Magnifying power of objective lens

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        Biology 1001                                                 Laboratory 4



        - Read this exercise before you come to the laboratory.
        - Search the internet for images of Elodea cells, cyclosis in Elodea cells and human cheek


At the end of this lab you should be able to:

        1. Give the name and function of parts of the compound microscope.

        2. Align the light source of a compound microscope to give optimum illumination of a
           specimen at all magnifications.

        3. Find a specific part of a specimen under low power and change to high power without
           disrupting the field of view.

        4. Determine the three-dimensional shape of objects viewed with a microscope.

        5. Accurately determine the size of a microscopic specimen.

        6. Prepare a temporary whole mount.

        7. Prepare a stained whole mount.

        8. Make a proper biological drawing of a microscopic specimen.


        1. Set up a compound microscope for use.

        2. Answer the questions on the lab assignment sheet.

        3. Fully label a drawing of a cell from an Elodea leaf.

        4. Make a fully labeled drawing of epithelial cheek cells.
               (you must pass in this drawing for marking)

        5. Upon completion of the lab, have a demonstrator check that you have properly cleaned
                  your microscope and set it up for storage.
                                   THE LIGHT MICROSCOPE


        The light microscope is an indispensable tool of a working biologist. Its proper care and use is
essential for success in Biology 1001. Even if you have used a microscope before, do not
omit this lesson. This will be a good opportunity to review, and at the same time, to become familiar
with the workings and quirks of the microscopes in this lab. Most people, even those who use a
microscope daily, tend to become negligent and forgetful of the best procedures. IF AT ANY TIME

       This lab is divided into two parts. First, you will learn about the parts of the compound
microscope and their functions, and you will learn how to properly set up and care for these delicate
and expensive instruments. In the second part of this lab, you will use your new microscope skills to
examine living cells. You will be guided through this lab by doing the TASKS and LAB
ASSIGNMENTS in order. There are 8 TASKS and 11 ASSIGNMENTS to be completed.




                 There is a microscope that corresponds to your seat number, either on the bench top or
stored in the under-bench cupboard. USE BOTH HANDS TO HOLD AND CARRY IT - one hand
under the base, the other holding the arm.

        Put the microscope on your bench directly in front of you, so that when you are seated, you
can look into it without twisting or straining. Read the following descriptions of the parts of the
microscope and find these parts on your own scope. Refer to Figure 4.1.

       Compound microscopes were designed to observe fine details of specimens. Most compound
microscopes use transmitted light. The light usually originates in a source in the base of the

        The light must be concentrated and organized into coherent, parallel beams before it can be
used. A condenser below the specimen stage of the microscope does this job. These beams must be
focused on the specimen. Thus the condenser is attached to the microscope by a rack and pinion
device, so it can be moved up and down for proper focus.

        As the light reaches the specimen, some of it is absorbed by dense or coloured areas; some of
it may pass undisturbed through clear areas of the specimen and some of it may be refracted (bent) by
dense areas of the specimen. Thus we can perceive differences in a specimen.
        Eventually the light after passing through the specimen enters the objective lens and the
image is magnified. The image is magnified again by the ocular lens at the top of the body tube.
(See Figure 4.1).

Make sure you can find and name the following parts of the microscope and can give their functions:

Ocular (lens) - Often called the eyepiece. It is the topmost series of lenses through which an object is
viewed. Its magnification is ten times (10x). This lens is unattached and will slip out of the body tube
unless the microscope is kept upright.

Body tube - Joins the nosepiece to the ocular lens.

Arm - Supports the body tube and provides a carrying handle.

Figure 4.1 The Olympus compound microscope.

Nose piece - The revolving part to which the objective lenses are attached. It must be firmly
clicked into position when the objective lenses are changed.

Objective lenses - There are four objective lenses on the nose piece of your microscope. The
magnifying power of each is marked on side of the lens. Notice that when an object is in focus under
the low-power objective it is also in focus under the high-power objective as well and    vice-versa.
In other words, these objectives are said to be parfocal.

        Scanning Objective - This objective has a wide field of view at relatively low magnification,
        and is used to get a general view of a specimen on a slide, or to examine at low magnification
        an object too large to be seen in its entirety with the other objectives. The magnification given
        by the scanning objective is 4x.

        Low-Power Objective - The low power objective is the normal working objective of the
        microscopes. Its magnifying power is usually 10x.

        High Power Objective - The high-power objective is to be used when the magnification of
        the low-power objective is not adequate. When preparing to use the high-power objective,
        always bring the specimen into focus with the low-power objective first, then turn the nose
        piece to bring the high-power objective into line with the body tube of the microscope. The
        magnifying power of the high-power objective is usually 40x.
        ADJUSTMENT KNOB which might cause you to CRUSH THE MICROSCOPE SLIDE.

        Oil Immersion Lens - The magnifying power of this lens is usually 100x. NEVER, UNDER

Slide holder - Holds the slide firmly in place. Control knobs on this mechanical stage allow you to
move the slide back and forth, and from side to side.

Stage - Supports the slide that is held onto it by the slide holder. Has a hole so the light can shine up
through the specimen.

Condenser - A lens located under the stage which focuses and concentrates the light before it passes
through the specimen. Its position is controlled by a knob.

Iris Diaphragm - Controls how much light and lamp heat go through a specimen. It is controlled by a
lever on the side of the condenser.

Coarse Focus Adjustment - Moves the stage up and down to bring the object into approximate
focus; used only with scanning and low-power objectives.

Fine Focus Adjustment - Moves the stage up and down very slightly to bring the object into precise
focus. The only adjustment used with high-power and oil immersion objective.

Light source - An attached lamp that directs a beam of light up through the object.

Base - Gives the microscope a firm, steady support.


-       ALWAYS carry a microscope in BOTH HANDS. One hand holds the arm securely while
        the other hand is under the base to support it. Do not tilt the microscope - carry it in an
        UPRIGHT position.

-       Check over your microscope each time you use it. You share this scope with other students.
        If something is wrong, please report it. Call an instructor. DO NOT ATTEMPT TO FIX IT

-       If you must wear mascara, please clean the oculars when you are finished.

-       Don't touch the lenses with your fingers. Oily fingerprints attract dust and are hard to
        clean off.

-       The lenses should ONLY be cleaned with FRESH CLEANING TISSUE and LENS
        CLEANING SOLUTION or water. These are found in each student bench. Use gentle
        pressure when cleaning a lens; the glass is soft and easily scratched. For this reason, also, you
        should never use a dry tissue on the lens, there should always be a liquid with the tissue.

        WHEN YOU ARE FINISHED with the microscope, BE SURE that:
        1. The shortest objective lens is in line with the body tube.
        2. No slide is left on the stage.
        3. The microscope is clean - no water or dust on the stage or lenses. Make a routine habit of
                cleaning both the lenses and the stage of your scope after each use.
        4. The cord is coiled around the base to avoid entanglement in the cabinet. Make sure the cord
                is not pinched under the condenser gears.
        5. Replace the dust cover and return the microscope to where you found it.

Your microscope will be checked after each lab session to ensure that it has been put away properly.


                                     * * * * * TASK 1 * * * * *


         This microscope (Figure 4.2) enables you to observe fine details of very small or thinly
sectioned subjects in transmitted light. The specimen must be properly illuminated in order to see .
Here is the procedure for setting up the illumination of the microscope. It must be followed each time
you begin to use the microscope.

1.      Plug the microscope into the electrical outlet on your lab bench.

2.      Turn on the microscope light using the on/off switch on the base.
3.      Put the scanning objective lens (4x) into working position.

4.      Using the light intensity lever, increase the light intensity until a reasonable amount
        of light is visible when you are looking in the oculars.

5.      Place slide 81 (cross section of corn stem) on the stage and use the arms of the slide holder to
        grip the slide. Use the slide holder controls to centre the specimen over the hole in the stage.
        (This must be done before any further adjustments are made to insure the correct position of
        the light at the level of the specimen.

6.      Look through the right ocular and use the coarse focus knob to carefully move the stage up
        until the specimen can be seen.

7.      While looking through the eyepieces with both eyes, hold the right and left eyepiece tubes
        with both hands and push the tubes together, or pull them apart laterally, whichever is
        required, until the two circles of light merge into one and you obtain binocular vision. You
        should be able to see down both tubes at the same time.

8.      Look at the image through the right eyepiece with your right eye, and focus on the specimen
        with the focus adjustment knobs.

9.      Next, look at the specimen through the left eyepiece (with your left eye) and rotate the ring
        on the left eyepiece to focus the specimen without touching the coarse and fine focus knobs.

10.     Using the condenser focus knob, put the substage condenser all the way up.

12.     Remove one of the ocular lenses and look down the body tube to the circle of light. Use the
        iris diaphragm lever to adjust the circle of light until it fills about 3/4 of the field of view.
        Put the ocular lens back in.

13.      The microscope is now ready for use. Each time you use the microscope, you should
        repeat this procedure.



        Have a demonstrator check your microscope to insure that you have set it up properly. If you
have, the demonstrator will sign on the assignment page. If you haven't succeeded, try this exercise
again. You will need to properly set up your microscope each time that you start to use it. With
practice this will become second nature to you. Trying to use an improperly set up microscope is an
exercise in frustration - not only will you be unable to see what you should - you may also develop
headaches and eyestrain.


      1.      Examine only specimens on prepared slides, or on slides after mounting in liquid and
              covered by a cover slip. Before using a prepared slide, clean it with lens
              tissue and lens cleaner, if necessary.

      2.      Try to keep both eyes open; it lessens eye strain.

      3.      Always study the specimen first under the 10x objective lens. Centre the part you are
              interested in before switching to the 40x objective.

      4.      Use only the fine focus with the 40x objective.

      5.      Adjust the fine focus almost continuously when viewing a specimen in order to get a
              three-dimensional appreciation of the specimen. Even microscopic tissues have depth!

      6.      Don’t forget that you can change the intensity of illumination of the specimen by
              adjusting the light intensity knob or the iris diaphragm lever. Hidden structures can be
              observed by examining a specimen under different light intensities!

      7.      If the image is weak or blurred, check the adjustment of the condenser, then
              look for dirt on eyepiece or objective. If this does not correct the trouble, call an


                                   * * * * * TASK 2 * * * * *


Focusing - Low Power

      1.      Obtain slide #102B of the letter e from your slide box. Look at it with the slide
      label on the left and the cover slip uppermost.

      2.      Put the letter e slide on your microscope stage centering it over the hole in the stage.
              Make sure the scanning objective is in line with the body tube. Using the coarse focus
              knob put the stage all the way up. Now look in the microscope and, using the coarse
              focus knob, slowly increase the distance between the objective lens and the stage until
              the object, the letter e, comes into focus.

      3.      Move the slide away from you. In which direction did the e in the microscope move?

      4.      Now move the slide to your right. In which direction did the e in the microscope

          What you have just observed is called inversion. The image in the microscope is inverted,
that is, it is upside down to the actual specimen. Also, the image in the microscope is reversed
meaning that the actual right side of a specimen is viewed as the left side in the microscope. Keep in
mind the fact that microscope images are inverted and reversed as you study various microscopic
specimens during the year.

Focusing - High Power

        The lenses in compound microscopes are parfocal, that is, if an object is in focus under low
power, it should also be in focus under high power.

        To switch to higher power objective use the following procedure.

        1.     Make sure the object, in this case the letter e, is in the centre of the field and is in

        2.      Rotate the nose piece so that the 10x objective, the low power objective, clicks into
                place in line with the body tube. If the objective has not clicked into place, you will
                be able to see down the body tube.

        3.      Locate the object in the field of view. Put the part you are interested in, in the centre
                of the field of view.

        4.      To switch to high power, the 40x objective, these steps are repeated. It is very
                important to remember that once you put the 40x objective in line with the body
                tube, USE ONLY THE FINE ADJUSTMENT KNOB. The distance between the
slide           and the objective lens is so small that you must be very careful or you will crack the
                slide and possibly damage the lens.

        5.      Removing a slide - When you are finished with your observations of this slide (or any
                slide), rotate nose piece back until the 4x objective clicks into place and only then
                remove the slide from the stage. If you try to remove a slide while the microscope is
                still on high power, you may scratch or damage to objective lens.

        You should observe these steps each time you put a slide on the microscope, switch to high
power, then switch back to low power and then remove the slide.



Based on what you have done in Part D answer questions 2, 3 and 4 on the assignment pages.


         The magnification of the image that you see through the microscope is given by the formula:

i.e. Using the low power objective, the total magnification is 100x = 10x (eyepiece) x 10x (low power

What is the total magnification of your microscope when the 40x objective is in use?

Please note that this magnification will not be the magnification of a drawing that you make of an
observed specimen. This will have to be calculated in another way, as explained in a later section of
this lab.


     * * * * * TASK 3 * * * * *


       1.       Obtain slide #85b, a stage micrometer slide containing part of a millimeter ruler
from your slide box and put it on the stage so that the ruler is visible as a line along the diameter of the
scanning power field. Estimate the number of millimeters that you can see in the diameter of the field
when you are using the 4x lens.

         2.      Carefully change objectives to the 10x objective and again calculate the diameter of
the field for low power. Is it the same as scanning power?

         3.      Carefully try to do the same thing for the 40x objective lens. Record these diameters

                         Diameter of field for scanning power (4x) = _____________ mm

                         Diameter of field for low power (10x) = ______________ mm

                         Diameter of field for high power (40x) = _____________ mm



      Based on what you have done in Part F answer questions 5 and 6 on the assignment pages.
                                                         4 - 10

                                      * * * * * TASK 4 * * * * *

         Lenses have a plane of focus. This is the thickness of the plane in which an object appears to
be in focus. This is true for the lens of your eye as well as for the lens in the microscope. To illustrate
this principle, extend your fist at arms length in front of you and hold your thumb up. Look at your
thumb continuously while noticing that the objects past your thumb on the other side of the room are
not clearly seen. Do not look at these objects past your thumb, but just concentrate on your thumb.
You have focused the lens of your eye on your thumb and in order to see objects farther away it would
be necessary to look away from your thumb - to refocus. We are so used to refocusing the lens of our
eyes that we don't even think about it. Similarly with a microscope, when it is focused on one surface,
the surfaces lower or higher will be out of focus and not seen so clearly. You will notice that the plane
within which objects can be seen clearly will become narrower as the magnification of the microscope
is increased. The distance within which objects can be seen clearly is called the depth of field or
depth of focus.

        1.        From your slide box obtain slide #102A with three coloured threads mounted
together. With the 4x objective, find a point where the threads cross. Slowly focus up and down.
Notice that all three threads seem to be in focus.
        2.        Change to the 10x objective and use the fine focus to slowly focus up and down. Now
when one thread is in focus, the others seem blurred. This is because the 10x objective lens         has
a smaller depth of field then the 4x lens.
        3.        If you are very, very careful, you could switch to the 40x objective. Remember to
only use fine focus adjustment. The vertical distance that remains in focus at one time is called the
depth of focus. Which appears to have a greater depth of focus, the 4x, 10x, or 40x objective lens?
        4.        Determine the order of the threads and decide which thread is on top and which is on
the bottom.

If you make constant use of the fine adjustment knob when viewing a slide with the 40x lens, you will
get an idea of the specimen's three-dimensional form



        Answer question 7 on the assignment pages.


                                      * * * * * TASK 5 * * * * *
                                                         4 - 11

          Since you know the diameter of each of the fields of view, you can make an educated guess
about the size of an object you view in the microscope. (Is it half the size of the 10X field or does it
fill the whole 40X field, etc.). However, it is much better to be able to measure the size of an object

         To measure microscopic objects, microscopists use a device called an ocular micrometer.
You may already have noticed that when you look in your microscope, you can see what looks like a
tiny ruler. This is the ocular micrometer that is in the ocular lens. When you rotate your eyepiece, this
scale will also rotate. Notice that it is divided into 100 units and some of these are marked - 0, 10, 20,
30, etc. The whole scale is 100 ocular units.

        To be useful, the ocular scale has to be calibrated - that is, the exact size of one ocular unit
must be measured at each different magnification. You will notice that as you change magnifications,
the diameter of the field of view changes, but the ocular scale, because it is in the eyepiece, does not.
This means that the length of one ocular unit is different for each of the magnifications. Here are the
approximate values for your microscopes. (You will learn to calibrate your microscope in Biology
1501, next term) Please note that 1 micron = 1/1000mm.


                 Objective        Calibration
                 4X               1 ocular unit (o.u.)     = 0.025 mm       = 25 m

                 10X              1 o.u.                   = 0.010 mm       = 10 m

                 40X              1 o.u.                   = 0.0025 mm      = 2.5 m

                 100x             1 o.u.                   = 0.001 mm       =1 m

1 micron = 1/1000mm (the micron is very useful for measuring very small things like cells)

       Each time you want to know the size of a microscopic specimen, you can calculate it by
measuring how many ocular units it is and knowing what objective you are using.

        For example, if your specimen measured 22 ocular units with the 10X objective you can
calculate its size to be 22 o.u. x 0.01 mm = 0.22 mm or 220 m.

        Mark this page of measurements in your lab manual. You will need to quickly refer to it
each time you draw microscopic specimens.
                                                        4 - 12
          Depth can be measured if the fine focus knob on your microscope has a micrometer etched on
it. If so, by focusing from one level to another, depth can be determined directly from the focus


       Measure the width (diameter) of one of the threads on the crossed thread slide using the
scanning objective and the low power objective lenses. Answer question 8 on the assignment pages.



       Slides may be either temporary (usually made with water), or permanent (made with a
mounting medium that lasts for many years).

Preparation of Temporary Wet Mounts

         In the Biology l001 laboratory, washed glass microscope slides are provided for you. They
may be found in the glass jar on the front or side benches. Make sure the slide is perfectly clean. If
the slide is badly scratched, throw it out in the SHARPS container and take another. Wipe carefully
with paper towel. Make sure the slide is perfectly dry.

        When you are finished with this slide, you must clean it and return it to the jar.

        You will also need a cover slip. Boxes of new cover slips may be found in each lab bench
cupboard. Cover slips are only used once, then discarded in the SHARPS container for safety (never in
the general garbage containers).


First, one edge of the coverslip contacts the drop of water, then the coverslip is gently lowered to expel
the air.

Figure 4.2 Preparation of a temporary wet mount slide.
                                                           4 - 13

                                        * * * * * TASK 6 * * * * *

J. UNSTAINED WHOLE MOUNT – Elodea (pond weed)

        1.      Put a drop of water in the centre of a clean slide.

        2.      Transfer one whole Elodea leaf to the drop of water, making sure that it is wetted in
                the drop.

        3.      Apply a second drop of water over the specimen.

        4.       Holding the cover slip by its edges, lower it so that one edge contacts the drop of
        water first, then lower the rest of the cover slip carefully so that all he air is expelled. It is
        often convenient to support the upper edge of the cover slip on the point of your
        tweezers or a pin as it is lowered into place. See Figure 4.2.

        The amount of water you use is critical. Too little water will not support and float the cover
slip. Too much water means that your specimen will not stay in your field of view and you will get the
microscope stage wet.

        Do not squash down on the cover slip, it needs to float on the drop of water.
If you got large air bubbles under the cover slip that obscure the specimen, make a new preparation.

        5.       Place your slide of the Elodea leaf on the microscope stage. Centre the specimen over
        the light source. Bring it into focus with the scanning objective (4x objective).

        6.       Examine the specimen carefully by moving the slide around to see what is there. This
        is called scanning the slide. Can you see the individual cells? Using what you know about the
        diameter of your field of view, estimate the length and width of your leaf.

        7.       Now choose one area of the specimen (the leaf) and increase the magnification by
        changing to the 10x objective. Look carefully over all of the leaf, both at the edges and in the
        centre. You should be able to see the cells more clearly. If it seems too dark, you can increase
        the light to the specimen by opening the iris diaphragm a bit more.

         Can you figure out how many layers of cells there are? (Hint, use the fine focus knob to focus
up and down through the leaf, a new cell layer comes into view when the cell boundaries seem to
suddenly shift). You might want to increase the magnification even more by going up to the 40X
objective lens. Do this carefully; as long as the cells are in focus with the 10X objective lens, then you
will be able to swing the high power objective into place without trouble. Remember, the distance
between the slide and the 40x objective lens is very small - use the fine focus only!
                                                         4 - 14
         Are all the cells of the leaf the same shape or are there differences? Locate the cell walls.
Inside the cells will be cytoplasm, a granular material containing cell organelles such as chloroplasts.
Cytoplasm in mature plant cells is often displaced to the perimeter of the cell by the large central
vacuole. The vacuole itself is hard to see in these live cells, it looks like a large empty space. Each of
the cells will also have a nucleus, seen as a clear rounded area in the cell, although many of these may
be hard to see. Just inside the cell will also be a cell membrane (also called the plasma membrane),
although this is difficult to see. Try looking closely at the corner of the cell.

[Demonstrations - Cell membranes may be difficult to see, especially in live whole mount
preparations. To help, we have prepared a slide of onion skin cells that are in a saline solution. A
saline solution draws water out of the cell, causing the cell membranes to pull away from the cell
walls. This should make the membranes more visible. Also, a slide showing stained Elodea nuclei
may also be seen on the demonstration bench]

         Do all the cells of the Elodea leaf contain green chloroplasts? Which ones do and which ones
don't? Can you see any movement of the chloroplasts within any of the cells? Be patient; you should
be able to. Such movement of chloroplasts around the interior of the cell gives evidence that the
cytoplasm within a cell circulates. This cytoplasmic movement is termed cyclosis.

------------------------------------ -----------------


        Answer questions 9 and 10 on the assignment pages



         Now that you know how to measure cells in the microscope, fill in the “Cell Measures”
portion of the assignment pages by measuring the length and width of one cell from the middle rib of
the leaf. Measure the length and width of one cell from the blade (i.e. neither the edge cells nor the
midrib cells). Which type of cell is longer? Which type of cell is wider?


                                                         4 - 15

Label the drawing of an Elodea cell, Figure 4.3. Since this is a drawing of a plant cell, double lines are
used to demonstrate the cell wall. Also, it is not a solitary cell existing by itself, it is attached to
neighbouring cells. These attachments are indicated in the drawing. Label cell wall, cytoplasm,
nucleus, cell membrane, chloroplasts, vacuole. Review the instructions for biological drawings, items
8 through 13 on pages A-8 and 9.


                          * * * * * TASK 7 * * * * *

K. STAINED WHOLE MOUNT - Human Epithelial Cells


         The cells from the Elodea leaf are easy to see in a microscope for two reasons. First, they
contain many small green chloroplasts which are very visible. Secondly, being plant cells they have a
thick, rigid cell wall made of cellulose.

        It is not so easy to look at animal cells since they do not have cell walls nor do they contain
coloured, visible organelles like chloroplasts. In fact, because many animal cells are so transparent
and colourless, it is the usual practice to stain them in order to increase the contrast between the
specimen and the background.
                                                          4 - 16
          One commonly used stain is methylene blue. When it is prepared with water, methylene blue
is a vital stain, that is, it will stain cells without killing them. You will find a bottle of methylene blue
in the stain tray at each lab bench.

        There are two ways in which you can add stain to a temporary whole mount. One, you can
add a drop of the stain to the water used in making slide before putting on the cover slip. Or you can
add the stain afterward to one edge of the cover slip and draw it through underneath the cover slip as is
shown in Figure 4.4.

         Epithelial cells are the covering or lining cells in animals. The cells making up the lining of
the inside of your mouth are epithelial cells which are easily rubbed off. Using your own epithelial
cells, make a slide in the following manner.

        1.       On a clean microscope slide place drop of water and a small drop of methylene

        2.        Using the blunt end of a toothpick, gently scrape off some of the epithelial tissue
                 that covers the inside of your cheek and stir the scraping in the drop of stain. Place
                 the used toothpick directly in a garbage can. Do NOT place it on the lab bench.

        3.        Place a cover slip over the preparation and examine under low and then high power.

        4.       On your slide you should find both single cells and groups of cells that are clustered
                 together. Locate the nucleus, plasmalemma (plasma membrane) and

A. Before applying the coverslip

      Add a drop of methylene blue to the specimen and then position coverslip as described for a

B. After applying the coverslip

Figure 4.4. Two methods of staining wet mounts.
                                                       4 - 17



Measure the diameter of a typical epithelial cell. How does it compare in size and shape to the plant
cells? What structures are lacking or are different than those you observed in the plant cells? What
structures are present in both the animal and the plants cells? Answer question 11 on the lab
assignment pages.



Using high power, make a detailed drawing of a clump of two or three epithelial cells from your
cheek. Label plasma membrane, cytoplasm, nucleus. Don’t forget a proper title, scale, etc.
Refer to page A-8 and 9 in the appendix of this lab manual for instructions for making proper


Permanent Slides

         Permanent slides are ones in which the specimen has been fixed or preserved and dehydrated
before being mounted on a slide using a drop of transparent permanent mounting medium.
Many tiny organisms can be mounted whole, that is without being cut into sections. In such a
case, the slide is termed a whole mount (w.m.) because the whole uncut specimen is on the slide.

          Often, entire organisms and pieces of tissue are too thick or opaque to be observed as whole
mounts. They must be "sectioned" or cut into thin slices. After fixation and dehydration the specimen
is infiltrated with a sectionable medium (paraffin or epoxy resins). The specimen and the hardened
medium are then cut into a block from which thin slices (l0 microns thick) are shaved. These sections
are then mounted on a glass microscope slide in a drop of transparent medium as before.

         Both whole mounts and sectioned specimens may be found as permanent slides in your slide
box. The label on the slide should tell you whether the material to be studied is a whole mount (w.m.)
or a cross section (c.s.; t.s.; x.s.) or longitudinal section (l.s.).


                                    * * * * * TASK 8 * * * * *
                                                        4 - 18


WHEN YOU ARE FINISHED with the microscope, prepare it to be put away. In putting a
microscope away, BE SURE that:

1.      The shortest objective lens is in line with the body tube.

2.      No slide is left on the stage.

3.       The microscope is clean - no water or dust on the stage or lenses. Make a routine habit of
cleaning both the lenses and the stage of your scope with lens tissue after each use. Boxes of lens
tissue and lens cleaner are stored in the cupboard of each lab bench. Remember to always use a liquid
with the tissue when you clean a lens.

4.      The stage is in a lowered position.

5.      The cord is coiled around the base to avoid entanglement in the cabinet. Make sure the cord is
not pinched under the condenser gears or under the bottom of the stage.



       When you are finished with your microscope, clean it and arrange it for storage. Have a
demonstrator check it and sign your assignment page.

                                                         4 - 19


1.    This student's microscope was properly set up.

                                          Demonstrator's signature_______________________

2.     A represents the letter e as it appears on your slide. In B print the letter e as it appears in your

                         A                                 B

3.      On the e you put in Figure 2B, draw a dotted circle to mark the area you observed under the
10x objective lens. Next draw a solid circle to mark the area you observed under the 40x objective

4.      Make a summary statement about the relationship between magnification and field of view.




5.    Objective lens              Diameter of Field

                 4x                       __________ mm

                 10x                      __________ mm

                 40x                      __________ mm
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6.       If you were observing a live specimen under the 40x objective lens and it moved out of your
field of view, explain how could you find it again quickly and easily?




7.    On the crossed thread slide, which thread is in the middle? _________________________

8.    Diameter of thread:
                                        Ocular Units     Diameter

                4x objective            _________        _______

                10x                     _________        _______

9.    Elodea whole leaf:       length ______________

                             width ______________

                        number of layers ______________

ASSIGNMENT 7: Cell Measures:
10. Elodea cells: Typical midrib cell   - length __________

                                        - width ____________

                Typical blade cell       -length __________

                                        - width ____________

11.     Why did you observe chloroplasts only around the edges of the plant cells?



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12. Cheek epithelial cell:      diameter ____________

13.     Compare and contrast the plant cells and the animal cells you observed.






11.     This student's microscope was cleaned and put away properly.

        Demonstrator's signature   __________________________________

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