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Name: ___________________________________ TOC#____ Background Ever since the first microscope w as used , biologists have been interested in stud ying the cellular organization of all living things. After hund red s of years of observations by m any biologists, the cell t heory w as d eveloped . The cell theory states that the cell is the structural and functional unit of living things. One w ay cells are classified is by the structures they contain. All cells contain 3 parts; cytoplasm , genetic m aterial, and a m em brane. H ow ever, d ifferent types of organism s like prokaryotes and eukaryotes have d ifferent organelles. Ad d itionally, even d ifferent eukaryotic organism s like plants and anim als have d ifferences in their cells. In plant and anim al cells, both sim ilarities and d ifferences exist w ith respect to structure. In this investigation, you w ill com pare the structures of a typical bacteria (prokaryote) cell, plant cell and anim al cell (eukaryote cells). Focus Questions By the end of this lab, you should be able to answ er the follow ing questions 1. What are the proper techniques of using a m icroscope and preparing slid es 2. What structures d o cells contain? 3. H ow are plant, anim al, and bacterial cells alike? H ow are they d ifferen t? Pre-Lab Questions 1. What is cell theory? 2. What d o all cells contain? 3. What is a prokaryote? 4. What is a eukaryote? 5. What is an organelle? Materials • Forceps • Micro d ropping pipet • Water plant leaf • Water • Microscope • Glass slid e • Coverslip • Toothpicks • Methylene blue stain • Paper tow el • Lens paper Safety Use caution w hen hand ling glass slid es as they can break easily and cut you. Alw ays use special caution w hen w orking w ith laboratory chem icals, as they m ay irritate the sk in or cause staining of skin or clothing. N ever touch or taste any chem ical unless instructed to d o so. 1. 2. 3. 4. 5. 6. Procedure Part A. Examining Prokaryotic Cells - Bacteria A few select fixed bacterial slid es are available for you to view . Slid es are labeled w ith the species represented , or source of sm ear. These slid es feature heat -fixed , d ead bacteria cells that have been stained to m ake view ing them easier. You are not expected to see a nucleus. Why? Proced ures: With your group, place the m icroscope about 10 cm Flow Chart: from the ed ge of the laboratory table. Obtain a fixed bacterial slid e. To view a slid e: a) if need ed , clean any sm ud ges by lightly buffing the slid e w ith lens paper. b) place the slid e on your stage w ith the m ost highly stained region of the slid e d irectly over the opening in the stage. c) Focus the slid e using the 4x (low -pow er) objective lens. Proceed to 10x (m ed -pow er) and finally, only after the stained sm ear is in focus, focus a section of the slide on 40x (high -pow er). Once the sm ear/ cells are in focus on high -pow er, select a section of a few cells and d raw them in Data Table 1. Id entify and label im portant structures on one of the cells in your d raw ing. Return the slid e to the d esignated area and repeat the above proced ures for 2 ad d itional bacterial slid es. Proceed to Part B D ata Table 1 Slide N ame: Slide N ame: Slide N ame: D r a w i n g 2 Comparing Cells Lab Part B. Examining Eukaryotic Cells – Plant Cells 1. Obtain a glass slid e, a coverslip, and a forceps. 2. Using the d ropping pipet, place a d rop of w ater in the center of your clean glass slid e. 3. Using the forceps, rem ove a leaf from the supplied w ater plant and place the leaf on the d rop of w ater on the slid e – BOTTON SIDE OF LEAF UP. Make sure that the leaf is flat and not fold ed . 4. Carefully place a coverslip over leaf, and press d ow n gently until the leaf is perfectly flat, no airbubbles. 5. Place the slid e on the stage of the m icroscope w ith the leaf d irectly over the opening in the stage. 6. Using the 4x (low -pow er) objective lens, locate the leaf by turning the coarse ad justm ent knob until the leaf com es into focus. 7. Sw itch to the 10x (m ed -pow er). Use the fine focus knob to ad just your view . 8. Sw itch to the 40x (high-pow er) objective lens. Use the fine focus knob to ad just your view . At this m agnification sm all ad justm ents of the fine focus knob w ill allow you to w itness the 3-d im ensionality of the leaf, as the leaf is com posed of m any layers of cells. You can focus on as m any as three d ifferent layers of cells, by sim ply scrolling ‘ up’ or ‘ d ow n’ w ith the fine focus ad justm ent. 9. Closely observe the cells of the leaf. Com plete Data Table 2 by d raw ing a section of plant cells and labeling all im portant structures/ organelles you see. 10. When your lab group has finished using your leaf slid e, rem ove the coverslip, throw aw ay the leaf, rinse and pat-d ry both your slid e and coverslip – then return your slid e and coverslip to w here they belong. D ata Table 2 D raw three cells in a single row at 400x - label each structure/ organelle you can see for one of the cells - Flow Chart: Additional D ata 1. Thoroughly d escribe these plant cells and their pattern w ithin a leaf. 3 Comparing Cells Lab Part C. Examining Eukaryotic Cells – Human Cheek Cells 1. Using a m icro d ropping pipet, place a very sm all Flow Chart d rop of w ater in the center of a clean glass slid e. 2. Using the end of a toothpick, gently scrape the insid e of your cheek. CAUTION : Do not use force when scraping the inside of your cheek. The end of the toothpick has m any cheek cells stuck to it, though you m ay see nothing. 3. Stir the w ater on the slid e w ith the end of the toothpick to m ix the cheek cells w ith the w ater. (See Figure 2).D ISPOSE of the toothpick in the trashcan. 4. Put one small d rop of methylene blue stain on top of the d rop of w ater containing the cheek cells.CAUTION : methylene blue stainins hands and clothing. 5. Wait one m inute, and then carefully place a coverslip over the stained cheek cells. 6. To rem ove the stain from und er the coverslip and replace it w ith clear w ater, place a piece of paper tow el at the ed ge of one sid e of the coverslip. Then place a very sm all d rop of w ater at the ed ge of the coverslip on the opposite sid e. (See Figure 3). The paper tow el w ill absorb the stained w ater und er the coverslip. As the stain is rem oved , the clear w ater next to the coverslip on the opposite sid e w ill be d raw n u nd er the coverslip. Discard the paper tow el after it has absorbed the stained w ater. 7. Place the slid e on the stage of the m icroscope w ith the center of the coverslip d irectly over the opening in the stage. 8. Using the low -pow er objective lens, locate the region of the slid e w ith a fairly high concentration of cheek cells. N ote: Y ou may need to reduce the amount of light coming through the slide in order to see the cells more clearly. A djust the diaphragm as necessary. 9. Sw itch to the m ed ium pow er, and then the high pow er objective lens. 10. Observe a few cheek cells at 400x. Select tw o d ifferent looking cheek cells. Draw each cell in Data Table 3. Label all im portant structures/ organelles you see. 11. Carefully rinse, d ry, and return your coverslip and slid e. Figure 2 Figure 3 4 Comparing Cells Lab D ata Table 3 D raw an enlarged view of one cheek cell - label each structure/ organelle you can see - Additional D ata Thoroughly d escribe this anim al cell. D raw an enlarged view of another cheek cell - label each structure/ organelle you can see - Additional D ata Thoroughly d escribe this anim al cell. Analysis and Conclusion Questions Directions: Answ er the follow ing questions using complete sentences. 1. Consid er all 3 cell types observed in this lab. Based on your observations, d escribe the d ifferences you observed betw een prokaryotic (bacteria) and eukaryotic (plant and anim al) cells. 2. Consid er the eukaryotic cells you observed in this lab. Based on your observations, d escribe the sim ilarities you observed betw een plant and anim al cells. 5 Comparing Cells Lab 3. Consid er the eukaryotic cells you observed in this lab. If you w ere given a slid e containing living cells of an unknow n organism , how w ould you id entify the cells as either plant or anim al? *note: be very thorough and include in your answer a full description of every structure, and characteristic, one would expect to be able to use to differentiate between plant and animal cells. 4. Why is it an ad vantage to use a w et-m ount preparation instead of a d ry-mount preparation in the stud y of living cells? 5. Why are stains often used w hen observing cells und er the m icroscope? 6. Explain w hy you think an oak tree leaf w as not chosen for the plant cell part of this lab. 6 Comparing Cells Lab