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Let's Eat!

When you get hungry, what do you do? You might decide to raid the refrigerator or try to convince your mom to take you to a fast food restaurant. You do those things because you are a heterotroph (or consumer). Heterotrophs are organisms that need to get their energy from the foods they eat. Humans and animals are heterotrophs — so are parasites like fleas, ticks, and tapeworms!

Conifers, like other green plants, can't just reach in the fridge for a quick snack. They have to make their own food. Green plants are called autotrophs (or producer). Autotrophs use light energy from the sun to produce the food they need. To understand how this works, we need to learn about photosynthesis.

The Word

Sometimes you can learn a lot about something by looking closely at the word that describes it. Photosynthesis is one of those things. The word photosynthesis is made up of a prefix (photo) and a root word (synthesis).

Now that we know how the word is put together, we can look at a formal definition of photosynthesis. A dictionary says photosynthesis is

"the production of carbohydrates from carbon dioxide and water, using sunlight as the source of energy and with the aid of chlorophyll."

The Process

Photosynthesis is a process. It's a set of steps that happen in a certain order inside the cells of green plants. Let's think of photosynthesis as a recipe — the plant version of a making a batch of chocolate chip cookies!

Before you begin cooking, you need to be sure you have all of the ingredients. Then you can get started! It's the same with plants.

What might a recipe for photosynthesis look like?

The recipe above is a very simple way to think about photosynthesis. It's really a very complicated process and scientists are still learning exactly how it works.

About the Ingredients

Plants need the right ingredients to produce the carbohydrates they need. The definition of photosynthesis tells you that sunlight is needed for energy. Now, let's look more closely at the other ingredients.

You already know that plants collect the water they need through their roots. What you may not know is that water is a compound made up of many smaller parts. Those parts are called molecules.

A water molecule is made with the elements hydrogen and oxygen. In each molecule of water, there are 2 hydrogen atoms and 1 oxygen atom. You can tell this by looking at its formula — H2O.

Many water molecules bond, or join, together to make the substance we know as water.

Carbon dioxide is another ingredient needed for photosynthesis. The air we breathe is made up of several gasses. Carbon dioxide is one of them.

Carbon dioxide is also a molecule. Its formula is CO2. Using what you know about the water molecule, can you guess what atoms make up a carbon dioxide molecule?

If you guessed 1 atom of carbon and 2 atoms of oxygen, you are exactly right!

Without chlorophyll a plant would not be able to make the food it needs. Chlorophyll is a pigment found in green plants. It's what makes the needles of a REAL TREE look green.

Chloroplasts are special parts of most green plant cells. They are where you find chlorophyll. This is where the action of photosynthesis takes place!


REAL TREES and other green plants are active food factories. They use photosynthesis to create the food they need to grow and reproduce. Without them, other organisms would be without a food source.

the mixture of nitrogen, oxygen, argon, carbon dioxide, hydrogen, neon, helium, and other gases that surrounds the earth

the smallest part of an element

an organism that uses energy to produce the food they need

the green pigment of a plant; needed for photosynthesis

a substance made up of two or more elements that are always put together in the same way

a substance that cannot be separated into simpler substances

an organism that gets energy from the foods they eat

atoms joined together

the production of carbohydrates from carbon dioxide and water using sunlight as the source of energy with the aid of chlorophyll

a substance that makes color in the tissues of organisms

In your study of photosynthesis have you ever asked, "Why should I learn this?"

Some folks as Arizona State University have some answers for you!

ASU: Why Study Photosynthesis?

More info on photosynthesis, including a video from Avas Flowers: www.avasflowers.net

Conifer needles need just the right amount of sunlight for the tree to produce food. The triangle shape of the tree is an adaptation that allows more needles to "see" the sun.

As a tree grows older and taller, less sunlight reaches the needles on the lower part of the tree. When this happens, the lower areas shed their needles - and eventually - their branches.

These books tell more about photosynthesis.

by Alvin Silverstein

The Usborne Illustrated Dictionary of Biology
by Corinne Stockley

The Usborne Illustrated Dictionary of Chemistry
by Jane Wertheim, Chris Oxlade, and Corinne Stockley

Photosynthesis (World of Wonder)
by Frank J. Staub

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