Purpose (1 point) Investigate differences to cell size and shape across various kingdoms

Transcription

1 Living Cells Lab 61 points total As will be seen through this lab, there is no such thing as a typical cell. Though both prokaryotic and eukaryotic cells are often shown as general cells (p. 206), rarely do they actually look anything like it. During this lab, you will have an opportunity to observe a variety of cells from a wide range of organisms, representing multiple domains and kingdoms. In addition to observing differences to size and shape, a variety of techniques will be used to attempt to locate as many organelles and internal structures as possible. Elodea canadensis is an aquatic plant native to North America. It is often used in aquariums as a decorative plant. The plant lives entirely underwater and may grow in a wide range of conditions. It may even continue to grow unrooted! Although Elodea plays an important role within native ecosystems, it has been introduced around the world and is now considered a problem as an invasive species. Saccharomyces cerevisiae is a species of yeast. It is part of the fungi kingdom, and exists as a unicellular organism. It reproduces by budding, and is commonly referred to generally as budding yeast. S.cerevisiae is the most useful yeast (in terms of human activities), involved in food production like baking, brewing, and winemaking for centuries. It is also one of the most extensively studied organisms in molecular and cellular biology. A large number of human proteins were discovered by studying similar versions in S.cerevisiae. Kingdom Protista, the protists, are a very diverse group of organisms, loosely grouped together based on how they get food/energy, ways they move, and how they reproduce. As a whole, they do not share a large number of characteristics in common except that they all have relatively simple organization. Protists may be unicellular, or multicellular without specialized tissues. Though no longer used for classification purposes, they are informally divided into one of three groups based on similarities: animal-like, plant-like, and fungus-like. The cheek cells of Homo sapiens are an example of epithelial tissue, one of the four types in animals (others are connective, muscle, and nervous). When seen as a tissue, human cheek cells are much layered. As the area is subject to constant abrasions, it allows for frequent sloughing off of the topmost layers, while still protecting the other tissues that underlie them. This layering and easy removal of cells is also what allows cells to be removed for observation (like in lab) or to obtain DNA (for medical/genetics procedures). Purpose (1 point) Investigate differences to cell size and shape across various kingdoms Hypothesis None necessary for this lab Key Terms Field of View (FOV) Diameter of the circle of light looking through a microscope Depth of Field (DOF) Thickness of the layer of material in focus looking through the microscope

2 Materials Blank Slide Coverslip Beaker of Water Plastic Pipette (Each sample has its own) Toothpicks Iodine Methylene blue Methyl Cellulose (optional) Protist Identification Guide Colored Pencils Elodea leaf Yeast Cells Human Cheek Cells Prepared Human Tissue Protists (from Pond Water ) Amoeba (Type of protist, but separate) Safety Treat microscopes with respect they are expensive Once placed on the table, microscopes should stay in that place You move to the scope, the scope does not move to you Use caution with iodine solution as it is toxic Return or dispose of all materials properly (general - do not write) Wipe down table once materials are returned (general do not write) Wash hands thoroughly after completing the experiment (general do not write) Prelab (8 points) Write out the questions entirely & use complete sentences for your answers 1. How are the concepts of magnification and field of view related? 2. Identify the function of the diaphragm. Explain why it may be useful to adjust it. 3. Use p in your textbook to identify the three main types of movement that protists utilize to move around their environment. Briefly describe each one. 4. Use p in your textbook to contrast how amoeba and ciliates differ in the ways they obtain food? 5. Based on your cell charts, what structures would you expect to be present in the Elodea cells that would be absent in the human cheek cells? 6. Looking back at the Estimating Size Lab, clearly indicate the diameter of the field of view for each objective lens in both millimeters (mm) and micrometers (μm).

3 Procedure (40 points minimum) All images must be drawn using color where appropriate Sample Data Collection organization shown to the right does not accurately show scale or necessary information read procedure carefully Part 1 Elodea Plant Cells 1. Create a wet-mount slide using one drop of water and ONE LEAF of Elodea 2. Use a ruler to determine & record the length and width of the leaf that you are using (It will be needed later) 3. Observe using LOW POWER Record at least one observation 4. Observe using MID POWER: Draw the image exactly as you see it in the microscope Write at least ONE observation about what you see 5. Repeat step 4 using HIGH POWER: LABEL the Cell Wall, Cytoplasm, and Chloroplast on your image Count & record the average number of chloroplasts per cell 6. Choose one objective lens to determine the size of a single Elodea cell (provide both length and width) Part 2 S.cerevisiae Yeast Cells 1. Repeat steps 1-5 from Part 1 using S.cerebisiae from the prepared culture Do not label any cell structures on HIGH POWER (they are not easily visible) 2. Choose one objective lens to determine the size of a single S.cerevisiae cell Part 3 S.cerevisiae Yeast Cells with Methylene Blue 3. Create a wet-mount slide using one drop of yeast culture AND one drop of methylene blue Note Methylene blue may be used to determine survival of yeast cells. Cells that are alive are able to take methylene blue in and break it down, leaving the cell remaining normal in color. Dead yeast cells are unable to break down the stain as it enters the cell and are turned blue. 4. Observe using LOW POWER and focus on an area with a large number of cells 5. Observe using MID or HIGH POWER Accurately draw the image exactly as you see it in the microscope 6. Determine the percent of yeast cells in your field of view that are living Part 4 Human Cheek Cells with Iodine 1. Create a wet-mount slide using one drop of IODINE as your liquid 2. Carefully scrape the inside of your cheek with the rounded end of your toothpick 3. Rub the end of the toothpick around in the drop of iodine 4. Repeat steps 3-5 from Part 1 On HIGH POWER, label the Cell Membrane, Cytoplasm, and Nucleus on your image 5. Choose one objective lens to determine the size of a single human cheek cell

4 Part 5 Human Cheek Cells with Methylene Blue 1. Repeat the procedure from Part 4, using one drop of methylene blue instead of iodine NOTE The topmost layers of your cheek cells (the ones you can easily scrape off) are no longer living. Therefore, unlike the yeast cells, where numbers of living versus dead can be compared by observing which cells turn blue, all cheek cells should take methylene blue in and remain blue in color. Part 6 Prepared Human Tissue 1. Obtain a prepared slide of your choosing 2. Record the name of the type of sample 3. Repeat steps 3-6 from Part 1 Do not label any cell structures on HIGH POWER 4. Repeat steps 1-3 for at least 3 different tissue samples Part 7 Protists Amoeba (This may take a little time ) 1. Create a wet-mount slide using 1-2 drops from the Amoeba container 2. Observe using LOW POWER until you get an amoeba in focus 3. Observe using MID POWER: Sketch the amoeba exactly as you see it in the microscope 6. Wait about one minute, sketch the amoeba again (include an arrow showing direction of movement) 7. Wait another minute, accurately draw the amoeba a third time 4. Choose one objective lens to determine the size of an amoeba Part 8 Protists 1. Create a wet-mount slide using 1-2 drops from the Mixed Protists containers 2. Observe using LOW POWER until protists are in focus 3. Observe using MID POWER and/or HIGH POWER: o Use the Protist Identification Guide to IDENTIFY the species of protist observed o Accurately draw a species of protist exactly as you see it Write the lens magnification that your drawing was done at Record at least TWO observations (Movement, Unique Characteristics, Interactions with Others, etc) 4. Choose one objective lens to determine the size of the protist 5. Repeat steps 3 & 4 to observe at least SIX DIFFERENT SPECIES of protists for possible full credit NOTE If protists are moving too quickly to make detailed observations, you may use one drop of methyl cellulose along with one drop of pond water. Methyl cellulose is very viscous and should slow the movement of the organisms substantially. **You will need to create new slides throughout class as pond water evaporates**

5 Conclusion & Analysis (12 points) DO NOT WRITE IN NOTEBOOK UNTIL COMPLETED WITH THE LAB Must be answered in your notebook using complete sentences Answers Only, don t write questions 1. Contrast the size of the cells from each of the four kingdoms you observed. Place them in order from smallest to largest. 2. Describe the movement of the amoeba. If you were able to observe the amoeba consuming something, describe the process of phagocytosis as observed through the microscope. 3. After carefully observing Volvox, describe what makes it different or unique from other unicellular protists observed? 4. Compare the staining of the human cheek cells using iodine and methylene blue. Identify differences you noticed between the two. Was it easier to identify structures with one? Were you able to see additional structures with one? If so, describe what was seen and what it may be. 5. Keeping in mind that an Elodea leaf is three cells thick, use your size estimate for one cell to determine how many cells would be in the single leaf you observed. How many chloroplasts were in one leaf cell? Using these two estimates, predict how many chloroplasts would be in the Elodea to the right. Show all work. 6. Euglena is a protist that is able to perform photosynthesis. They are producers, and contain chloroplasts - just like plants. They are motile - just like animals. Although they don t have eyes, they have an eyespot that contains specialized cells sensitive to light. a. What would be the purpose of this structure (eyespot) in Euglena? b. How could this structure be used to help collect Euglena in a pond for research?