WACE Biology · Year 11 Unit 1
Ecosystems & Biodiversity
WACE Biology ATAR Year 11 Unit 1 Ecosystems and Biodiversity examines how living organisms interact with each other and their physical environment. These 20 free flashcards and 20 true/false quiz questions cover biotic and abiotic factors, habitat and niche, food chains and food webs, trophic levels and energy flow (10% rule, GPP vs NPP), biogeochemical cycles (carbon and nitrogen), species interactions (predation, competition, mutualism), biodiversity, conservation and Australian case studies from jarrah forest and kwongan heathland. Every card aligns with the SCSA Biology ATAR Year 11 syllabus (Unit 1 Ecosystems and biodiversity) and supports foundational revision that underpins Year 12 Units 3 and 4.
Key Terms
- Biotic vs Abiotic Factors
- Biotic factors are the living components of an ecosystem (producers, consumers, decomposers, parasites); abiotic factors are the non-living physical and chemical components (temperature, rainfall, light, soil, pH). SCSA expects WACE responses to organise ecosystem descriptions around both categories.
- Niche
- The functional role of an organism in its ecosystem — what it eats, when it is active, how it reproduces and its interactions with other species. Distinct from habitat (its physical address). Competitive exclusion states two species cannot occupy an identical niche indefinitely.
- Trophic Level
- A feeding position in a food web: producers, primary consumers, secondary consumers, tertiary consumers, with decomposers operating across all levels. The 10% rule describes the typical energy transfer efficiency between adjacent levels.
- Gross vs Net Primary Productivity
- GPP is the total energy fixed by producers; NPP = GPP − respiration losses, representing the energy available for consumption by primary consumers. SCSA WACE exams set numerical calculation questions on this relationship.
- Nitrogen Fixation
- The conversion of atmospheric N₂ to ammonia (NH₃) by nitrogen-fixing bacteria (e.g. Rhizobium in legume root nodules, free-living Azotobacter). A critical step in the nitrogen cycle frequently tested in WACE short-response questions.
- Biodiversity Hotspot
- A region with high species endemism and significant habitat loss. The South-West Australia Floristic Region qualifies as a global hotspot, making it the standard SCSA-aligned case study for WACE responses on biodiversity and conservation.
Sample Flashcards
Q1: Distinguish between biotic and abiotic factors in an ecosystem.
Biotic factors are the living components of an ecosystem — producers, consumers, decomposers, parasites and their interactions (predation, competition, mutualism). Abiotic factors are the non-living physical and chemical components — temperature, rainfall, light intensity, soil type, pH, salinity, wind and nutrient availability.
Q2: Define the terms habitat, niche and community.
Habitat: the physical environment where an organism lives (its "address"). Niche: the functional role of an organism in its ecosystem, including what it eats, when it is active, how it reproduces and its interactions with other species (its "job"). Community: all the populations of different species living and interacting in the same area at the same time.
Q3: Explain the difference between a food chain and a food web.
A food chain is a single linear pathway showing the flow of energy from one organism to the next (producer → primary consumer → secondary consumer → tertiary consumer). A food web is a network of interconnected food chains showing the complex feeding relationships within an ecosystem, providing a more realistic picture of energy flow.
Q4: Name and describe the four main trophic levels.
1) Producers (autotrophs) — photosynthetic organisms (plants, algae, cyanobacteria) that convert light energy to chemical energy. 2) Primary consumers (herbivores) — eat producers. 3) Secondary consumers (carnivores/omnivores) — eat primary consumers. 4) Tertiary consumers (top predators) — eat secondary consumers. Decomposers (bacteria, fungi) break down dead organisms at all levels, recycling nutrients.
Q5: Explain the 10% rule and why energy decreases at each trophic level.
Approximately only 10% of energy at one trophic level is transferred to the next. The remaining ~90% is lost as: heat from cellular respiration, energy used for life processes (movement, growth, reproduction), energy in uneaten parts, and energy in undigested waste (faeces). This progressive energy loss limits food chains to typically 4-5 trophic levels.
Q6: What is the difference between gross primary productivity and net primary productivity?
Gross primary productivity (GPP) is the total amount of energy (or carbon) fixed by photosynthesis in producers per unit area per unit time. Net primary productivity (NPP) is GPP minus the energy used by producers for their own respiration: NPP = GPP − R. NPP represents the energy available for consumption by primary consumers.
Q7: Describe the carbon cycle, including the role of photosynthesis and respiration.
The carbon cycle moves carbon through the biosphere, atmosphere, hydrosphere and lithosphere. Key processes: Photosynthesis removes CO₂ from the atmosphere, converting it to organic carbon in producers. Respiration (all organisms) releases CO₂ back to the atmosphere. Decomposition releases carbon from dead organisms. Combustion of fossil fuels releases stored carbon. Ocean absorption dissolves atmospheric CO₂.
Q8: Outline the nitrogen cycle and explain the role of nitrogen-fixing bacteria.
The nitrogen cycle converts nitrogen between forms: 1) Nitrogen fixation — N₂ converted to NH₃ (ammonia) by nitrogen-fixing bacteria (Rhizobium in legume root nodules, or free-living Azotobacter). 2) Nitrification — NH₃ oxidised to NO₂⁻ then NO₃⁻ by nitrifying bacteria (Nitrosomonas, Nitrobacter). 3) Assimilation — plants absorb NO₃⁻ to make amino acids/proteins. 4) Ammonification — decomposers convert organic nitrogen back to NH₃. 5) Denitrification — bacteria convert NO₃⁻ back to N₂ gas.
Sample Quiz Questions
Q1: Temperature, rainfall and soil pH are examples of biotic factors in an ecosystem.
Answer: FALSE
Temperature, rainfall and soil pH are abiotic (non-living) factors. Biotic factors are living components such as producers, consumers, decomposers and their interactions.
Q2: An organism's niche describes its functional role in the ecosystem, including its feeding relationships and habitat requirements.
Answer: TRUE
A niche encompasses an organism's complete ecological role — what it eats, what eats it, when and where it is active, how it reproduces, and all its interactions with biotic and abiotic factors.
Q3: A food web provides a less accurate representation of feeding relationships than a single food chain.
Answer: FALSE
A food web is MORE accurate than a single food chain because it shows the complex, interconnected feeding relationships in an ecosystem. Food chains oversimplify by showing only one linear pathway.
Q4: Producers (autotrophs) form the first trophic level in all ecosystems.
Answer: TRUE
Producers (plants, algae, photosynthetic bacteria) are always the first trophic level because they convert light energy into chemical energy through photosynthesis, forming the base of all food chains.
Q5: Approximately 90% of energy at one trophic level is transferred to the next level.
Answer: FALSE
Only approximately 10% of energy is transferred between trophic levels. The remaining ~90% is lost as heat from respiration, used for life processes, or lost in undigested waste.
Why It Matters
Ecosystems and biodiversity is the foundation unit of WACE Biology Year 11, building the conceptual vocabulary used across the rest of the ATAR sequence. Understanding biotic and abiotic factors, habitats, niches, food webs and trophic levels lets you trace energy flow and nutrient cycles through real WA ecosystems — jarrah forest, kwongan heathland, seagrass meadows and arid rangelands. The carbon and nitrogen cycles connect ecosystem function to climate change, bushfire recovery and soil fertility, all of which WACE examiners routinely use as applied contexts. Mastering biodiversity measures and the South-West Australia Floristic Region as a global biodiversity hotspot sets up the Year 12 Unit 3 content on population genetics and evolution, where the same species interactions shape gene-pool change. Applied extended-response questions commonly ask you to predict ecosystem-scale effects of disturbance (fire, land clearing, introduced species) or to compare biogeochemical cycles across ecosystems; confident handling of Year 11 vocabulary is what makes those questions tractable under exam time pressure.
Key Concepts
Biotic and Abiotic Factors
Ecosystems are defined by living (biotic) and non-living (abiotic) components. WACE responses benefit from organising your answer into these two categories, with WA-specific examples such as jarrah forest soils, seasonal rainfall and the fire regime.
Food Webs and Trophic Levels
Food webs show branching feeding relationships across producers, primary, secondary and tertiary consumers with decomposers acting across all levels. Be able to trace how the removal of one species ripples through the web — a common WACE exam scenario.
Energy Flow and the 10% Rule
Approximately 10% of energy transfers between trophic levels, with 90% lost to respiration, movement, uneaten biomass and faeces. Use energy pyramids to illustrate this loss and practise calculating energy available at higher trophic levels.
Biogeochemical Cycles
The carbon cycle (photosynthesis, respiration, decomposition, combustion, ocean absorption) and the nitrogen cycle (fixation, nitrification, assimilation, ammonification, denitrification) move matter between biotic and abiotic reservoirs. Name the specific bacteria at each nitrogen-cycle step for full marks.
Common Mistakes to Avoid
- Describing food chains where a food web better represents the ecosystem — WACE exams reward branched webs that show multiple feeding relationships and the cascading effect of removing a species.
- Omitting decomposers from trophic-level discussions — decomposers operate across all levels and recycle nutrients, a point SCSA marking guides allocate marks for mentioning.
- Confusing GPP and NPP — GPP is total energy fixed, NPP subtracts the producer's own respiration, and only NPP is available to consumers. WACE calculation questions test this distinction.
- Not naming the specific bacteria in the nitrogen cycle — SCSA marking guides reward naming Rhizobium, Nitrosomonas, Nitrobacter and Azotobacter at the correct step rather than referring generically to "bacteria".
Study Tips
- Draw the carbon and nitrogen cycles from memory with all reservoirs and arrow-labels, then check against the SCSA syllabus glossary.
- Practise energy-pyramid calculations — given GPP, compute NPP and energy available at each trophic level using the 10% rule.
- Build a table pairing each species interaction (predation, competition, mutualism, parasitism) with a specific Australian example.
- Name the bacteria at each step of the nitrogen cycle (Rhizobium, Nitrosomonas, Nitrobacter) and the reaction they catalyse.
- Use the South-West Australia Floristic Region (SWAFR) as your go-to biodiversity-hotspot case study for applied questions.
- Review past WACE exam questions that ask you to evaluate the impact of a disturbance (fire, land clearing, introduced species) on food-web stability.
- Work through the practice questions in this set at least twice using spaced repetition — testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Frequently Asked Questions
What does WACE Biology Year 11 Unit 1 Ecosystems cover?
Year 11 Unit 1 covers biotic and abiotic factors, habitat and niche, food webs, trophic levels, energy flow, biogeochemical cycles (carbon and nitrogen), species interactions, biodiversity and conservation, aligned to the SCSA Biology ATAR syllabus.
What is the difference between a habitat and a niche?
A habitat is the physical environment where an organism lives (its "address"). A niche is the organism's functional role in the ecosystem — what it eats, when it is active, how it reproduces and its interactions with other species (its "job").
Are these flashcards aligned to the SCSA WACE syllabus?
Yes — every flashcard and quiz question is mapped to the SCSA Biology ATAR Year 11 syllabus for Unit 1 Ecosystems and biodiversity.
Last updated: March 2026 · 20 flashcards · 20 quiz questions · Content aligned to the SCSA Curriculum