Science · Grade 6 · Life Systems: Diversity and Survival · Term 1

Food Webs and Energy Flow

Students model the flow of energy through food chains and food webs, identifying trophic levels.

• Ontario Curriculum Expectations
• MS-LS2-3

About This Topic

Food webs represent interconnected feeding relationships that show energy flow through ecosystems. Grade 6 students construct food webs for local Ontario ecosystems, such as a pond or mixed forest, classifying organisms as producers, primary and secondary consumers, and decomposers. They model trophic levels and trace energy paths from sunlight through herbivores to top predators. This aligns with Ontario curriculum expectations in Life Systems for understanding diversity and survival.

Students investigate energy transfer between trophic levels, noting that only about 10 percent moves to the next level due to losses in respiration, movement, and waste. They predict impacts of disruptions, like a drop in primary consumer populations, which could starve predators or allow overgrowth of producers. These explorations build skills in modeling complex systems and making evidence-based predictions essential for scientific inquiry.

Active learning suits this topic well. Students gain deep insight by physically assembling food webs with cards and string, then simulating changes by removing organisms. Group discussions of outcomes make abstract energy losses concrete and highlight ecosystem interdependence in ways lectures cannot.

Key Questions

1. Construct a food web for a local ecosystem, identifying producers, consumers, and decomposers.
2. Explain how energy is transferred between trophic levels in an ecosystem.
3. Predict the impact on a food web if a primary consumer population significantly decreases.

Learning Objectives

• Classify organisms within a given food web as producers, primary consumers, secondary consumers, or decomposers.
• Explain the transfer of energy from one trophic level to the next, identifying the approximate percentage of energy transferred.
• Create a model of a local Ontario ecosystem's food web, illustrating the flow of energy.
• Predict the cascading effects on a food web if the population of a specific organism is significantly altered.

Before You Start

Characteristics of Living Things

Why: Students need to understand what defines life and the basic needs of organisms to identify them within an ecosystem.

Basic Needs of Living Things

Why: Understanding that organisms need energy for survival is fundamental to grasping the concept of energy flow through feeding relationships.

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 webs.
Consumer	An organism that obtains energy by feeding on other organisms. Consumers are categorized as primary (herbivores), secondary (carnivores or omnivores), and tertiary.
Decomposer	An organism, such as bacteria or fungi, that breaks down dead organic material, returning essential nutrients to the ecosystem.
Trophic Level	The position an organism occupies in a food chain or food web. Each level represents a step in the transfer of energy.
Food Web	A complex network of interconnected food chains showing the feeding relationships and energy flow within an ecosystem.

Watch Out for These Misconceptions

Common Misconception

Energy cycles endlessly in food webs like water in the water cycle.

What to Teach Instead

Energy flows one way from sun through trophic levels and dissipates as heat; it does not recycle. Building physical models helps students trace paths and see losses at each step, while group disruptions reveal no return flow.

Common Misconception

All consumers can eat anything at lower levels.

What to Teach Instead

Feeding relationships are specific; not every predator eats every prey. Role-playing with yarn connections clarifies dependencies, and station activities reinforce trophic specificity through hands-on sorting.

Common Misconception

Removing one species has little effect on the whole web.

What to Teach Instead

Ecosystems are interdependent; changes cascade. Simulations where students remove pieces and track ripples correct this by making predictions visual and testable in collaborative settings.

Active Learning Ideas

Card Sort: Local Food Web Builder

Provide cards with local Ontario organisms, arrows for energy flow, and labels for trophic levels. In pairs, students sort and connect cards into a food web on large paper, justifying placements with research notes. End with labeling producers, consumers, and decomposers.

30 min·Pairs

Stations Rotation: Energy Transfer Models

Set up stations with pyramid diagrams: one for numbers, biomass, and energy. Small groups add cutouts of organisms to each pyramid, calculating 10 percent energy loss between levels. Rotate and compare results.

45 min·Small Groups

Simulation Game: Disruption Role-Play

Assign whole class roles as organisms in a food web. Use balls of yarn to show connections. Remove primary consumers and observe chain reactions as predators 'starve' by dropping yarn. Discuss predictions versus outcomes.

35 min·Whole Class

Individual: Prediction Journal

Students draw a food web, then predict and sketch changes if a species decreases. Use before-and-after comparisons with annotations on energy flow impacts.

20 min·Individual

Real-World Connections

• Ecologists studying the impact of invasive species, like zebra mussels in Lake Ontario, use food web models to predict how these new organisms will affect native populations and overall ecosystem health.
• Conservationists designing wildlife management plans for Algonquin Provincial Park analyze food webs to understand how changes in prey availability might affect predator populations, such as wolves and deer.
• Farmers and agricultural scientists consider food webs when managing pests. Understanding the natural predators of crop pests can lead to biological control methods rather than relying solely on pesticides.

Assessment Ideas

Quick Check

Provide students with a list of organisms from a local ecosystem (e.g., pond: algae, tadpole, frog, heron, bacteria). Ask them to draw arrows showing the energy flow and label each organism with its trophic level (producer, primary consumer, etc.).

Discussion Prompt

Pose the scenario: 'Imagine a disease drastically reduces the population of rabbits in a forest ecosystem. Discuss with your group: What organisms would be most affected? How would the producers and top predators likely respond? What might happen to the decomposer population?'

Exit Ticket

On a slip of paper, have students write the definition of a producer in their own words and give one example found in an Ontario forest. Then, ask them to explain why only about 10% of energy is transferred to the next trophic level.

Frequently Asked Questions

How do you teach food webs in Ontario Grade 6 science?

Start with local ecosystems students know, like schoolyards or nearby wetlands. Have them research organisms, then build food webs using cards for species and yarn for connections. Follow with energy pyramid models to show 10 percent transfer rule. This sequence matches curriculum expectations and engages students through observation and modeling.

What are common misconceptions about energy flow in food webs?

Students often think energy recycles or that trophic levels are interchangeable. Address these with hands-on pyramids where they calculate losses and simulations of disruptions. Peer teaching during group builds reinforces correct flow as one-directional from producers upward.

How can active learning help students understand food webs?

Active approaches like constructing physical models with organism cards and string let students manipulate connections, simulate population changes, and observe cascades firsthand. Collaborative predictions and discussions build systems thinking, turning abstract interdependencies into tangible experiences that stick better than diagrams alone.

How to predict impacts on food webs if a population decreases?

Guide students to trace energy paths from the affected species up and down the web. Use before-after sketches or role-plays to show predator starvation or prey overgrowth. Local examples, like beaver declines affecting wetlands, make predictions relevant and testable with class data.