Chapter 6 Flashcards
What year were microscopes invented?
1590 and further refined during the 1600s
Cell walls were first seen by…
Robert Hook in 1665
-They were from the bark of an oak tree
Light Microscope (LM)
In a LM, visible light is passed through the specimen and then through glass lenses.
Three important parameters in microscopy:
Magnification
Resolution
Contrast
Magnification
Is the ratio of an object’s image size to its real size.
Light microscopes can magnify effectively to about _____ times the actual size of the specimen
1,000
Resolution
-Is a measure of the clarity of the image
- It is the minimum distance two points can be separated and still be distinguished as separate points.
The light microscope cannot resolve detail finer than about _____________ or ___________
0.2 micrometer, 200 nanometers
Contrast
Is the difference in brightness between the light and dark areas of an image.
Methods for enhancing contrast
Staining or labeling cell components to stand out visually.
Organelles
The membrane-enclosed structures within eukaryotic cells.
When was the electron microscope introduced to biology?
1950s
Electron microscope (EM)
The EM focuses a beam of electrons through the specimen or onto its surface.
Resolution is inversely related to…
The wavelength of the light (or electrons) a microscope uses for imaging.
Electron beams have much shorter wave lengths than visible light.
True
Modern electron microscopes can theoretically achieve a resolution of about _____
0.002 nm (nanometers)
The scanning electron microscope (SEM) is especially useful for…
Detailed study of the topography of a specimen.
How does a SEM work?
-The electron beam scans the surface of the sample, usually coated with a thin film of gold.
- The beam excites the electrons on the surface.
- The patterns of electrons are translated into an electronic signal sent to a video screen
- An image of the specimen’s surface appears in 3-dimensions.
The transmission electron microscope (TEM) is used to…
Study the internal structure of cells.
How does a TEM work?
-The specimen is stained with heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell.
- The electron beam is scattered in the denser regions.
- The image displays the pattern of transmitted electrons.
Instead of using glass lenses, the SEM and TEM use…
Electromagnets
Disadvantage of electron microscopy
The methods used to prepare the specimen kill the cells.
Super-resolution microscopy
Technique that allows LM to break the limit of resolution.
Cytology
The study of cell structure.