Chapter 3
The Cell
Figure 3.1 Microorganisms vary visually in their size and shape, as can be observed microscopically; but they also
vary in invisible ways, such as in their metabolic capabilities. (credit “microbacterium tuberculosis bacteria”:
modification of work by NIAID)
Chapter Outline
3.1 Spontaneous Generation
3.2 Foundations of Modern Cell Theory
3.3 Unique Characteristics of Prokaryotic Cells
3.4 Unique Characteristics of Eukaryotic CellsIntroduction
Life takes many forms, from giant redwood trees towering hundreds of feet in the air to the tiniest known microbes,
which measure only a few billionths of a meter. Humans have long pondered life’s origins and debated the defining
characteristics of life, but our understanding of these concepts has changed radically since the invention of the
microscope. In the 17th century, observations of microscopic life led to the development of the cell theory: the idea
that the fundamental unit of life is the cell, that all organisms contain at least one cell, and that cells only come from
other cells.
Despite sharing certain characteristics, cells may vary significantly. The two main types of cells are prokaryotic cells
(lacking a nucleus) and eukaryotic cells (containing a well-organized, membrane-bound nucleus). Each type of cell
exhibits remarkable variety in structure, function, and metabolic activity (Figure 3.1). This chapter will focus on the
historical discoveries that have shaped our current understanding of microbes, including their origins and their role in
human disease. We will then explore the distinguishing structures found in prokaryotic and eukaryotic cells.
Chapter 3 | The Cell 79