Download Preparing a Wet Mount 2 - Experimental Skill and Investigation

Preparing a Wet Mount
Introduction
In science, and especially in the field of biology, microscopes are very
important tools. Without them, an entire world of microscopic organisms
and cells would be a mystery to us. Microscopes use slides that contain
material for viewing. In our class we will be viewing slides under our
microscopes. However, we will go one step further and will be making the
slides ourselves. To do this we must prepare a wet mount. Now what does
this mean? A mount is the arrangement of a specimen for examination
(usually on a microscope slide). A wet mount is prepared by adding water to
the specimen which increases its translucency and makes it easier to stain. It
also has a tendency to cause the specimen to flatten which makes the
specimen easier to view.
Safety Considerations
The only safety consideration in regards to the actual preparing of the wet
mount is being careful with the handling of the glass microscope slide. If
broken, or even chipped, the slide can cause a deep cut. So before you grab
the slide, inspect it for any sharp edges and show caution with handling it.
Obtaining a specimen can present another safety consideration. In certain
cases, a razor blade may be used to slice off a sample. In this situation, it is
extremely important that you show caution. In some cases, the teacher will
have already prepared specimens, and it is up to you to simply prepare the
wet mount.
Curriculum Objectives
This activity fits in to the Biology 30S curriculum under Cluster 0: Skills
and Attitudes. Specifically it addresses the following specific learning
outcome:
S3B-0-S4
Select and use scientific equipment appropriately and safely.
Examples: microscopes, dissection equipment, prepared slides
Materials
Slide (x 2)
Cover Slip (x 2)
Water
Water Dropper
Tweezers
Specimens (paper with a printed letter, onion skin)
Skill Procedures
The skill that you will be learning today is how to prepare a wet mount. As
you follow through the steps, the teacher will also be going through the
procedures with you to make sure there is no confusion.
First of all, you must obtain a clean, dry slide. Then, using the water
dropper, place a single drop of water in the center of the slide.
Why is it important to make sure our slide is clean and dry before using it?
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Now we must obtain our specimen. For this practice run, we will be using a
small piece of paper with a letter printed on it. Cut out a single letter from
the scrap documents the teacher has provided. Once you have your letter,
using the tweezers, place the letter into the drop of water.
Why is it important to have the slide (with a drop of water) ready before
obtaining the specimen? (Imagine we were using an organic specimen
instead of a piece of paper)
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At this time, we would add a drop of dye (eg. iodine, methylene blue) to
help increase visibility if needed. Now it is time to add our cover slip.
Carefully place the cover slip upright next to the edge of the water. Slowly,
lower the top part of the cover slip down so that the cover slip is covering
the water drop containing the specimen. See Figure 1 below to see how the
cover slip should be lowered.
FIGURE #1
Jarrett Seidler
Why do you think this method of placing the cover slip in the slide is
important to do as opposed to just dropping the cover slip straight down on
top of the water drop? (The teacher will do an example using the proper
technique, and an example using the improper technique. Use these
examples to find your answer to this question).
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Congratulations! You have just prepared your first wet mount. Now our
slide is ready to be viewed. You should all remember the proper procedures
for using a microscope as we covered this last class. Turn on the microscope
and place the slide on the stage. Using the low power objective lens (4X),
focus on the letter. Draw what you see in the eyepiece in the space provided
below. Repeat this for the 10X objective and the 100X objective.
4X Objective
10X Objective
100X Objective
Jarrett Seidler
Skill Application
Now that you have gained the skill of how to prepare a wet mount, we are
ready to apply this skill to a biological investigation. We will be
investigating the differences between plant and animal cells.
To carry out this investigation, we will prepare wet mounts of a plant cell
and an animal cell separately. Once this is done, we will examine each slide
through a microscope and analyze each type of cell to locate similarities and
differences.
What are some methods that you can think of that we could implement to
obtain a plant cell for our wet mount? (Try to come up with at least three)
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What are some methods that you can think of that we could implement to
obtain an animal cell for our wet mount? (Try to come up with at least three)
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For the plant cell wet mount, we will be using an onion. Using tweezers,
peel a small piece of the delicate, transparent, inner surface of the onion. The
piece only needs to be half a centimeter across. Once you have obtained a
piece of the onion skin, prepare a wet mount of the specimen using the
procedures we have already gone over for preparing a wet mount (make sure
to add a drop of iodine before placing the cover slip on the slide). Using a
microscope, observe the specimen under low power (4X). Draw what you
see in the space provided on the next page. Repeat this procedure with
medium power (10X), and then high power (100X). Make sure to focus the
eyepiece before moving to each power level.
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4X Objective
10X Objective
100X Objective
Describe the appearance of the cells you see.
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What cell structures and organelles can you see?
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For the animal cell mount, we will be obtaining animal cells from the inside
of our cheeks! Using the blunt end of a clean toothpick, gently scrape the
inside of your cheek (you do not need to press very hard). You should get
some cells on the end of the toothpick. Prepare a wet mount (using the
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guidelines already covered) of the cells from your cheek (make sure to add a
drop of methylene blue before placing the cover slip on the slide). Using a
microscope, observe the specimen under low power (4X). Draw what you
see in the space provided below. Repeat this procedure with medium power
(10X), and then high power (100X).
4X Objective
10X Objective
100X Objective
Describe the appearance of the cells you see.
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What cell structures and organelles can you see?
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Jarrett Seidler
Follow up Questions
1) The onion skin we viewed lacked chloroplasts which are found in many
plant cells. Why is this?
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2) Many of the cells you observed in the animal cell wet mount may have
appeared folded or wrinkled. Why is this?
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3) What are some similarities between plant and animal cells?
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4) What are some differences? Construct a chart in the space below that
contrasts the differences you’ve observed.
Jarrett Seidler
References
GreatScopes Activity: Wet Mounting a Specimen. (n.d.) Retrieved
December 15, 2006 from http://www.greatscopes.com/act005.htm
Lab Activities. (n.d.) Retrieved December 15, 2006 from
http://www.edu.pe.ca/gray/class_pages/rcfleming/cells/lab.htm
Jarrett Seidler