Food Chains, Food Webs, and Trophic Levels

Students model energy flow in ecosystems best when they physically manipulate organisms and energy transfers. Hands-on activities turn abstract trophic levels into concrete examples they can see and adjust. This kinesthetic approach builds lasting understanding of energy loss and interdependence.

• Grade 9
• Science
• 4 activities
• 25 min–45 min

Learning Objectives

1. Construct a complex food web for a specific Ontario ecosystem, identifying producers, primary consumers, secondary consumers, and tertiary consumers.
2. Analyze the impact of removing a specific trophic level, such as a primary consumer, on the stability and energy flow of a food web.
3. Compare and contrast the roles and energy transfer efficiency between different trophic levels within an ecosystem.
4. Explain the concept of energy loss at each trophic level using the 10 percent rule.

Concept Mapping

⏱ 30 min·Pairs

Card Sort: Local Food Chains

Provide cards naming Ontario organisms, energy arrows, and trophic labels. Pairs sequence them into three food chains, labeling levels. Pairs then share one chain with the class for feedback on accuracy.

Prepare & details

Construct a complex food web for a local ecosystem, identifying all trophic levels.

Facilitation Tip: During Card Sort: Local Food Chains, circulate to listen for misconceptions like 'deer eat plants because plants are consumers,' intervening immediately with guiding questions.

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

⏱ 45 min·Small Groups

Yarn Connect: Ecosystem Food Web

Small groups pin organism photos to a large board and link with yarn to show multiple feeding relationships. Groups tug yarn to demonstrate connections, then remove one organism to observe changes.

Prepare & details

Analyze the impact of removing a primary consumer on the entire food web.

Facilitation Tip: In Yarn Connect: Ecosystem Food Web, stand back to let students struggle with overlapping threads, only stepping in when groups hit dead ends.

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·Whole Class

Ripple Effect: Disruption Role-Play

Assign whole class roles as trophic levels in a wetland web. One student removes a primary consumer; others react by adjusting positions or numbers to show population shifts. Debrief with drawings.

Prepare & details

Differentiate between the roles of producers, primary consumers, secondary consumers, and tertiary consumers.

Facilitation Tip: For Ripple Effect: Disruption Role-Play, assign roles randomly to push students beyond familiar examples and reveal unexpected cascade effects.

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·Individual

Pyramid Build: Energy Trophic Models

Individuals stack blocks or draw pyramids showing decreasing biomass per level. Add local examples and calculate 10 percent energy transfer. Share to compare designs.

Prepare & details

Construct a complex food web for a local ecosystem, identifying all trophic levels.

Facilitation Tip: When building Pyramid Build: Energy Trophic Models, provide calculators to let students quantify energy loss at each level, reinforcing the 10 percent rule.

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

Teach this topic by starting with local examples students recognize, like boreal forests or wetlands, to build relevance. Avoid abstract global examples until they master local systems. Use frequent quick-checks to catch misconceptions early, especially around energy loss and decomposer roles. Research shows students grasp trophic levels best through repeated modeling, so cycle back to earlier activities when introducing new ecosystems.

What to Expect

Students will correctly identify trophic levels and energy transfer rules in local ecosystems. They will explain why top predators are rare and how disruptions ripple through food webs. Models will show complex connections, not simple chains, with decomposers closing the cycle.

Watch Out for These Misconceptions

Common Misconception

During Card Sort: Local Food Chains, watch for students who arrange consumers above producers, assuming animals capture energy directly.

What to Teach Instead

Ask them to revisit the energy rule: only producers capture solar energy. Have them place a solar panel image above the producers and trace energy arrows downward.

Common Misconception

During Yarn Connect: Ecosystem Food Web, watch for students who create isolated chains without overlaps.

What to Teach Instead

Prompt them to pull yarn between shared prey and ask, 'What else eats this organism?' Encourage them to add threads until no organism stands alone.

Common Misconception

During Ripple Effect: Disruption Role-Play, watch for students who assume all effects are immediate and negative.

What to Teach Instead

Have them map short-term and long-term effects on separate sheets, using different colored markers to highlight unpredicted outcomes like increased plant growth from reduced herbivory.

Assessment Ideas

Quick Check

After Card Sort: Local Food Chains, collect completed chains and circulate to check if students correctly labeled trophic levels and energy arrows. Provide immediate feedback on mislabeled organisms or missing energy transfers.

Discussion Prompt

During Ripple Effect: Disruption Role-Play, listen for groups to identify secondary and tertiary effects of their disruption. Ask probing questions like 'How might this change affect the decomposers?' to assess depth of understanding.

Exit Ticket

After Pyramid Build: Energy Trophic Models, collect pyramids and check if students quantified energy loss at each level. Read responses to the 10 percent question to identify lingering misconceptions about energy transfer.

Extensions & Scaffolding

• Challenge students who finish early to research an invasive species in Ontario and model its impact on a local food web using yarn and organisms.
• For students who struggle, provide pre-sorted sets of organisms grouped by trophic level to reduce cognitive load during card sorts.
• Allow extra time for students to research a decomposer’s role in a specific ecosystem and present findings to the class using their pyramid models as visuals.

Key Vocabulary

Producer	An organism, typically a plant or alga, that produces its own food using light, water, carbon dioxide, or other chemicals. They form the base of most food chains.
Consumer	An organism that obtains energy by feeding on other organisms. Consumers are categorized into primary, secondary, and tertiary levels based on their diet.
Trophic Level	A position an organism occupies in a food chain or food web. Each level represents a step in the flow of energy through an ecosystem.
Food Web	A complex network of interconnected food chains showing the feeding relationships and energy flow within an ecological community.
Biomass	The total mass of organisms in a given area or volume. Biomass generally decreases at higher trophic levels due to energy loss.