Unit 1: Biology – The study of Life
(Grade 11 College Prep)
Lesson 2: The Microscope and its Many Uses
We should take a look at the importance of the microscope in the development of biology, as we have already seen
a little in our first lesson. It is important to note that there are different types of microscopes. We will explore their
many different uses and some skills that you will need to be able to do to use it effectively.
You have already had the chance to use a microscope once in class. As we have said it is a very useful tool in biology.
Describe how you would go about using one to view a specimen on high power.
1. The microscopes that we use in class, and most other microscopes, have the ability to view specimens at various
magnifications. In fact, some of the most powerful microscopes can magnify up to 20M times more than the human
eye can see.
A. The total magnification can be calculated by multiplying each lenses individual magnification factor:
Mag(t) = Mag(oc) X Mag(ob)
Complete the table using the information you collect and that which you will acquire in a sec.
Table 1: _________________________________
Magnification
Power of ocular Power of
Setting
lens
objective lens
Low
Medium
High
Total
magnification
Diameter of the
field of view
B. When you look through the microscope you see a bright circle, this is the field of view. It is the magnification of
your specific microscope that will determine how big that circle is. The lower the magnification, the
__________ the field of view. And so, the higher the magnification, the __________ field of view.
But how do you determine the field of view? It is not as hard as it seems. Let’s go through it with
the microscope we already have.
Procedure
1.
Place a clear acetate ruler on a slide and focus it on low power.
2.
Use the ruler to observe and measure the actual diameter of the field of view through the microscope. You now have the diameter of the field
of view at low power
3.
Focus on high power. You may notice that less of the ruler is showing. (It may even be hard to get a direct measurement)
No worries I have another formula for you: FOV(m) = FOV(l) X Mag(m) / Mag (l)
4.
5.
Determine the formula for high power. Find the field of view at high power.
Here is some space for you to do your calculations. Show all your work!
2. Now that we know our field of view it is possible to estimate the size of the specimen we are viewing. All we need
to do is compare it the diameter of the sphere. So simply, if the field of view is 2 cm and the specimen covers half of
the field of view then it is 1 cm in diameter. As a formula this can be written:
ECD = FOV(d) / # specimen fit across FOV
3. So let’s look at a sample before we try it with a real microscope
Estimate the size of the specimen in the field of view below
Figure 1: Hydra at 10ox magnification – Field of view = 1.75 mm
Solution(show all your work)
Solution:
4. Now let’s see if we can do it using our microscope.
Procedure
1.
Obtain a prepared slide of your choice and focus it on the highest power you can see it clearly
2.
Estimate the number of times that the specimen would fit across the FOV. You have already measured the FOV of your microscope
3.
Use the formula to estimate the size of the specimen
Estimate the size of the prepared specimen you viewed (show all your work)
5. Now that we can use the microscope to view and measure objects, it is time to learn one way of documenting
your observations. A Biological Diagram is used in both microscopic and macroscopic observations.
Important Features of Biological Diagrams

The drawing should be in proportion

Use pencil for drawings, not pen.

Use stippling (point-like pencil marks) to show darker areas instead of sketched lines or shading.

Give your drawing a title.

If possible place all the labels on the right hand side of the drawing, with straight lines extending from area you are labelling.

Include magnification of the drawing using the following formula at the bottom. (Mag(d) = S(d) / S(o))

If any stains or special techniques used, list them. (maybe in the title)
We will do a series of drawing and some new skills along the way. Let’s get at ‘er!
A. Choose a prepared slide of your choice to view through the microscope.
Draw a diagram using the criteria above.
2. OK, we still need to learn a couple of more skills: how to prepare a Wet Mount Slide and how to Stain a Slide. We
will use onions and cheek cells (which most of you have viewed) to practice these skills.
In order to view living specimen you may be asked to prepare a using the technique of wet mounting. Water, is
usually used in a wet mount, or the water can be treated with other substance to elicit responses or simply for
better viewing. In some cases, you may need to add a dye or other substance to your wet mounted specimen.
Here is a diagram showing how to stain a wet mounted slide. In your own words explain how you would first prepare a wet mount and the stain the slide.
Now it is time to try it. Notice that we will be drawing your specimen at the end some go through it carefully so you
get good results.
We can start with the onion.
Procedure
1.
Prepare a wet mount of the inner skin of an onion.
2.
View at all powers. Record your results in writing.
3. Add Luigol’s Iodine solution.
4. View at all powers. Carefully observe the changes made by the stain.
Draw a diagram showing several onion cells. Label any important structures you can see. Make sure your follow the criteria for biological diagrams.
Moving on to the cheek cell
Procedure
1.
Using a tooth pick, gently swab your cheek for cells. Smear the collection onto a clean slide and prepare it as a wet mount.
2.
View at all powers. Record your results in writing
3. Add Methyl Blue solution.
5. View at all powers. Carefully observe the changes made by the stain.
Draw a diagram showing several cheek cells. Label any important structures you can see. Make sure your follow the criteria for biological diagrams.
So what can we take away from this?
What differences did you notice each stain was added to the slide? Where any structures visible?
Iodine added to the onion slide
Methyl blue to the cheek slide
These cells looked different from one another. Highlight these differences.
We will practice other microscope later in course.
Let’s do some practice so you can show me on the test!
A. Magnification
Power of ocular lens
Power of objective lens
10x
100x
30x
450x
200x
Total magnification
600x
B. Field of view
a. What is the diameter of these fields of view?
b. Find the diameter of the field of view indirectly.
Givens:
FOV(m) = .1mm
Mag(m) = 50x
Mag(h) = 200x
c. How big is the object in the field of view?
Figure 1: Amoeba at 300x magnification – Field of view = 0.75 mm
d. What is the magnification of the drawing?
Figure d – Butterfly head
Let’s think a little about all this
1. Why was the microscope such an important invention?
2. List the basic microscope skill that you learned in this lesson.
Solution (show all your work)
Givens:
S(a) = 1.5 µm (0.0015 mm)
S(d) = you measure on diagram