OVERVIEW Cells are the building blocks of everything living and are considered to be the most basic units of life, as well as the smallest unit of life. They are called these things, because all living organisms are made up of cells and they are the smallest part of any being. It is nearly impossible to see a single cell with a naked eye, a microscope is generally needed. Most organisms are made up of a large amount of cells, working together to make the organisms function, grow and survive. For example, humans are made up of approximately 37 trillion cells, depending on the size of them. There are also lifeforms that are only single-celled organisms (unicellular), like bacteria and archaea.
Different Functions of Cell Cells share several functions, like they make energy and reproduce, but they can look extremely different from one another. Some also have very different functions and this is because, through evolution and adaption, cells have changed to thrive in a wide variety of environments and conditions. For example, nerve cells (Image above) are long thin cells that can stretch for meters. They are shaped like that to transmit signals quickly and efficiently, like cords that are used to connect DVD players to TVs. While plant cells (Image on the left) are blocked shaped cells with a rigid outer layer. They are block shaped because it allows them to be stacked closely together and they have the rigid layer to make the cells strong and hard to move. These factors working together provide the needed structural support for plants.