are certain skills that are needed to perform lab activities.
Lab Skills There
Certain instruments and chemicals must also be used.
A simple microscope is also known as a magnifying glass
A Compound Light Microscope is the major tool used to study cells. The school
microscopes usually have a magnification up to 500X.
Mrs. Degl
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In a compound light
microscope:
The course adjustment is
used to focus under low
power.
The fine adjustment is used
to focus under high power
and used to “fine tune” the
image (make the image
clearer).
Total Magnification = Ocular (Eyepiece) X Objective
Mrs. Degl
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Some Key Points to remember when focusing on a
specimen with the compound light microscope.
1.) The image of the specimen is reversed (backward) and inverted (upside
down).
2. Do not touch the lenses. If they are dirty, ask the teacher for special lens
paper or ask the teacher to clean the lenses for you.
This is a letter F observed under low power with the
compound microscope. Note that the image is
reversed and inverted as seen by the viewer.
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2.) Always begin focusing on the lowest possible power. Remember to
center the specimen you are observing in the field of view before
switching to a higher power. Make certain that you move the objectives
away from the specimen when focusing so their is no collision between
the objective being used and the slide/cover slip/specimen which may
damage the objective lens.
3.) As you switch from low to high power, the field of view becomes
darker. To deal with this the diaphragm needs to be opened to allow in
more light. (Frequently on low power the diaphragm needs to be partially
closed as it is too bright.)
4.) As you switch from low to high power the field of view becomes
smaller. This decrease in size of the field of view is the inverse of the
increase in magnification. For example if the magnification goes from
100 X to 400 X this is a four times increase in magnification, so the size of
the field of view is quartered (X 1/4).
Mrs. Degl
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Estimating the Size of Specimens
The size of a microscopic field of view can be determined on low power using a
device called an optical micrometer. An economy version of this can be made by
placing a clear metric ruler on the stage of a microscope and using it to estimate
the field of view. An example of this appears below.
If you observe the field of view at the
left, it can be observed that there are
approximately 3 1/2 divisions equal to
a length of 3.5 mm. Therefore this
field of view is equal to 3.5 mm
or 3,500 micrometers.
Remember that there are 1,000 micrometers in 1 mm (millimeter).
Mrs. Degl
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Solution: It can be noted that
the two cells in this field take up
a field of view of one millimeter.
What is the average size of
each cell in this field of view in
micrometers?
Therefore, the size of the
specimen is equal to
1 mm/2 cells or 0.5 mm per
cell.
There is 500 micrometers in 0.5
mm., so the average size of
each cell is 500 micrometers.
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Solutions:
1.) It is sometimes tough to
approximate the approximate size
of the field of view, but this ameba
Problem 1: The field of view under considered lengthwise appears to
occupy approximately 1/3 of the
low power on the left is equal to 3
field of view.
mm. How large is this ameba in
3 mm X 1/3 = 1 mm length = 1,000
length in micrometers
micrometers for the approximate
(approximately)?
length of this ameba.
Problem 2: The second image on
2.) The student is viewing the
the right is of the same organism
same ameba on high power. The
as the first image on the left in
field of view gets smaller which
problem # 1. What happened to
makes the ameba appear larger in
form the image on the right?
this field.
Mrs. Degl
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Solution:
Problem # 3:
3.) The increase in
A student determines the
magnification going from low
field of view at 40 X
power at 40 X to high power
magnification using a
at 100 X is 10 times. The
compound microscope to be field of view will change
5 mm. The student then
inversely to the increase in
switches to high power with a magnification. Therefore, 5
total magnification of 400 X.
mm. X 1/10 = 1/2 or 0.5 mm.
which equals 500
What is the new calculated
micrometers. Therefore the
size of the field of view on
field of view on high power in
high power in micrometers?
this example is
500 micrometers.
Mrs. Degl
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Electron Microscope
Electron Microscopes are scientific
instruments that use a beam of highly
energetic electrons to examine objects on
a very fine scale.
It can magnify original image up to
250,000 times the original size.
Allows for detailed observation of small organelles within the cell, like mitochondria.
Capillary Image from EM
Red Blood Cell Image from an EM
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Dissecting Microscope
Allows viewer to see the image in a three-dimensional view. Light cannot pass
through the specimen (it is opaque), allowing for the three-dimensional view.
These are used for dissecting small animals and plants.
Mrs. Degl
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Microscope Handling Rules
1. Always carry the microscope with two hands - one on the arm and one
underneath the base of the microscope. Hold it up so that it does not hit tables
or chairs. Never swing the microscope.
2. Do not touch the lenses. If they are dirty, ask the teacher for special lens paper
or ask the teacher to clean the lenses for you. Teachers - you may use a soft
cloth dipped in a small amount of isopropyl alcohol to clean the lenses.
3. If using a microscope with a mirror, do not use direct sunlight as the light
source. Eye damage can result. If using a microscope with a light, turn off light
when not in use.
4. Be cautious when handling glass slides and cover slips. Notify teacher if a slide
or cover slip breaks. Students should not handle broken glass.
5. Always clean slides and microscope when finished. Store microscope set on
the lowest objective with the nosepiece turned down to its lowest position
(using the coarse adjustment knob). Turn off light.
6. Cover microscope with dust cover and return microscope to storage, if
requested by teacher.
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Centrifuges are used to
separate cell parts based on
density. Cells are spun around
at high speeds.
Micro-dissection Instruments
Tools used to perform dissections of individual cells or
smaller cell parts.
They are most commonly used with Electron Microscopes
because they have the highest magnification.
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Staining Techniques are used to make it possible for an
observer to see the structures of a cell easier under a
microscope.
1. Iodine – used to stain the nucleus of a cell and preferably used
to stain plant cells.
Lugol’s (iodine) Solution is especially
good for staining plant cells, like onion
cells.
Visible nuclei in
onion cell
2. Methylene Blue- used to stain animal cells.
This stain does not immediately kill the
specimen, so it is ideal to observe animal
cells.
Cheek cell
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Cell staining procedure (with methylene blue):
1. Place specimen on slide with forceps.
2. Lower the cover slip over the slide at a 45
degree angle to reduce the air bubbles.
3. Place a drop of water on the cover slip.
4. Place a drop of methylene blue beside and under
one corner of the cover slip.
5. Place a small towel on the opposite side of the
cover slip in the water beside the cover slip (This
will draw the stain through the entire specimen
within a few seconds and also remove any left
over bubbles).
6. Observe.
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