Cell Lab Livingston Public Schools

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Cell Lab Livingston Public Schools Powered By Docstoc
					Biology Honors
              Animal & Plant Cells: The Basic Units of Life




Materials:
       Compound microscope             methylene blue solution        microscopic slides
       Coverslips                      toothpicks                     iodine
       Elodea                          onion                          forceps
       paper toweling                  pencil

Introduction:
       In 1665, Robert Hooke published a book in which he described the appearance of cork cells
under the microscope. This was the first published description of cells.

       For approximately 200 years biologists have recognized the cell as a basic unit of life. A cell
is composed of many smaller units called organelles. The organelles of a cell are made of complex
chemical compounds. Each type of organelles has a specific function which contributes to the total
function of the cell. Although a variety of cells exist and many of them differ in shape and size, they
frequently share many common organelles. A knowledge of basic cell structure is necessary to
understand the process of both simple and complex life forms.

         There really is no typical cell in which you can see all of the features that a cell might have,
so you will instead look at three ordinary cells to observe what they are like. You will be able to see
those organelles which are readily visible with your compound microscope, some organelles would
be visible with your microscope if they were stained properly but we will not be staining all the
cells in today’s lab.




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Procedure- Part 1 – Viewing Onion Epidermal Cells
1. Obtain a piece of cut onion and with your thumb and forefinger, hold the piece of
   onion near it’s center. Bend the onion sharply toward you so that the back surface
   snaps. This will leave a tin p piece of onion epidermis that can be easily peeled
   off with forceps.




2. Place a small piece of the epidermis on a clean glass slide. Straighten out the
   epidermis. MAKE SURE IT IS NOT WRINKLED. Add 1-2 drops of
   iodine solution (IODINE STAINS CLOTHING!!). Then place a coverslip
   on top of the onion and iodine, PLACE THE COVERSLIP DOWN ON
   AN ANGLE TO AVOID TRAPPING AIR BUBBLES. Allow the slid to
   sit for about 60 seconds or the iodine will not properly stain the cell.

3. After allowing the iodine to stain the cell, place a folded piece of paper
   toweling over the slide and gently press down, this will remove any excess iodine stain which
   could hinder your view. (Do not apply to much pressure and break the slide.)


4. Observe first LOW POWER, adjusting the focus and light intensity until it is favorable. The
   onion epidermis is a tissue.


5. Use the fine adjustment on your microscope to focus on one area and switch to high power


6. Observe the cells under high power taking note of the following features. – If you are having
   trouble viewing the cell under high power you can switch back to low power and make
   observations under low.
   a. Cell wall- a rigid but porous structure composed of the polysaccharide cellulose and several
       other substances. The cell wall gives the plant a rigidity that is absent in animal cells.

   b. Cytoplasm – solution containing many small granules but otherwise transparent; it is
      located inside the cell wall and cell membrane (which is not visible).

   c. Cell vacuole – a large fluid sac occupying most of the central part of the cell and pressing
      against the cytoplasm. You will not be able to see the vacuole but you will be aware of its

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       presence if your onion cell is rigid and you cannot see any gaps between your cell wall and
       your cell membrane.

   d. Nucleus- spherical structure located in the cytoplasm. It contains several smaller spherical
      structures called nucleoli (singular- nucleus) Chromosomes are present but not visible in
      the cell that is not dividing.

Onion Epidermal Cell

***Steps to making a correct biological drawing
   1. ALWAYS DRAW IN PENCIL
   2. ALWAYS DRAW THE CELLS IN PROPORTION TO THE FIELD OF VIEW. You
      will be measuring these cells and will need to the correct proportions to do this.
   3. ALWAYS TITLE the drawing and document what power you are drawing it from.

1. Sketch and label several onions epidermal cells, you only have to show detail in one cell &
   label one cell.
                Label the cell wall, nucleus, nucleoli, cytoplasm and cell membrane.

   Title_______________________                             Power____________________




                                            Field of View

2. What is the shape of a typical onion epidermal cell?_________________________________

3. Estimate the size of a typical onion epidermal cell:______________________________
   Show work for cell measurements




4. How many nucleoli do you see in each nucleus? (if you can’t see any in your slide look at the
   videoscope at the front of the room)_______________________

5. What structure common to most plant cells is missing? _____________________
   Why?_______________________________________________________________________
                                                                                                   3
Procedure – Part 2 – Viewing Green Plant Cells
1. Obtain a sprig of Elodea, an aquatic green plant. With your forceps, spread apart a cluster of
   leaves at the tip of the sprig and pull of on the smallest leaves. Prepare a wet mount by adding a
   drop of water to an Elodea leaf on a microscope slide and carefully place a coverslip on the
   slide.




2. Observe first under LOW POWER, adjusting the focus and light intensity until it is favorable.
3. Use the fine adjustment on your microscope to focus on one areas and switch to high
   power.
4. Observe the cells under high power taking note of the following features.

   a. Cell wall – a rigid but porous structure composed of the polysaccharide cellulose and
      several other substances. The cell wall gives the plant cells a rigidity that is absent in animal
      cells.

   b. Cytoplasm- solution containing many small granule but otherwise transparent; it is located
      inside the cell wall and cell membrane (which is not visible).

   c. Cell vacuole- a large fluid filled sac occupying most of the central part of the cell and
      pressing against the cytoplasm. You will not be able to see the vacuole but you will be
      aware of its presence by watching the path of your chloroplasts.

   d. Chloroplast- small spherical green organelles moving around in the cytoplasm.

   e. You will not be able to view a nucleus because the cells have not been stained.

5. Observe a chloroplast as it moves about in the cytoplasm of one of the larger cells. You should
   be able to determine its shape as it moves about. If the cell is in good condition, the cytoplasm
   should stream (move) continuously. This movement is called cytoplasmic streaming.



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Elodea Leaf Cell

1. Sketch and label several Elodea cells under high power in the space provided.

   Label the cell wall, cytoplasm, chloroplasts and cell membrane.

Title_______________________                               Power______________________




                                          Field of View

2. Does every Elodea cell have the green circular structures? ____________

   What are these structures?____________________

   What is their function? __________________________________________


3. What structure might occupy the space in the cell where no chloroplasts are located?
   __________________
   (HINT: Reread above)

4. When using fine focus, why does the image of the Elodea cells under the microscope seem to
   change appearance?____________________________________________________________

5. Estimate the size of a typical Elodea cell:__________________________
       Show work for cell measurements




                                                                                                5
   Procedure – Part 3 – Viewing Animal Cells
1. Gently scrape the inside of your cheek with a clean, flat toothpick.
   Stir the scrapings onto a clean microscope slide. Add one drop of
   methylene blue stain and a coverstrip. Wait at least 60 seconds for
   the cells to stain and blot up the excess stain as was done with
   iodine in part 1 of this lab.




2. Observe first under LOW POWER, locate some cells by moving
   the slide around until you see the cells that are separate rather than
   clumped together. Adjust the focus and light intensity until it is
   favorable.
3. Use the fine adjustment on your microscope to focus on one or
   two cells and switch to high power.

Cheek Epithelial Cell
1. Sketch and label several cheek epithelial cells under high power in the space provided.
2. Label the cytoplasm, nucleus, nucleoli (if they can be seen) and cell membrane.

Title___________________________                              Power_________________________




                                     Field of View- High Power

1. Why can’t you see all the organelles such as the golgi, mitochondria, ER, ribosomes, and other
   structures we talked about in class? (2 reasons)
   _____________________________________________________________________________
   _____________________________________________________________________________

2. Estimate the size of a typical cheek cell: ________________________
   Show work for cell measurements

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       Cellular Organization: cells  tissue organ  system organism

1. Explain the level of cellular organization present in specimen #1. (onion epidermis)
   What level of organization are you viewing? Explain how you know this.




2. Explain the cellular organization seen in specimen #2. (elodea)
   What level of organization are you viewing? Explain how you know this.




3. Explain the cellular organization seen in specimen #3. (cheek)
   What level of organization are you viewing? Explain how you know this.




Observing some plant cell characteristics in more detail.
In this section you will be observing starch grains stored in plant cells. You will be observing cells
in a banana, and observing the stored starch by staining the cells with iodine. Remember, when
iodine interacts with starch, it turns a black color.

Note: You should prepare two specimens on the same slide for this section. Divide the slide in
half, and put the material explained in number 1 below on one side of the slide, and the material
explained in number 2 on the other side of the slide. Each specimen will be prepared in the same
way, and be covered with a separate coverslip.

1. Before class, your teacher will make a hole through the skin of the banana, into the soft fruit
   where the cells are that you will sample. Insert a toothpick into the hole in the skin of the
   banana, and remove a small amount of banana tissue. Place this material on a slide, and add one
   drop of iodine. Then add a coverslip, and view under high power in your light microscope.
   Diagram what you see in the circle below that represents the field of view.
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2. On the same slide, you will be preparing a wet mount in the same way, but this time you will be
   sampling the tissue from an extremely ripe banana. You will also view the specimen under high
   power.


Describe and explain any differences that you observed between the two samples. Why does one
cell appear dark and the other one light? Answer completely
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________




Unripe Banana                                                        Ripe Banana

Remember: unripe                                                     Remember: ripe
bananas are not                                                      bananas are sweet
sweet




What organelles usually store starch in plant cells?
________________________________________________________________________________
________________________________________________________________________________
________________________________________________________________________________




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