Lab Topic 2
Techniques in Microscopy

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STUDENT OBJECTIVE

Students learn the parts and functions of compound and dissecting microscopes and view various specimens. Using a stage micrometer, students calibrate an ocular micrometer. Students also learn how to measure the size of structures shown in scanning and transmission electron micrographs.

EQUIPMENT AMOUNT
  (Class of 24 with 8 groups)
Compound microscope 1/student
Dissecting microscope 1/student
Ocular micrometer (can be set up as demonstration) 1/student
Stage micrometer (can be set up as demonstration) 1/student
Materials  
Electron micrographs Five to ten large posters made with photos from textbooks—include a variety of cells from different organisms Display
Ruler, 15 cm clear plastic in mm 12/lab
Scissors and dissecting needles 12/lab
Old newspapers for letters "e" and "a" 6/lab
Red and white thread 1 spool/lab
Forceps 6/lab
Blotting tissue 2 boxes/lab
Slides 2/student
Coverslips, #1 small square (18 mm ¥ 18 mm) 1/2 oz/lab
Lens tissue, 2" ¥ 4" (cut from standard tissue package) 8 pkg/lab
Dropper bottle with distilled water 8/lab
Specimens for dissecting scopes Variety of dead insects, flowers, seeds
Immersion oil 8 bottles/lab

PREPARATION

At Least One Week before Lab

Microscopes should be checked for repair or replacement and supplies ordered. Dried insects, flowers, seeds, and such can be collected at this time.

CLASSROOM SUGGESTIONS

  1. A display can be made including scanning and transmission electron micrographs, pictures of microscopes, and associated equipment. These can be obtained from the library, advertising pamphlets, and catalogs.
  2. Films or slides on microscopy may be used to augment the exercise.
  3. This exercise is short and can be done in conjunction with Exercise 2 to fill a three-hour lab period.
  4. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/

ANSWERS TO CRITICAL THINKING QUESTIONS

  1. Adjust the interpupillary distance of the eyepieces to correspond to your interpupillary distance by moving the eyepieces closer together until the two separate circles of light merge.

    If your field is dark, check first on your illumination source, next make sure that your objective lens has clicked into place. Also, check your iris diaphragm to make sure it has not been shut completely.

    When moving from low to higher power magnification, make sure that the object of interest is centered in the field of view.

  2. Use a dissecting microscope to observe the sea star and the live fruit fly. Use a compound light microscope to look at the fruit fly chromosomes. Do not use an electron microscope to view anything living. The fixing and infiltration procedures "kill" the tissue.

SUPPLEMENTAL MATERIALS