Do you remember when you were learning to write?  You had to learn a lot of rules about things like using periods, spelling words, and putting together sentences.  These rules are important because they help other people easily read and understand what you are writing about.  If you do not follow the rules of writing, then a sentence or a paragraph will not make sense.

A paragraph is made up of sentences, sentences are made up of words, and words are made up of letters.  If the letters of a word are not placed together in the right order, then the word will not make sense.  For example, the word "purple" cannot be written as "urpple" because that is not a color.  The same is true with sentences.  If the words are not placed together in the right order, then the sentence will not make sense.  Look at this sentence: "The doll had a purple dress."  That makes sense, but it does not mean anything when written as "The purple had a dress doll."

Two pages, who can write two whole pages?

When something is put together in the correct way or order, it is organized.  Letters are organized into words, and words are organized into sentences.  The bodies of animals and plants are organized as well.  You will never find a person's arms connected to his or her head, or the leaves of a tree buried in the ground next to the roots.  The correct place for a heart is in the chest, and the correct place for leaves is out in the air, where they can soak up the sunlight.

Animals and plants are organized on the inside, too.  Cells are the tiny parts that make up all living things.  If something is alive, it is made up of one or more cells.  In people, our cells all work together in different ways and make it easy for us to do all different things that people can do.  Cells can organize themselves into parts called  tissues.  Tissues are groups of cells that work together and have one specific job.

If you look closely at a hammer, you will notice that it is made up of different pieces that are each meant to do very different jobs.  There is the biggest part of the hammer, the handle, which you hold.  It is probably made out of wood or plastic.  There is also the part of the hammer that hits the nail to push it into the wall.  This is probably made out of metal.  Each part comes together to make the whole hammer work. 

A hammer is more useful than a pen for nailing.

Both parts of the hammer work together so that you can use the hammer.  These different parts are like tissues in your body.  Let's say that the hammer is just one tool in a toolbox.  The hammer's job is to hit things.  The saw, screwdriver, ruler and wrench are all made out of the same stuff as the hammer (metal, wood and plastic), but they have very different jobs.  Some of them cut, some make holes, and some of them twist things.  You have many parts in your body that are like this.  Different parts of your body are made of the same kinds of tissues that work together.

Your heart is a very important body part.  The heart moves blood to all the different parts of the body to give them what they need in order to stay alive and take away their waste.  It has one main job to do, but different tissues come together to help it do this job.  One part is the muscle that squeezes the heart, another part keeps the heart in the shape that it needs to be in, and a different part tells it when to beat.  These different kinds of tissues work together so the heart can do its job.  Organs are parts of your body that are made of different tissues that work together to do a job.  Even though organs are very well organized, none of your organs could do their job alone.  They all need the help of other organs.

Can you think of some things that work together?  What about a nail, hammer, and a board?  If you are trying to build a house, nails, a hammer and boards are all needed to do the job.  Some organs inside of animals work together as well.  For example, your lungs take in the oxygen from the air, and your heart pumps it through your blood vessels.  If your heart was not there, there would be no way for your lungs to send the oxygen out to the rest of your body.  Your mouth and stomach are also a part of a group of organs that work together to get energy from the food you eat.  Organs that work together to do a job are called organ systems.  Together, the heart and lungs make up an organ system.

Systems come together piece by piece.

Today we learned that all of the organs inside of animals are organized, and that multiple organs work together as an organ system in order to do a certain job.  Each organ is made up of many pieces called tissues, which fit together the way that the different parts of a hammer fit together.  Tissues fit together to make organs, and organs work together to make organ systems, just like letters are put together to make words, and words are put together to make sentences.