Our sun makes almost all the energy that keeps living things on earth alive.  Plants are small factories that take the sun's light and make the sugars that fuel most of the living things on earth.  When you eat lettuce, you are eating the sugars and fiber the plant made using the sun's energy.  When you eat a hot dog, the meat gives your body fuel that began with the sun and plants.  Plants use a special process to change the sun's energy into food.

Here comes the sun.

Plants need a few everyday ingredients to make their factories work.  They need water, just like you do.  They also need a gas, one that you breathe out.  There is very little of this gas in the air, mostly because plants use up so much of it to make energy.  To grow 10,000 corn plants, you would need so much of this gas that it would weigh as much as your school bus.  The gas that you breathe out and plants use to make sugars is called carbon dioxide.

Making energy happens in special cells inside the plant.  Carbon dioxide enters the plant through little holes in the leaves, just like the ones you have on your skin.  From there, the gas moves into the cells along with the water.  The cells where this happens are home to the plant's green coloring.  Their job is to soak up sunlight.  Sunlight warms things up in the cells, allowing the plant to change water and the gas into sugars.  The green color in a plant that soaks up the sunlight is called chlorophyll.

The grass is greener right here.

Plants use the sugars they make for food.  If they do not need the sugars right away, they can store them for later.  Plants also use those sugars to make wood, fibers that we turn into materials like cotton and linen, and other things.   These keep the plant stems, trunks and other parts strong and healthy.  Photosynthesis is the name for the process that changes light energy into sugars that plants can use for the energy that keeps them alive.  In fact, if you dried out a green plant, almost all of what is left behind was made in this way.

Carbon dioxide goes in, oxygen and water come out.

Sugars are only one part of photosynthesis.  In the beginning, the sun's energy breaks apart water.  The plant uses one part of the water to make sugar.  The plant returns the other part of the water to the air as waste.  The waste from this process is oxygen, the gas that people need to breathe in to live.  This gas makes up about a fifth of the air you breathe.

Almost all life on earth depends upon the sun's energy and photosynthesis.  This is the way plants make food that they, and we, can use.  People also depend upon it for the air we breathe.  In return, we breathe out carbon dioxide, the gas the plants need.  There is very little of this gas in our air because plants quickly pull it into their energy factories.  Plants and people were made to live together.