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1 Science 9 Mitosis in Whitefish Cells Lab Instructions: Put your name, block, date, and lab report title at the top of your lab report. Then read the Problem and Background Information. Problem. What is the frequency of each event in the cell cycle? Background information. Cells at different phases in the cell cycle can be observed by looking at a sample of cells. Most cells will be in interphase, but a few cells will be in other phases. The cells in interphase are actively performing their regular duties, while the cells that are undergoing mitosis are reproducing to make new cells. Hypothesis. Copy and complete the following hypothesis on your lab report. Remember to use a pen to do the writing in your lab report. “If a sample of whitefish cells are observed under the microscope, then…” Predictions. Copy and complete the table below. Remember to use a pencil and a ruler to draw the table lines. Fill out the table to predict the percentage of the total number of cells that will be at each phase of the cell cycle. Make sure your percentages add up to 100 %. Table 1. Predictions of percentages of cells that will be at each phase of the cell cycle. Phase Interphase Prophase Metaphase Anaphase Telophase Cytokinesis Total Predicted % of cells that 100 will be at that phase Materials. With your lab partner, gather the following materials, and set up at one of the power outlets. 1 “Mitosis in whitefish” slide 1 microscope 1 calculator 1 textbook 1 lined piece of paper per person 1 unlined piece of paper per person 1 pencil per person 1 pen per person Procedure. 1. Plug in and turn on your microscope. 2. Make sure the stage is all the way to the bottom. Use the coarse focus knob to move the stage. 3. Place the slide on the stage, and secure it beneath the clip. Try to position one of the pink dots on the slide over the centre of the light. 4. Make sure that you are using the lowest power objective lens. 2 5. If you wear glasses, remove them when you look into the microscope. Peer into the eyepiece. If you can’t see a pink blur, slowly move the slide around until you can see one of the pink dots. 6. Use the coarse focus knob to slowly raise the stage to focus the cells. Make sure you are peering into the eyepiece the entire time so that you can see when it comes into focus. 7. Once the cells are in focus, position the pink circle so that it is in the centre of your viewing area. Make sure you are looking into the eyepiece as you reposition your slide. 8. Switch the objective lens to the next highest power. 9. Use the coarse focus knob and then the fine focus knob to bring the cells into focus. 10. Re-position the slide so that the pink dot is in the very centre of the viewing area. 11. Switch to the next highest power objective lens. As you are turning the nosepiece, watch to make sure the lens does not touch the slide. 12. Focus the cells using only the fine focus knob. 13. Most of the cells you see are in interphase. Their nuclei are all pink, and the chromosomes are not visible. 14. The cells that are undergoing mitosis have purple chromosomes that are visible. Review the microscope images on pp. 156-158 of your textbook to try to match the mitotic cells you see under your microscope to their correct stages of mitosis. 15. The cells undergoing cytokinesis have two distinct cells side-by-side. Try to find a cell undergoing cytokinesis. 16. Make an Observations section in your lab report. Copy Table 2 below into your Observations section. Note: For steps 17-20 below, you might have to make some educated guesses as to which phase of mitosis you see in each cell. It will be helpful to look at all the mitotic cells first and compare them in order to decide which cells are in which phases. 17. Count how many cells are in prophase. Hint: cells in prophase have visible chromosomes clumped together (not lined up) in the centre of the nucleus. Write down this number in the appropriate cell of Table 2. 18. Count how many cells are in metaphase. Hint: cells in metaphase have their chromosomes lined up in the centre of the nucleus. Write down this number in the appropriate cell of Table 2. 19. Count how many cells are in anaphase. Hint: cells in anaphase have their chromosomes starting to move away from each other. Write down this number in the appropriate cell of Table 2. 20. Count how many cells are in telophase. Hint: cells in telophase have their chromosomes at opposite poles of the cell (farther apart than the chromosomes in anaphase). Write down this number in the appropriate cell of Table 2. 21. Count how many cells are in cytokinesis. Hint: cells in cytokinesis have 2 distinct cells side-by-side. Write down this number in the appropriate cell of Table 2. 22. Count how many cells are across the diameter of your viewing area. Imagine a line running across the centre of your viewing area. How many cells fall on that line? Double-count just to be sure. 23. Now use the formula for area of a circle (A = πr2) to get an estimate for the total number of cells in your viewing area. Remember to divide diameter by 2 to get radius! Write down your answer in the appropriate cell of Table 2. 24. To find the number of cells in interphase subtract the total of all the other cells you have counted thus far (prophase + metaphase + anaphase + telophase + cytokenisis) from the total number of cells you found in step 23 above. Write down your answer the appropriate cell in Table 2. Table 2 should now be complete. 25. Choose one of the cells you can see that is undergoing mitosis. Draw this cell on your unlined piece of paper. Be sure to follow the “Things to Remember when Making a Scientific Drawing”. Because you are only drawing one cell and not the entire field of view, you will not need to include the scale of this drawing. 3 26. Put away your slide and your microscope as you found them. 27. Return to your seat to work on your lab report questions. Observations. Table 2. Frequency of whitefish cells undergoing stages of the cell cycle. Cell cycle Interphase Prophase Metaphase Anaphase Telophase Cytokinesis Total phase Number of cells visible Questions. Make a Questions section in your lab report below your Observations. Remember to answer all questions in complete sentences, include the question in the answer, and write in pen. 1. Why are the chromosomes not visible for cells that are in interphase? 2. a) Show all your work for how you calculated the total number of cells in your viewing area (procedure step 23). b) Show all your work for how you calculated the number of cells in interphase. 3. Why are there so many more cells in interphase than in the other phases? 4. Calculate the percentage of the number of cells in each phase of the cell cycle. Reminder: Show all your work. 5. Display your results for question 4 in a table (call it Table 3, and give it an appropriate title). Hint: this table will look very similar (but not identical) to Table 1. 6. Were your predictions correct? Explain by comparing the percentages in Table 1 to the percentages in Table 3. 7. Compare your results in Table 3 to another group’s results. Are your results different? If so, what might be some of the reasons for the differences? 8. Suppose the cell cycle for whitefish cells lasts 16 hours. Use your percentages in Table 3 to calculate how long each phase of the cell cycle will last. Show all your work. 9. Are whitefish cells animal cells or plant cells? State two ways you know this answer is correct. Conclusion. Write a proper scientific conclusion for this lab.
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