Chapter 2: How We See the Invisible World Slides Flashcards
What effect does the wavelength of radiation have on microscopy?
Shorter wavelengths have better resolution and higher magnification.
What causes magnification?
The light spreading out from the microscope.
What is refraction?
The change of light rays as it passes through one medium to another.
What is magnification?
How close the object appears.
What is resolution?
How close 2 objects can be and still look apart.
What are the two things that affect resolution?
Wavelength and numerical aperture.
What is numerical aperture?
How much light actually makes it to your eye.
What is contrast?
Differences in intensity between two objects, or an object and its background.
What can we do to increase contrast?
Staining.
True or False: Contrast is not important in determining resolution.
False.
How many lenses does a simple microscope contain?
One.
Who used simple microscopes to discover microorganisms?
Leeuwenhoek.
How may lenses does a compound microscope contain?
A series of lenses for magnification.
How do we determine the total magnification of a compound microscope?
Magnification of objective lens times the magnification of the ocular lens.
How does light pass through the microscope?
Light passes through specimen into objective lens.
How many ocular lenses are in a compound microscope?
One or two.
What do most compound microscopes have to direct light through a specimen?
Condenser lenses.
What does oil immersion do?
Reduces light scattering
Increases resolution
When is the use of a dark-field microscope best?
When observing pale objects.
What light rays enter the objective lens?
Only light rays scattered by the specimen.
How does the specimen appear in the microscope?
Specimen appears light against a dark background.
Why do we use dark-field microscope?
Increases contrast and enables observation of more details.
What do fluorescence microscopes do?
Direct UV light source at specimen.
What does UV light increase?
Resolution and contrast.
True or False: Some cells are naturally fluorescent; others must be stained.
True.
Why do we use fluorescence microscopy in immunofluorescence?
It is used to identify pathogens and to make visible a variety of proteins.
True or False: In fluorescence microscopy, the specimen radiates energy back as a shorter, visible wavelength.
False: It radiates energy back as a longer, visible wavelength.
What do confocal microscopes do?
Use fluorescent dyes
Use UV lasers to illuminate fluorescent chemicals in a single plane
What is increased with confocal microscopes?
Resolution is increased because emitted light passes through pinhole aperture.
What constructs the 3D images in confocal microscopy?
A computer.
What can an electron microscope see?
Detailed views of bacteria, viruses, internal cellular structures, molecules, and large atoms.
What can electron microscopes do better than light microscopes?
They have greater resolving power and magnification.
What are the two types of electron microscopes?
Transmission electron microscope (TEM)
Scanning electron microscope (SEM)
Where does electron microscopy take place?
In a vacuum.
How does a TEM work?
Electron beam will send electrons through the specimen against the lens, and it picks up the image.
How does a SEM work?
Images are formed from electrons bounced off the specimen.
Why do we use stains?
Coloring specimen with stain increases contrast and resolution.
What is the colored portion of the dye for staining?
Chromophore
What are simple stains?
One dye is used to create contrast.
What are differential stains?
Dyes different organisms different colors.
What are some common differential stains?
Gram stain
Acid-fast stain
Endospore stain
Histological stain
What does an HE stain show?
Cell contents (cytoplasm, nucleus, organelles, extracellular, components).
What are some simple stains?
Negative stains
Flagellar stains
Fluorescent stains
What do stains for electron microscopy contain?
Chemicals containing heavy metals (gold).
When do we use a GMS (gomori methenamine silver) stain?
On tissues.
