MicroscopeIntroductionThe first technological breakthrough in the study of biology, the microscope opened the eyes of scientists into the previously unknown and thus unexplored world of cells. In 1665, Robert Hooke, an English scientist, made some of the earliest biological observations using a primitive microscope. In viewing thin slices of cork tree bark, he found the cork to be composed of “a great many little boxes”. To him they resembled monastery rooms or cells and so his boxes were named ‘cells’. Further discovery found that plants were filled with ‘juice filled’ cells.Shortly thereafter, Antoni van Leewenhoek, a Dutch scientist, using his microscopes,discovered the world of pond water. He named the organisms seen, “animalcules”, which we now identify as paramecium, amoebas, etc. His subsequent investigations of blood, sperm, and insect eggs helped blow holes in the then common belief of spontaneous generation e.g. fleas were generated spontaneously from dust.It wasn’t until 150 years later that the microscopic work of a German zoologist, Thomas Schwann found that animals possessed cells like unto plants. He published a cell theory that declared cells to be the elementary particle of both animals andplants. In the 1850’s, Matthias Schleiden, a German botanist, added to the developing cell theory writing that cells formedthe fundamental basis of life. saFETY CONCERN: When transporting microscopes ALWAYS use 2 hands.1One of Hooke’s microscopes with drawing of cork cell wallsSAFETY CONCERN: Use electric receptacle to the front of your counter top. Do not string cord between counters.DO: Plug in the microscope and accomplish the following:SAFETY CONCERN: Use provided lens paper to clean lenses. Use of other paper, cloth, etc. will scratch the lens. DO: Clean the glass of the ‘field iris diaphragm’ and the lens of the condenser. Today you will be learning how light microscopes function and using both the compound light microscope and the stereoscopic dissecting microscope investigate plant and animal cells.2Compound Light Microscope FigureLight microscopes use light rays that are magnified and focused by means of lenses. You see objects 2 dimensionally with a compound light microscope because there is only one pathway from your eye to the specimen being viewed. Some compound scopes are binocular i.e. they have 2 eyepieces but you still see objects 2 dimensionally because you converge eye paths into one objective lens via the use of a prism.There is a limit to how much you can magnify an object using a light microscope and still see specimen parts clearly. We define this limit as the resolving power 3of a microscope: the ability to distinguish two objects that are very close together as separate; it allows us to see detail. This limit is determined by the quality of the microscope’s lenses, the amount and type of illumination, and if the object is stainedor not. Additionally, the quality of your own eyes will play a part on how clearly yousee the object. The resolving power of light microscopes is about 1 micrometer (a millionth of a meter) or about 1500X. Compound light microscopes have revolving nosepieces capable of attaching 2-5 objective lenses. Your microscope’s nosepiece has 4 objective lenses attached: the shortest, a scanning lens; a longer lens, the low power lens; a longer yet, the high power lens; and the longest, the oil immersion lens, which we never, never use. Lens power is written on the barrel of the lens e.g. 40x/0.65. The number to the leftof the slash (/) is the power of the lens (in this example it is 40) Eyepiece (ocular lens) magnification appears also on its barrel. Total magnification = magnification of the eyepiece times magnification of the objective lensDO: Calculate the total magnification for the lens combinations on your microscope. Since we never use the immersion lens, it is not included.Scanning power: eyepiece _____X times objective _____X = _____XLow power: eyepiece _____X times objective _____X = _____XHigh power: eyepiece _____ X times objective _____X = _____XProblem: You are using a microscope with an eyepiece 15X and an objective lens of 100X. Explain why you can or cannot see the specimen clearly.4Problem: Two microscopes have the same magnification. One ‘sees’ the same specimen better than the other. Why might this be?More Microscope Parts, Terms, and FunctionsWorking Position: the position when after rotating the nosepiece, it ‘clicks in’allowing an objective lens selected to be used. DO: Move the rotating nosepieceand feel it click into place.Stage: platform on which the slide holding the specimen is placed. It has a holein its center permitting light to pass through. Affixed to the stage is a mechanical“movable stage fixture”. DO: Select the “e” slide to see how it works.5Specimen lighting may come from an external light source or a built-in light. If thelight is external, then a mirror is used to ‘direct’ the light upward. If the light isbuilt in, a condenser is used to focus the light into a beam. When the beam isproperly aligned, an image of stained cells will be seen in focus. DO: With the scanning lens in the working position move the stage via coursefocus knob to its highest position. Then move the condenser by using its heightadjustment knob (2) while looking through the eyepieces until cells come into focus.The light beam is now properly aligned/focused. 6Integrated into the condenser is the diaphragm. It is a mechanical device whichdetermines how much light passes through by controlling the width of the lightbeam. An “aperture scale” (1) ranges from 0.1 and 1.25. This scale corresponds to the sizeof the diaphragm opening. The width of the opening is determined by moving thelever (2). It functions much like the pupil of your eye. The resolution, contrast, and depth of field of an objective lens depends in part onhow much light passes through the objective. How much for the lenses on yourmicroscope has been determined during the manufacturing process and beenassigned a “resolution” value. This “resolution” value is the second set of numberson the barrel of an objective lens e.g. 10x/0.25, where the 0.25 is the value. Settingthe lever to the corresponding aperture scale permits the objective to function at isoptimum. Pretty fancy, eh!? DO: Move