This image shows a human cell as it looks under an electron microscope. The image makes the cell look thousands of times bigger than it really is. Clearly, cells are very small in size. However, their small size belies their importance to life. Like all other living things, you are made of cells. In fact, your body contains trillions of cells. Without cells, life as we know it would not exist. You’ll learn more about these amazing building blocks of life when you read this chapter.