Observing Microorganisms


Unaided eye

examining your cat for the presence of fleas

Light microscopy

-examining a clinical specimen, such as a sputum smear, for the presence of bacteria
-examining a blood smear for the presence of malarial parasites

Scanning electron microscopy

-viewing the three-dimensional shape of a protozoan and the arrangement and distribution of cilia on its surface
-determining the three-dimensional shape and arrangement of bacterial cells

Transmission electron microscopy

-confirming the 9 + 2 microtubule arrangement in a eukaryotic flagellum
-viewing a cross section of poliovirus (30 nm)
-viewing the layers of the gram-negative cell wall in cross section
-viewing ribosomes (20 nm) within a bacterial cell

Smallest to Largest

1. Bacterial Plasmids (20 nm)
2. Mastadenovirus (30 nm)
3. Gram-positive bacteria (6 um
4. Giardia lamblia (7 um)
5. Clonorchis sinensis (5 mm)

Chlamydia trachomatis elementary bodies measure approximately 0.25 micrometers in diameter. What is this measurement expressed in nanometers (nm)?

250 nm
(multiply by 1000)

A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)?

0.15 mm
(divide by 1000)


controls how much light from the illuminator reaches the specimen

Fine focus knob

used after initial focusing to sharpen the image

Coarse focus knob

used for initial focusing; should never be used when the high-power objective lens or oil immersion objective lens is in place (brings the stage upwards)

Ocular lens

lens that you look through


platform on which the slide is placed for viewing

Condenser lens

used to focus the light from the illuminator onto the slide

Objective lens

lens that is closest to the slide and provides initial magnification of a specimen