Biol 227 Lab Exam
body of microscope - arm and base
light source - Projects light upwards through the diaphragm, the specimen, and the lenses. Has
on/off switch and intensity knob
eyepiece - Contains the ocular lens
ocular lens - magnifies the image 10x
total magnification - objective lens x ocular lens
field of view - The area visible through the microscope eyepiece
objective lens - the part of a compound light microscope that is located directly above the specimen
and that magnifies the image of the specimen (4x, 10x, 40x, 100x)
working distance - distance between objective lens and specimen
stage of microscope - Holds the slide or object you are looking at. (move with x and y knobs)
focus adjustment knobs - course adjustment knob for larger focusing and fine adjustment knob for
precision focusing
condenser - focuses light through the specimen
condenser focus knob - raises and lowers the condenser relative to the stage (vertical height
adjustment)
diaphragm - Regulates the amount of light on the specimen
,aperture iris diaphragm lever (contrast lever) - Adjust intensity of image in precise increments; left
increases intensity, right decreases intensity
field iris diaphragm - controls the amount of light entering the condenser
interpupillary distance - distance between eyepieces
diopter adjustment - Useful as a means to change focus on one eyepiece so as to correct for any
difference in vision between your two eyes.
Using a microscope - Clean lenses, eyepiece, and objectives with lense paper
turn on light to midlevel
Raise condenser to highest position
Place slide on stage and center
Using 100x objective, raise stage until slide almost touches
Find specimen with 4x
Rotate 10x and bring into focus with fine adjustment
Adjust interpupillary distant and diopter adjustments
Kohler illumination
Purpose of Kohler illumination - Allows for high contrast and resolution with reduced heat on the
specimen
Kohler illumination - Contrast level/aperture iris to middle
close field iris diaphragm, center the circle
lower condenser until polygon is clear
open field iris to edge of FOV
bright field - dark specimen on bright background
dark field - bright specimen on dark background (good for transparent specimen)
, Oil Immerision - drop of oil on slide, turn to 100x, focus with fine adjustment
measuring field of view - move stage until lines of ruler align with edge, count (in mm), convert to
microm (1mm=1000microm)
CFU/mL - colony count/total dilution factor
total dilution factor - dilution factor x volume transferred
serial dilution factor - diluted several times in sequence
colony morphology - the properties and characteristics of colonies such as shape, margin, and the
elevation
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