Solar Power All living things need to eat to survive. Animals eat plants and other animals. What do trees eat? T ey don’t hunt. T ey can’t move around, so they don’t forage. Instead, trees and other plants make their


own food from sunlight. T is process is called photosynthesis. Photo is a Greek word that means “light.” Synthesis is a Greek word that means, “putting things together.”


PHOTOSYNTHESIS


A leaf turns sunlight, water, and carbon dioxide into food and oxygen.


light energy enters leaf


water enters leaf


Food Factories Plants are food factories. As long as they have three things—sunlight, water, and carbon dioxide—they can make food. Carbon dioxide is a gas in the air we breathe out of our lungs. When we breathe it out, plants take it in. T ey combine it with sunlight and water to make sugars and oxygen. When sugar is made in the cells of the leaves, it feeds the tree. For this process to work, plants must rely on


their leaves. Each leaf cell has a special packet inside called a chloroplast. T is is where the food is made. T e chloroplast soaks up the energy from


the sun. T en the chloroplasts wrangle water molecules and carbon dioxide molecules together to make sugar molecules. T is gives the plant energy. In the treetops, photosynthesis is going on


every day. Every cell of every leaf is making food for the tree. Every cell in every leaf is also putting oxygen into the atmosphere. Without plants, animals, including us, would not have air to breathe.


sugar exits leaf


oxygen is released


carbon dioxide enters leaf


Growing Up and Out Trees use the food they make to grow. As a tree grows, it gets taller. Branches reach up so leaves can collect sunlight. T e roots grow, too. T ey reach out wider and wider underground to collect more water and nutrients from the soil. Most trees also grow wider trunks. Every


year, growth slows down during the winter months. T e pattern of growth in a year shows up as a ring inside the trunk. Every year a tree adds a new ring to its trunk just beneath the bark. T e number of rings determines the age of a tree.


A tree's age is refl ected in its rings.


14 NATIONAL GEOGRAPHIC EXPLORER


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