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.
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.
4.
Ask students:
- 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?
7.
Ask:
- What is the process that single-celled organisms like
the paramecium or amoeba use to reproduce asexually?
How genetically similar are their offspring?
- "There are millions of clones walking on earth."
What do you think this statement means?
8.
Then have students explore the different points of view in the
On Human Cloning article.
Discuss the following:
- What would it mean to "clone" a human?
- How would a cloned human be different from
other humans?
- Besides helping infertile couples, in what other
ways might cloning help people?
- From a scientific point of view, what are the
strengths and weaknesses of each researcher's argument?
- Do you think the word cloning means something
different to a scientist than to a layperson?
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