In this topic you will learn about how plants make food.

All living things need energy to survive. A plant gets this energy from light, especially sunlight. Light is a form of energy that plants use to make their food. The food-making process that uses sunlight is called photosynthesis.

Sunlight strikes the green part of a plant, such as a leaf. The leaf contains a green chemical called chlorophyll, which helps the plant make its food. Inside the leaf, water and carbon dioxide from the air combine to make sugar and oxygen. This reaction could not take place without the help of light energy. The sugar produced by the Sun's energy goes to all parts of the plant. The oxygen produced by the plant goes into the air. Animals must breathe oxygen to stay alive. At the same time, animals breathe out carbon dioxide, which plants need.

A plant's cells use oxygen to break apart the sugar produced by the Sun's energy. When the sugar breaks apart, it gives out energy that the plant uses. This process is called respiration. Respiration is the release of energy from food (in this case, sugar). This is the same process that releases energy in animals.

Leaves of all plants, except evergreens, appear to change color in the fall. Actually, all the yellows and oranges you see in fall have been present in the leaves since summer. However, you could not see them because of the large amount of green chlorophyll inside the leaves. As the temperature begins to drop, the leaves of trees other than evergreens stop making chlorophyll. Slowly the chlorophyll that remains begins to break down and vanish. Now you can see the yellow and orange colors. If the weather is especially cool and the sky is clear most of the time, the color red will appear in leaves. This extra color was not in the leaves to begin with—it is made only by leaves in places where the climate is cool and clear.

A plant must efficiently move water from its roots to all its parts. The cells of every part of a plant need water to carry out vital chemical reactions, including photosynthesis. Water also helps plants stay firm. Plants constantly lose water through transpiration.

Whether you know it or not, you have eaten all parts of a plant: roots, stems, leaves, seeds, fruit, and even bark and sap. Plants are the food and oxygen producers. They provide the food we eat and the oxygen we breathe.

Plants and animals need each other in order to survive. Animals need the food and oxygen plants make during photosynthesis. Plants need the carbon dioxide animals give off when they breathe out.