In the 1830s, Matthias Schleiden and Theodore Schwann proposed that individual cells constitute the fundamental unit of life. This first formulation of the cell theory was based on observations made with rather primitive light microscopes. Modern cell biologists have many more-powerful tools for revealing cell architecture. For example, variations of standard light microscopy permit scientists to view objects that were undetectable several decades ago. Electron microscopy, which can reveal extremely small objects, has yielded much information about subcellular particles and the organization of plant and animal tissues. Each technique is most suitable for detecting and imaging particular structural features of the cell (Figure 5-41). Digital recording systems and appropriate computer algorithms represent another advance in visualizing cell architecture that has spread widely in the past decade. Digital systems not only
Transmission electron microscopy
▲ FIGURE 5-41 The range in sizes of objects imaged by different microscopy techniques. The smallest object that can be imaged by a particular technique is limited by the resolving power of the equipment and other factors.
can provide microscopic images of improved quality but also permit three-dimensional reconstructions of cell components from two-dimensional images.
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