Look around the room you are in or look out a window.  Wherever you look, you will see living things. All living things have one important thing in common: They are all made of cells. In this first activity, you will learn what a cell is.        

Cells are the basic building blocks of living things. All living things, including humans, are made up of cells. The cell is the basic unit of life.

Some living organisms are very simple, containing only one cell. Multi-celled organisms are made up of more than one cell, and they may contain various types of cells.

An adult human body is an amazing and very complex machine that is made up of approximately 100 trillion cells. That's 100,000,000,000,000! Each cell has a job to do that is necessary in keeping you alive.

Amsel, Sheri. "Levels of Organization in the Body - Cells to Organisms (Color)" Exploring Nature Educational Resource ©2005-2021. May 12, 2021 < http://www.exploringnature.org/db/view/Levels-of-Organization-in-the-Body-Cells-to-Organisms-Color

Each type of cell performs some particular function. Nerve cells, for example, send messages throughout your body. Should you happen to touch a hot object, the nerve cells tell your body immediately to pull away!

In 1665, a scientist named Robert Hooke was the first person to identify cells. He was looking at a piece of cork under a series of magnifying lenses when he saw the open grid work of the cell walls. Since then, more powerful microscopes have been invented and the smallest details of the inside of a cell have been examined.

Each cell is made up of smaller parts called organelles, which are the parts of the cell that do a special job. Organelles do jobs inside cells just like organs (such as heart and lungs) do jobs inside our bodies.

Each organelle performs a specific role inside the cell. Organelles on their own cannot survive. Put them together in a cell and let them communicate with other organelles, and they survive and keep the cell functioning. If an organelle breaks down or stops functioning, the cell will also stop functioning.

The circle diagram below illustrates the building blocks of the human body. Notice the organelles (org) in the very centre of the diagram. This shows that the organelles make up the cells that make up the tissues, organs, organ systems, and the human body. Without these organelles, the human body would not exist!