Biology 186 Midterm PART 2 Flashcards
What is magnification?
The ratio of an object’s image size to its real size
Resolution?
A measure of the clarity of the image; it is the minimum distance two point can be separated and still be distinguished as 2 separate points
Contrast?
The difference in brightness between the light and dark areas of an image
What methods enhance the contrast?
Staining or labelling cell components to stand out visually
Organelles?
The membrane inclosed structures within eukaryotic cells
Rather than focusing the light, the ____ ______ focuses a beam of electrons through the specimen or onto its surface
Electron Microscope
Brightfield? (unstained specimen)
Light passes directly through the specimen; the image has little contrast
Brightfield? (stained specimen)
Enhances contrast
Phase-contrast?
Variations in density within the specimen are amplified to enhance contrast in unstained cells, which is especially useful for examining living, unpigmented cells
Differential interference contrast?
Optical modifications are used to exaggerate differences in density, making the image appear almost 3D
Fluorescence?
The locations of specific molecules in the cell can be revealed by labelling the molecules with fluorescent dyes which absorb UV radiation and emit visible light
Confocal?
Using a laser, this optical sectioning technique eliminates out of focus light from a thick sample creating a single plane of fluorescence in the image, and 3D reconstruction can be created
Deconvolution?
This process digitally removes out of focus light and reassigns it to its source, creating a much sharper 3D image
Super resolution?
Sophisticated equipment is used to light up individual fluorescent molecules and record their position, combining information from many molecules in different places breaks the limit of resolution
Scanning electron microscopy?
Micrographs taken with a scanning electron microscope showing a 3D image of the surface of a specimen (reveals surface details)
Transmission electron microscopy?
Profiles a thin section of a specimen (reveals internal details)
How do scanning electron microscopes work?
The electron beam scans the surface of the sample which excites the electrons of the surface, and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen, the result is an image of the specimens survive that appears three dimensional
How do transmission electron microscopes work?
Aims an electron beam through a very thin section of the specimen, and the specimen has been stained with atoms of heavy metals, the electrons passing through the specimen are scattered more int he denser regions, so fewer are transmitted. The image displays the pattern of transmitted electrons
Instead of using glass lenses, both ___ and ___ use electromagnets as lenses to bend the paths of the electrons, focusing the image onto a monitor for viewing
SEM
TEM
What is the disadvantage of using an electron microscope?
The methods used to prepare the specimen kill the cells
Cell fractionation?
A useful technique for studying cell structure and function; takes cells apart and separates major organelles and other sub cellular structures from one another
What application does cell fractionation have?
Used to isolate cell components based on size and density
What technique does cell fractionation use?
Cells are homogenized in a blender to break them up, the resulting mixture is centrifuged, the supernatant (liquid) is pure into another tube and centrifuged at a higher speed for a long time, the “differential centrifugation” results in a series of pellets each containing different cell components
What does cell fractionation enable researchers to do?
Prepare specific cell components in bulk and identify their functions
