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Studying Cells Tutorial

Size and Biology

Sizes of cells, viruses, and other small things
Biology is a visually rich subject area. However, many of the most interesting biological events and structures are smaller than the unaided human eye can see. In fact, human eyes have a resolution of about 100 µm. On the chart below, notice that of all the structures listed, only the plant cell is within our resolution--just barely.
Illustration of the relative sizes of cells and their components The light microscope
The light microscope has a limit of resolution of about 200 nm (0.2 µm). This limit is due to the wavelength of light (0.4-0.7 µm). Cells observed under a light microscope can be alive, or fixed and stained Light micrograph of bone
Image courtesy of WebPath 		Illustration of a light microscope
The Transmission Electron Microscope (TEM)
The Transmission Electron Microscope (TEM) has a limit of resolution of about 2nm. This is due to limitations of the lens used to focus electrons onto the sample. A TEM looks at replicas of dead cells, after fixation and heavy metal ion staining. Electrons are scattered as they pass through a thin section of the specimen, and then detected and projected onto an image on a fluorescent screen. TEM of muscle tissue
Image courtesy of WebPath 		Illustration of Transmission EM
The Scanning Electron Microscope (SEM)
The Scanning Electron Microscope (SEM) also has a limit of 2nm. Like the TEM, the SEM allows you to look at replicas of dead cells, after fixation and heavy metal ion staining. With this technique, electrons are reflected off the surface of the specimen. Micrograph of SEM of stressed liver cells
Image courtesy of CIPE 		Illustration of scanning EM

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