Download Comparing Plant and Animal Cells

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Comparing Plant and Animal Cells
Ever since the first microscope was used, 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 the cell is the structural
and functional unit of living things. Cells contain structures celled organelles that carry out
life processes. Cells can be classified by the types of organelles they contain. In plant and
animal cells, similarities and differences exist because of varied life functions. In this
investigation, you will compare the structures of a typical plant cell and a typical animal cell.
Materials (per person)
Forceps
Medicine dropper
Water
Onion piece
Microscope
Glass slide
Coverslip
Toothpick
Methylene Blue stain
Iodine
Paper towel
Lens paper
Safety: While preparing slides, you must wear goggles. When you have completed staining
your samples and are ready to look at them under the microscope, you may remove your
goggles. Iodine and methylene blue are stains – they will stain your skin and your clothes. If
you get any stain on your skin, be sure to rinse thoroughly. The slides that you are using are
glass. Be sure to handle them carefully, and if they happen to break, notify the teacher
immediately.
Procedure 1: Onion Cells
1. Clean the eyepiece and objectives on microscope with lens paper
2. Obtain a piece of onion and remove one layer of “skin” from the onion. The sample
must be thin or the light will not penetrate the sample, resulting in a dark area in the
viewing area.
3. Place the onion sample on the center of a clean slide. Place a few drops of water on
top of the onion.
4. Place the coverslip on top of the water drop by slowly lowering it on an angle to
prevent air bubbles from forming.
5. Place the slide on the stage of the microscope and focus the scope in low power.
6. Draw what you see in appropriate size and detail in the observation section of the lab
and label any organelles that you can identify.
7. Switch your objective to high power. Be careful to look at the objective from the side
of your microscope so that the objective does not damage or scratch the slide. Focus
using only the fine adjustment knobs.
8. Draw what you see in appropriate size and detail in the observation section of the lab.
Label any organelles that you can identify
9. Remove your slide from the stage of the microscope and place it back on the lab
bench.
10. Follow the next steps for staining the onion cells (refer to picture below)
i. Place one drop of iodine next to the coverslip.
ii. On the opposite side of the coverslip, place a piece of paper towel at the
edge of the coverslip. The stain will be drawn under the coverslip and
stain the cell.
11. Place the slide back on the stage and view again in low and high power. Just as
before, draw what you see in the observation section and label any organelles that you
can see.
12. Clean the slide by removing the coverslip and sample and throw it in the garbage.
Clean the slide with soap and water and dry with a paper towel. Once totally dry, wipe
it streak free with lens paper.
Procedure 2: Cheek Cells
1. Using the flat end of a toothpick, gently scrape the inside of your cheek. Do not use
force when scraping the inside of your cheek. Only a few cells are needed. The end
of the toothpick will have several cheek cells stuck to it even though you may see
nothing but a drop of saliva.
2. Rub the toothpick in the center of the slide, allowing some of the cells to come off on
the slide.
3. Place a drop of water on top of the area that the cells are located.
4. Place the coverslip over the top of the water, just as you did with the plant cell, with
proper techniques.
5. View the cheek cell on high and low power and draw what you see in each in the
observation section. Label any organelles that you can identify.
6. Remove the slide from the stage and stain the cells with methylene blue. Follow
procedure #10 above, using methylene blue in place of iodine.
7. Discard the coverslip and the slide.
Procedure 3: Pond Water
1. Prepare a wet mount of pond water.
2. Locate any organisms and sketch what you see.
3. Try to locate other types of organisms.
Conclusion
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7.
What is the shape of an onion cell?
What is the general location of the nucleus in an onion cell?
What is the shape of a cheek cell?
What is the general location of the nucleus in a cheek cell?
How are plant and animal cells similar in structure?
How are plant and animal cells different in structure?
Why are stains such as methylene blue used when observing cells under the
microscope?
8. What is an advantage of using a wet-mount preparation instead of a dry-mount
preparation in the study of living cells?
9. Explain why you could not use an oak leaf in this investigation.
10. Why is it possible to easily collect cells by gently scraping the inside of your cheek?
11. In general, the surface of a tree has a harder “feel” than does the surface of a dog.
What cell characteristic of each organism can be used to explain this difference?
12. If you were given a slide containing living cells of an unknown organism, how would
you identify the cells as either plant or animal?