Solar Power All living things must eat to survive. But trees can’t hunt or forage. Instead, trees and other plants make


their own food from the light of the sun. T is process is called photosynthesis. Photo is a Greek word that means “light.” Synthesis 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 sunlight, water, and carbon dioxide, they can make food. Carbon dioxide is a gas. It is 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. 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. When it combines with water and carbon dioxide, it makes sugar. T is gives the plant energy. In the treetops, photosynthesis is going


sugar exits leaf


on every day. Every cell of every leaf is making food for the tree. Every cell is also putting oxygen into the air. Without plants, animals would have no food to eat or air to breathe.


oxygen is released


carbon dioxide enters leaf


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


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 underground to collect water and nutrients. Trees also grow wide trunks. T e pattern


of growth in a year shows up as a ring inside the trunk. Every year a tree adds a growth ring to its trunk just beneath the bark. T e number of rings shows the age of a tree.


14 NATIONAL GEOGRAPHIC EXPLORER


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