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Ask A Scientist

How do trees make oxygen?

Asked by: Jennifer Ackley
School: Maine-Endwell Middle School
Grade: 6
Teacher: Mr. K Wagstaff
Hobbies/Interests:  Dance, Art
Career Interest: Artist, dancer

Answer from Lucas Sabalka

Riley Assistant Professor

Research area: Geometric group theory
Family: 1 spouse and 2 cats
Interests/hobbies: The environment, cards, movies, and Do-It-Yourself projects

This is an important question, because without trees and other plants, Earth would be uninhabitable.  We need trees so that they can make the oxygen we breathe.  So how do they do it?  Trees convert carbon dioxide into oxygen through a process called photosynthesis.  Photosythesis means "to put together with light."  The light is sunlight, shining on the tree, and the pieces being put together are carbon dioxide and water.  When a tree has these three ingredients it uses the energy from the sunlight to combine the carbon from the carbon dioxide with the water to make a carbohydrate, or more simply, a sugar.  The sugar is food for the tree, just as people eat sugar and carbohydrates.  When the tree makes the carbohydrate, there is extra oxygen from the water, which luckily for us gets released into the air, giving us the oxygen we breathe.  Each adult tree is made up of trillions of cells.  The cells in the leaves of a tree are where photosynthesis occurs, in special parts of the cell called chloroplasts.  Each cell in a tree can contain up to 100 chloroplasts.  Inside of a chloroplast, there are pigments that absorb light.  The most common pigment, chlorophyll, is green, which is why most plants look green.  The tree leaves get water from the ground by drinking through the roots, trunk, and stems of the tree.  The leaves also have tiny pores in them that they can use to breathe in carbon dioxide -- the gas humans and animals breathe out -- from the air.  Then, when light hits the chlorophyll, the chloroplast uses the light\\\'s energy to cause photosynthesis.  The tree keeps the carbohydrate as food, and breathes out the oxygen through the pores on its leaves. So while we inhale oxygen and exhale carbon dioxide, a tree breathes in carbon dioxide and exhales oxygen. To be precise, this is the chemical equation for photosynthesis:

 2n CO2 + 2n H2O + photons ® 2(CH2O)n + 2n O2 which means:

    n is a whole number, and 2n carbon dioxide molecules + 2n water molecules + light become 2 carbohydrate molecules of length n and 2n oxygen molecules.

Last Updated: 9/18/13