Figure 12. Proximaldistal relationships.
Section II. CELLS, TISSUE, AND TRANSPORT PROCESSES
INTRODUCTION TO THE CELL
A cell is the fundamental organizational unit of life capable of reproduction. Not
long ago, the cell was considered to be a fairly simple structure that contained a nucleus
and various enzymes. Today, however, the cell is known to be an extremely complex
entity. With the advent of electron microscopy in the early 1940's, several distinct
cellular structures called organelles were clearly recognized (figure 13). A typical
animal cell contains the following structures: nucleus, nucleolus, nuclear membrane,
centrioles, endoplasmic reticulum, golgi apparatus, ribosomes, mitochondria,
lysosomes, vacuoles, and the cell membrane (unit membrane).