Explore how energy moves through nature — from producers to apex predators — with two hands-on interactive activities, original diagrams, and a scored practice quiz.
Every living thing needs energy, and almost all of that energy starts in one place: the sun. Food chains and food webs are the maps ecologists use to trace how that energy travels — from sunlight, into plants, into the animals that eat plants, and onward into the animals that eat those animals. Along the way, energy is used up and lost at every single step, which is why nature has far more grass than grasshoppers, and far more grasshoppers than hawks. This article builds the idea from the ground up, then lets you test it yourself with two interactive activities: a food chain builder and a live energy pyramid you can control.
An ecosystem is a community of living organisms — plants, animals, fungi and microorganisms — interacting with each other and with the non-living parts of their environment, such as sunlight, water, air and soil. Ecosystems can be as large as a rainforest or ocean, or as small as a garden pond or a fallen log.
Within every ecosystem, energy and nutrients are constantly being passed between organisms. Understanding who eats whom, and in what order, is the first step to understanding how an entire ecosystem stays balanced.
An ecosystem includes both biotic (living) factors like plants and animals, and abiotic (non-living) factors like temperature, sunlight and rainfall. Both shape which organisms can survive there.
Every food chain starts with a producer — usually a green plant, algae, or photosynthetic bacterium — that makes its own food using sunlight through photosynthesis. Producers are the only organisms that can capture energy directly from the sun and convert it into a usable, edible form.
Everything else in the chain is a consumer, an organism that gets its energy by eating other organisms:
Decomposers (bacteria, fungi, earthworms) break down dead organisms and waste, releasing nutrients back into the soil so producers can use them again. Without decomposers, nutrients would stay locked inside dead material forever.
Omnivores like bears or humans don't fit neatly into one level — they can act as primary consumers when eating plants and secondary or tertiary consumers when eating meat, depending on the meal.
A food chain is a single, straight-line sequence showing who eats whom: producer → primary consumer → secondary consumer → tertiary consumer. Arrows in a food chain always point in the direction energy is flowing — from the organism being eaten to the organism doing the eating.
Real ecosystems rarely run on just one food chain, because most animals eat more than one type of food and are eaten by more than one type of predator. That's where food webs come in.
Choose an ecosystem below, then tap each organism in the order energy flows — from producer to top predator. Tap "Check Chain" when all four slots are filled.
A food web is a network of many interconnected food chains within the same ecosystem. Most animals eat more than one kind of food and are eaten by more than one kind of predator, so a realistic map of "who eats whom" looks like a tangled web rather than a straight line.
Food webs are more stable than single food chains. If one species in a web disappears, other connections can often keep energy flowing through the ecosystem — though a serious loss can still cause major disruption.
In a food web, a hawk might eat both rabbits and snakes. If the rabbit population crashes one year, the hawk can still survive by hunting more snakes — something impossible in a single, isolated food chain.
Each step in a food chain is called a trophic level. Ecologists model how energy moves between trophic levels using an energy pyramid, which is wide at the base (producers) and narrows sharply toward the top (apex predators).
The pyramid narrows because of the 10% rule: on average, only about 10% of the energy available at one trophic level is transferred to the next. The rest is used up by the organism itself — for movement, growth, body heat and everyday life — or lost as waste, and is never available to the next level up.
The 10% rule explains why food chains rarely have more than four or five levels, and why there are always far more producers than apex predators in a healthy ecosystem — there simply isn't enough energy left to support many top predators.
Drag the slider to set how much energy (in kcal) the producers capture, and watch how little survives by the time it reaches the top predator.
Predator and prey populations naturally rise and fall in connected cycles. When prey (like rabbits) are plentiful, predator (like fox) populations tend to grow because food is easy to find. As predators increase, they eat more prey, causing the prey population to fall — which then causes the predator population to fall too, since food becomes scarce. Eventually prey numbers recover, and the cycle repeats.
This natural balance is why removing a predator — even with good intentions — can backfire. Without predators to control their numbers, prey populations can grow so large that they run out of food, leading to starvation and a population crash anyway.
Human activity can disrupt food webs in several ways. Habitat destruction removes the producers and shelter a whole chain depends on. Overhunting or overfishing can remove a key species entirely, which can ripple through every connected chain. Introducing a non-native species to an ecosystem can be especially damaging, since local predators may not recognise it as prey, allowing it to spread unchecked.
When sea otters were hunted to near-extinction along parts of the Pacific coast, sea urchin populations exploded because their main predator was gone. The urchins then destroyed vast underwater kelp forests — an entire ecosystem collapsed because one link in the food web was removed.
Conservation efforts, such as protecting habitats and reintroducing key species, work by restoring the connections in a food web rather than treating each species in isolation.
Misconception 1: "Food chains only have three links." Chains typically have three to five links, limited mainly by how much energy remains after repeated 10% losses — not by any fixed rule.
Misconception 2: "Predators are 'bad' for prey species." Predators actually help keep prey populations healthy and in balance with available food and habitat, preventing damaging overpopulation.
Misconception 3: "Removing one species from a food web only affects that species." Because food webs are interconnected, removing one species can affect many others up and down the web, sometimes in surprising ways.
Misconception 4: "Decomposers are unimportant." Decomposers recycle nutrients back into the soil — without them, nutrients would stay locked inside dead organisms and producers would eventually run out of what they need to grow.
This article is original EDUSAMBAM educational writing. The following open resources were used for factual cross-checking and are provided for further study; they are not reproduced as article text.
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