Learners trace the path of energy through ecosystems, from the sun through producers and consumers. Students build food chains and food webs, apply the energy pyramid to explain why ecosystems need far more plants than animals, and explore how removing or adding one species can ripple through an entire ecosystem.

Key Ideas

• A food chain shows how energy moves from one organism to the next. Every chain begins with a producer that captures energy from the sun.
• Energy is lost as heat at every step in a food chain. Only about ten percent of energy passes from one level to the next.
• Because energy is lost at every step, ecosystems need far more producers than primary consumers, and far more primary consumers than top predators. This is the energy pyramid.
• Real ecosystems are food webs, not simple chains. Most animals eat more than one thing and are eaten by more than one predator.
• Removing or adding even one organism can change an entire food web. Predators keep prey populations in check, and prey populations support predator populations.
• Invasive species are organisms introduced to a new environment where they have no natural predators. They can outcompete native species and disrupt ecosystem balance.

Vocabulary

• Food Chain: The path energy follows as it moves from one organism to the next.
• Food Web: A network of overlapping food chains showing how energy flows through an ecosystem.
• Energy Pyramid: A diagram showing that each level of a food chain has much less available energy than the level below it.
• Producer: An organism that makes its own food using energy from the sun.
• Consumer: An organism that must eat other organisms to get energy.
• Ecosystem: All the living things in an area and how they interact with each other and their environment.
• Invasive Species: A plant or animal introduced to a new environment that spreads in ways that harm native species.

Hands-On Activity: Build a Food Web

Supply List

• A set of organism cards (written on index cards or slips of paper): Sun, Grass, Oak Tree, Mouse, Rabbit, Deer, Snake, Hawk, Fox, Owl, Earthworm, Mushroom
• String or yarn
• Tape or sticky tack to attach cards to a wall or table
• Pencil and paper for backup drawing

Instructions

• Lay all organism cards out on a table or stick them to a wall.
• Start with the sun. Draw or lay a piece of string from the sun to every producer (grass, oak tree). Arrows point from energy source to energy receiver.
• Now connect each producer to the organisms that eat it (grass to rabbit and mouse, oak tree to deer and mouse). Keep adding strings.
• Continue until every organism is connected to at least one other. Remember: some animals appear in multiple chains.
• Step back and look at your web. Find the organism with the most connections. What would happen if that organism disappeared? Pull its card away and discuss the ripple effects.
• Now add a new card: an Invasive Predator that eats rabbits, mice, AND snakes with no natural enemies. How does the web change?

Discussion: Ask learners why a food web is a more accurate picture of nature than a single food chain. What does the web shape tell us about how fragile or resilient an ecosystem might be?