Where does the energy go?

Classroom resources

Load these into Waypoints Prepare: choose Load URL and paste the copied address, or download the file and import it. In Prepare, the worksheet's Teacher edition shows the answers; the student copy hides them.

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Students will be able to

• I can trace the direction of energy through at least three levels of a food web.
• I can explain that energy is lost at each level.
• I can explain the difference between energy flow and matter cycling.

Timing

Engage and Explore 8 min · Explain 9 min · Evaluate 3 min · Typical adds 2 min, Wider about 2 min

Before class

A concept tutorial for introducing or revising the idea; it does not replace an energy pyramid built from real data. Set the width with ?width=minimum, typical (default) or wider.

The hinge risk is conflating energy flow with matter cycling: students then predict energy "coming back" in node 4.

Board notes: the board shows energy by feeding level with the 10% rule (10 000, 1 000, 100, 10 kJ). The 10% rule is an average; real transfers range from about 5% to 20%. Animals that feed at more than one level (the kookaburra) are shown at their highest level.

Running the lesson

1. Engage: most predict half or more. Write the chain on the board with each prediction.
2. Explore: ask students to trace two different chains and compare the energy at the top.
3. Explain: the sort names where the 90% goes; the third question separates energy from matter.
4. In your own words: the 'energy flows, matter cycles' paragraph is the evidence.

The hard part (on purpose)

Seeing that energy is lost at each step and not recycled, while matter is. When a student says decomposers recycle energy, ask what they give back to the soil.

When students get stuck

Answers to the checks

1. Engage: how much gets through?: Grass captures 10 000 kJ of energy from sunlight. A grasshopper eats grass, a lizard eats grasshoppers, a kookaburra eats lizards. About how much of that energy reaches the kookaburra?
   About 10 kJ. Roughly 90% is used or lost as heat at each step, so only about 10% passes on: 10 000 → 1 000 → 100 → 10.
2. Explore: follow the energy: Trace a food chain of at least four organisms, from a producer to the top.
   
3. Down the levels: A lizard gets 100 kJ from the grasshoppers it eats. About how much reaches a kookaburra that eats the lizard, in kJ?
   10
   About 10% passes on: 100 × 0.1 = 10 kJ.
4. Where it goes: Where does the other 90% go at each step?
   Heat given off by the animal's body → Not passed to the next level; Energy used for moving, breathing and keeping warm → Not passed to the next level; Parts not eaten (bones, fur, roots) → Not passed to the next level; Energy stored in the eaten animal's body → Passed to the next level
5. Energy and matter: Which statement is true?
   Energy flows one way through a web and is lost as heat; matter (the atoms) is recycled by decomposers
   That's why every food web needs a constant supply of sunlight, but no new atoms.
6. Mix it up: Looking back at food webs: in the chain grass → grasshopper → lizard → kookaburra, which is the secondary consumer?
   The lizard
   A secondary consumer eats a primary consumer. The lizard eats the grasshopper, which eats the grass.
7. Elaborate: why so few eagles?: Why are there far fewer wedge-tailed eagles than grasshoppers in an ecosystem?
   So little energy reaches the top of the food chain that it can only support a few large predators
   Each level up gets about a tenth of the energy, so it can support far fewer organisms.
8. Elaborate: a desert and a rainforest: A rainforest's plants capture far more energy each year than a desert's. What would you predict about their food webs?
   The rainforest can support more organisms and more levels of consumers
   Energy captured by producers sets the size of everything above them.

Stretch and support

Stretch: If humans ate grain directly instead of feeding it to cattle and eating the beef, how much more energy would reach us? Use the 10% rule.

Support: Give a four-row energy pyramid template to fill in while tracing.

Coach prompt (optional)

For a student who has done the lesson and is still stuck. They paste it into an AI tool your school allows; it asks questions about this lesson's one idea and doesn't give answers. Students see it on the course recap page only through a link ending in ?coach=1: recap with coach prompts.

You are a patient science coach for a Year 7 student in Australia. Help me understand ONE idea only, from the lesson "Where does the energy go?".

The idea: Matter and energy flow: I can explain the direction and loss of energy through trophic levels and distinguish energy flow from matter cycling.

What understanding looks like:
- States that energy is lost at each trophic level
- Correctly distinguishes energy flow from matter cycling in an explanation
- Traces the direction of energy through at least 3 trophic levels

Mistakes students often make here:
- A student says decomposers recycle energy.
- A student thinks the eaten animal passes on all its energy.
- A student reverses the arrows when tracing.

How to coach me (rules from the Waypoints Kit coach):
- Ask me one short question at a time (2 to 4 sentences) and wait for my answer. Never give me the answer before you have heard my thinking, and don't hide the answer inside your question.
- Start in Discover: ask me to explain the idea in my own words, or to predict what happens in a simple example. I can switch any time: "teach it back" (you play a beginner and I explain), "spot the flaw" (you show me an answer with one common mistake and I find it), or "check" (I explain, and you tell me what is solid and what to revisit).
- If I am stuck or say "just tell me", ask what I think first, then give a small hint or a simpler example. Explain only after I have had a real go.
- If I seem to be missing the idea that comes before this one (From food chains to food webs), check it quickly, then come back.
- Stay in this idea: don't teach later ideas or add extra content. If I ask about something else, say it is for another lesson and bring me back.
- After you help, ask me one reflective question, such as how I know my answer is right or what I would check.
- Praise my effort and method, not my ability.
- You can be wrong: if I rely on something you said, remind me to check it against my notes or the lesson. If you don't know, say so.
- Use simple words.
- Stop when I can explain the idea in my own words and get one new example right. Then tell me to go back to the lesson "Where does the energy go?".

Exit ticket

Why does a food chain rarely have more than four or five levels?

Only about 10% of the energy passes to each level, so after four or five steps there is too little left to support another population.

What each step is for

• Engage: how much gets through?: Students who think energy is passed on whole (or recycled) will choose those options; the trace makes the 90% loss visible.
• Explore: follow the energy: Tracing a chain click by click, with the energy shrinking at each level, connects arrows to energy flow and loss.
• Explain: flow, loss and cycling: Stating the one-way flow with losses, then contrasting it with matter cycling, stops the 'energy is recycled' error that breaks node 4 predictions.
• Mix it up: Energy flows along the arrows between producers and consumers, so the roles in a web come back before counting the energy at each step.
• Elaborate: why so few eagles?: Connecting energy loss to population size explains why top predators are rare, the link to node 4.
• Elaborate: a desert and a rainforest: Comparing two ecosystems' energy input applies the flow principle to ecosystem structure.

Where it leads

Next: abiotic factors (node 3), then biotic factors and cascades (node 4), where energy flow explains why removing a species changes the others.

In class: build an energy pyramid with blocks (10 for grass, 1 for grasshoppers…); measure the heat from a compost heap.