Energy - From the Sun to Living Things
The Sun is the source
Nearly all energy in food can be traced back to the Sun. Plants capture light energy and use it, along with water and carbon dioxide, to make sugar - their own food. That energy is stored in the sugar and in the plant’s tissues. Animals cannot make food from sunlight, so they obtain energy by eating plants or by eating animals that ate plants.
Following energy along a chain
Trace the steps: Sun → grass → cow → hamburger → your muscles. At every step some energy is used for growth and body warmth and some is released as heat, so less energy is available near the top of a chain. That is why a food chain can support many plants but only a few top predators.
Traps to watch for
- “Plants get their food from the soil.” Soil supplies water and dissolved minerals, but the energy and most of the material a plant builds into its body come from sunlight, air, and water.
- “Energy disappears when an organism is eaten.” Energy is transferred and transformed, often into heat, never destroyed.
- “Animals produce energy by resting.” Animals release energy from food; resting only slows how fast they use it.
- “Sunlight only gives light.” Sunlight also warms surfaces, drives weather, and powers the water cycle.
Rule of thumb
Ask two separate questions about any living thing: Where does its energy come from? Where does its material come from? For a plant, energy comes from sunlight; the material comes mostly from air and water.