Cells are the basic structural and functional units of all living organisms. Cells are made up of the biological macromolecules; carbohydrates, fats, proteins, nucleic acids as well as water. The word cell was first used by the 17th century scientist Robert Hooke to describe the small pores in a cork that he observed under a microscope. Cells are very small structures. In fact, the human body is made up of more than 10 trillion cells. In this tutorial, we will begin exploring the cell.