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Cell Biology OLM, Experiment #1. The Discovery of Cells.
Experimental Protocol
A.
Microscopic Study of Cork
Cork was one of the many materials Robert Hooke studied with his microscope. It was through his description of
his microscopic observations of cork, published in 1665 in his monograph Micrographia, that he coined the term
“cell” in reference to the microscopic compartments that make up cork tissue.
Hooke's Protocol:
Hooke's report of his study of cork is found in the section of Micrographia entitled Observ.
XVIII. Of the Schematisme or Texture of Cork, and of the Cells and Pores of some other such frothy Bodies. In
describing his basic methodology, he wrote:
I took a good clear piece of Cork, and with a Pen-knife sharpen'd as keen as a Razor, I cut a piece of it off, and
thereby left the surface of it exceeding smooth, then examining it very diligently with a Microscope, me
thought I could perceive it to appear a little porous; but I could not so plainly distinguish them, . . .
. . . , I with the same sharp Penknife, cut off from the former smooth surface an exceeding thin piece of it, and
placing it on a black object Plate, because it was it self a white body, and casting the light on it with a deep
plano-convex Glass, . . .
Cell Biology OLM Protocol:
Your protocol is similar to Hooke's.
1. Randomly retrieve 3 corks from the bowl of corks.
2. Using the hand microtome, slice a very thin section from one of the three corks with a sharp single-edge
razor blade. Then, using a pair of forceps, carefully place the section on a clean microscope slide (Do not add
water).
3. Place the slide on the stage of your microscope, turn on the illuminating lamp and focus on the specimen
with the 4X objective lens. Once the specimen is in focus, rotate through the objectives (4X, 10X and 40X) and
study the microscopic structure of the specimen at each magnification. As you study your specimen,
determine whether the specimen is thin enough to get a clear view of the microscopic structure of the
specimen. If it isn't, try to make thinner sections in the following steps.
4. Prepare two additional slides of cork from samples taken from the other two corks in a fashion similar
to that above (for a total of three slides). Do your best to cut thin sections. Like the first slide, place each slide
on the microscope stage, turn on the illuminating lamp and focus on the specimen with the 4X objective lens.
Once the specimen is in focus, rotate through the objectives (4X, 10X and 40X) and study the microscopic
structure of the specimen at each magnification.
As you study your specimen, determine whether the microscopic structure seen in each slide is consistent
with that seen in the other slides. If the structure is consistent from slide to slide, any one of the slides
would be a good representation of the structure of the cork from which you took your samples.
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5. Assuming the microscopic structure seen in each slide is consistent with that seen in the other slides, choose
one of the slides as a representation of your thin sections of cork, place it on the microscope and view the
specimen at the magnification that appeals to you. Record the image by either drawing a simple sketch of the
observations or by photographing the microscope image through the eyepiece.
B.
Microscopic Study of Carrot
Cork was not the only plant structure studied by Hooke. He also studied a variety of other plants, including
carrots. After describing his microscopic observations of cork in Observ XVIII of Micrographia, Cooke wrote:
Nor is this kind of Texture peculiar to Cork onely; for upon examination with my Microscope, I have found that
the pith of an Elder, or almost any other Tree, the inner pulp or pith of the Cany hollow stalks of several other
Vegetables: as of Fennel, Carrets, Daucus, Bur-docks, Teasels, Fearn, some kinds of Reeds, &c. have much such
a kind of Schematisme, as I have lately shewn that of Cork, save onely that here the pores are rang'd the longways, or the same ways with the length of the Cane, whereas in Cork they are transverse.
Cell Biology OLM Protocol:
1. Randomly retrieve 3 carrot pieces from the bowl of carrot pieces.
2. As was done with cork, slice a very thin section of carrot from one of the three carrot pieces with a sharp
single-edge razor blade and the hand microtome. Then, using a pair of forceps, carefully place the section on a
clean microscope slide (Do not add water).
3. Place the slide on the stage of your microscope, turn on the illuminating lamp and focus on the specimen with
the 4X objective lens. Once the specimen is in focus, rotate through the objectives (4X, 10X and 40X) and study
the microscopic structure of the specimen at each magnification. As you study your specimen, determine
whether the specimen is thin enough to get a clear view of the microscopic structure of the specimen. If it
isn't, try to make thinner sections in the following steps.
4. Prepare two additional slides of carrot from samples taken from the other two carrot pieces in a
fashion similar to that above (for a total of three slides). Do your best to cut very thin sections. Like the first
slide, place each slide on the stage of your microscope, turn on the illuminating lamp and focus on the
specimen with the 4X objective lens. Once the specimen is in focus, rotate through the objectives (4X, 10X and
40X) and study the microscopic structure of the specimen at each magnification.
As you study your specimen, determine whether the microscopic structure seen in each slide is consistent
with that seen in the other slides. If the structure is consistent from slide to slide, any one of the slides
would be a good representation of the structure of the carrot from which you took your samples.
5. Assuming the microscopic structure seen in each slide is consistent with that seen in the other slides, choose
one of the slides as a representation of your thin sections of carrot, place it on the microscope and view the
specimen at the magnification that appeals to you. Record the image by either drawing a simple sketch of the
observations or by photographing the microscope image through the eyepiece.
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C.
Microscopic Study of Green Algae
Antoni van Leeuwenhoek is credited with the first published observations of living cells. One of his very first
discoveries was that of the organism that we now know as the green alga Spirogyra. He discovered it in a vial
of pond scum taken from a small lake near Delft, Holland. In a letter to the Royal Society dataed 1674,
Leeuwenhoek writes:
About two hours distant from this Town there lies an inland lake, called the Berkelse Mere, whose bottom in
many places is very marshy, or boggy. Its water is in winter very clear, but
at the beginning or in the middle of summer it becomes whitish, and there are then little green clouds floating
through it; which, according to the saying of the country folk dwelling thereabout, is caused by the dew, which
happens to fall at that time, and which they call honey-dew. This water is abounding in fish, which is very
good and savory. Passing just lately over this lake, at a time when the wind blew pretty hard, and seeing the
water as above described, I took up a little of it in a glass phial; and examining this water next day, I found
floating therein divers earthy particles, and some green streaks, spirally wound serpent-wise, and orderly
arranged, after the manner of the copper or tin worms, which distillers use to cool their liquors as they distil
over. The whole circumference of each of these streaks was about the thickness of a hair of one's head. Other
particles had but the beginning of the foresaid streak; but all consisted of very small green globules joined
together: and there were very many small green globules as well.
Cell Biology OLM Protocol:
1. Using a pasteur pipette, take a random sample from the Spirogyra culture and prepare a wet mount of the
green alga.
2. Place the slide on the stage of your microscope, turn on the illuminating lamp and focus on the specimen
with the 4X objective lens. Once the specimen is in focus, search the slide for Spirogyra. Once located, rotate
through the objectives (4X, 10X and 40X) and study the microscopic structure of the specimen at each
magnification.
3. Now prepare two additional slides (for a total of three slides), using fresh, random samples from the culture
for each slide. Like the first slide, place each slide on the stage of your microscope, turn on the illuminating
lamp and focus on the specimen with the 4X objective lens. Once the specimen is in focus, search the slide
for Spirogyra. Once located, rotate through the objectives (4X, 10X and 40X) and study the microscopic
structure of the specimen at each magnification.
As you study your specimen, determine whether the microscopic structure seen in each slide is consistent
with that seen in the other slides. If the structure is consistent from slide to slide, any one of the slides
would be a good representation of the culture from which you took your samples.
4. Assuming the microscopic structure seen in each slide is consistent with that seen in the other slides, choose
one of the slides that is a good representation of Spirogyra, place it on the microscope and view the
specimen at the magnification that appeals to you. Record the image by either drawing a simple sketch of
the observations or by photographing the microscope image through the eyepiece.
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D.
Microscopic Study of Pond Water
In 1702, nearly 30 years after his description of Spirogyra, Leeuwenhoek reported, for the first time,
observations of a wide variety of living "animalcules", as they were called at the time, in pond water. Based on
his decriptions and drawings, we now know he observed ciliated protozoa Vorticella and Stentor, the colonial
protozoon Volvox, diatoms and rotifers.
Cell Biology OLM Protocol:
You are going to prepare three independent samples of pond water and from each of those samples identify
as many different single celled organisms as possible.
1. Using a pasteur pipette, take a random sample of pond water and prepare a wet mount.
2. Place the slide on the stage of your microscope, turn on the illuminating lamp and focus on the specimen with
the 4X objective lens. Once the specimen is in focus, search the slide for the single celled "animalcules". Once
located, find the objective that gives you the best view of these organisms. Then, using the identification guide
provided, identify those organisms you can find.
3. Repeat steps 1 and 2 two additional times so that you have identified organisms in each of three samples of
pond water.
E.
Homework Assignment
Your instructor will give you a homework assignment. Make sure you understand the assignment before you
leave lab today.
F.
Clean Up
Before you leave you must clean up your place so it looks the way it did when you walked into lab today.
CellBiologyOLM is authored by Stephen Gallik, Ph. D.| Copyright; 2011, 2012, 2013 by Stephen Gallik, Ph. D.
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