Tracing Food Energy Back to the Sun

Energy is the ability to do work or cause change. All living things need energy to grow, move, and survive. Understanding where this energy comes from helps us see how all living things are connected.

Plants get their energy directly from the sun through a process called photosynthesis. During photosynthesis, plants use sunlight, water, and carbon dioxide from the air to make their own food in the form of sugars. These sugars store the sun's energy inside the plant. This is why plants are called producers—they produce their own food using energy from the sun.

Animals cannot make their own food like plants can. Instead, animals are consumers—they must eat other living things to get energy. When a rabbit eats grass, the energy stored in the grass moves into the rabbit's body. When a fox eats the rabbit, that same energy moves again into the fox. Even though the energy passes from one living thing to another, it all started as energy from the sun.

Scientists use models to show how energy moves from the sun to plants to animals. A model is a simple diagram or drawing that represents something more complex. You can create an energy flow model by drawing the sun, then an arrow pointing to a plant, then another arrow pointing to an animal that eats the plant, and finally an arrow pointing to an animal that eats other animals. The arrows show the direction that energy moves. Think of the arrows like a path that energy travels, similar to how water flows down a slide at a playground—it only goes one direction.

Creating your own energy flow model helps you see that the energy in a hamburger, a bowl of cereal, or an apple all came from the sun originally. The cereal came from wheat plants that captured sunlight. The hamburger came from a cow that ate grass or corn, which also captured sunlight. No matter what food you trace back, you will always end up at the sun as the original energy source.

Interesting Fact: A single leaf can capture enough sunlight energy in one day to power a small LED light bulb for several hours!