Download Part D: Observing Prokaryotic Cells

NAME _____________________
BLOCK _____________________
Introduction
Ever since the first microscope was developed, biologists have been interested in studying the cellular organization
of all living things. After hundreds of years of observations by many biologists, the cell theory was developed. The
cell theory states that all living things are made of cells; the cell is the primary unit of structure and function of living
things; and that cells can only come from preexisting cells. Cells contain structures called organelles that carry out
the life processes. In multicellular organisms, not all cells are able to carry out all of the functions that are necessary
to the llife of the organism. Some cells perfom highly specialized jobs. This is called division of labor. All types of
cells are structurally differetn from one antoher because they are adapted to carrying out particular funcitons. This is
called cell specialization.
Objectives
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To identify and observe various types of cells- bacterial, cork, ontion, green plant, potato, carrrot, red pepper,
and human cells.
To relate the structure of each type of cell to its function.
To compare and contrast the structure of plant and animal cells.
To list four structural characteristics unique to plant cells.
Materials
Forceps
Medicine Dropper
Elodea Leaf
Water
Sample Human Tissue Slides
Yogurt
Microscope
Glass slide
Cork
Razor blade, single edge
Onion
Iodine Stain
Potato
Carrot
Coverslip
Red Pepper
Toothpicks
Methylene Blue Stain
Paper Towel
Lens Paper
Making Drawings using the Microscope
Drawing specimens as seen under the microscope is an important skill in biology. It is important to draw the
specimens as accurately as possible. Keep in mind the following: Positioning- center the diagram in the space
provided and leave room for labels. Size – the drawing should look the same size in the space available as the
specimen is under the microscope. Detail- show as much detail as possible to aid in understanding. Often a small
section with lots of detail will work. Accuracy- draw the specimen exactly as it looks not a filled-in version or
interpretation. Labels- all parts of the diagram must be labeled accurately using verticle or horizontal lines. The lines
should not cross. Drawings must include a title, magnification (or scale), names of structures, and any movements in
living specimens. Examples are listed below:
Procedure
Part A. Observing Cork Cells
Cork cells were the first to have been documented as being seen under a microscope. Robert Hooke looked at a thin
slice of cork cell under a microscope. The cork was found to be made of small semi-rectangular shaped structures.
Cork cells appear to be empty because they are dead and there is no water, organelles, or other material found
within them.
Shave a very thin slice of cork using a razor blade. Place the piece of cork on a slide and prepare a wet-mount slide
by placing a drop of water and coverslip on the thin piece of cork. Observe the specimen under high power. Draw a
picture of the cork cell, being sure to label the cell wall.
Part B. Examining Plant Cells (all cells should be viewed under high power)
Elodea
Prepare a wet mount slide of an Elodea leaf. Draw the Elodea leaf exactly as it is seen. Observe the thick cell wall,
thinner cell membrane, cytoplasm, nucleus, and cholorplasts. In addition, a large central vacuole should be
apparent. Label these structures in your diagram. The structures characterize a generalized plant. Answer question
4 on your data sheet. Label the following structures: cell wall, chloroplasts, cell membrane, vacuole.
Onion
Onions have layers of modified leaves (scales) that can easily be separated from one another. Peel off a portion of
one layer. Examine the concave side of the piece you have obtained. The surface is covered by a thin layer of cells,
the epidermis. Remove a small piece of the epidermis by breaking the scale gently, leaving the epidermis intact.
Peel the epidermis from one of the halves of the scale. Prepare a wet mount slide of the isolated epidermis. Observe
onion cells using low power and then high power. Add a drop of Lugol’s solution at the edge of the coverslip. Draw
the onion cells exactly as they are seen. Answer questions 5 and 6 on your data sheet. Label the nucleus, cell wall,
vacuole, and cell membrane in your diagram.
Potato
Use a razor blade to slice a piece of tissue, as thin as possible, from a potato. Be careful not to cut your fingers.
Prepare a wet mount slide using a drop of water. Study the slide at low power and then at high power. Add iodine
solution to the side of the coverslip and observe the cells as the iodine solution makes contact with them. Draw the
potato cells exactly as they are seen. Answer questions 7 – 10 on your data sheet. Label the cell wall and the
leucoplasts.
Plastids are membrane bound organelles unique to plants. You have already been introduced to 2 types –
chloroplasts (containing chlorophyll) and leucoplasts (containing starch). Chromoplasts contain several types of
pigment including carotenoids, which give plants an orange or yellow color.
Carrot
Use a razor blade to slice a piece of tissue, as thin as possible, from the outer portion of a peeled carrot. Prepare a
wet-mount slide. Draw the carrot cells exactly as they are seen. Label the cell wall and chromoplasts.
Red Pepper
Use a razor blade to slice a piece of tissue, as thin as possible, from a red pepper. Prepare a wet-mount slide. Answer
question 11 on your data sheet. Draw the red pepper cells exactly as they are seen. Label the cell wall and
chromoplasts.
Part C. Observing Animal Cells
In this section you will examine the cell structure of human epithelial (cheek) cells. Note the differences between
these animal cells and the green plant cells studied in part B.
Cheek Cells
Gently scrape the inside of your cheek with a clean toothpick. Prepare a wet-mount of the material that you have
scraped. Add a drop of methylene blue and a coverslip. Examine the cells under low power of the microscope.
Switch to high power. Carefully look for the outer edge of the cytoplasm. Answer questions 12 and 13 on your data
sheet. Draw the cheek cells exactly as they are seen. Label the cell membrane, cytoplasm, and nucleus.
Muscle Cells
Obtain a prepared slide of a Skeletal Muscle cross section. Observe the slide under high power on the microscope.
Muscle cells are very long and have several nuclei and a series of lines called striations that will be visible. Carefully
observe and draw the muscle cells exactly as they are seen. Label the nuclei, striations, and cell membranes.
Nerve Cells
Obtain a prepared slide of a Mammal Neuron Motor Nerve Cells. Observe the slide under high power on the
microscope. Nerve cells are very long and have many long extensions for conducting nerve impulses. These highly
branched portions of the cell are called Axons and Dendrites. Carefully observe and draw the muscle cells exactly as
they are seen. Label the nuclei, axons and dendrites.
Part D: Observing Prokaryotic Cells
Bacteria
All bacteria are prokaryotic. This means that they lack an organized nucleus and membrane-bound organelles. To
find bacteria, smear a very small portion of yogurt across a slide using a toothpick. Add a small drop of water to
make a wet mount slide. Have your instructor put a very tiny amount of methylene blue stain to the slide and cover it
with a cover slip. View the slide under the microscope under high power. The bacterial cells will be tiny moving oval
or capsule shaped objects. Carefully observe and draw the bacterial cells exactly as they are seen. Label the cell
walls.
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Analysis Questions
1. Describe the structure of the cork cells. ____________________________________________
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2. Explain how the structure of these cells is different than the other cells in this investigation. Explain why the
cork cells are so different. ____________________________________________________________________________
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3. What is the general shape of the Elodea cells? _______________________________________
4. Onion cells lack one of the structures that is very conspicuous in Elodea cells. What is this structure?
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5. Explain why Elodea Cells have this structure while onion cells lack them. __________________
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6. Describe the reaction of iodine with the potato cells and describe how that compares with what you observed
when iodine was added to the onion epidermis preparation.
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7. What does this tell you about the differences between the storage products in onions and potatoes?
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8. Do you see any chloroplasts in the potato cells? Why or why not? ________________________
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9. You will probably see some small oval shaped blue-black structures. These are leucoplasts and they store
starch. Explain why they turned blue. ______________________________________
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10. Describe the appearance of the chromoplasts that you saw in the carrot and red pepper.
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11. What is the general shape of the cheek cell? ________________________________________
12. What is the general location of the nucleus in the cheek cell? ___________________________
13. Describe at least two important ways that the muscle cells differed from the cheek cell. _______
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14. Why might the nerve cell have so many tiny extensions? _______________________________
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15. Describe the major ways in which the bacterial cells differed from the other cells when viewed under the
microscope. _________________________________________________________
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Summary Questions
16. List at least four differences between plant and animal cells. _____________________________
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17. Define cell specialization. Give an example of cell specialization that was observed during this lab.
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18. List three differences between prokaryotic and eukaryotic cells. __________________________
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