Energy Flow: Food Chains and Food Webs

Active learning helps students grasp energy flow because energy transfer is invisible and abstract. Moving, touching, and building models makes the 10 percent rule concrete and the complexity of webs visible. Working in teams also lets students argue about connections and corrections in real time, which strengthens understanding better than listening alone.

• Grade 7
• Science
• 4 activities
• 25 min–40 min

Learning Objectives

1. Construct a food web for a specific Ontario habitat, identifying producers, primary consumers, secondary consumers, tertiary consumers, and decomposers.
2. Analyze the impact of removing a keystone species from a constructed food web, predicting the cascading effects on other populations.
3. Compare and contrast the flow of energy in a simple food chain versus a complex food web, explaining the concept of energy loss at each trophic level.
4. Explain the role of decomposers in nutrient cycling within an ecosystem, relating their function to the overall health of the food web.

Concept Mapping

⏱ 35 min·Small Groups

Card Sort: Building Food Webs

Provide cards with local organisms, arrows for energy flow, and habitat labels. In small groups, students first arrange into simple food chains, then connect them into a food web, labeling trophic levels. Discuss interconnections and predict effects of species removal.

Prepare & details

Analyze the impact of removing a keystone species from a food web.

Facilitation Tip: During Card Sort: Building Food Webs, arrange desks in small groups and place one set of organism cards and arrows at each table so students physically move pieces to test multiple configurations.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 25 min·Whole Class

Yarn Web Simulation

Students stand in a circle holding cards for organisms. Toss yarn balls to represent feeding links while naming trophic roles. Remove a 'keystone' student and observe web collapse, then reconstruct and analyze stability.

Prepare & details

Differentiate between a food chain and a food web using specific examples.

Facilitation Tip: During Yarn Web Simulation, have one student from each group hold the center yarn and rotate partners to add strands, forcing repeated connections and overlaps.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 40 min·Small Groups

Energy Pyramid Layers

Groups stack foam blocks or draw pyramids representing trophic levels, adding organism cutouts and calculating 10% energy rule with sample data. Compare pyramids before and after removing a producer.

Prepare & details

Construct a complex food web for a given habitat, identifying trophic levels.

Facilitation Tip: During Energy Pyramid Layers, assign color-coded blocks to groups so they can stack and compare sizes before writing energy values on sticky notes.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Concept Mapping

⏱ 30 min·Pairs

Digital Food Web Builder

Use free online tools like Food Web Designer. Individually or in pairs, input a habitat's species, link them, and run removal scenarios to graph population changes.

Prepare & details

Analyze the impact of removing a keystone species from a food web.

Facilitation Tip: During Digital Food Web Builder, circulate with a checklist of key terms students must include in their final web to ensure rigor.

Setup: Tables with large paper, or wall space

Materials: Concept cards or sticky notes, Large paper, Markers, Example concept map

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Teaching This Topic

Start with simple food chains to build confidence, then shift to webs as soon as students can name producers and consumers. Avoid starting with pyramids; many students confuse energy loss with population numbers until they see real webs first. Research shows that students who build webs with yarn remember trophic relationships 30 percent better than those who only diagram, likely because the physical tension in the strings mimics energy transfer constraints.

What to Expect

Students should be able to trace energy paths through at least three trophic levels, quantify energy loss between levels, and explain how decomposers close the loop. They should describe webs as dynamic networks with shared links rather than separate chains and identify keystone roles that stabilize or destabilize energy flow.

Watch Out for These Misconceptions

Common Misconception

During Card Sort: Building Food Webs, watch for students who arrange organisms in equal rows or stacks, assuming energy stays constant.

What to Teach Instead

Prompt them to measure energy loss by assigning each arrow a label that drops the energy value by 90 percent, forcing them to shrink block sizes or reduce candy amounts as energy moves up levels.

Common Misconception

During Yarn Web Simulation, watch for students who treat each yarn strand as a separate chain rather than part of a shared network.

What to Teach Instead

Ask each group to tug one strand and notice which other strings jiggle, explicitly linking shared consumers like omnivores to multiple energy sources.

Common Misconception

During Energy Pyramid Layers, watch for students who exclude decomposers from the cycle or place them at the top of the pyramid.

What to Teach Instead

Have them physically move decomposer blocks from the side into the base of the pyramid and trace arrows back to producers, clarifying nutrient recycling.

Assessment Ideas

Exit Ticket

After Card Sort: Building Food Webs, collect each group’s final web and one sentence per student explaining why energy decreases as it moves up. Use these to check if they grasp the 10 percent rule and decomposer role.

Quick Check

During Yarn Web Simulation, pause the activity and ask each group to point to one omnivore and one tertiary consumer in their web, then predict one direct consequence of removing the primary producer.

Discussion Prompt

After Energy Pyramid Layers, display three student pyramids with different block sizes and facilitate a class vote on which pyramid best represents a real ecosystem with energy loss, followed by a brief journal reflection on why.

Extensions & Scaffolding

• Challenge students who finish early to add a scavenger or detritivore to their food web and explain how it fits into the energy pyramid without breaking the 10 percent rule.
• For students who struggle, provide a partially completed web template with missing arrows so they focus on relationships rather than starting from scratch.
• Deeper exploration: Have students research an invasive species in a local ecosystem, map its connections in a digital food web, and present how it shifts energy flow and threatens native species.

Key Vocabulary

Producer	An organism, typically a plant or alga, that produces its own food using light, water, carbon dioxide, or other chemicals. Producers form the base of a food chain or food web.
Consumer	An organism that obtains energy by feeding on other organisms. Consumers can be herbivores (plant-eaters), carnivores (meat-eaters), or omnivores (eating both).
Trophic Level	The position an organism occupies in a food chain or food web. Each level represents a step in the transfer of energy, from producers to various levels of consumers and decomposers.
Food Web	A complex network of interconnected food chains showing the feeding relationships within an ecological community. It illustrates the flow of energy through multiple pathways.
Keystone Species	A species that has a disproportionately large effect on its environment relative to its abundance. Its removal can cause significant changes to the structure of the ecosystem.