a multi-step calculation. Concentration in earthworms = 0.003 ppm * 10 = 0.03 ppm. Concentration in shrews = 0.03 ppm * 20 = 0.6 ppm. Concentration in owls = 0.6 ppm * 10 = 6.0 ppm.

Question 7

[HL] During primary succession on bare rock, which of the following describes the general trend for gross production (GP), ecosystem respiration (R), and net production (NP) as the community progresses from pioneer species to a mature forest?

  1. GP and R both increase, while NP is highest in early-to-mid succession and then declines. (correct answer)
  2. GP, R, and NP all increase steadily until the climax community is reached, where they all plateau.
  3. GP remains relatively constant, while R increases, causing a steady decline in NP.
  4. NP is always close to zero, while GP and R are both low in early stages and high in late stages.
Explanation: In early succession, biomass is low, so GP and R are low. Because there are few consumers and decomposers, production exceeds respiration (P > R), so Net Production (NP = GP - R) is positive and biomass accumulates. As the community matures, biomass increases, leading to increases in both total GP and total ecosystem R. In a climax community, the system is in equilibrium, and R becomes nearly equal to GP, so NP approaches zero. Therefore, NP peaks during the intermediate stages of succession when biomass is accumulating rapidly.

Question 8

Microplastics are a pervasive pollutant in marine environments. Which mechanism is a primary cause of physiological harm in a filter-feeding bivalve that ingests large quantities of microplastic particles?

  1. The plastic particles provide a high-energy but indigestible food source, leading to obesity.
  2. The particles cause internal abrasion and can trigger a persistent, energy-consuming inflammatory response. (correct answer)
  3. The plastics are rapidly metabolized by the bivalve's cells, releasing toxic by-products.
  4. The plastics alter the salinity of the water passing over the gills, disrupting osmoregulation.
Explanation: Ingested microplastics can cause physical damage (abrasion) to the delicate tissues of the digestive tract. The organism's immune system may also recognize these as foreign bodies, triggering a chronic inflammatory response. This response consumes significant energy, diverting it from growth and reproduction, and causing physiological stress.

Question 9

In a savanna ecosystem, lions prey on wildebeest. The grazing of wildebeest controls the growth of tall grasses, which allows a greater diversity of smaller flowering plants (forbs) to grow. These forbs support a wide range of insect pollinators.

Based on the passage, what would be the most probable indirect effect of a disease that drastically reduces the lion population?

  1. A decrease in the abundance and diversity of insect pollinators. (correct answer)
  2. An increase in the biomass of tall grasses and a decrease in the wildebeest population.
  3. An increase in the population of forbs due to reduced competition from tall grasses.
  4. An immediate stabilization of the wildebeest population at the ecosystem's carrying capacity.
Explanation: This describes a trophic cascade. A reduction in lions (top predator) would lead to an increase in wildebeest (primary consumer). More wildebeest would lead to more intense grazing, favouring the dominant tall grasses and reducing the abundance of forbs. A decrease in forbs (producers) would lead to a decrease in the insect pollinators that depend on them.

Question 10

A rewilding project proposes reintroducing wolves to a large national park. How does this approach fundamentally differ from traditional conservation in a fenced wildlife sanctuary for an endangered deer species?

  1. Rewilding focuses on a single charismatic species, whereas sanctuaries aim to protect entire ecosystems.
  2. Rewilding prioritizes restoring ecosystem processes and trophic levels, while sanctuaries focus on species protection through active management. (correct answer)
  3. Rewilding is an example of ex situ conservation, while sanctuaries are a form of in situ conservation.
  4. Rewilding aims to create a stable, unchanging climax community, whereas sanctuaries manage for dynamic change.
Explanation: The core philosophy of rewilding is to restore natural processes and self-regulating ecosystems, often by reintroducing keystone species or top predators to reinstate trophic cascades. Traditional sanctuaries often involve more intensive human management (like providing food or controlling predators) to protect a specific population, rather than restoring the entire system's autonomy.

Question 11

A lake is suffering from advanced cultural eutrophication. Which of the following interventions would most directly address the root cause of this problem, rather than just treating its symptoms?

  1. Introducing a species of herbivorous fish that grazes heavily on the algae.
  2. Using mechanical aerators to pump oxygen into the deep water of the lake.
  3. Restoring wetlands and creating buffer zones around agricultural fields that drain into the lake. (correct answer)
  4. Periodically harvesting the excess aquatic weeds and algae from the lake surface.
Explanation: The root cause of cultural eutrophication is excessive nutrient (nitrate and phosphate) input from sources like agricultural runoff. Options A, B, and D treat the symptoms (algal blooms, low oxygen). Option C addresses the root cause by intercepting and filtering the nutrient-rich runoff before it can enter the lake and trigger the blooms.

Question 12

A logging company claims its operations are sustainable. Which of the following observations would provide the strongest evidence to refute this claim?

  1. The mass of timber harvested each year is less than the forest's calculated net primary production.
  2. The company primarily harvests trees that are part of the forest's climax community.
  3. Satellite imagery shows a gradual but consistent decrease in total forest canopy cover over a decade. (correct answer)
  4. The logging operations provide significant employment for local communities.
Explanation: Sustainability means meeting present needs without compromising the ability of future generations to meet theirs. Ecologically, this means the resource is not being depleted over time. A consistent decrease in canopy cover is direct evidence that the rate of harvesting exceeds the rate of regrowth, meaning the forest resource is being depleted. This directly refutes the claim of sustainability.

Question 13

[HL] Which statement best describes the nature of a climax community?

  1. It is a final, static stage of succession where species composition and biomass are unchanging.
  2. It is the stage with the highest possible net primary productivity, allowing for the maximum rate of biomass accumulation.
  3. It is characterized by the complete absence of pioneer species and a very low level of gross primary productivity.
  4. It is a community in dynamic equilibrium, where species composition is relatively stable despite turnover of individuals. (correct answer)
Explanation: A climax community is not static. While the overall structure, species composition, and biomass remain relatively constant over time, there is a constant turnover of individuals (death and replacement). It is best described as being in a state of dynamic equilibrium. Net primary productivity is low (close to zero) because gross production is balanced by ecosystem respiration, not at its highest possible value.

Question 14

[HL] A grassland ecosystem in a region with enough rainfall to support a forest is prevented from doing so by frequent, naturally occurring fires. In this context, what is the ecological role of fire?

  1. It acts as the primary limiting factor that reduces the carrying capacity for all species.
  2. It is a density-dependent factor that primarily controls the herbivore populations.
  3. It is an abiotic factor that arrests succession, maintaining the ecosystem in a subclimax state. (correct answer)
  4. It accelerates primary succession by repeatedly creating bare ground for colonization.
Explanation: Succession is the process of change in community structure over time. A climax community is the theoretical end point. When a recurring disturbance, like fire, prevents the community from reaching its potential climax state (a forest), it is said to be arrested. The resulting stable community (the grassland) is known as a subclimax or fire-climax community. Fire is an abiotic, density-independent factor.

Question 15

[HL] During primary succession, pioneer species like lichens play a crucial role in facilitating the establishment of later species. What is the primary mechanism by which they achieve this?

  1. They provide a food source for the first herbivores that colonize the area.
  2. They fix large amounts of atmospheric nitrogen, making the environment immediately fertile for trees.
  3. They chemically and physically break down rock and contribute organic matter, initiating soil formation. (correct answer)
  4. They have deep root systems that stabilize the bare rock, preventing erosion by wind and water.
Explanation: The most fundamental role of pioneer species in primary succession is soil creation. Lichens secrete weak acids that begin to chemically weather the rock surface. As they die and decompose, they contribute the first layer of organic matter (humus). This gradual process of weathering and organic accumulation creates the first primitive soil, which is essential for later, more complex plants to establish themselves.

Question 16

How does the process of eutrophication typically affect species richness and species evenness in an aquatic ecosystem?

  1. Both species richness and species evenness increase as higher nutrient availability supports more life.
  2. Species richness increases due to new nutrient sources, but evenness decreases as a few species dominate.
  3. Both species richness and species evenness decrease as conditions favour a few tolerant species. (correct answer)
  4. Species richness decreases due to anoxia, but evenness increases as dominant competitors are removed.
Explanation: Eutrophication leads to a decrease in biodiversity. Species richness (the number of different species) declines because many species cannot tolerate the low-oxygen conditions. Species evenness (the relative abundance of species) also declines sharply because a few nutrient-tolerant species, like certain types of algae, become extremely dominant, while all other species become rare or are eliminated.

Question 17

Following an algal bloom triggered by eutrophication, a massive die-off of algae occurs. What is the immediate biochemical process responsible for the subsequent development of an anoxic "dead zone"?

  1. The decomposition of dead algae by aerobic bacteria consumes large amounts of dissolved oxygen. (correct answer)
  2. The dead algae release lipid-soluble toxins that directly kill fish and other aquatic organisms.
  3. The high density of dead algae blocks sunlight, preventing photosynthesis and oxygen production by other plants.
  4. The algae, during their bloom, consumed all available dissolved oxygen for their own respiration at night.
Explanation: The primary cause of anoxia (lack of oxygen) after an algal bloom is the massive amount of decomposition. Aerobic bacteria break down the dead organic matter (the algae), and this process of aerobic respiration consumes dissolved oxygen from the water faster than it can be replenished, leading to hypoxic or anoxic conditions.

Question 18

Scientists are assessing a new industrial chemical. Which combination of properties would make this chemical most likely to undergo significant biomagnification in terrestrial food webs?

  1. High water solubility, chemically unstable, and rapidly excreted by organisms.
  2. Chemically stable, high water solubility, and not lipid-soluble.
  3. Gaseous state at room temperature, biodegradable, and water-soluble.
  4. Lipid-soluble, chemically stable, and not readily metabolized by organisms. (correct answer)
Explanation: For a substance to biomagnify, it must be persistent in the environment (chemically stable), taken up by organisms, and retained in their tissues. Lipid-solubility causes it to be stored in fatty tissues rather than being excreted in urine (which is water-based). Being not readily metabolized means it stays in the body for a long time. These three properties lead to its accumulation and magnification up the food chain.

Question 19

The reintroduction of a top predator into an ecosystem as part of a rewilding initiative can increase long-term stability. However, what is a likely short-term consequence of such a reintroduction?

  1. An immediate and uniform increase in the populations of all producer species.
  2. A rapid stabilization of all prey populations to their historical carrying capacities.
  3. A rapid decrease in overall ecosystem respiration due to reduced consumer biomass.
  4. A period of population fluctuations as the food web reorganizes around the new predator. (correct answer)
Explanation: Introducing a top predator is a major perturbation. Prey populations may initially crash, and their behaviour will change (e.g., avoiding certain areas). This will cause ripple effects throughout the food web. The system will likely experience a period of instability and oscillation before it settles into a new, more complex dynamic equilibrium. Stabilization is a long-term goal, not an immediate effect.