CELL OBSERVATION LAB
COMPARE PROKARYOTIC CELLS WITH EUKARYOTIC CELLS
Objective: To compare features of prokaryotic and eukaryotic cells. To compare features with animal and plant cells.
Background Questions:
Neatly write your responses to the following questions in paragraph form.
1. How has technology enabled scientists to advance their understanding of cells?
2. Who were the early “pioneers” of cellular discoveries? What is the theory that they helped to develop?
3. What are the two basic categories that all cells can be organized into? What differences should you be able to observe through your microscope in this class?
4. Plant and animal cells are two types of eukaryotic cells. What structures should you be able to observe in a plant cell, but not an animal cell?
Materials:
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Slide, coverslip
Microscope
Water Dropper bottle
Iodine dropper bottle
Yeast
Yogurt
Aquatic plant
Onion
Toothpick
Pond water
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Procedure:
Fungi: YEAST
1. Scoop ONE grain of yeast onto a slide. Add a drop of water and gently apply the coverslip.
2. View the specimen under low power first and bring into focus. Move the slide to an area where there is more open space, and it is NOT cloudy. Look for tiny, bubble-like cells.
3. View under medium and then high. Sketch the yeast cells under the best power. Change the diaphragm to make the light dimmer and look for tiny structures inside the yeast cells. Record observations and draw accurate sketches to scale. Use arrows in your sketches to identify the cells and their organelles.
4. Rinse your slide and coverslip well, and pat dry.
Bacteria: YOGURT
1. Use a toothpick and smear a thin layer of yogurt in the center of the slide. Add a drop of water and carefully apply the cover slip.
2. View the specimen under low power first and bring into focus. Move the slide to an area where it is NOT cloudy and focus on a space between the grayish blobs of yogurt.
3. View the yogurt cells under medium and high power. Look for really tiny, dust-like cells. This yogurt contains more than 5 different types of bacteria; so, the cells will be different shapes and sizes. Sketch and label the prokaryotes under the best power—try to point out the 5 types. Point out the gray yogurt blobs.
4. Rinse your slide and coverslip well, and pat dry.
Protists: MILL CREEK
1. Using a pipette, place a drop of pond water in the center of a clean slide. Try to include some of the sediment—most of the protozoa are there. Carefully add a cover slip.
2. View the specimen under low and medium power and focus on an area around the sediment. While looking through the microscope, slowly move the slide and look for any movement! Sketch and label the organisms (including algae if present) under the best power. Find a second location on your slide with organisms, sketch and label.
3. Rinse your slide and coverslip to clean and pat dry.
Plant: ONION
1. Place a drop of Iodine in the middle of a slide.
2. As shown in class, gently fold the onion with the natural curve and peel the skin from the inside layer of the onion. Place the onion skin flat on the slide in the iodine. It is important that you do not have chunks of onion! Discard remainder of onion.
3. Add a second drop of Iodine on top of the onion skin and carefully add a cover slip. Avoid air bubbles. Wait for 2 minutes.
4. Focus on low. Then switch to medium and high power. Under the best power, draw and label the cell wall, cell membrane, cytoplasm and nucleus (nucleoli?). Record additional observations.
5. Discard onion skin, rinse your slide and coverslip to clean and pat dry.
Plant: ELODEA
1. Place a drop of iodine in the middle of the slide
2. Tear off a single leaf near the top of the sprig of elodea. (gently slide the leaf between your fingers to make sure it is a single leaf)
3. Place the elodea leaf in the drop of iodine on the slide, add a second drop on top of the leaf and carefully add a coverslip.
4. Focus on low power. Then change to medium and focus. Notice how when you change the focus, you can see some cells clearly, but not others? Elodea has two layers of cells, and you can only focus on one layer at a time.
5. Under the best power, draw and label the cell wall, cell membrane, chloroplasts and vacuole. Do you see any movement? You may not be able to find the nucleus.
6. Discard elodea leaf, rinse your slide and coverslip to clean and pat dry.
Animal: CHEEK CELLS
1. Place a drop of iodine in the middle of a slide.
2. As shown in class, gently scrape the inside of your cheek (inside of your mouth). Do NOT dig into your mouth! There should not be chunks of skin or blood!
3. Stir the toothpick in the iodine on the slide.
4. Carefully add a cover slip and avoid air bubbles.
5. On low power, scan the slide for tiny yellow specks. Focus on these specks; they are your cells.
6. View the cells on medium and high power. Cheek cells are like sheets of tissue paper; they wrinkle and fold easily. Move the slide to find cells that are flat and not overlapping.
7. Under the best power, draw and label cell membrane, nucleus and cytoplasm.
8. Rinse your slide and coverslip to clean and pat dry.
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Cell Observation Lab Name ______Date ______Block _____
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Conclusion Questions:
Neatly write your responses to the following questions in complete sentences.
1. What observations did you make today that supported the statements of the Cell Theory?
2. Which cells did you observe that were prokaryotic? Which cells were eukaryotic? Based on your observations, how was viewing the prokaryotic cells different from viewing the eukaryotic cells? What challenges did you experience?
3. Which cells did you observe that were plant cells? Which were animal cells? What differences were you able to observe?
4. What was the purpose of the iodine when you observed the onion and cheek cells? Why didn’t you need iodine to view the elodea cells?
5. Describe some of the organisms you observed in the pond water. Were these prokaryotes or eukaryotes? How can you tell?
6. As technology continues to advance, scientists will learn more and more about cells and how they function. Research how microscope technology today is helping advance science. Cite your sources using Noodle Tools.
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