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Cells are the smallest form of life—the functional and structural units of all living things. Your body contains trillions of cells, organized into more than 200 major types.

At any given time, each cell is doing thousands of jobs. Some of these tasks are so essential for life that they are carried out by virtually all cells. Others are done only by cells that are highly skilled for the work, whether it is covering up your insides (skin cells), preventing you from sloshing around like a pile of goo (bone cells), purging your body of toxic chemicals (liver cells), or enabling you to learn and remember (brain cells). Cells also must make the products your body needs, such as sweat, saliva, enzymes, hormones, and antibodies.

In Chapter 1, "An Owner's Guide to the Cell," we'll explore some of the basic structures that allow cells to accomplish their tasks and some of the ways scientists study cells. In Chapter 2, "Cells 101: Business Basics," we'll focus on the functions shared by virtually all cells: making fuel and proteins, transporting materials, and disposing of wastes. In Chapter 3, "On the Job: Cellular Specialties," we'll learn how cells specialize to get their unique jobs done. In Chapters 4, "Cellular Reproduction: Multiplication by Division," and 5, "The Last Chapter: Cell Aging and Death," we'll find out how cells reproduce, age, and die.

Much of the research described in this booklet is carried out by cell biologists at universities and other institutions across the nation who are supported by U.S. tax dollars, specifically those distributed by the National Institute of General Medical Sciences (NIGMS) a component of the National Institutes of Health. NIGMS is keenly interested in cell biology because knowledge of the inner workings of cells underpins our understanding of health and disease.

Although scientists daily learn more about cells and their roles in our bodies, the field is still an exciting frontier of uncharted territory and unanswered questions. Maybe someday, you will help answer those questions.