Biology • Year 11 • Module 4 • Lesson 21
Human Impacts — Habitat Destruction, Fragmentation, Pollution and Introduced Species
Lock in the vocabulary of habitat destruction, fragmentation, pollution and invasive species, and recall the key mechanisms and Australian case studies.
1. Term–definition match
The ten definitions below are shuffled. In the right-hand column write the matching term from this list: habitat destruction, habitat fragmentation, species-area relationship, minimum viable population, edge effects, extinction debt, eutrophication, biomagnification, invasive species, multi-stressor synergy. 10 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The removal or conversion of habitat (deforestation, urban sprawl, agriculture) — the single largest driver of global biodiversity loss. | |
| 1.2 | The division of continuous habitat into isolated patches surrounded by an inhospitable matrix. | |
| 1.3 | The principle that larger habitat areas support more species, with loss accelerating below a critical threshold. | |
| 1.4 | The smallest population that can persist without high extinction risk from inbreeding, drift or random fluctuations. | |
| 1.5 | The altered microclimate at patch boundaries (hotter, drier, windier, more light) that favours generalists and invaders. | |
| 1.6 | Species committed to eventual extinction due to habitat loss even though they persist temporarily in a fragment. | |
| 1.7 | Excess N and P → algal bloom → algal death → bacterial decomposition → oxygen depletion → fish death. | |
| 1.8 | Fat-soluble toxins (DDT, mercury) accumulating in tissues and concentrating up the food chain. | |
| 1.9 | Non-native species that outcompete locals, prey on them, or disrupt food webs (e.g. common carp). | |
| 1.10 | When multiple human impacts act together, their combined effect often exceeds the sum of the individual effects. |
2. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line provided. 10 marks (1 T/F + 1 correction where needed)
2.1 Habitat destruction is the single largest driver of global biodiversity loss. T / F
2.2 In eutrophication, fish die because the algae are directly toxic to them. T / F
2.3 Biomagnification occurs because fat-soluble, stable pollutants accumulate in tissues and become more concentrated at each higher trophic level. T / F
2.4 Edge effects make the effective habitat area of a fragment larger than its measured area. T / F
2.5 In the Murray-Darling Basin, several stressors act together (synergistically), driving native fish to less than 10% of pre-European levels. T / F
3. Cloze paragraph — fill the blanks
Complete the paragraph using terms from the word bank below. Each term is used once. 9 marks
Habitat removes living space, but more often habitat is divided by into isolated patches. Small patch populations suffer and may fall below their population size. Isolation reduces between patches, while altered microclimate at the margins creates that shrink usable habitat. Some species persist for a while but are doomed — an . Pollution adds further pressure: eutrophication depletes dissolved and kills fish. When several impacts combine, their effects show — worse than the sum of their parts.
4. Short recall
Answer each in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 State the sequence of eutrophication from excess nutrients to fish death.
4.2 Why are small populations in habitat fragments at higher risk from genetic drift and inbreeding depression?
4.3 Explain why DDT reached lethal concentrations in eagles and peregrine falcons even though it was applied at low concentrations.
4.4 What does the species-area relationship predict will happen as habitat area falls below a critical threshold?
5. Build a concept map
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. "leads to", "reduces", "amplifies", "below"). Aim for at least 6 labelled arrows. 6 marks
Supplied terms: habitat fragmentation • small population • genetic drift • extinction debt • edge effects • multi-stressor synergy.
Q1 — Term–definition matches (10 marks)
1.1 habitat destruction • 1.2 habitat fragmentation • 1.3 species-area relationship • 1.4 minimum viable population • 1.5 edge effects • 1.6 extinction debt • 1.7 eutrophication • 1.8 biomagnification • 1.9 invasive species • 1.10 multi-stressor synergy.
1 mark per correct match.
Q2 — True / false with correction (10 marks)
2.1 True.
2.2 False. Correction: fish die because bacteria decomposing the dead algae consume dissolved oxygen, making the water hypoxic — it is oxygen depletion, not direct algal toxicity, that kills the fish.
2.3 True.
2.4 False. Correction: edge effects make the effective habitat area smaller than the measured area, because the degraded edges are unsuitable for forest specialists.
2.5 True.
1 mark for each correct T/F identification; 1 mark for each correct correction (false statements only).
Q3 — Cloze paragraph (9 marks)
In order: destruction / fragmentation / genetic drift / minimum viable / gene flow / edge effects / extinction debt / oxygen / synergy.
1 mark per correct blank.
Q4.1 — Eutrophication sequence (2 marks)
Excess N and P (from fertiliser or sewage) → explosive algal growth (bloom) → algae die → bacteria decompose them, consuming dissolved oxygen → water becomes hypoxic → fish and aerobic organisms die [1 for correct order; 1 for identifying bacterial decomposition/oxygen depletion as the lethal step].
Q4.2 — Small populations and genetic risk (2 marks)
In small populations, allele frequencies change more by chance (genetic drift), reducing genetic diversity [1]. Mating between related individuals becomes more likely, so harmful recessive alleles are expressed more often (inbreeding depression), lowering survival and reproduction and increasing extinction risk [1].
Q4.3 — DDT in raptors (2 marks)
DDT is fat-soluble and chemically stable, so it is stored in body tissues rather than excreted, and accumulates in each organism over its life [1]. As it passes up the food chain (insects → small birds → raptors) it concentrates at each trophic level (biomagnification), so by the apex predator the concentration is high enough to cause eggshell thinning and reproductive failure [1].
Q4.4 — Species-area relationship (2 marks)
As habitat area decreases the number of species supported decreases, and not proportionally [1]. Below a critical threshold, species loss accelerates because populations fall below their minimum viable size and become prone to extinction [1].
Q5 — Sample concept map (6 marks)
A correct map should include arrows such as:
- habitat fragmentation —leads to→ small population
- small population —suffers→ genetic drift
- habitat fragmentation —creates→ edge effects
- edge effects —shrink usable area, worsening→ small population
- small population —below MVP results in→ extinction debt
- multi-stressor synergy —amplifies→ extinction debt (or small population)
Any biologically valid linking phrases are accepted. Award 1 mark per correctly labelled, directionally appropriate arrow, up to 6 marks.