HSC Exam Practice

Sample response. Biodiversity is the variety of all living organisms in an ecosystem. Genetic diversity is variation in alleles within a species or population. Species diversity refers to the variety of species present and how evenly individuals are distributed across them. Ecosystem diversity refers to the variety of habitats, communities and ecological processes in a region.

Marking notes. 1 mark for biodiversity definition. 1 mark for genetic diversity (allele variation within a species). 1 mark for species and ecosystem diversity distinguished from each other (species = variety of species; ecosystem = habitats + communities + processes).

Sample response. Species richness is the number of different species in an area. Species evenness measures how equally individuals are distributed across those species. Both are needed because a community can have high richness but low evenness (one species dominates) which lowers overall diversity, while a community with fewer species may have higher diversity if individuals are more equally distributed.

Marking notes. 1 mark for correctly defining both terms. 1 mark for explaining why both are needed (richness alone does not capture distribution / evenness matters for true diversity assessment).

Sample response. Australia is described as megadiverse because it contains exceptional biodiversity, including a very high proportion of endemic species — species found only in Australia [1]. This is linked to Australia’s long geographic isolation after separating from Gondwana, which allowed distinctive lineages such as marsupials and monotremes to evolve and diversify independently over millions of years [1].

Marking notes. 1 mark for exceptional biodiversity / high endemism. 1 mark for linking this to long isolation from Gondwana / long evolutionary history.

Sample response. High genetic diversity means a population contains many different alleles [1]. If conditions change (e.g. new disease, drought, temperature shift), there is a greater probability that some individuals already carry alleles that confer resistance or tolerance to the new condition. Those individuals survive and reproduce, and the population persists. With low genetic diversity, if no individual carries a useful allele, the entire population may be at risk [1].

Marking notes. 1 mark for linking high allele variation to greater probability of having useful traits. 1 mark for explicitly explaining the mechanism (some individuals survive change; population persists).

Sample response. Three reasons: (1) Resilience — diverse ecosystems are better able to absorb disturbance and continue functioning, because redundancy in species roles means the loss of one species is less likely to collapse the system. (2) Ecosystem services — biodiversity provides pollination, soil health, water filtration and nutrient cycling that support agriculture and human welfare but are not commercially traded. (3) Intrinsic value — species and ecosystems have value independent of direct human use.

Marking notes. 1 mark each for any three distinct reasons. Each reason must be explained with more than a single word. Accept: resilience, ecosystem services (pollination/soil/nutrient cycling), intrinsic value, genetic resources for future medicine/crop breeding, cultural value.

Sample response. Both grasslands have the same species richness of 4 [1]. However, Grassland X has higher species evenness: individuals are distributed approximately equally across all four species (25–30 each out of 110 total). Grassland Y has much lower evenness: Grass A dominates with 72 out of 100 individuals (72%), while the other three species each have only 9–10 individuals [1].

Marking notes. 1 mark for correctly stating that both communities have richness of 4. 1 mark for correctly comparing evenness (X is higher because distribution is more equal; Y is lower because one species strongly dominates).

Sample response. Grassland X has greater species diversity [1]. Although both grasslands have the same species richness (4 species), species richness alone is insufficient because it does not capture how individuals are distributed across those species [1]. Grassland Y is dominated by Grass A, which makes up 72% of all individuals. This means that the functional roles, ecological interactions and resilience contributions of the other three species are severely underrepresented. Grassland X’s near-equal distribution means all four species contribute more equally to the community’s function and diversity [1].

Marking notes. 1 mark for identifying Grassland X has greater species diversity. 1 mark for explaining why richness alone is insufficient (does not capture evenness/distribution). 1 mark for a clear explanation of how evenness differences affect the meaning of the diversity comparison.

Sample response. Grassland X is more resilient [1]. Biodiversity (particularly species evenness) contributes to resilience — diverse systems are better able to absorb disturbance and continue functioning. In Grassland X, Grass A accounts for about 27% of individuals; losing 60% of that species removes about 16% of all individuals, which is significant but the other three species can sustain the community. In Grassland Y, Grass A accounts for 72% of individuals; losing 60% of it removes 43% of all individuals and severely disrupts the community that is almost entirely dependent on one species. Higher species evenness in Grassland X provides greater functional redundancy and therefore greater resilience [1].

Marking notes. 1 mark for correctly identifying Grassland X as more resilient. 1 mark for a clear explanation linking species evenness/biodiversity to resilience (less dependence on one species; greater functional redundancy).

Sample response. The claim that biodiversity is only relevant at the species level is incorrect. Biodiversity operates at three levels, each of which is independently important and cannot be fully captured by the others.

Genetic diversity refers to variation in alleles within a species or population. Even if species numbers remain stable, a population with low genetic diversity may be unable to adapt to changing conditions such as new diseases or climate shifts. A koala population with several alleles linked to immune response, for example, is more resilient to disease outbreaks than one with limited allele variation. Loss of genetic diversity is a biodiversity crisis even when no species has yet gone extinct.

Species diversity considers both richness (how many species) and evenness (how equally distributed). A community dominated by one species has lower species diversity than one with fewer but more evenly distributed species. Both dimensions matter for ecosystem function and resilience. Australia’s exceptionally high endemism — many species found nowhere else — means its species diversity is irreplaceable; losing endemic species is a permanent global loss.

Ecosystem diversity refers to the variety of habitats, communities and ecological processes. The Great Barrier Reef illustrates this: its mosaic of coral gardens, seagrass beds, mangroves and open-water zones supports far greater overall biodiversity than any single habitat could. Disruption of one habitat type can cascade through connected communities. The Daintree Rainforest illustrates a different aspect: long evolutionary isolation after Gondwana separation preserved ancient lineages and produced Australia’s high endemism, which is directly tied to ecosystem-level stability over deep time.

All three levels are interconnected and independently relevant. Biodiversity at only the species level is incomplete because a species can disappear genetically (low allele diversity) before it goes numerically extinct, and ecosystems can degrade as habitat diversity is lost even if species counts remain temporarily unchanged.

The claim is therefore false: biodiversity is relevant at genetic, species and ecosystem levels, and protecting any one level in isolation is insufficient for ensuring long-term ecological stability or resilience.

Marking criteria (9 marks).

• 1 mark — Explicit evaluative judgement: the claim is incorrect.
• 1 mark — Correct definition of genetic diversity (allele variation within a species/population).
• 1 mark — Explains why genetic diversity matters independently (adaptation/resilience to change) with an Australian example from the lesson.
• 1 mark — Correct definition of species diversity including both richness and evenness.
• 1 mark — Explains why species diversity matters independently, with reference to Australian endemism.
• 1 mark — Correct definition of ecosystem diversity (habitats, communities, ecological processes).
• 1 mark — Explains why ecosystem diversity matters independently, with at least one Australian example (Daintree or Reef).
• 1 mark — Explains the interconnection between levels and/or why species level alone is insufficient.
• 1 mark — Reaches a synthesised evaluative conclusion using precise lesson vocabulary throughout.