1. Why is it important that health care professionals know about microorganisms?
2. What is the main difference between prokaryotic and eukaryotic cells?
3. Why is it important to use immersion oil when using the 100X objective?
4. Are there things that are too small to be seen with a light microscope? Explain.
5. Of the organisms you have looked at today, which are unicellular and which are multicellular?
6. Fill in the blanks: As magnification increases, the area of the field of view _________________, the depth of the field of view _______________________, the working distance __________________, and the amount of light required ____________________.
7. Distinguish between morphology and arrangement.
8. What do you think would happen if you tried to view a slide using the oil immersion lens but forgot to add the oil?
9. Use the information below to label the parts of the microscope on Figure 1.3.1.
Parts of the Microscope
a) Ocular (eyepiece): what you look through to view your slide. Our microscopes are binocular, which means they have two eyepiece tubes and both eyes are used (monocular microscopes have only one tube). Typically ocular lenses magnify an image 10X, although some have other magnifications (ex: 12X). Binocular microscopes allow for adjustment of the distance between pupils so that both eyes can be used to observe one image.
b) Objective lenses are the lenses close to the stage. Usually microscopes will have 3-5 lenses of different magnifications (ours have 4—4X, 10X, 40X and 100X magnifications). Objective lenses are located on a rotating turret to allow for changes in magnification.
c) Coarse adjustment knob: the larger (and outermost) of the two focusing knobs—moves the stage toward or away from the objectives to bring the image into focus at low power.
d) Fine adjustment knob: smaller knob within the coarse adjustment knob—used for “fine-tuning” an image. Only fine focus can be used when the 40X and 100X objectives are in place.
e) Stage: the platform where the slide to be viewed is placed. A mechanical stage holds the slide in place and allows for the movement of the slide to view different areas.
f) Illuminator (light source): found at the base (bottom) of the microscope below the stage.
g) Condensor/iris diaphragm assembly: found directly beneath the stage. This assembly can be raised and lowered using a knob at the side of the microscope. For our purposes, the assembly should be positioned very close to the bottom of the stage. The condenser is a lens that focuses the light from the illuminator onto the specimen. The iris diaphragm controls the amount of light that passes through the specimen. The iris diaphragm can be opened and closed by twisting the ridged ring of the assembly.
h) Base: the bottommost part of the microscope that contains the illuminator.
i) Arm: positions the objective lenses and the oculars above the stage. When moving the microscope, the base should be supported with one hand, while the arm is grasped with the other hand.
There are other less common bacterial morphologies (e.g., filamentous, squares, etc.) that are not shown here.