However, the light microscope is not sufficiently powerful to reveal fine details of cell structure, for which resolution-the ability of a microscope to distinguish objects separated by small distances-is even more important than magnification. Since most cells are between 1 and 100 μm in diameter, they can be observed by light microscopy, as can some of the larger subcellular organelles, such as nuclei, chloroplasts, and mitochondria. Contemporary light microscopes are able to magnify objects up to about a thousand times.
The light microscope remains a basic tool of cell biologists, with technical improvements allowing the visualization of ever-increasing details of cell structure. The “cells” that Hooke observed were actually only the cell walls remaining from cells that had long since (more.) A reproduction of Robert Hooke's drawing of a thin slice of cork examined with a light microscope. Thus, the cell achieved its current recognition as the fundamental unit of all living organisms because of observations made with the light microscope. Shortly thereafter, it was recognized that cells are not formed de novo but arise only from division of preexisting cells. Microscopic studies of plant tissues by Schleiden and of animal tissues by Schwann led to the same conclusion: All organisms are composed of cells. The proposal of the cell theory by Matthias Schleiden and Theodor Schwann in 1838 may be seen as the birth of contemporary cell biology. Using a microscope that magnified objects up to about 300 times their actual size, Antony van Leeuwenhoek, in the 1670s, was able to observe a variety of different types of cells, including sperm, red blood cells, and bacteria. Indeed, the very discovery of cells arose from the development of the microscope: Robert Hooke first coined the term “cell” following his observations of a piece of cork with a simple light microscope in 1665 ( Figure 1.23). Because most cells are too small to be seen by the naked eye, the study of cells has depended heavily on the use of microscopes.
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