Australian Curriculum v9 / ACiQ Year 7 Science - Unit 4 - Matter and energy in ecosystems

Matter and energy in ecosystems

Use ecosystem models to distinguish energy flow from matter transfer and recycling.

Updated 2026-07-24 - 8 min read

Use ecosystem models to distinguish energy flow from matter transfer and recycling. This note connects the core scientific model to a worked example, an inquiry design and the limits of the evidence.

Core model

Energy enters, changes form and flows through feeding pathways. Matter is transferred in food, gases and waste and can return through decomposition. The same arrow may represent both transfers, but their overall system patterns differ.

Accessible diagram description: Sunlight points to grass, grass to wallaby, wallaby to dingo. Separate matter arrows connect every organism and its waste or remains to decomposers, then to soil and air materials used by producers. A note states that energy does not loop back.

A model is useful because it highlights relationships that help explain or predict evidence. It is not a perfect copy of reality. Always state what the representation includes, what its arrows or symbols mean, and one relevant limitation.

Authored representation workshop

Energy flow and matter recycling

Accessibility description: Sunlight transfers energy to grass, then energy moves through wallaby to dingo and to the surroundings. Matter moves through organisms, waste and remains to decomposers, then through soil and air materials back to producers. Energy does not loop back to the Sun.

Represented parts

  • Sunlight energy
  • Grass producer
  • Wallaby consumer
  • Dingo consumer
  • Energy transferred to surroundings
  • Decomposers
  • Soil and air materials

Represented relationships

  • Sunlight energy -> Grass producer (energy enters)
  • Grass producer -> Wallaby consumer (matter and energy)
  • Wallaby consumer -> Dingo consumer (matter and energy)
  • Grass producer -> Decomposers (waste and remains)
  • Wallaby consumer -> Decomposers (waste and remains)
  • Dingo consumer -> Decomposers (waste and remains)
  • Decomposers -> Soil and air materials (matter returned)
  • Soil and air materials -> Grass producer (matter reused)
  • Grass producer -> Energy transferred to surroundings (energy transfer)
  • Wallaby consumer -> Energy transferred to surroundings (energy transfer)
  • Dingo consumer -> Energy transferred to surroundings (energy transfer)

Learner action: Use two verbal traces through the diagram: first trace energy from sunlight to the surroundings, then trace matter from grass through an animal, decomposers and back to a producer. Explain why only the matter trace forms a cycle.

Leaf-litter mass during decomposition

Accessibility description: Moist litter usually loses more mass than dry litter. Moist container 3 changes very little, so its moisture and airflow should be checked.

| Condition | Container | Starting mass (g) | Final mass (g) | Mass loss (%) | | --- | --- | --- | --- | --- | | Moist | 1 | 20.0 | 12.1 | 39.5 | | Moist | 2 | 20.0 | 12.7 | 36.5 | | Moist | 3 | 20.0 | 18.9 | 5.5 | | Dry | 1 | 20.0 | 17.5 | 12.5 | | Dry | 2 | 20.0 | 17.8 | 11.0 | | Dry | 3 | 20.0 | 17.6 | 12.0 |

*Teacher-prepared sealed breathable containers; no direct handling by learners.*

Learner action: Evaluate a teacher-prepared decomposition plan rather than handling material. Specify starting mass, moisture treatment, weighing schedule and disposal; use the supplied table to calculate and compare mass loss, investigate moist container 3, and state why mass change cannot identify every matter pathway.

The representation and table are supplied evidence. Do not replace a represented value, relationship or anomaly with an expected result. If a visual version is created, preserve this text-equivalent information and define every symbol, arrow, heading and unit.

Worked example

The reasoning routine is:

  1. identify the observation, measurement or represented relationship
  2. select the relevant science idea
  3. connect the idea to the evidence in a complete sentence
  4. qualify the answer when the evidence or model has a boundary

Inquiry connection

Question: How does leaf-litter mass change during decomposition under moist and dry conditions?

Reasoned hypothesis: If litter is kept moist, its mass will decrease faster because decomposer activity is generally greater with available water.

  • Independent variable: moisture condition
  • Dependent variable: leaf-litter mass over time
  • Relevant controls: leaf type, starting mass, container, temperature and measurement interval
  • Hazard: decaying material may contain microorganisms or irritants
  • Risk control: use sealed breathable teacher-prepared containers, gloves and handwashing
  • Reproducibility detail: state litter mass, moisture volume, container setup, weighing schedule and disposal method

Possible data finding: moist litter lost 38% mass and dry litter lost 12%, while one moist container changed very little.

Evidence-based interpretation: The larger moist loss supports the hypothesis; the unusual container should be checked for a blocked opening or different moisture.

Limitation: Mass change alone does not identify which organisms or gases carried the matter away.

This investigation frame recurs across Year 7 Science. A sound response names a testable relationship, matches the hypothesis to the same variables, manages a realistic risk, specifies quantities and measurement rules, analyses the full data pattern, supports a claim with evidence and states what the evidence cannot establish.

Common errors and corrections

  • Error: Saying energy is recycled like matter. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Saying matter disappears when organisms die. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Leaving decomposers and waste out of every model. Correction: Return to the core model and identify the exact evidence or relationship before answering.
  • Error: Treating sunlight as the matter plants are built from. Correction: Return to the core model and identify the exact evidence or relationship before answering.

Practice

  1. Trace energy through three organisms.
  2. Trace one carbon atom through feeding and decomposition.
  3. Add waste and decomposers to a food-web model.
  4. Explain one quantity the model does not show.

Transfer task

Apply the topic to the investigation below without relying on a teacher or AI to mark the reasoning.

Evidence status: activity only. Use the task-specific rubric below for self-review or teacher feedback; completion does not automatically award mastery.

Context: How does leaf-litter mass change during decomposition under moist and dry conditions?

  1. Rewrite the question if it does not clearly name the relationship and measurable outcome.
  2. Write the matching reasoned hypothesis: include the expected direction and the science idea that justifies it.
  3. Identify the independent variable, dependent variable and at least three relevant controlled variables.
  4. Write a six-step reproducible method. Include equipment, quantities, units, an ordered measurement rule and at least three repeated trials for each condition.
  5. State the hazard, possible harm and a practical control. The control must address the stated hazard rather than being generic advice.
  6. Design a results table with headings and units. State which graph or other representation would best show the relationship and why.
  7. Use this possible finding: moist litter lost 38% mass and dry litter lost 12%, while one moist container changed very little. Describe the overall pattern, identify any anomaly and state a reasonable check.
  8. Write a conclusion using claim, specific evidence and scientific reasoning. Finish with this limitation: Mass change alone does not identify which organisms or gases carried the matter away.

Correction guide: Compare the question and hypothesis to confirm they use the same two variables. In the method, circle every quantity and unit and underline every controlled condition. In the data response, separate the broad pattern from any anomalous result. In the conclusion, highlight the evidence sentence and box the limitation. If one of these parts is absent, revise that part before checking the scientific vocabulary.

An excellent transfer response is precise without pretending the evidence is perfect. It makes the chain from question to method to data to claim visible, and it explains how the core model applies in the unfamiliar context.

Task-specific inquiry rubric

  • Question and hypothesis for moisture condition and leaf-litter mass over time: Names the same measurable relationship in both and gives a scientific reason. Revise if needed: Align the changed factor, measured outcome and predicted direction.
  • Fair, safe and reproducible method: Controls leaf type, starting mass, container, temperature and measurement interval, manages "decaying material may contain microorganisms or irritants", and specifies quantities, units, measurement rules and repeats. Revise if needed: Replace vague directions and generic safety advice with operational detail.
  • Data and analysis plan: Provides labelled headings and units, an appropriate representation, a way to describe the whole pattern and a rule for checking anomalies. Revise if needed: Show how evidence will answer the question before collecting it.
  • Scientific interpretation and boundary: Links the expected evidence to matter and energy in ecosystems and anticipates this boundary: Mass change alone does not identify which organisms or gases carried the matter away. Revise if needed: Explain the science link and state what the design cannot establish.

Self-check

For each response, check:

  • Did I use the correct scientific vocabulary?
  • Did I refer to the specific evidence, feature or data?
  • Did I explain the link rather than only naming it?
  • Did I avoid claiming more than the model or data support?
  • If an investigation is involved, did I address question, hypothesis, variables, safety, reproducibility, data, evidence and limitations?

Sources