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.

Discussion

• Why does every food chain begin with a producer? Where does the producer get its energy?
• If only about 10% of energy passes to the next level, why do you think ecosystems need so many more plants than top predators?
• Why are real ecosystems better described as food webs instead of simple food chains? Can you think of an animal that eats more than one kind of food?
• What do you think would happen to a food web if one important predator suddenly disappeared? What other populations might be affected?
• Why can an invasive species cause problems even if it doesn't directly harm or eat another species? What might happen when it competes for the same food or space?