Main->Readings->4th Grade Readings->Plants->Part 4

Part 4: Photosynthesis

Plant food

In order to stay alive, animals must eat other living things. Some animals eat other animals, some eat only plants, and others eat plants, animals, and even fungi like mushrooms. Plants, however, do not have to eat other living things. They make their own food out of air, sunlight, and water. Photosynthesis (foht-oh-SIHN-thuh-siss) is the process by which plants make food.

Somehow, in the early years of life on earth, the ancestors of the plants came up with something called chlorophyll (KLOR-uh-fil). Chlorophyll makes plants green, but it is not just a pretty color. Chlorophyll is the substance in plants which traps the energy of sunlight so plants can make food.

How it works

Step by step, here is how the plant does it. 1. Carbon dioxide in the air comes in through the stomates (those little holes in the leaf). 2. Water comes into the leaf from the roots. 3. Sunlight strikes the surface of the leaf and its energy is trapped by the chlorophyll. 4. The energy helps change part of the water to hydrogen (HYE-druh-jun) and oxygen (OX-uh-jun). 5. The hydrogen joins with the carbon dioxide to make food for the plant. 6. Oxygen gas comes out of the leaf through the stomates. In Figure 6, you can see the numbered steps.

When you look at this process, you might notice something important. You know that animals breathe in oxygen and breathe out carbon dioxide. That means there is more carbon dioxide being produced every day, and less oxygen. This is where the plants are important. If it were not for plants, we might use up all our breathable air. In fact, scientists believe that most of the oxygen in our atmosphere was produced by photosynthesis. Not only that, but plants make the food that keeps all other living things alive. Although a lion may eat only other animals, the animals it eats probably eat plants. So the next time you go outside and look around, pay attention to the plants. They are keeping you alive.

One final thing: When trees and other plants change their color in the fall, this is caused by the chlorophyll draining out of the leaves and showing the colors that were there all along (though if the leaves turn red, the red color was made in the previous few weeks).

Homework

1. Name three things a plant uses to make food.
2. Why do animals need plants?
3. If you were a space explorer trying to survive on a planet with no plants, what problems would you have to solve?

Go on to Unit Review

Return to table of contents

This page last modified on October 30, 2002