L2-5.10 Comparing Plant And Animal Cells Opt

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ComparingPlant and Animal Cells Pre-Lab Discussion Ever since the first microscope was used, biologists have been interested in studying the cellular organizationof 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 called organelles that carry out life processes.Cells can be classifiedby the types of organellesthey contain. In plant and animal cells, similarities and differencesexist becauseof varied life functions. In this investigation,you will compare the structures of a typical plant cell (Elodea) and a typical animal cell (human).

Problem How are plant and animal cells alike?How are they different?

Materials (per group) Forceps Medicinedropper Elodea leal Water Microscope Glassslide Coverslip Toothpicks Methylene blue stain Paper towel Lens paper

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Put on a laboratory apron if one is available.Put on safety goggles.Always handle the microscope with extreme care. You are responsible for its proper care and use. Use caution when handling glass slides as they can break easily and cut you. Always use special caution when working with laboratory chemicals,as they may irritate the skin or cause staining of the skin or clothing. Never touch or taste any chemical unless instructed to do so. Note all safety alert symbols next to the steps in the Procedure and review the meaningsof each symbol by referring to the symbol guide on page 10.

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Procedure Part A. Examining Plant Cells l. Take a microscope from the storage area and place it about l0 centimeters from the edge of the laboratory table. 2. carefully clean the eyepieceand objective lenseswith lens paper. ,&

3. Place a drop of water in the center of a clean glass slide. 4. With the forceps, remove a leaf from the Etodeaplant and place it on the drop of water on the slide. Make sure that the leaf is flat. If it is folded, straighten it with the forceps. .5. carefully place a coverslip over the drop of water andElodea leat. 6. Place the slide on the stage of the microscope with the leaf directly over the opening in the stage. 7. Using the low-power objective lens, locate the leaf under the microscope.Turn the coarse adjustment knob until the leaf comes into focus. 8. Switch to the high-power objective lens. CAUTION: Whentuming to the high-powerobjectiue lens, you should always look at the objectiue from the side of your microscopeso that the objectiue lens does not hit or damage the stide. 9. Observe the cells of the Elodeo leaf. Draw and label what you see in the appropriate place in Observations.Record the magnificationof the microscope.

,& tO. Carefully clean and dry your slide and coverslip. Part B. Examining Animal Cells ,&

l. Place a drop of water in the center of a clean glass slide.

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2. Using the flat end of a toothpick, gently scrape the inside of your cheek.SeeFigure 1. CAUTION: Do not use force when scraping the inside of your cheek. Onty o few cellsare 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. 3. Stir the water on the slide with the end of the toothpick to mix the cheek cells with the water. see Figure 2. Disposeof the toothpick as instructed by your teacher.

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4. Put one drop of methylene blue stain on top of the drop of water containing the cheek cells. CAUTION: Use care when worhing with methylene blue to auoid staining hands and clothing. 5. Wait one minute, then carefully place a coverslip over the stained cheek cells. 6. To remove the stain from under the coverslip and replace it with clear water, place a piece of paper towel at the edge of one side of the coverslip. Then place a drop of water at the edge of the coverslip on the opposite side. SeeFigure 3. The stained water under the coverslip will be absorbed by the paper towel..As the stain is removed, the clear water next to the coverslip on the opposite side will be drawn under the coverslip. Discard the paper towel after it has absorbed the stained water.

Papertowel

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Methylenebluestain

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Place the slide on the stage of the microscope with the center of the coverslip directly over the opening in the stage.

8. Using the low-power objective lens, Iocate a few cheek cells under the microscope. Note: /ou will need to reduce the amount of light coming through the slide in order to see the cells more clearly. Adjust the diaphragm as necessary. 9. Switch to the high-power objective lens. CAUTION: Whenturning to the high-powerobjectiue lens, you should always look at the objectiue from the side of your microscopeso that the objectiue lens does not hit or damage the slide.

1 0 . Observe some cheek cells. Draw and label what you see in the appropriate place in Observations.Record the magnificationof the microscope.

l& rr. Carefully clean and dry your slide and coverslip. 12. Return your microscope to the storage area.

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Magnification

Magnification

Elodea Cells (Plantcells)

Observations

l. What is the shapeof an Elodeocell?

2. What is the general location of the nucleus in an Elodea cell?

3. What is the shape of the cheek cell?

4. What is the general location of the nucleus in a cheek cell?

Analysisand Conclusions l. How are plant and animalcellssimilarin structure?

2. How are plant and animal cells different in structure?

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Cheek Cells (Animalcells)

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3. Why are stains such as methylene blue used when observing cells under the microscope?

CriticalThinkingand Application l. What is an advantageof using a wet-mount preparation instead of a dry-mount preparation in the study of living cells?

2. Explain why you could not use an oak leaf in this investigation.

3. Why is it possible to easily collect cells by gently scraping the inside of your cheek?

4. 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?

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t 5. If you were given a slide containing living cells of an unknown organism,how would you identify the cells as either plant or animal?

Going Further l. Removethe skin from fruits and vegetablessuch as tomatoes, onions, and leeks.Prepare wetmount slides for each skin and observe the cells under the low-power and high-power objectives of your microscope. Sketch and label what you see. What cell structures do these cells have in common?How do these cells compare with animal cells? 2. Make a wet-mount slide of an Elodea leaf using a l0% salt solution (10 g of table salt dissolved in 100mL of water) instead of water. Examinethe leaf under low power and high power. Describe any differencesin characteristics between these Elodea cells and the cells observed in water.

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