ABL 1 – Microscopes

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How does the optical microscope work?
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It uses light waves or modified light waves in order to visualize specimens.
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How does the electron microscope work?
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It uses an electron beam in order to visualize specimens.
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What is a bright-field microscope?
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This is the standard compound binocular or monocular microscope that is usually associated with biology laboratory.
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How does a bright-field microscope work?
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Light waves from the sun or lamp, after passing through a condenser lens, pass through a specimen on a slide, then an objective lens of varying magnification, and finally through an ocular lens before entering the eye for imaging and interpreting.
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What does monocular mean?
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Monocular vision is vision in which each eye is used separately.
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What is a dissecting microscope?
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This is a variation of the bright-field microscope. This microscope is used to visualize surface features of specimens. The light waves from similar sources are reflected off the surfaces and pass through objective and ocular lenses before entering the eye.
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Define ocular.
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eyepiece: combination of lenses at the viewing end of optical instruments.
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What is a inverted microscope?
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It is similar to the bright-field microscope, this unit is characterized by the location of the objective and ocular lenses, which are below the specimen. It is of particular value in viewing live tissue cultures and other specimens held in flat dishes.
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What is a dark-field microscope?
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These microscopes utilize a hollow cone of light formed by a special condenser. Specimens viewed with this microscope are typically very small organisms like bacteria and parts of organisms such as flagella and cilia. When light hits these objects, it is scattered making the object appear bright against a dark background (field).
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What is a phase-contrast microscope?
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This microscope, with a special condenser and objective lenses, is usually primarily for observations of living cells. As the light waves pass through specimens, they are retarded to different degrees by the structure of the specimen. The amount of retardation is due to the thickness of the various parts of the specimen.
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What is a differential interference phase contrast microscope?
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This system (DIC or Nomarski) is valuable for studying living cells and organisms, particularly because it eliminates the halo of the phase-contrast system and gives the observer a \”3-D\” image of the specimen.
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What is a polarizing microscope?
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This microscope measures the birefringence ( = the capacity of an object to split a beam of light into two beams with different refraction angles) of components of biological specimens by using polarizing filters below the condensor and above objective lens. Samples seen with this type of microscope have a crystalline or regular repeating pattern.
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What is a fluorescence microscope?
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This microscope is valuable in detecting biological specimens that fluoresce, that is, emit light of a different wavelength than that used to irradiate the specimen. It has become of major use in detecting fluorescent dyes that are attached to particular cells or parts of cells (DNA for example).
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How does transmission electron microscope (TEM) work?
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Using a high voltage to generate a beam of electrons through electromagnetic lenses and specially prepared specimens. The image of the specimen is seen on a phosphorescent screen.
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How does a scanning electron microscope work?
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Similar to the transmission microscope in utilizing electrons as the source of energy, in this case the SEM operates much like a dissecting microscope in that the electrons are reflected off the surface of specimens. The electrons then are picked up by a detector that digitizes the images and transmits it to a TV monitor for observations.
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What are the two most useful instruments in the animal biologist’s laboratory?
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The compound and dissecting microscopes.
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What is the compound microscope used for?
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This particular instrument is used for studies of small, generally translucent animals, cells, tissues, and other structures. It utilizes transmitted light passing through a specimen located between two lens systems.
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What is an Ocular lens?
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The lens closest to the eye. Usually 10x in magnification
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What is a Body Tube?
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The primary cylindrical portion of the microscope that houses the lens systems.
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What is a Nosepiece?
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A revolving unit that holds a set of three or more objective lenses. It is moved by carefully grasping with the fingers and rotating it until it clicks into position for a lens.
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What are objective lenses?
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Each are a complex set of small lenses that magnify the specimen according to the power engraved ont he side of the lens. Our microscopes typically have 4x, 10x, and 40x lenses.
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What is the arm?
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It is the main structural support for the body tube. Use this element to carry the microscope.
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What is the stage?
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It is a platform with clips to hold a slide in place under the objective lens. Some microscopes have mechanical stages that clamp the slide into a special bracket which is then moved by knobs.
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What is the aperture of the stage?
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It is the hole in the stage which allows light to pass through from the condenser.
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What is a condenser lens?
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A sub-stage lens system that focuses the light on the specimens. This lens may be locked in position or adjustable.
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What is an iris diaphragm?
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It is an adjustable opening under the condenser lens that controls the amount of light entering this lens.
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What is a coarse adjustment knob?
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This is a knob that is used to raise or lower the body tube to initially focus the specimen. It is used only with low magnification lenses.
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What is the fine adjustment knob?
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It is a knob that is generally somewhat smaller and outside the coarse adjustment knob, it is used for final adjustment of focus and varying the plane of focus through the depth or thickness of a specimen.
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How do you keep the microscope clean?
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1. Use only lens paper for cleaning the lenses. Do not use any cloth or paper that might scratch the glass of the objective or ocular lens. 2. Do not touch lens surfaces with your fingers – they are oily! 3. Clean up all spills, including water, immediately.
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How should one go about observing a slide?
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When beginning to observe a slide always start with the lowest power lens and advance sequentially to the higher power lenses. The latter lenses are longer than the low power lenses, and thus, have less \”working distance\” from the microscope. Be especially careful when switching to a high lens. Thick mounted specimens usually cannot be observed with the high power lenses.
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What does the coarse adjustment knob alter?
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It alters the distances between the objective lens and the stage by either moving the objective lens, or by moving the stage. Note which direction of rotation brings the lens and stage farther apart – this is how you prepare the microscope for changing to a different lens.
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How many lens systems does the compound microscope have?
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The compound microscope has two separate lens systems; the ocular and objective lenses.
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How does one find the total magnification of the compound microscope?
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The total magnification of the microscope is equal to the product of the two lenses being used.
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What type of microscope is the dissecting microscope?
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The dissecting microscope is a stereoscopic microscope, providing a three-dimensional view of specimens on the microscope stage. It is particularly useful for observations of zoological specimens of small to moderate size where great magnification may not be necessary.
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What are the advantages of making temporary slides?
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Temporary slides have the advantage of short preparatory time; but because they dry out rather quickly, they are of little long term value.
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What does a wet mount involve?
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It involves suspending a specimen, such as a living organism or material that needs to be kept moist in a drop of water on a slide. This material to be observed is suspended in water and, following the placement of a cover slip, can be observed using a compound microscope.

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