Year 11 Biology Module 4 · IQ1 Lesson 1 of 18 ~35 min

Introduction to Ecosystems — Components, Structure and the Web of Life

A single hectare of Australian coastal wetland contains over 10,000 species interacting through nutrient exchange, competition and predation. Every organism occupies a specific role, and the removal of just one species can reshape the entire community. Understanding how ecosystems are structured is the foundation of everything in Module 4.

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Think First

How Is a Coral Reef in the Coral Sea Organised?

Imagine you are diving on the Great Barrier Reef. In the shallow, sunlit water you see seaweed and coral. Small fish dart between the coral branches. A sea turtle grazes on the seaweed. A reef shark patrols the drop-off. Tiny crabs and worms crawl through the sand beneath the coral.

Now consider this: if you removed every seaweed plant from this reef, what would happen to the small fish? To the turtle? To the shark? And what would happen to the coral itself?

Before reading on, answer both questions:

Q1: Why do you think species cluster in zones and layers on a reef? What does each species need from its immediate surroundings that determines where it lives?

Q2: If all the seaweed disappeared overnight, predict three changes that would occur in the reef community within one month. Explain the reasoning behind each prediction.

✏️ Write your answers in your book before reading on.

Know

  • The definition of an ecosystem and its two main components
  • The levels of biological organisation from individual to biosphere
  • The major biotic and abiotic components of ecosystems
  • That energy flows one-way while matter is cycled

Understand

  • Why ecosystems require a continuous energy input
  • How biotic and abiotic components interact in a coral reef
  • Why distinguishing producers, consumers and decomposers matters for nutrient flow

Can Do

  • Identify biotic and abiotic factors in any given ecosystem
  • Classify organisms into trophic roles using their feeding mode
  • Explain why removing one component affects the whole system
Key Terms — scan these before reading
Ecosystem A community of organisms interacting with each other and their non-living environment.
Biotic factor A living or once-living component of an ecosystem (e.g. plants, animals, bacteria).
Abiotic factor A non-living physical or chemical component of an ecosystem (e.g. sunlight, temperature, pH).
Producer An organism that synthesises organic compounds from inorganic sources using energy (photoautotroph or chemoautotroph).
Consumer An organism that obtains energy by eating other organisms (herbivore, carnivore, omnivore).
Decomposer An organism that breaks down dead organic matter and returns nutrients to the soil or water.
Biosphere The global sum of all ecosystems — the zone of life on Earth.
Core Content
1

What Is an Ecosystem?

The basic unit of ecology — living organisms plus their physical environment

An ecosystem is not just a collection of plants and animals. It is a functional unit consisting of all the organisms in a given area that interact with one another and with their non-living environment. The word itself comes from Greek oikos (house) and systema (organised whole) — an ecosystem is the "house" that organisms share, and every resident depends on the structure of that house.

Ecosystem components showing biotic and abiotic factors

Ecosystem components showing biotic and abiotic factors

Two components define every ecosystem:

  • Biotic components — all living or once-living organisms: producers (plants, algae, cyanobacteria), consumers (herbivores, carnivores, omnivores), and decomposers (bacteria, fungi). Detritivores such as earthworms and woodlice ingest dead organic matter whole, increasing surface area for microbial decomposers.
  • Abiotic components — all non-living physical and chemical factors: sunlight, temperature, water availability, salinity, pH, atmospheric gases (oxygen and carbon dioxide), soil texture and mineral content, and topography.

Neither component functions independently. Coral polyps (biotic) cannot build calcium carbonate skeletons without dissolved carbonate ions in seawater (abiotic). Seaweed (biotic) cannot photosynthesise without sunlight penetrating the water column (abiotic). The biotic and abiotic components are continuously exchanging matter and energy — this exchange is what makes an ecosystem a system rather than just a list of species.

HSC Tip In an exam, define an ecosystem by stating both components explicitly: "An ecosystem is a community of organisms (biotic component) interacting with each other and with their non-living environment (abiotic component)." A definition that omits either component will not earn full marks.
2

Levels of Biological Organisation — From Individual to Biosphere

Understanding scale is critical: what happens at one level shapes every level above it

Ecology operates across multiple scales of organisation. A student who confuses population with community, or ecosystem with biosphere, will struggle to answer questions that require precise terminology. Memorise this sequence and the defining feature of each level.

LevelDefinitionExample (Great Barrier Reef)
IndividualA single living organismOne staghorn coral colony
PopulationAll individuals of the same species in a defined areaAll staghorn coral colonies on a single reef flat
CommunityAll populations of different species in a defined areaCorals, fish, turtles, algae, and microbes on a reef flat
EcosystemCommunity plus its abiotic environmentReef flat community + sunlight, water temperature, salinity, dissolved gases
BiosphereAll ecosystems on Earth combinedAll coral reefs, oceans, forests, deserts, and tundra globally

Notice that each level includes everything below it but adds a new organisational property. A population is not just a group of individuals — it has properties that individuals lack, such as population density and age structure. A community is not just a collection of populations — it has properties such as species diversity and trophic structure. An ecosystem adds energy flow and nutrient cycling. The biosphere adds global biogeochemical cycles.

Common Error Students write "an ecosystem is all the living things in an area." This defines a community, not an ecosystem. The critical distinction is the inclusion of abiotic factors. Always check your definitions: did you mention the non-living environment?
3

Biotic Components — Producers, Consumers and Decomposers

Every organism has a trophic role determined by how it obtains energy and nutrients

All energy in almost every ecosystem enters through producers. Without producers, there is no energy base to support consumers or decomposers. Understanding the categories of biotic components is therefore not just taxonomy — it is understanding how energy and matter move through the system.

Producers (autotrophs)

Producers synthesise organic compounds from inorganic sources. They do not eat other organisms — they make their own food.

  • Photoautotrophs use light energy to fix carbon dioxide into glucose via photosynthesis. Examples: all green plants, algae, cyanobacteria. On a coral reef, zooxanthellae (symbiotic algae living inside coral polyps) are the primary photoautotrophs — they provide up to 90% of the coral's energy needs.
  • Chemoautotrophs use chemical energy from inorganic reactions to fix carbon. Examples: nitrifying bacteria in soil, sulfur-oxidising bacteria around hydrothermal vents. These are rare in most ecosystems but critically important in nutrient cycling.

Consumers (heterotrophs)

Consumers obtain energy by eating other organisms. They cannot synthesise their own organic compounds.

  • Primary consumers (herbivores) eat producers. On a reef: parrotfish grazing coral algae, sea turtles eating seagrass, zooplankton consuming phytoplankton.
  • Secondary consumers (carnivores) eat primary consumers. On a reef: small predatory fish eating herbivorous fish.
  • Tertiary consumers (top carnivores) eat secondary consumers. On a reef: reef sharks, large barracuda.
  • Omnivores eat both producers and consumers. On a reef: many crabs and some fish species.

Decomposers and detritivores (saprotrophs)

Decomposers break down dead organic matter and waste products, releasing mineral nutrients back into the environment.

  • Decomposers (bacteria and fungi) secrete enzymes that digest dead matter externally, then absorb the nutrients. They are the primary agents of nutrient recycling.
  • Detritivores (earthworms, millipedes, woodlice, some crustaceans) ingest detritus whole, physically fragmenting it and increasing the surface area available for microbial decomposers. They are not the same as decomposers — they work alongside them.
Common Error Students treat "decomposer" and "detritivore" as interchangeable. They are not. Decomposers use extracellular digestion (enzymes released outside the cell). Detritivores use intracellular digestion (food is ingested and digested inside the body). In an exam, name the correct group for the mechanism you are describing.
4

Abiotic Components — The Physical and Chemical Environment

Abiotic factors determine which organisms can live where and how productive the ecosystem is

Abiotic factors are not just background conditions — they are active determinants of ecosystem structure. A coral reef exists only where water temperature stays between 18°C and 30°C, salinity is stable, and light penetrates to support photosynthesis. Change any of these factors, and the reef collapses.

Abiotic factorWhy it mattersReef example
SunlightDrives photosynthesis; determines depth limit of producersReef-building corals limited to photic zone (<50 m); zooxanthellae need light
TemperatureAffects enzyme activity, metabolic rates, and coral bleaching thresholdCorals bleach when temperature exceeds ~30°C for extended periods
WaterRequired for photosynthesis, nutrient transport, and as a medium for aquatic lifeWater clarity affects light penetration and photosynthesis rate
SalinityAffects osmotic balance of cells; determines which species can surviveReef corals require stable marine salinity (~35‰); cannot survive in estuaries
pHAffects enzyme function and calcification ratesOcean acidification (lower pH) reduces carbonate ion availability, slowing coral skeleton growth
Atmospheric gasesCO2 for photosynthesis; O2 for aerobic respirationDissolved CO2 and HCO3- provide carbon for coral calcification
Soil / substrateProvides anchorage, minerals, and habitat structureHard substrate required for coral larval settlement; soft sediment excludes reef corals
TopographyCreates microhabitats and affects water flowReef slope, crest and flat each host different communities due to wave exposure and light
Link Ahead These abiotic factors will be explored in depth in Lesson 6 (Abiotic Factors), where you will learn about tolerance ranges, limiting factors, and how abiotic conditions determine species distribution. For now, recognise that every ecosystem is shaped by its specific abiotic conditions.
5

Energy Flows One-Way — Matter Is Cycled

The most fundamental principle of ecosystem dynamics: energy enters, degrades, and leaves; matter is reused indefinitely

Ecosystems require a continuous energy input because energy is not recycled. Nearly all ecosystems on Earth are powered by sunlight captured by photoautotrophs. A tiny fraction — deep-sea hydrothermal vent communities — are powered by chemical energy from inorganic compounds. In both cases, energy enters the ecosystem, flows through trophic levels, and is ultimately lost as heat. Matter, by contrast, is continuously recycled.

Energy Flow

  • Enters as sunlight (or chemical energy)
  • Captured by producers via photosynthesis (or chemosynthesis)
  • Transferred to consumers through feeding
  • Lost as heat at every transfer via cellular respiration
  • Cannot be recycled — must be continuously replenished
  • Flows in one direction: sun → producers → consumers → heat

Matter Cycling

  • Carbon, nitrogen, phosphorus and other elements are finite in an ecosystem
  • Producers absorb inorganic nutrients from soil or water
  • Consumers obtain elements by eating other organisms
  • Decomposers release nutrients back to the environment
  • Reused repeatedly — no continuous input required
  • Loops continuously: soil/water → producers → consumers → decomposers → soil/water

Why does this distinction matter? Because it explains why ecosystems can run out of energy (if sunlight is blocked, photosynthesis stops) but do not run out of matter (the same carbon atoms cycle between organisms and the environment for millions of years). It also explains why pollution can accumulate in ecosystems — matter is not destroyed, only moved around.

HSC Tip The exam frequently tests whether students understand this distinction. The correct statement is: "Energy flows through an ecosystem in one direction and is lost as heat, while matter is cycled between biotic and abiotic components." Never write that energy is "recycled" — this is one of the most common errors in HSC Biology.
Real-World Anchor — Australian Coastal Wetlands

Why Coastal Wetlands Are Among Australia's Most Productive Ecosystems

Australian coastal wetlands — including Moreton Bay in Queensland, the Hunter Wetlands in New South Wales, and the Peel-Yalgorup system in Western Australia — are among the most productive ecosystems on the continent. They receive abundant sunlight, have nutrient-rich sediments from river input, and support extraordinary biodiversity.

A typical coastal wetland ecosystem includes: phytoplankton and aquatic plants (producers), zooplankton and aquatic invertebrates (primary consumers), small fish and waterbirds (secondary consumers), larger predatory fish and raptors (tertiary consumers), and bacteria and fungi (decomposers). The abiotic components include: shallow, sunlit water; muddy, nutrient-rich sediment; seasonal temperature variation; and tidal flushing that replenishes oxygen and removes waste.

These wetlands are not just biologically rich — they provide critical ecosystem services: filtering pollutants from agricultural runoff, storing carbon in sediments, buffering coastlines from storm surges, and serving as nurseries for commercially important fish species. Understanding their structure is the first step toward protecting them.

Priority Misconceptions — Ecosystem Structure

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"Energy is recycled like matter." — Energy is not recycled. It flows through an ecosystem in one direction, is transferred between trophic levels, and is lost as heat at every step via cellular respiration. Only matter (carbon, nitrogen, phosphorus) is cycled.

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"Decomposers and detritivores are the same thing." — Decomposers (bacteria, fungi) secrete enzymes that digest dead matter externally and absorb the nutrients. Detritivores (earthworms, millipedes, woodlice) ingest detritus whole and fragment it. They work together but use different mechanisms.

Image Slot 1: Diagram showing levels of biological organisation — individual (one coral polyp) → population (colony) → community (reef flat with multiple species) → ecosystem (community + water, sunlight, temperature) → biosphere (all ecosystems on Earth). Each level labelled with its defining feature.

Image Slot 2: Australian coastal wetland cross-section showing biotic and abiotic components. Biotic: algae, aquatic plants, invertebrates, fish, waterbirds, bacteria. Abiotic: sunlight, water, sediment, dissolved oxygen, temperature gradient. Arrows showing energy flow (one-way) and matter cycling (loop).

Copy Into Your Books

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Ecosystem Definition

  • A community of organisms interacting with each other
  • And with their non-living (abiotic) environment
  • Two components: biotic (living) and abiotic (non-living)

Levels of Organisation

  • Individual → one organism
  • Population → same species, same area
  • Community → all populations in an area
  • Ecosystem → community + abiotic environment
  • Biosphere → all ecosystems on Earth

Biotic Components

  • Producers (autotrophs): photoautotrophs + chemoautotrophs
  • Consumers (heterotrophs): herbivores, carnivores, omnivores
  • Decomposers: bacteria, fungi (extracellular digestion)
  • Detritivores: earthworms, woodlice (ingest detritus whole)

Energy vs Matter

  • Energy: flows one-way, lost as heat, not recycled
  • Matter: cycled between biotic and abiotic components
  • Nearly all energy enters as sunlight via photoautotrophs
Activities
Sort + Classify — Activity 1

Biotic or Abiotic? Producer, Consumer or Decomposer?

For each item below, classify it as biotic or abiotic. If biotic, further classify it as producer, consumer (herbivore/carnivore/omnivore) or decomposer/detritivore.

1 Cyanobacteria living on the surface of a coral colony

✏️ Classify and justify in your book.

2 Dissolved nitrate ions (NO3-) in wetland water

✏️ Classify and justify in your book.

3 A parrotfish grazing on coral algae

✏️ Classify and justify in your book.

4 Fungi breaking down a fallen mangrove leaf

✏️ Classify and justify in your book.

5 Water temperature at 26°C on a reef flat at midday

✏️ Classify and justify in your book.
Analyse + Connect — Activity 2

Applying Ecosystem Concepts to a New Scenario

A student is studying a semi-arid shrubland ecosystem in western New South Wales. They observe: mulga trees (Acacia aneura), kangaroos grazing on grasses, dingoes hunting kangaroos, termites feeding on dead wood, and soil bacteria decomposing leaf litter. Abiotic factors include: intense summer heat (up to 45°C), low annual rainfall (<250 mm), sandy soil with low nitrogen, and high UV radiation.

Using this information:

✏️ Answer all parts in your book using ecosystem terminology.
Multiple Choice
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Test Your Understanding

UnderstandBand 3

1. Which statement best describes the difference between a community and an ecosystem?

A
A community includes only producers and consumers; an ecosystem also includes decomposers
B
A community is all the populations of different species in an area; an ecosystem is the community plus its abiotic environment
C
A community is all the individuals of one species; an ecosystem is all the individuals of all species
D
A community includes abiotic factors; an ecosystem includes only biotic factors
B
A community is all the populations of different species in an area; an ecosystem is the community plus its abiotic environment
C
A community is all the individuals of one species; an ecosystem is all the individuals of all species
D
A community includes abiotic factors; an ecosystem includes only biotic factors
UnderstandBand 3

2. In a coral reef ecosystem, zooxanthellae (symbiotic algae) living inside coral polyps provide up to 90% of the coral's energy via photosynthesis. How should zooxanthellae be classified?

A
Consumers, because they live inside another organism and depend on it for shelter
B
Decomposers, because they break down waste products produced by the coral polyp
C
Photoautotrophs, because they use light energy to synthesise organic compounds from carbon dioxide
D
Chemoautotrophs, because they use chemical energy from the coral's metabolic waste
B
Decomposers, because they break down waste products produced by the coral polyp
C
Photoautotrophs, because they use light energy to synthesise organic compounds from carbon dioxide
D
Chemoautotrophs, because they use chemical energy from the coral's metabolic waste
AnalyseBand 4

3. A student states: "Energy is recycled through ecosystems, just like carbon and nitrogen." Which statement best explains why this is incorrect?

A
Energy is not recycled because it is destroyed by decomposers before it can be reused
B
Energy is recycled but only between producers and primary consumers, not at higher trophic levels
C
Energy is not recycled because it escapes into space as infrared radiation
D
Energy flows through ecosystems in one direction and is lost as heat at each trophic transfer via cellular respiration; only matter is cycled because atoms are rearranged but not destroyed
B
Energy is recycled but only between producers and primary consumers, not at higher trophic levels
C
Energy is not recycled because it escapes into space as infrared radiation
D
Energy flows through ecosystems in one direction and is lost as heat at each trophic transfer via cellular respiration; only matter is cycled because atoms are rearranged but not destroyed
UnderstandBand 3

4. Which of the following best distinguishes a detritivore from a decomposer?

A
Detritivores ingest dead organic matter whole and fragment it internally; decomposers secrete digestive enzymes externally and absorb the nutrients
B
Detritivores are animals; decomposers are plants — this is the only distinction
C
Detritivores break down living organisms; decomposers break down only dead matter
D
There is no meaningful distinction — the terms are interchangeable in ecology
B
Detritivores are animals; decomposers are plants — this is the only distinction
C
Detritivores break down living organisms; decomposers break down only dead matter
D
There is no meaningful distinction — the terms are interchangeable in ecology
EvaluateBand 5

5. A marine reserve manager is designing a monitoring program for a coastal wetland. She needs to measure both the living organisms and the environmental conditions that affect them. Which combination of measurements would best characterise the ecosystem (as opposed to just the community)?

A
Counting all fish species and measuring waterbird population sizes — these are the biotic components that define the ecosystem
B
Measuring water temperature and salinity only — these abiotic factors determine everything else
C
Recording species diversity (fish, invertebrates, plants) AND measuring dissolved oxygen, pH, temperature, and nutrient concentrations — this captures both biotic and abiotic components
D
Mapping the wetland boundaries on a GPS — the geographic area alone defines the ecosystem
B
Measuring water temperature and salinity only — these abiotic factors determine everything else
C
Recording species diversity (fish, invertebrates, plants) AND measuring dissolved oxygen, pH, temperature, and nutrient concentrations — this captures both biotic and abiotic components
D
Mapping the wetland boundaries on a GPS — the geographic area alone defines the ecosystem
Short Answer
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Short Answer Questions

ApplyBand 4

6. A coastal wetland contains the following: phytoplankton, zooplankton, small fish, herons, bacteria in the sediment, and water snails that feed on dead plant matter. Classify each of these organisms into their trophic role (producer, primary consumer, secondary consumer, tertiary consumer, decomposer, or detritivore). Explain your reasoning for the water snails. 4 MARKS

✏️ Answer in your book.
AnalyseBand 4–5

7. Explain why an ecosystem requires a continuous input of energy but does not require a continuous input of carbon. In your answer, distinguish between the pathway of energy and the pathway of carbon through an ecosystem, naming the processes involved at each stage. 5 MARKS

✏️ Answer in your book.
EvaluateBand 5–6

8. The Great Barrier Reef has experienced repeated mass coral bleaching events in recent years. During bleaching, stressed corals expel their zooxanthellae (symbiotic algae), losing their primary energy source. Using your knowledge of ecosystem components and the coral reef as an Australian ecosystem, predict and justify three consequences of a large-scale bleaching event on the reef community. 6 MARKS

✏️ Answer in your book.

Revisit Your Thinking

Return to your Think First responses at the start of this lesson.

Comprehensive Answers

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Activity 1 — Biotic or Abiotic?

1. Cyanobacteria: Biotic; producer (photoautotroph). Cyanobacteria are living organisms that carry out photosynthesis, using light energy to fix carbon dioxide into organic compounds. They are autotrophs and therefore producers.

2. Dissolved nitrate ions: Abiotic. Nitrate is a dissolved inorganic chemical compound. It is not living and never was living. It is an abiotic factor that producers absorb as a nutrient.

3. Parrotfish grazing on coral algae: Biotic; consumer (herbivore / primary consumer). The parrotfish is a living organism that obtains energy by eating producers (algae). It cannot synthesise its own food.

4. Fungi breaking down a mangrove leaf: Biotic; decomposer. Fungi secrete digestive enzymes externally onto dead organic matter and absorb the nutrients. This is extracellular digestion, the defining feature of decomposers.

5. Water temperature at 26°C: Abiotic. Temperature is a non-living physical factor. It affects metabolic rates and enzyme activity but is not itself an organism.

Activity 2 — Semi-Arid Shrubland Scenario

(a) Producers: mulga trees (Acacia aneura), grasses. Consumers: kangaroos (primary consumer/herbivore), dingoes (secondary or tertiary consumer/carnivore). Decomposers/detritivores: soil bacteria (decomposer), termites (detritivore — they ingest dead wood).

(b) Three abiotic factors limiting mulga distribution: (1) Low rainfall (<250 mm) — limits photosynthesis and growth; mulgas have deep taproots to access groundwater. (2) High summer temperatures (up to 45°C) — causes water loss via transpiration and can denature enzymes; mulgas have small leaves to reduce surface area. (3) Sandy soil with low nitrogen — limits protein synthesis and chlorophyll production; mulgas form symbioses with nitrogen-fixing bacteria in root nodules to compensate.

(c) Energy must continuously enter because it is lost as heat at every trophic transfer via cellular respiration and cannot be recycled. The ecosystem depends on a constant input of solar energy captured by producers. Nitrogen does not need continuous input because it is cycled — nitrogen fixed by bacteria is incorporated into plant proteins, transferred to consumers through feeding, and returned to the soil by decomposers and detritivores as ammonium and nitrate. The same nitrogen atoms are reused indefinitely.

(d) Without dingoes, kangaroo populations would likely increase due to reduced predation pressure (predator removal). Increased kangaroo grazing would reduce grass cover, potentially leading to soil erosion and changes in plant community composition. This illustrates a trophic cascade — the removal of a top predator affects lower trophic levels.

Multiple Choice

1. B — A community is all populations of different species in an area; an ecosystem adds the abiotic environment. Option A is wrong because both include decomposers. Option C confuses population with community. Option D reverses the definitions.

2. C — Zooxanthellae are photoautotrophs because they use light energy for photosynthesis. Option A confuses symbiosis with consumption. Option B is wrong because they do not break down waste. Option D is wrong because they use light, not chemical energy.

3. D — Energy flows one-way and is lost as heat; matter is cycled. Option A is wrong because energy is not destroyed by decomposers — it is lost as heat at all trophic levels. Option B is wrong because energy is not recycled at any level. Option C is wrong because the heat is not the key point — it is lost to the surroundings, not specifically to space.

4. A — Detritivores ingest and fragment; decomposers use extracellular digestion. Option B is wrong because decomposers are not plants. Option C is wrong because detritivores do not attack living organisms. Option D is wrong — the distinction is important.

5. C — An ecosystem requires measurement of both biotic and abiotic components. Option A measures only community. Option B measures only abiotic factors. Option D measures only geography.

Short Answer Model Answers

Q6 (4 marks): Phytoplankton: producer (photoautotroph) [0.5]. Zooplankton: primary consumer (herbivore) [0.5]. Small fish: secondary consumer (carnivore) [0.5]. Herons: tertiary consumer (top carnivore) [0.5]. Bacteria: decomposer [0.5]. Water snails: detritivore [0.5] because they feed on dead plant matter by ingesting it whole and fragmenting it internally, increasing surface area for microbial decomposers [1]. They are not decomposers because they do not secrete extracellular digestive enzymes [0.5]. Total: 4 marks.

Q7 (5 marks): Energy pathway: Energy enters the ecosystem as sunlight [0.5] and is captured by producers via photosynthesis [0.5], converting light energy into chemical energy stored in glucose. This energy is transferred to consumers through feeding (consumption) [0.5]. At each trophic level, energy is lost as heat via cellular respiration [0.5] — approximately 90% is lost at each transfer. Because energy is continuously lost and cannot be recycled [0.5], a continuous input is required to maintain the ecosystem. Carbon pathway: Carbon enters as carbon dioxide [0.5] and is fixed by producers into organic compounds via photosynthesis [0.5]. Carbon is transferred to consumers through feeding [0.5]. Carbon is returned to the environment as carbon dioxide via cellular respiration [0.5] and as organic matter via decomposition. The same carbon atoms cycle repeatedly [0.5], so no continuous input is needed. Total: 5 marks.

Q8 (6 marks): Consequence 1: Primary consumers that feed directly on coral tissue or coral mucus (such as some butterflyfish and parrotfish) would decline due to reduced coral health and coverage [1]. Justification: Without zooxanthellae, corals lose their primary energy source, reducing growth, reproduction, and tissue production — less food available for specialist coral feeders [1]. Consequence 2: Secondary consumers (predatory fish that eat herbivorous fish) would also be affected, though perhaps with a time lag [1]. Justification: The decline in coral health reduces structural complexity, which provides shelter for small fish. Reduced shelter means reduced prey populations, which cascades up to predators [1]. Consequence 3: Decomposer activity would initially increase then decrease [1]. Justification: Bleaching causes coral mortality, producing a pulse of dead organic matter that decomposers break down. However, once the dead material is consumed, the long-term reduction in primary production means less organic matter entering the detrital pathway, reducing decomposer populations over time [1]. Total: 6 marks.

Mark lesson as complete

Tick when you have finished all activities and checked your answers.

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