Solar Power Trees and other plants make their own food. As long as plants have three things, they can make


their own food. Plants need sunlight, water, and carbon dioxide.


Carbon dioxide is a gas in the air. We breathe it out of our lungs. When we breathe carbon dioxide out, plants take it in.


Growing Up and Out As a tree grows, it gets taller and wider. Branches reach up so leaves can soak in sunlight. Roots reach down and out to pull in water and nutrients from the soil.


A tree’s growth shows up as a ring inside the trunk. Every year, a tree gets wider as it adds another ring to its trunk.


A tree's age is shown in its rings.


14 NATIONAL GEOGRAPHIC EXPLORER


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