Science 10 Assignment 3.2 (48 marks)
Identify the following parts of the microscope below:
Using the compound light microscope: (fill in the blanks)
You must use both hands to hold the microscope. One on the arm and the other
holding the base of the microscope.
Be sure the Power switch is off before you connect the plug.
Place the prepared microscope slide on the Stage.
Rotate the objective lens into position.
Lower the low power lens as close to the lens as possible, without touching the
lens to the stage.
Use the coarse adjustment first to lower the body tube close to the stage.
Then, turn the coarse adjustment towards you as you peer through the eyepiece.
Bring the object into rough focus and then use the fine focus to get a sharp image.
You may rotate the lenses to the next higher power for greater magnification.
Virtual Microscope Lab - Using the
Microscope to Measure Objects
Name
________________
Date _______________
Go to this site to find your virtual lab.
http://www.udel.edu/biology/ketcham/microscope/s
cope.html
Examine the virtual microscope and familiarize
yourself with its parts. There are a few differences
between this compound microscope and regular
monocular microscopes. For example, you will note
that in order to move the slide you must use the
slide holder as opposed to your fingers.
1. Magnification
There are four objective lenses as opposed to three on
regular microscopes. We will not use the 100X objective in this lab. The magnification
of the ocular lenses (eyepiece) is ____10X_______. Normally this is marked on the
single ocular microscopes.
What is the total magnification of the:
Scanning or Low Power objective 4 X
Medium Power Objective 10 x
High Power Objective 40 X
100 X objective 100 X
What is the total magnification for each lens (multiply ocular times objective)
Scanning or Low Power _40X__ Medium Power 100X__
High Power _400X__ 100X Power ___1000X_
Before continuing with this lab, please review the tour provided on the
website. You will need to operate the microscope virtually in order to
complete the rest of this lab.
2. Diaphragm
The diaphragm at the bottom of the microscope is dynamically adjustable which means
that you can open and close the diaphragm in order to adjust the amount of light being
used to illuminate the object.
Examine the diaphragm.
Which setting makes the specimen the lightest? _____Narrow__
The darkest? _Closed_________
How does this compare to other microscopes you have used?
3. Lenses and Field of View
Having two ocular lenses make this a compound microscope. What do you have to do
in order to see a clear image? ______Focus the image.__
The field of view is the region that can be seen under the microscope (the big white
dot). In it you should see a bunch of lines that can be used to measure your specimen.
Note that although the image changes when you change magnification, the scale looks
the same. Because of this, the size of the measurement the scale represents also
changes with the magnification.
4. Measuring with a Microscope
In the virtual microscope, there is a scale of
measurement in the field of view. When you
change objectives, the scale looks the same. This
is deceiving because the length of the fields of
view change when you change the magnification
power.
Each of the marks on the scale under low power
represent 0.2 mm or 200 um (1mm = 1000um)
Estimate the length (diameter) of your viewing field
in micrometers under low power magnification
__4000 um_____ .
How long is the line?______4 mm_______________
In order to determine the length of the field of view under other powers of magnification,
you must use a mathematical calculation:
High power field diameter = low power field diameter x low power magnification / high
power magnification
= 4000 um x 40/1000 = 160 um
What is the diameter (in micrometers) of your high power
field?__160um um___________ The length of the line? ______80 um________
Under low power: F.o.v = line is
4000um long
Magnification = 40X
Under high power: F.o.v = line is 80 um
long
Magnification = 1000 X
4. Viewing a Slide
Select the prepared ‘e’ slide. Focus the slide first with the low power setting. Make sure
you meet all of the requirements of the checklist in the simulation. Then switch your
view to medium power. Finally, focus the slide under high power. Remember, at high
power, you should ONLY use the fine adjustment knob.
Draw the ‘e’ exactly as it appears in your viewing field for each magnification. The
circles below represent your viewing field. The ‘e’ should take up as much space in the
drawing as it does in your viewing field while you're looking at it. Estimate the
dimensions of the letter in micrometers by using the scale in your f.o.v. to measure it.
Low or Scanning Power
Medium Power
High Power
5. Making a Wet Mount of a Slide (for your understanding only)
1. Gather a few strands of cotton from a cotton ball using forceps. If your specimen is
too thick, then the coverslip will wobble on top of the sample like a see-saw, and you will
not be able to view it under High Power.
2. Place ONE drop of water directly over the specimen. If you put too much water, then
the coverslip will float on top of the water, making it hard to draw the specimen, because
they might actually float away. (Plus too much water is messy)
3. Place the coverslip at a 45 degree angle (approximately) with one edge touching the
water drop and then gently let go. Performed correctly the coverslip will perfectly fall
over the specimen.
What is the purpose of a coverslip? __To stabilize/immobilize the specimen
7. Staining a Specimen (for your information)
1. Place one drop of stain (methylene blue) on the edge of the coverslip. Caution:
Methylene Blue will stain clothes and skin!
2. Place the flat edge of a piece of paper towel on the opposite side of the coverlip. The
paper towel will draw the water out from under the coverslip, and the cohesion of water
will draw the stain under the slide.
3. As soon as the stain has covered the area containing the specimen, you are finished.
The stain does not need to be under the entire coverslip. If the stain does not cover as
needed, get a new piece of paper towel and add more stain until it does.
4. Be sure to wipe off the excess stain with a paper towel.
In the virtual simulation, take the cheek slide out and do the following.
Draw your specimen as it appears under low power. Used color pencils to show how the
stain appears. It may appear darker or lighter in spots. Use shading to show darker and
lighter spots.
Scanning
Low Power
High Power
Questions.
1.
What is the difference between a simple and a compound microscope ? ( 1 mark)
A simple microscope only has one lens and a compound microscope has 2 lenses.
2. Using the medium-power (10X) objective lens, a student measured the diameter of the field of
view as 1.5 mm. Convert this diameter to micrometers. (3 marks)
1.5 mm x 1000 mm/um = 1500 um
3.
Use the value you found in the previous question to calculate the field diameter when the
student used the high power (40X) objective lens. (3 marks)
FOV = medium powered FOV X medium power objective = (1500 um) x (10x) = 375 um
High power objective
(40X)
4.
What are the advantages and disadvantages of using a light microscope ? (4 marks)
Compound light microscopes pros
-it has been extremely important in the development o the biological sciences and lots of medicine
-easy to use
-inexpensive compared to other microscopes
-can look at live samples
cons
-viruses, molecules and atoms cannot be viewed
can’t magnify more than 2000 times.
2 DIMENSIONAL
5. Explain why investigators need to stain cells. (1 mark)
Staining allows investigators to see desired structures with greater clarity.
Stains and dyes are frequently used in biology and medicine to highlight structures in biological
tissues for viewing, often with the aid of different microscopes. Biological staining is also used to mark
cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis.
So they would use it for DNA testing
6. When would there be a need for using an electron microscope ? (1 mark)
When wanting to view viruses, or looking at something that is very small, and you would need
a 2000x or more close up.
7. Describe similarities in the ways in which a light microscope and a TEM work. (2 marks)
1. In both microscopes, the specimen is located at the end of the microscope structure
2. In both microscopes, what is reflected off the specimen is focused to create an image.