Human beings need cells because they are the building blocks for all living structures. While the human body produces a wide variety of cell types, collectively, they are how the human body builds everything from skin to bones to internal organs. The cell is the simplest entity that exhibits life, and while most organisms are composed of millions or billions of cells, some organisms are composed of a single cell.
The human body builds all of its macro structures in essentially the same way. Cells are the starting point for the entire process. Similar cells combine together to form tissues. When enough tissues have been constructed, the tissues combine to form organs, such as the skin or lungs. Similar organs function together as part of an organ system, such as blood vessels, lungs and heart of the circulatory system. Several organ systems combine to form an organism, such as a human being.
Cells have extraordinarily different characteristics and properties, based on their needed function. For example, human red blood cells are red in color, numerous and lack nuclei. By contrast, nerve cells, also called neurons, have large nuclei, are much less numerous than blood cells and may reach up to 3 feet in length.