BiologyWho Eats Whom: Energy Flow and Matter Cycling in a Meadow
Atlas the guide kneels at the edge of a sunny green meadow, pointing to a grasshopper on a blade of grass while a hawk soars overhead and mushrooms sprout near a fallen log.
- Trace the path of energy from the Sun through a food web using arrows that point toward the eater.
- Explain why energy flows in one direction while matter (atoms) cycles and gets reused.
- Identify the roles of producers, consumers, and decomposers in an ecosystem.
- Predict how removing one organism would affect others in the same food web.
Key terms
- Producer
- An organism such as grass that captures sunlight to make its own food.
- Consumer
- An organism that gets energy by eating other living things, like a grasshopper or hawk.
- Decomposer
- An organism such as a mushroom or bacterium that breaks down dead matter and returns atoms to the environment.
- Energy flow
- The one-way movement of energy from the Sun through organisms and out as heat.
- Matter cycling
- The repeated reuse of atoms as they move among organisms, soil, and air.
Energy Flows, Matter Cycles
The central puzzle of an ecosystem is that energy and matter behave in opposite ways. Energy arrives fresh from the Sun, passes from producers to consumers, and steadily leaks away as heat, so it travels in one direction and never returns. Matter, the actual atoms of carbon and minerals, is never lost: it moves from grass into a grasshopper, into a hawk, and after death back into the soil and air through decomposers. Because the atoms keep returning to producers, matter cycles endlessly while energy must be resupplied each day.
Reading Food-Web Arrows
A food web is a map of who eats whom, and its arrows carry a strict rule: each arrow points from the organism being eaten toward the organism doing the eating. The grass-to-grasshopper arrow means energy and matter move into the grasshopper. This trips many students up because it feels backward, but the arrow simply follows the direction the energy travels next. Decomposers connect to many parts of the web at once, since they break down dead organisms from every level, not only the top predators.
Worked examples
Predict the meadow effects if all grasshoppers suddenly vanished.
- Find what grasshoppers eat: they consume grass, so without them the grass faces fewer grazers and may grow thicker.
- Find what eats grasshoppers: hawks and other predators lose a food source and have less to eat.
- Trace the ripple: predators may go hungry or seek other prey, showing every organism is linked.
Answer: Hawks would have less food and the grass would likely grow thicker, because losing one species disturbs both its predators and its prey.
Activity
Put these in the correct order to show how energy flows through this meadow food web.
Practice
Draw a four-organism food chain for this meadow and add arrows pointing toward each eater.
Explain why energy must keep arriving from the Sun while matter does not need resupplying.
Common mistakes to avoid
- Energy is recycled like atoms areEnergy leaves as heat at every step and cannot loop back, so only matter is recycled by decomposers.
- Decomposers only break down top predatorsDecomposers act on dead organisms at every level of the food web, returning atoms for reuse.
Check your understanding
In a food web, what does an arrow drawn from grass to a grasshopper mean?
Why does energy flow in one direction through an ecosystem instead of cycling like matter?
What role do decomposers like mushrooms and bacteria play in the meadow?
If a disease wiped out all the grasshoppers in this meadow, what would most likely happen first?
Recap
In an ecosystem, energy from the Sun flows one way through producers and consumers and escapes as heat, while matter cycles endlessly as decomposers return atoms to the soil and air for producers to reuse.
Reflect
Which organism in this meadow would you remove to cause the biggest change, and why?