Comparing Cell Structures and Organelles

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Megan Clark
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1 Introduction A cell is the smallest unit of life. There are two main classifications for cells and organisms: prokaryotic and eukaryotic. Prokaryotic organisms are comprised of single cells that lack a membrane-bound nucleus and usually lack membrane- bound organelles. Cells containing a membrane-bound nucleus and membranebound organelles are classified as eukaryotes. The quantity and types of cell structures and organelles in cells depend on the function of the cell. Not all bacteria, plant and animal cells look or function the same way. The cell models used in this lab are just one example of bacteria, plant, and animal cells. Essential Question How can we explain the function and diversity of cell structures and organelles? Materials: microscopes slides coverslips toothpicks Elodea or Egeria najas cell components table post-it notes onion Spirillum volutans prepared slide forceps absorbent paper student data sheet or science notebook lens paper micrographs resource materials cell scenarios cell case studies dropper bottles of methylene blue, iodine, and distilled water Procedure 1. Prior to conducting microscopic investigations complete the Expected column on the Comparing Cell Structures and Organelles Cell Components Table. 2. Use a microscope to observe a representative slide of the following cell types: bacteria, plant, and animal. Record detailed descriptions and draw all observations on the student data sheet provided or in a science notebook. Be very descriptive and detailed in documenting observations as this qualitative data will be used in step four. Pay close attention to size, shape, structures, and boundaries. Write so that the reader can visualize the structures observed. Follow all directions carefully in steps 1A 1D. A. Observe a prepared slide of a Spirillum volutans. Sketch and describe observations. Slide Preparation Not applicable as the slide for Spirillum volutans is a prepared slide Slide Observation - Using the 4X scanning objective, bring the bacteria into focus; switch to the 10X low power objective to locate and focus the specimen. Sketch and describe observations. Switch to the 40X high dry objective. Sketch and describe observations. Compare the 10X and 40X sketches. Identify and label any structures observed. Predict the function of each structure being observed and how it may interrelate to other structures in the cell. B. Prepare and observe stained cells using the skin of an onion. Sketch and describe observations. Page 1 of 10

2 Slide Preparation Use forceps to remove the thin membrane of the surface layer of onion and place it on a clean slide making sure the membrane is flat. Carefully place a drop of iodine or methylene blue on the membrane to stain the transparent cells. Wait 2 minutes, and then carefully place a coverslip over the stained membrane. To place the coverslip, hold it at a right angle to the slide and gently lower it into place. This will help to avoid air bubbles. Remove excess stain with absorbent paper placed at the edge of the coverslip. Slide Observation - Using the 4X scanning objective, bring plant tissue into focus; switch to the 10X low power objective to locate and focus the specimen. Sketch and describe observations. Switch to the 40X high dry objective. Sketch and describe observations. Compare the 10X and 40X sketches. Identify and label any structures observed. Predict the function of each structure being observed and how it may interrelate to other structures in the cell. C. Prepare and observe a wet mount using a leaf of elodea. Sketch and describe observations. Slide Preparation - Obtain one Elodea or Egeria najas leaf. Place the leaf onto a clean slide. Carefully place a drop of water on the leaf. Hold a coverslip at a right angle to the slide and gently lower it into place. Remove excess water with absorbent paper placed at the edge of the coverslip. Slide Observation - Using the 4X scanning objective, bring plant tissue into focus; switch to the 10X low power objective to locate and focus the specimen. Make sure to move the stage to see the edges of the leaf as well as the interior tissue. Sketch and describe observations. Switch to the 40X high dry objective. Again, examine the edges of the leaf as well as the interior. Sketch and describe observations. Compare the 10X and 40X sketches. Identify and label any structures observed. Predict the function of each structure being observed and how it may interrelate to other structures in the cell. D. Prepare and observe stained cheek cells. Sketch and describe observations. Slide Preparation - Place a drop of methylene blue in the center of a clean slide. Use the flat side of a toothpick to gently scrape the inside of your cheek. Roll the toothpick around in the drop of stain until the wet area is about the size of a dime. Dispose of the toothpick. Carefully place a coverslip at a right angle to the slide and gently lower it into place. Remove excess stain with absorbent paper placed at the edge of the coverslip. Slide Observation - Using the 4X scanning objective, locate a few cheek cells. Reduce the amount of light to better view the cells if needed. Switch to the 10X low power objective, focus on a few cheek cells. Sketch and describe observations. Predict the function of each structure being observed and how it may interrelate to other structures in the cell. Compare and contrast slides from other students. When done, place cheek cell slides in a disinfectant beaker. 3. Share findings and drawings with group members and revise or enhance journal/data entries. Complete the Cell Components Table. 4. Using an electronic device or post-it note tweet, send a tweet to inform your teacher of your most notable discovery. Be as descriptive as possible. Page 2 of 10

3 5. Compare and contrast cell structures in bacteria, plant, and animal cells: A. Review data from microscope observations in lab. Construct a list of cell structures observed in lab and record those structures in the Venn Diagram provided using a green colored pencil. B. Use micrographs and visual images to identify cell structures and organelles not observed in lab. Revise the Venn diagram to include the additional structures and organelles obtained from the micrographs and visual images. Just as Robert Hooke and some of the early cell scientists were limited by technology in what they could visualize, so are scientists of today. While current compound light microscopes produce more detailed images than those in the 1600 s, they have limitations. Electron microscopes can reveal details and structures that are not visible with the use of a compound light microscope. A micrograph is a photograph or digital image taken through a microscope. The micrographs used in this activity were taken using a transmission electron microscope (TEM). 6. Conduct research using a variety of resources on the diversity and function of cell structures and organelles. See a suggested list of resources below. A minimum of three resources is required. Record detailed notes on the functions and interrelationships of assigned cell structures and organelles. Use this information to design a cell machine. Be sure to explain its function in detail for teacher approval before completing step seven in this procedure. Suggested resources - These are just a few possible resources. Use other valid resources to complete this activity: Textbook Primary documents Illustrations Science Journals o Miniseries: Illustrating the Machinery of Life Eukaryotic Cell Panorama, Biochemistry and Molecular Biology Education, Vol. 39, No. 2, pp , 2011, Hudson Alpha s icell (download from itunes) Compose a letter to an early scientist (Robert Hooke, Anton van Leewenhoek, Matthias Schleiden, Theodor Schwann, Rudolph Virchow) to describe the cell machine s function and interrelationships Page 3 of 10

4 with other cell structures, organelles, and cells. Include an account of how microscopy has advanced over time. 8. Work in pairs to complete cell scenarios. Share and compare with other pairs. 9. Become a doctor for a day. Analyze an assigned case study and write a diagnosis based on a knowledge of cell structures and organelles. Include a detailed description of evidence that led to the diagnosis. Page 4 of 10

5 Excerpts from the writings of Anton van Leeuwenhoek ( 160 ) XVI. A Letter from Mr. Anthony van Leeuwenhoek, F.R.S. containing some further microscopial observations on the Animalcula found upon Duckwwe. &c. June 28, 1713 In my letter of the 4 th of November, 1704, I took notice of the wonderful figure of an Animalculum that was fix d in a little scabboard or sheath, fastened to some of the small green weeds that are found in ditches full of water. I view d one of these Animalcula for a good while together, till I was almost weary, and observed several times one after another, that when the Animalculum thrusts its body out of the sheath, or case, and that the wheellike or indented particles mov d in a circle at the same time, out of a clear and transparent place. A little round particle appeared, which without nice viewing, could hardly be perceived; which particle growing bigger, moved with great swiftness, as it were about its own axis, and continued without any alteration in its place, till the animalculum had drawn part of its body back into its sheath. From this discovery we may conclude, that since this kind of Animalculum cannot move from place to place in the water, nor consequently seek its food as other creatures do, (that are endued with motion) being fastened by the tail or other parts of the body, it must necessarily be provided with such instruments as are fit to move the water, and by that means come at the particles floating in it, which serve for the nourishment, increase and defense of its body Page 5 of 10

6 Student Data Sheet NAME DATE Microscopic Investigations of Cells - Notable Characteristics when describing cells and cell structures: Size, shape, position, volume, quantity, boundaries IA. Cell type (Bacteria, plant, or animal): _ Scientific Name: Detailed description of structures, boundaries, and organelles IB. Cell type (Bacteria, plant, or animal): _ Scientific Name: Detailed description of structures, boundaries, and organelles Page 6 of 10

7 IC. Cell type (Bacteria, plant, or animal): _ Scientific Name: Detailed description of structures, boundaries, and organelles ID. Cell type (Bacteria, plant, or animal): _ Scientific Name: Detailed description of structures, boundaries, and organelles Page 7 of 10

8 NAME DATE Before conducting microscopic observations, indicate the structures one should find when viewing cells with a compound light microscope by marking yes in the Expected column. As cells are observed with the microscope, record a yes or no under the Observed column below: Structure cell membrane cell wall cytoplasm flagella cytoskeleton nucleus chloroplast golgi body ribosomes Cell Components Table Bacteria Plant Expected Observed Expected Observed Animal Expected Observed 1. Explain why all of the expected structures were not observable. 2. How do scientists know that other cell structures exist? 3. The onion is a plant but no chloroplasts were observable. Why might this be? Page 8 of 10

9 VENN Diagram NAME DATE Complete the Venn diagram to compare and contrast cell components. Hint: Make a numbered list for components and write the number by each component into the diagram. Use green pencil for components observed in lab and a regular pencil for components obtained from micrographs. A minimum of 20 components is required. Animal Cell Bacteria Cell Plant Cell Page 9 of 10

10 Cell Scenarios NAME DATE It is important to remember that the cell illustrations we see in textbooks are a generalized model and do not represent all cell types and structures. The scenarios below are designed for review of cell components and their function. Note that some cells have more of certain structures than others based on cell function. 1. Some eukaryotic cells have a need to move around or require energy to produce movement. Examples include sperm cells and muscle cells. Because these cells need to turn food, usually sugar, into energy, what organelle would you expect to be VERY plentiful in these cells? 2. Plant cells contain chlorophyll to turn light energy into chemical energy. Chlorophyll, in plant cells, is stored in an organelle that is VERY plentiful in leaf cells. What are these organelles? 3. What cells, other than plant cells, contain chlorophyll? 4. A plant s need for water can be indicated by whether it is wilted or standing tall. What organelle in plants is designed to store water and nutrients? 5. White blood cells are especially active when a person is sick because they fight off infections due to the invasion of bacteria or viruses. Once they locate the invader, they engulf it. What organelle would be plentiful in white blood cells? 6. Two proteins are required in muscle cells for them to work. So that means muscle cells need a plentiful supply of organelles that make proteins. Sometimes these organelles freely float or can be found attached to another organelle. What organelles would you expect to be plentiful in protein rich muscle cells? To what organelle are these protein making organelles often found attached? 7. Red blood cells are made in the marrow of bones in mammals and only live a short time (about 3 months). Then they are recycled. Mammalian red blood cells have no real control center needed in order to reproduce. What organelle is missing from red blood cells in mammalians? Page 10 of 10

CELL LAB OBJECTIVES INTRODUCTION: CELL UNIT. After completing this lab you should be able to:

CELL LAB OBJECTIVES INTRODUCTION: CELL UNIT. After completing this lab you should be able to: AP BIOLOGY CELL UNIT ACTIVITY #3 NAME DATE HOUR CELL LAB OBJECTIVES After completing this lab you should be able to: 1. Compare and contrast prokaryotic and eukaryotic cells, 2. Prepare wet mount slides