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-also known as the optical microscope
-uses light to produce an image: enlarged view of object
-magnification: ratio of image size to original object size
-lenses: pieces of glass with curved surfaces
How It Works:
Light rays change direction when they pass from one transparent medium to another.
Lenses cause lights rays of object to bend producing an enlarged image.
a) The Simple Microscope
-magnifying glass (one lens)
Use:
Identifying specimens in field and making quick observations
b) The Compound Microscope
- Optical System, Mechanical System and Light System
Optical System:
-uses two lenses: Ocular and Objective
-one lens produces an enlarged image that is furthered magnified by second lens
Ocular- eyepiece
Objective- low power and high power
Low power- used to locate region of specimen to be examines
High power- used for further magnification
Mechanical System:
-structural parts that holds the specimen, lenses and permit focusing of image
-base: structure on which the microscope stands
-arm: supports body tube and course adjustment
-stage: platform protruding from arm that has opening where specimen is placed
-clips: attached to stage, hold slide in place
-body tube: holds lenses
-nosepiece: holds objective lenses
-coarse adjustment: large knob, used for focusing of low power objective
-fine adjustment: smaller knob, final focusing of low power objective
and for all focusing of high power objective
Both vary distance between
objective and specimen by moving either body tube (coarse adjustment) or
stage (fine adjustment)
Light System:
-mirror: under opening in stage, used to direct light up through specimen into objective
-stage illuminator: small electric light, used in SOME microscopes
-diaphragm: mounted below stage, regulates amount of light reaching objective
-condensers: lenses that concentrate light on specimen, located in/ below stage, used in SOME microscopes
Magnification:
-enlargement of image
-magnifying power: extent to which microscope magnifies image (enlargement in one direction)
-total magnification: objective x ocular
10 x 10 (low power x ocular)
43 x 10 (high power x ocular)
Resolution:
-ability of microscope to show two points that are close together as separate images (sharpness of image- not only enlargement of image.)
-depends on precision and quality of lenses
Preparation of Specimens:
-specimen must be thin enough for light to pass through it in order to observe under microscope, ex: microorganisms: organisms too small to be seen by the naked eye
- organisms that are too thick must undergo Fixation
- Fixation & How it Works:
-materials are cut into small pieces
-are soaked in fixative
-are embedded in liquid wax or plastic (allows it to harden)
-wax/plastic holds specimen so it can be sectioned
-microtome: instrument used for slicing thin sections
-staining: when certain structures absorb stains, causing contrast and enabling details to be seen
-vital stains: used with live tissue (do not kill the tissue)
*The Phase-Contrast Microscope*
-special kind of compound microscope which allows details to be seen without staining
-enhances differences when light passes through different regions of cell
*Stereomicroscope*
-type of light microscope used to study surface structure of specimen
- has ocular and objective and low magnifying power
-provide three dimensional image
-image not reversed
-used during dissections that require magnification
a) Transmission Electron Microscope (TEM)
-uses electron beams and electromagnetic lenses
-contains cameras to photograph image of specimen
-specimens must be dried, embedded in plastic and sliced thin before being mounted on grids and stained with metal to increase contrast
How It Works:
The electron beam is directed through a vacuum chamber that contains electromagnets.
The electromagnets serve as lenses to focus electron beam
Electrons hit specimen and those that are transmitted are focused on viewing screen.
Denser areas absorb the most electrons.
b) Scanning Electron Microscope (TEM)
-uses electron beams that have been focused to a point to reveal details of surface structures
How It Works:
The beam is passed back and forth over surface of specimen.
Electrons reflected/rejected are collected and used o create image of great depth.
Centrifugation:
-used to separate materials of different densities suspended in liquid
-ultracentrifuge: more powerful than centrifuge
-used to separate very light particles (e.g. various parts of cell)
How It Works:
The material is suspended in liquid in a test tube and is put into centrifuge.
The centrifuge spins the tube around allowing the heaviest particles settle in the liquid the fastest. (The layers pile up leaving the lightest at the top.)
Each layer can then be removed from the tube.
Microdissection:
-tiny instruments are used to perform various operations on living cells
-micromanipulator: controls tools used in microdissection, attached to microscope stage
-microelectrodes: used to measure or produce electrical currents in cell
-microknives & microneedles: used to remove cell structures
-micropipettes: used to introduce materials into or remove materials from the cell
Tissue Culture:
-maintains living cells or tissues in culture medium outside body
-used in biological and medical research
How It Works:
Cells from living organisms are placed in culture tubes.
Then they are bathed in fluid containing nutrients, oxygen etc.
Chromatography:
-separating different substances from each other based on their chemical and physical properties
How It Works:
The mixture is placed on a solid material and a solvent in introduced.
The substances that stick loosely to the material will float away first and those that stick tightly will be carried away last.
Colored substances- form colored spots/bands.
Colorless substances- react with chemicals that give them color
Electrophoresis:
-separating substances made of particles with an electrical charge
How It Works:
An electric current is run through solution containing variety of dissolved substances.
Substances are separated (because they move at different rates in electrical field).
Spectrophotometry:
-uses light to analyze samples
-spectrophotometer: instrument uses to make such measurements
Computers:-used to collect, store and analyze data
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