Chapter 2 Flashcards
What is resolution?
The smallest distance by which two objects can be separated and still be distinguished.
What part of the human eye has the finest resolution of two separate points?
Fovea
What is detection mean?
The ability to determine the presence of an object
What is magnification?
This means an increase in the apparent size of an image to resolve smaller separations between objects
What are some characteristics of eukaryotic microbes?
- Protozoa, algae, or fungi
- 10-100 um
Structures can be seen under a light microscope
What are some characteristics of prokaryotic microbes?
- Bacteria or Archaea
- .4-10 um
- Subcellular structures too small to resolve by light microscopy
What shape do bacilli refer to?
Rods
What shape do cocci refer to?
spheres
What shape do spirochetes or spirilla refer to?
Spirals
What is the wavelength of visible light (in nm)?
400-750nm
What three conditions must exist for electromagnetic radiation to resolve an object?
- Contrast between the object and it’s medium
- Wavelength smaller than the object
- Magnification
What is absorption?
This means that the photon’s energy is acquired by the absorbing light.
What does reflection mean?
This means that the wavefront bounces off the surface of an object.
What does refraction mean?
This means that the light bends as it enters a substance that slows its speed.
What does scattering mean?
This occurs when the wavefront interacts with an object smaller than the wavelength of light.
What requires the bending of light?
Magnification
How does refraction accomplish magnification?
Refraction magnifies an image when light passes through a refractive material shaped so as to spread its rays.
What does a lens of a microscope do?
The lens bends the light rays to intersect at a focal point.
What is a focal point?
The point of which parallel rays bend at an angle such to all hit the same point.
What ultimately limits the ability of what we can see with a microscope?
Resolution
What is empty magnification?
magnification increasing without detail
What limits the resolution of detail in microscopy?
The wave nature of light
What is Bright-field Microscopy?
Generates a dark image of an object over a light background
Name 5 ways to increase resolution.
- Use shorter wavelength of light
- Reduce Contrast
- Use immersion oil
- Use wider lens close to specimen
- Higher numerical aperture
What is a compound microscope?
A system of multiple lenses designed to correct or compensate for aberration.
What is total magnification?
Magnification of the ocular multiplied by that of the objective
What are the advantages of wet mounts?
- Observation of cells in natural state
What are the disadvantages of wet mounts?
- Little contrast between cell and background
2. Sample may dry out to quick
What is fixation?
Cells are made to adhere to a slide in a fixed position
What is staining?
- Cells are given a distinct color
2. Most stains have conjugated double bonds or aromatic rings, as well as one or more positive charges
What is a simple stain?
adds dark color specifically to cells, but not to the external medium or surrounding tissue
What is a differential stain?
stains one kind of cell but not another
Who developed the Gram stain in 1884?
Hans Christian Gram
What does Gram-positive mean?
peptidoglycan is present in the layer
What does Gram-negative mean?
peptidoglycan is not present in the layer
In what type of microscopy does the specimen absorb light of a defined wavelength and then emits light of lower energy?
Fluorescence Microscopy
What is the excitation wavelength?
light absorbed by the specimen
What is the emission wavelength?
light emitted by the specimen
What is a fluorophore?
fluorescent chemical compound
Who tracked the movement of DNA binding proteins during cell fission?
Lucy Shapiro and Moerner
What does phase-contrast microscopy exploit?
differences in the relative index between the cytoplasm and the surrounding medium or between organelles.
What is differential interference contrast microscopy?
enhances contrast by superimposing an image of the specimen onto a second beam of light that generates interference fringes
What must be present in order to use electron microscopy?
- The specimen must absorb electrons
2. The specimen must be coated with heavy metal
What is a transmission electron microscopy?
Reveals internal structures
Wha is a scanning electron microscopy?
Reveals external structures in 3D
What are two ways a specimen may be prepared for electron microscopy?
- Embedded in a polymer for thin sections(using microtome)
2. Sprayed onto copper grid
Cryo-electron Microscopy
- no staining
2. Specimen must be flash frozen
Tomography
the acquisition of projected images from different angles of a transparent specimen
Cryo-electron tomography
- avoids the need to physically slice the sample
What does scanning probe microscopy enable?
nanoscale observation of cells
What is the major tool to visualize a molecule?
X-ray diffraction analysis, or X-ray crystallography
