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# Cell Replication and Cancerous Cells

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### Overview

In this activity, students learn why cell growth is limited and requires cell division. They explore the different phases of mitosis in a Web activity. They learn about uncontrolled cell division -- cancer, the oncogenes that cause it, and possible treatments. Finally, as an optional exercise, they consider different points of view concerning the cloning of humans.

### Objectives

• Learn why cell growth requires cell division
• Explore how cells divide by the process of mitosis
• Understand the role of oncogenes in the development of cancer
• Analyze different points of view regarding human cloning

### Suggested Time

• Two to three class periods

### Materials

• Two round balloons (for cell growth demonstration)

### Before the Lesson

• Review the concepts of cell structure and function, using the lesson App Exception: tdc02.sci.life.cell.lp_strufx. Make sure students understand the gatekeeper role of the cell membrane.

### After the Lesson

• Do an experiment with students to demonstrate how the surface-area-to-volume ratio affects the rate of diffusion of substances into and out of cells. (See BSCS Biological Science: An Ecological Approach for a possible lab.)

### Part I

1. Blow up a balloon and tie it off. Tell students that the balloon represents a cell. Then blow up a second balloon larger than the first and tie it off. Ask students:

• As a cell grows, what happens to its surface-area-to-volume ratio (the size of the cell membrane compared to the amount of space taken up by the contents of the cell)? (Note: Assume a cell is a perfect sphere. The formula for calculating the surface area of a sphere is A = 4 π r2. The formula for calculating the volume of a sphere is V = 4/3 π r 3.)

Now explain how this changing ratio is related to cell division. Ask:

• How would a smaller ratio (i.e., a smaller surface area per volume) affect the cell's ability to function?
• How large do you think a cell could grow and still be able to function before it would need to divide?
• How can organisms like humans grow larger despite the constraints to cell size?

2. Show the Mitosis video with the sound off.

• Ask students to describe in their own words what is happening and how this process helps an organism stay alive and healthy.
• Say to students: In the time it took to watch this video, you lost 40,000 skin cells, yet you are not skinless. How does what you saw explain why this is so?

3. Show the Mitosis video again, this time with the sound on. Have students explore the How Cells Divide: Mitosis vs. Meiosis Web activity, and then ask them to draw and briefly describe each phase of mitosis.

• What would happen if mitosis within an organism were uncontrolled?
• What do you think regulates cell division in organisms?

5. Show the video How Cancer Cells Grow and Divide. Discuss the following:

• What other kinds of signals do you think cells would respond to that would make them grow and divide appropriately?
• Why do you think the oncogene acts as though it is stuck in the "on" position?
• How might scientists use knowledge about receptors and how metastasis occurs to find ways to stop cancer?

6. Have students explore the Web activity How Cancer Grows to learn more about cancer growth and treatments for cancer. Discuss the following:

• What are some ways cancer cells develop abnormally?
• What are some ways that cancer cells differ from normal cells of the same kind of tissue?
• How does the body respond to cancer cells?