Download File - Science with Mr. Davis

Broughton High School
Biological Microscope Techniques
"Invisible Microbes"
Biology 2014
Mr. Davis
Broughton High School
The Microscope
Introduction
The light microscope allows us to "see" details of cells and tissues of living organisms. The purpose of this
laboratory is to introduce you to the microscopes that you will use to observe many biological structures and
processes during this course. The familiarity that you gain with this exercise will allow you to spend your time in
subsequent labs more effectively.
The microscope used most frequently in the lab is the compound light microscope. The compound microscope is
used to magnify and resolve fine detail within a transparent specimen (one through which light can pass).
The compound light microscope is so called because it has two separate lens systems; an objective lens, located near
the specimen, which magnifies the specimen a certain amount, and an ocular lens, or eyepiece, which further
magnifies the image formed by the objective lens. The total magnification observed by the human eye is the
product of the magnification of the two lenses (objective X ocular).
The resolution, or resolving power, of the microscope is just as important as its ability to magnify an object.
Resolving power is the ability to discriminate two close objects as separate. To give you an idea of what
resolving power means, the human eye can distinguish two objects as separate when they are at least 0.1 mm apart
(objects closer than this will appear as one fuzzy image). A compound light microscope has the ability to resolve
objects 1000 times closer than the human eye can, while an electron microscope can distinguish objects as small as 0.2
nanometers. In general the more light delivered to the objective lens, the greater the resolution.
Biology 2014
Mr. Davis
Broughton High School
Activity 1: Identifying the Parts of the Microscope
In order to use a microscope properly you must be familiar with the optical and mechanical parts of the microscope.
You must also learn the appropriate care of this delicate and expensive instrument. The microscope gives you
the opportunity to see a world of things you may not have seen before, but you must know how to use it to enjoy the
experience.
Remove a microscope from the cabinet by its arm, supporting the base of the microscope with your free hand. Take
the microscope to your desk continuing to support the base with one hand and the arm of the microscope with your
other hand. The following diagram and list of terms and illustrations will help you to become familiar with the
microscope. As you read through the list locate each of the parts on you r microscope. If you don't
understand how something functions or can't find it on your microscope, check with your
instructor.
Once you have read through and located each of the features of the scope, point to and name each
of the microscope parts to your lab partner.
a. Adjustment Knobs
Your microscope has two adjustment knobs, which are used to focus the specimen to be studied. The largest is the
coarse adjustment knob. This is used for rapid (or coarse) focusing of the specimen when using the scanning
objective lens and the low power lens. The coarse objective knob is rotated until the specimen is roughly in focus
and then left alone. The fine adjustment knob controls precise focusing of the object. Only the fine adjustment
knob should be used with the high magnification lenses (high power and the oil immersion objective lenses). Moving
the fine adjustment knob also helps you to determine the third dimension (depth) of the specimen you are studying.
b. Stage
The stage holds the slide to be observed. The center of the stage has an aperture or hole through which light passes to
illuminate the specimen on the slide. Moving the coarse and fine adjustment knobs changes the working distance
between the specimen and the objective lens.
c. Mechanical Stage
Your slide is fixed into position on the stage with the mechanical stage. The slide is fastened into the mechanical
stage by using a small lever located on the mechanical stage. Two knobs located on the side of the mechanical stage are
used to move the slide around to locate your specimen. One knob moves the slide from side to side and the other
moves the slide forward and backward. The mechanical stage permits precision movements of your slide,
without you touching the slide itself.
d. Condenser
The condenser, located below the stage, contains a system of lenses that directs light from a light source through the
slide specimen. The condenser may be raised or lowered using the condenser knob. Most microscopes have a
built-in light source.
e. Iris Diaphragm
The iris diaphragm is located on the condenser. The lever of the iris diaphragm is used to adjust the amount of
light striking the object being studied. It is critical that you know the proper use of the condenser and iris diaphragm. A
common problem with microscope use is having too much light, which obliterates the object (more or less like
trying to see something while looking directly at the sun). You will have better contrast if you reduce light to a
minimum.
Biology 2014
Mr. Davis
Broughton High School
f. Objective Lenses
The pattern of light formed by the specimen is focused into a real image by the objective lens. When proper
illumination is provided the resolving power of a microscope depends on the quality of its objective lenses. Our
microscopes are provided with 4 objective
Lenses which are mounted on a rotating turret or nosepiece. As you rotate the turret you will feel the lens "click" into position
for proper viewing. If a lens is not properly locked in position you will observe a dark area as you look into the microscope.
The 4 objective lenses of your microscope and their magnifications are:




Scanning lens 4x magnification
Low Power Lens
10x magnification
High Power Lens
40x, 43x or 45x magnification
*Oil Immersion Lens 100x magnification
* Note: The magnification of the oil immersion lens requires using the lens with a special immersion oil for proper resolution.
Never use oil immersion lens without immersion oil. Serious damage might result. The oil immersion lens will not be used in
this class.
g. Ocular
The ocular lens, or eyepiece, further magnifies the image formed by the objective lens. It does not improve
resolution. Your microscope will probably have a monocular system (one ocular lens). A few of the
microscopes have adjustable binocular systems (two ocular lenses). The magnification of the ocular is 1 Ox.
The ocular may be equipped with a pointer or a numerical scale. They are useful in pointing out specific structures or
determining the real dimensions of the specimen you are observing.
Biology 2014
Mr. Davis
Broughton High School
Observing and Drawing Objects:
Activity 2: Microscope Image Drawings
Because the light rays from an object cross before reaching your eye, the image you see through our light microscopes
will be inverted and upside down.
Sitting on the stage
Viewed through the lens
When making drawings on your lab report, do the following:
1. For drawings only, use pencil - you can erase and shade areas.
2. Begin by identifying the area viewed through the microscope with a circle.
3. Specimens should be drawn to scale. If the specimen takes up the whole viewing field, make sure your drawing
shows this.
4. Drawings should be labeled with the specimen name and magnification.
5. Drawings should be large enough to view details and have significant details labeled.
 All labels should be written on the outside of the circle
Biology 2014
Mr. Davis
Broughton High School
Compound Light Microscope
Viruses
Biology 2014
Mr. Davis
Broughton High School
Biology 2014
Mr. Davis
Broughton High School
Activity 3: Labeling Parts of the Microscope
Compound Light Microscope
Biology 2014
Mr. Davis
Broughton High School
Activity 4: Human Buccal Image Drawings
Human Cheek Cells
Materials
Toothpicks
Microscope slides and cover slips
Iodine-water in plastic dropper bottles
Eye droppers if plastic dropper bottles are not used
Microscopes or a Flex-Cam with television monitor
Procedures
1. Put a microscope slide on a paper towel.
2. Put 1 drop of iodine-water solution on your slide.
3. Gently scrape the inside of your cheek two or three times
with a toothpick. It will look like nothing is on the
toothpick, but there will probably be plenty of cells to see
with the microscope.
4. Stir the cheek materials into the iodine-water solution on
your slide.
5. Carefully put a cover slip over the mixture on your slide.
Press down on the cover slip to clear out any air bubbles.
Microscope
6. Put the slide on the microscope, use the low power (lox)
objective lens, and set the light where it is best for you.
Biology 2014
7. Focus the microscope and draw what you
observe. To focus: look for small, irregularly
shaped objects and turn the adjustment knob
until the objects are clear. The iodine-water
solution will stain the cells so they are more
easily seen.
8. Identify as many parts of the cheek cell as
you can, and label them on your drawing.
You should be able to see the cell membrane,
cytoplasm, and nucleus.
9. Carefully change to the high power (40x)
objective lens, adjust the light setting and
refocus on the cheek cell.
10. Draw and label what you see on high power
Mr. Davis
Broughton High School
Human Cheek Cells
Biology 2014
Mr. Davis