Flashcards in Background And History 2 Deck (37):
Contributions of Zacharias Janssen?
> 1859: produced the first operational compound microscope with a magnification of 30x
Contributions of Robert Hooke?
> 1665: Robert Hooke described for another cells and introduced the term "cell"
> used an alcohol burner source of illumination and the "bulls eye" lens to focus the light onto the object
Contributions of Anthony Leeuwenhoek?
> 1674: Anthony Leeuwenhoek made over 247 simple microscopes capable of magnifications of around 100x. Sent 26 of them to the Royal society. Among his observations were RBCs, Protozoa, striations of skeletal muscle, sperm cells, bacteria
Who was credited with the theory that all living organisms are composed of cells?
> Schleiden and Schwann
Light waves transmitted through a vacuum do so at a __________ velocity?
>>> velocity is slowed through air, water, or glass
>>> each medium transmits light at a characteristic velocity
How do you calculate the refractive index?
R.I. = (Velocity of light)/(velocity of light inside transmitting medium)
What is the refractive index of air?
True or false: when light waves travel from one medium to another, they bend?
The degree to which light waves will bend is dependent upon what two things?
> angle at which light strikes the surface
True or False: light waves do not follow the same path in either direction?
> False: light waves follow the same path in either direction
True or False: light waves striking a perpendicular surface continues on through without bending?
What is refractive power?
> a measure of how much a lens bends light waves. It is measured in diopters
>>>1 diopter = 1 meter divided by the focal length of a lens
1 diopter is equal to what?
> 1 meter divided by the focal length of a lens
True or False: the thicker the lens, the more that it bends light?
What is the focal point?
> the point through which all parallel rays of light will pass after passing through each part of the lens
What is the focal length?
> the distance from the center of the lens to the focal point
Light waves traveling through which type of lens will converge at the focal point?
> convex lens
In relation to the focal point, when is a real image formed?
> a real image is formed when the object is placed OUTSIDE the focal point
Summarize a real image
> a real image is formed when the object is placed OUTSIDE of the focal point
>>> a real image is inverted
>>> a real image can be projected onto a screen
>>> a real image differs in size from the object
>>>>>greatest magnification will be obtained from lenses having a very short focal length with the object as close as possible to the focal point
When is greatest magnification achieved?
> greatest magnification will be obtained from lenses having a very short focal length with the object as close as possible to the focal point
When is a virtual image formed?
> a virtual image is formed when the object placed INSIDE of the focal point
When an object is place inside the focal point, what type of image is formed?
> virtual image
Summarize a virtual image
> a virtual image is formed when the object is placed inside the focal point
>>> a virtual image is not inverted
>>> a virtual image cannot be projected onto a screen
>>> a virtual image can be magnified
>>> no points exist at any plane in space at which rays radiating from the object are brought to focus
Definition of resolution?
> the ability of a microscope (or any optical instrument) to distinguish two small points as separate points
> to accomplish this, the diameter of diffraction lines around the points must be reduced
What equation would you use to calculate resolution?
> resolution = d = 0.61(wavelength of light)/ n sin(alpha)
How could you improve resolution?
> use a higher refractive index
> use shorter wavelengths
Highest resolution in a light microscope?
> about 0.5 um
Highest resolution in the TEM?
> Highest resolution in the TEM (transmission electron microscope) is 0.01 angstroms, but the actual resolution achievable is 5-10 angstroms (= 0.5-1.0 nm)
This microscope is also referred to as a bright-field microscope?
> compound optical (light) microscope
What are the components of the compound light microscope?
> light source
> objective lens
> ocular lens
Pros and cons of the compound optical (light) microscope?
> ability to magnify
> ability to solve structural detail
> specimen must be thin
> relatively little contrast in the unstained specimen
Summarize the characteristics of the phase contrast microscope
> converts phase shifts (invisible to the eye) in light passing through a transparent specimen to brightness changes (visible to the eye) in the image
> can be used to examine unstinted cells and tissues
> use for examination of living cells
> different parts of a cell have small differences in the refractive index
> light passing through these region becomes deflected and out of phase with the main stream of light waves
> out-of-phase wavelengths are matched with other induced out-of-phase wavelengths which cancels their amplitude
> this creates light waves that can be seen in contrast to other light waves that have not been retarded
Summarize the characteristics of the fluorescence microscope
> detects molecules that emit light of wavelengths in the visible
> detects naturally occurring fluorescent (auto fluorescent) molecules such as vitamin A
> most widespread application is to detect induced fluorescence
>>> detection of antigens of antibodies in immunochemical staining procedure
>>> detection of fluorescent tracers injected into animals or cells
Summarize the characteristics of the confocal scanning microscope
> patented in 1957 by Marvin Minsky
> increases optical resolution and contrast by means of adding a pinhole placed at the confocal plane of the lens to eliminate out-of-focus light
> enables the reconstruction of three-dimensional images
> combines light microscope components fitted with fluorescence equipment and a scanning system that employs a laser beam
> this illuminating laser light is strongly convergent and produces a shallow scanning spot
> light emerging from the spot is directed to a photomultiplier tube and analyzed
> a mirror system moves the laser beam across the specimen and data from each spot of the specimen is recorded and stored in a computer
> the information is the displayed on a monitor to create a visual image
What are the advantages to using a confocal scanning microscope?
> very thin optical images of the specimen are created (typically 1 um thick)
> out-of-focus images are subtracted from the image by the computer program
> computer can make 3D reconstructions of the specimen by stacking individual images
Summarize the characteristics of the transmission electron microscope
> TEM uses a beam of electrons rather than light