Arendezvous with the cell simultaneously opens the door to simplicity, complexity, and diversity. Although tiny, these fundamental units fill large roles in supporting life on Earth. Cells breathe, fuel chemical reactions, communicate with one another, and reproduce. The study of these minute factories in plants and animals has unravelled many mysteries of how organisms function and has provided a basis for the development of therapies to treat debilitating human diseases. This dynamic volume explains the structure, evo- lution, and intricacies of this versatile unit of life.

Adult organisms are composed of numerous distinct cells. Mammals, for instance, have more than 200 different types of cells. These are organized into tissues that contain many cells, each type performing a specific function. For example, the epithelial tissue lining the small intestine has cells that absorb nutrients, whereas other cells in the same tissue secrete mucus and enzymes. Plants also have differentiated cells, but they are not the same as those seen in animals.

Cells, based on their internal organization, are divided into two main forms: prokaryotes and eukaryotes. Prokaryotes are small in size and simple in structure. They lack a membrane-bound nucleus, which stores genetic information. Prokaryotic organisms, which date back to some of the first cells on Earth, are ubiquitous. They exist in large numbers in the air, soil, water, and human body. Perhaps the most well-known prokaryote is the bacterium. Though these prokaryotes can cause various diseases, such as anthrax and syphilis, and are even known to be responsible for tooth decay, bacteria are essential to ecological cycles. Bacteria like Escherichia coli, which live in the intestine, have also given the inquiring human mind an insight into the function of DNA.