Microscopic Observations of Cells

The smallest object that can be resolved with a microscope depends upon the wavelength of the radiation used to illuminate the specimen—the shorter the wavelength, the smaller the object that can be seen. With a light microscope, objects as small as 0.2 ^m in diameter can be resolved, whereas an electron micro scope, which uses electron beams instead of light rays, can resolve structures as small as 0.002 ^m. A greater resolution is achieved with an electron microscope because electrons behave as waves with much shorter wavelengths than those of visible light. Typical sizes of cells and cellular components are illustrated in Figure 3-2.

Although living cells can be observed with a light microscope, this is not possible with an electron microscope. To form an image with an electron beam,

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Cell Structure CHAPTER THREE

Cell Structure CHAPTER THREE

Typical Mitochondrion human cell Lysosome Ribosome

Plasma membrane

Diameter of period at end of sentence in this text

1000 |xm 100 |xm 10 |m 1.0 |m 0.1 |m 0.01 |m 0.001 |m 0.0001 |m

Hydrogen Protein molecule atom

Can be seen with:

Human eye

Light microscope

Electron microscope

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