Unit A Reproduction

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6. Rotate the nosepiece to the low-power objective lens, and remove the slide. 7. Place the whitefish embryo slide on the stage. Focus the image using the coarse-adjustment knob. Use the photographs in Figure 2 to help you. 8. Once you have located cells that are dividing, repeat steps 3, 4, and 5. 9. Compare your diagrams with your classmates’ drawings. Explain to each other any stages that one of you included but the other did not. Try to find any stages or structures that you could not locate on your own slide on your classmates’ slides. 10. Rotate the low-power objective lens into place, and remove your whitefish slide. A. prophase B. metaphase C. anaphase D. telophase Analysis (a) What differences did you observe between plant and animal cell division? Use a table to compare the appearance of the dividing plant cells with the appearance of the dividing animal cells. (b) Did your observations support your prediction? Explain. (c) Were any stages of mitosis easier or more difficult to identify? Explain why. (d) Which cell structures were the easiest to locate? Evaluation (e) (f) (g) (h) Why did you use plant root tips and animal embryos to view cell division? Explain why the cells you viewed did not continue to divide. How are the differences in cell division in plant and animal cells related to the differences in the structures of plant and animal cells? List one feature of each stage of mitosis that you observed that helped you identify the stage. Synthesis (i) Where else in plants and animals would you expect to observe rapidly dividing cells? (j) Why do biologists use dividing cells to determine the number of chromosomes in an organism? (k) How can knowing the stages of mitosis help scientists? (l) If a cell has 12 chromosomes, how many chromosomes will each daughter cell contain? E. daughter cells Figure 2 Cell division in a whitefish embryo (magnification: 450X) NEL Chapter 2 Investigation 65
2B Investigation Determining the Rate of Cell Division in Plant and Animal Cells An understanding of why and how cells undergo cell division is important to many fields of science. One of these fields is agriculture. A great deal of money is spent on chemicals to increase plant growth. Scientists can calculate the efficiency of these chemicals by studying rates of cell division. Question Can you tell how fast an organism is growing by looking at its cells? Hypothesis Write a hypothesis about how you can tell the rate at which an organism is growing by observing prepared slides. Prediction Predict what you will observe in the cells of an organism when it is growing. Experimental Design In Investigation 2A, you observed cell division and compared the process of mitosis in plant and animal cells. In Part 1 of this investigation, you will examine prepared slides of plant and animal cells under a microscope and determine the percentage of cells that are dividing. In Part 2, you will determine the rate of cell division by making a cell-division clock. Materials • microscope • prepared slide of an onion root tip • prepared slide of a whitefish embryo LEARNING TIP If you need to review how to write a hypothesis, refer to Chapter 1. INQUIRY SKILLS Questioning Hypothesizing Predicting Planning Procedure Conducting Recording Analyzing Evaluating Synthesizing Communicating Part 1: Determining the Percentage of Cells That Are Dividing 1. Focus the onion root tip slide under the low-power lens using the coarse-adjustment knob. Locate dividing cells, and centre them in the field of view. 2. Rotate the medium-power lens into place. Focus and centre the dividing cells. 3. Notice that the cells form lines that are roughly parallel to one another. Choose a line of cells with many cells in various stages of mitosis. Count 20 cells. Record the number of cells, in these 20 cells, that are in mitosis. 4. Calculate the percentage of cells that are dividing. For example, if you counted 10 cells dividing, you would calculate the percentage as follows: Percentage of cells dividing 10 100 % 50 % 20 5. Repeat steps 3 and 4 for two other lines of 20 onion cells. Record your results in a table. 6. Rotate the low-power lens into place, and remove the slide from the stage. 7. Predict whether the onion root tip or the whitefish embryo will have a greater percentage of dividing cells. Record your prediction, and give reasons for it. 8. Repeat steps 1 to 5 using the whitefish embryo, but instead of looking for a line of dividing cells, look for an area of dividing cells. Part 2: Designing a Cell Division Clock 9. Focus the onion root tip under the low-power lens using the coarse-adjustment knob. Locate dividing cells, and centre them in the field of view. 10. Rotate the medium-power lens into place. Focus and centre the dividing cells. 66 <strong>Unit</strong> A <strong>Reproduction</strong> NEL
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amniotic fluid placenta umbilical c
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Figure 7 The zygote has divided sev
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CORD BLOOD: BIOLOGICAL INSURANCE Sc
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Figure 2 The X chromosome (a) is fa
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Figure 2 The karyotype of Down synd
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4.6 Prenatal Procedures (a) (b) Fig
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4.7 Reproductive Technologies LEARN
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Sample Stakeholder Perspectives •
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CHAPTER 4 Review Human Reproduction
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Review Key Ideas and Vocabulary 1.
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UNIT A Review Reproduction Unit Sum
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15. Complete the following table to
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