age at which the unlucky number first appears would be the age
at which they developed colon cancer.
• Record how many students developed cancer under this model
at each age on the column labeled “Number of People Who
Developed Cancer—One Hit.”
• Students will now approximate what might happen if the two-hit
hypothesis were true. Ask students to imagine that if they encountered
the second “unlucky” number in the “Gene 2” column, it meant they
experienced a cancer-causing mutation in another gene in the same
cell that experienced a cancer-causing mutation. Explain that the age
at which the second unlucky number first appears in the column
“Gene 2” is the age at which they experienced this second mutation.
If the two-hit hypothesis were correct, they did not develop colon
cancer until the age at which they encountered both unlucky numbers.
• Record how many students developed cancer at each age under this
second model, and add the data to the appropriate column.
• Work with the class to accumulate the running total of cancer cases in
the population at each age under the one-hit and two-hit models.
Write the values in the last two columns on the transparency.
Ask students whether they see any pattern in the incidence of cancer
Page 79
in this population (that is, the class).
Step 11
Give one copy of Master 3.4 to each student. Have students work in
Page 79
pairs to construct two graphs that illustrate the chances a person in
Step 12
this class would have developed colon cancer by a certain age under
the two models.
85
Student Lesson 3
Cell Biology and Cancer
What the Teacher Does
Page and Step
Ask students to examine the graphs and decide which hypothesis best
Page 79
fits the actual data on the incidence of colon cancer.
Step 13
Ask students to predict what the results of a simulation such as this
Page 79
might be if three, four, or five mutations (hits) must occur prior to the
Step 14
onset of cancer.
Give each student a copy of Master 3.5. Direct students to work in
Page 80
their groups and use the Web-based simulation to test their predictions Step 15
and answer the questions on the master. Students should decide what
type of model best fits the observed incidence for the development of
colon cancer.
Convene a class discussion and have students share their answers to
Page 80
the questions on Master 3.5.
Step 16
Challenge students to evaluate the models they used to test the
Page 83
different hypotheses for the development of cancer.
Step 17
Give each student a copy of Master 3.7. Ask students to use their
Page 83
understanding of cancer as a multistep process to explain each
Step 18
observation listed.
= Involves copying a master.
= Involves making a transparency.
= Involves using the Internet ( http://science.education.nih.gov/supplements/nih1/cancer/
86
Lesson 3 Organizer: PRINT VERSION
What the Teacher Does
Page and Step
Remind students of the increase in cancer incidence with age observed Page 75
in Lesson 1. Explain that students will now investigate the biological
Step 1
basis for this increase.
Give one copy of Master 3.1 to each student. Ask students to work in
Page 75
pairs to answer the questions.
Step 2
Project Master 3.1 and invite students to share their answers to the
Page 75
questions.
Step 3
Point out that the last question is the central issue in this lesson. Explain Page 76
that many years ago, epidemiologists recognized that this change in
Step 4
cancer risk provided an important clue about the cause of cancer.
Remind students that one way scientists answer questions is by
Page 76
developing and testing hypotheses. Briefly describe the one-hit
Step 5
hypothesis and the two-hit hypothesis. Ask students if they can
tell by looking at the colon cancer graph which hypothesis best
explains the data.
Explain that scientists often use models to test their explanations.
Page 76
Tell students they will use two simple models to test alternate
Step 6
explanations for the development of cancer.
Give each student one data set from Master 3.2. Explain that students Page 77
will use these data to understand the implications of the following two Step 7
hypotheses for the incidence of cancer in a population (the class):
1. Cancer develops as a result of a single mutation (one-hit hypothesis).
2. Cancer develops as a result of two independent mutations
(two-hit hypothesis).
Explain that the data sets are called random-number tables. The
Page 77
numbers, ranging from 1 to 25, correspond with the students’
Step 8
imagined life spans. The first column represents the students’ ages,
and the second and third columns represent the random numbers.
Conduct the following exercise:
Page 77
• Ask a student to draw a number out of a hat. Write the number on Step 9
the board.
• Explain that this number represents a mutation in Gene 1. Ask students
to examine the column labeled “Gene 1” on their random-number
table to determine whether they have the number chosen. If they
do, they should circle it and note the age at which it occurred.
• Ask another student to draw a number out of the hat. Write the
number on the board.
87
Student Lesson 3
Cell Biology and Cancer
What the Teacher Does
Page and Step
• Explain that this second number represents a mutation in Gene 2.
Ask students to examine the column labeled “Gene 2” on their
random-number table to determine whether they have the second
number chosen. If they do, they should circle it and note the age
at which it occurred.
Project Master 3.3. Explain that you will use this table to tal y the number
Page 78
of people in the class who have developed cancer at each age if the one-
Step 10
hit or two-hit hypotheses for the development of cancer were true.
Explain that to discover the number of people who would have developed
cancer, students will need to examine their random-number tables:
• Tell students that they will approximate what might happen if the
one-hit hypotheses were true. Ask students to imagine that if they
found the first “unlucky” number in the column labeled “Gene 1,”
it meant a gene in one of their cells experienced a cancer-causing
mutation. Explain that if the one-hit hypothesis were correct, the
age at which the unlucky number first appears would be the age
at which they developed colon cancer.
• Record how many students developed cancer under this model
at each age on the column labeled “Number of People Who
Developed Cancer—One Hit.”
• Students will now approximate what might happen if the two-
hit hypothesis were true. Ask students to imagine that if they
encountered the second “unlucky” number in the “Gene 2”
column, it meant they experienced a cancer-causing mutation in
another gene in the same cell that experienced a cancer-causing
mutation. Explain that the age at which the second unlucky number
first appears in the column “Gene 2” is the age at which they
experienced this second mutation. If the two-hit hypothesis were
correct, they did not develop colon cancer until the age at which
they encountered both unlucky numbers.
• Record how many students developed cancer at each age under this
second model, and add the data to the appropriate column.
• Work with the class to accumulate the running total of cancer cases in
the population at each age under the one-hit and two-hit models.
Write the values in the last two columns on the transparency.
Ask students whether they see any pattern in the incidence of cancer
Page 79
in this population (that is, the class).
Step 11
Give one copy of Master 3.4 to each student. Have students work in
Page 79
pairs to construct two graphs that illustrate the chances a person in
Step 12
this class would have developed colon cancer by a certain age under
the two models.
88
What the Teacher Does
Page and Step
Ask students to examine the graphs and decide which hypothesis best
Page 79
fits the actual data on the incidence of colon cancer.
Step 13
Ask students to predict what the results of a simulation such as this
Page 79
might be if three, four, or five mutations (hits) must occur prior to the
Step 14
onset of cancer.
Give each student one copy of Master 3.5 and of Master 3.6. Direct
Page 80
students to work in their groups, follow the instructions to text their
Step 15
predictions, and answer the questions on Master 3.5. Students should
decide what type of model best fits the observed incidence for the
development of colon cancer.
Convene a class discussion and have students share their answers to
Page 80
the questions on Master 3.5.
Step 16
Challenge students to evaluate the models they used to test the
Page 83
different hypotheses for the development of cancer.
Step 17
Give each student a copy of Master 3.7. Ask students to use their
Page 83
understanding of cancer as a multistep process to explain each
Step 18
observation listed.
= Involves copying a master.
= Involves making a transparency.
89
Student Lesson 3
L E S S O N 4
Elaborate
Evaluating Claims
about Cancer
Focus
At a Glance
Students identify claims about UV-light exposure presented in a selection of
media items, then design, conduct, and report the results of an experiment
designed to test one such claim.
Major Concepts
Scientists use systematic and rigorous criteria to evaluate claims about
factors associated with cancer. Consumers can evaluate such claims by
applying criteria related to the source, certainty, and reasonableness of
the supporting information.
Objectives
After completing this lesson, students will
• understand that many people and organizations make claims about
factors associated with the development of cancer and about agents
that may help prevent or cure cancer;
• be able to explain that scientists evaluate such claims by applying
systematic and rigorous criteria;
• be able to apply criteria such as the source, certainty, and reasonableness
of the supporting information to media claims about cancer; and
• recognize that understanding the biology of cancer and the nature
of science can help individuals and society make reasoned choices
about factors related to cancer.
Prerequisite Knowledge
Students should have sufficient understanding of the methods of science
to develop a hypothesis, design an experiment to test that hypothesis,
and draw reasonable conclusions from the results.
Basic Science–Public Health Connection
This lesson provides the opportunity for students to discover how
science can help individuals and society evaluate claims about cancer.
Estimated Time: 45–50 minutes without experiment;
up to 90 minutes with experiment
91
Cell Biology and Cancer
Although most of your students will never acquire or need a detailed
Introduction
understanding of the biology of cancer, all of them will need to
understand and evaluate claims about cancer that they encounter in
casual conversation, in media items, and even in reports from healthcare
workers. Some of these claims may be vague, either in substance or in
origin. Some may be exciting and seem to offer great hope. Others may
be alarming. In some cases, these claims may conflict.
How do scientists evaluate claims about cancer? And how can your
students, as scientifically literate citizens, evaluate such claims, both
for their own satisfaction and as a solid foundation for thinking about
and voting on policy issues?
In this lesson, students examine several media items about exposure to the
sun and the development of skin cancer and work in groups to identify the
claims that each media item makes. Students are challenged to describe
ways that scientists might evaluate these claims, and then are introduced
to a model system involving yeast sensitive to UV (ultraviolet) light that
they can use to test aspects of these claims. Each group designs, conducts,
and presents the results of a controlled experiment testing one of these
aspects. The lesson ends with a class discussion of 1) how scientists
evaluate claims about cancer and 2) the criteria that nonscientists can
use to evaluate such claims.
Web-Based Activities
In Advance
None.
Materials and Preparation
Photocopies and Transparencies
Equipment and Materials
• Enough copies of Masters
• Order and prepare materials
4.1, 4.2, 4.3, and 4.4 for
for the lab exercise. See
one-fourth of the class*
“Laboratory Preparation,”
• 1 copy of Master 4.5 for
page 96.
each student
• 1 copy of Master 4.6 for
each student
* You will need one Media Item handout for each student in your class.
Note that every student in one group gets the same handout, and different
groups get different handouts.
92
DAY 1
Procedure
Estimated time:
1. Divide the class into four groups. Distribute the masters so that each
group has a different master; each member of a particular group
45–50 minutes
should have the same master.
without doing the
experiment; at least
2. Direct students to read their media items, then work together to
75 minutes with
identify the major claims that their assigned item makes about the
the experiment
product, ultraviolet (UV) light, and cancer. Ask students to also
describe the evidence on which these claims seem to be based.
Give the groups about 5 minutes for this discussion.
3. Conduct a brief class discussion about the media items by asking
the following questions:
• What claims did you find in the media items, and what evidence
did the items provide to support these claims?
Students should not find it difficult to identify these claims. Possible
answers include the following:
• Media Item 1: A new sunscreen gives 10 times more protection
against sunburn than others but still allows tanning.
• Media Item 2: A new brand of sunglasses protects eyes against
UV light.
• Media Item 3: Cellophane protects against sunburn but still
allows tanning.
• Media Item 4: Some clothing offers higher protection from
UV light than other clothing.
The media items do not provide any evidence to support these claims.
• What claims about such products and/or cancer have you heard
during your lifetime, and from whom (and where) do you hear
such claims?
Students likely have heard many claims. Allow them to list not only
outlandish claims that they may have heard in the media, but also
more reasonable claims that they may have heard from parents,
friends, and even reputable magazines and healthcare professionals.
Technically, any information that we hear or read about cancer is a
“claim” that someone is making.
• How do scientists evaluate such claims?
Students should already understand that scientists evaluate such
claims through rigorous experimentation, the requirement of
evidence to support a claim, careful review by other scientists of
procedures and conclusions, and the requirement that results be
93
Student Lesson 4
Cell Biology and Cancer
replicable. Look for these and similar answers from your students;
if they are not forthcoming, ask probing questions such as, “Is it
sufficient for a scientist to make a claim without providing evidence
to back it up?” and “If certain results can be obtained only by one
scientist working in a particular laboratory, what would you think
of claims based on these results?”
4. Explain that in this lesson, students will have an opportunity to test
claims that are similar to those they encountered in their media items
and will learn questions that citizens can ask about claims they hear
Students have the
in the popular press and from other sources.
opportunity here to
5. Give each student one copy of Master 4.5, Using a Model System to Test
experience how scientific
Claims about UV Light. Ask students to work in their groups to design experiments can lead to
and conduct a controlled experiment that tests a claim related to their
reasonable claims about
media item.
how individuals can help
prevent skin cancer. Point
You may wish to explain that often, scientists use model systems to
out that basic experiments,
evaluate certain claims that would not be appropriate to test using
such as the one they are
people as subjects. Often, these model systems involve other species.
about to conduct, have led
In this activity, students will use yeast as their model system.
to a variety of actions on
behalf of public health,
Circulate through the room as students read the information provided
including the banning of
on Master 4.5 and begin to design and execute their experiments.
certain food additives and
Notice that students will not be able to test the actual claims their
the warnings they see on
media items make, but they should be able to test related claims.
You may have to ask probing questions to help students see how
consumer products.
to use the yeast to test these claims. Following are suggestions for
possible experiments:
• Media Item 1: Students can test the relative abilities of
different brands of sunscreen or different SPF values to
protect the yeast from UV light.
• Media Item 2: Students can test the relative abilities of
different brands and types of sunglasses to protect the
yeast from UV light.
• Media Item 3: Students can test the relative abilities of
different colors of cellophane to protect the yeast from
UV light.
• Media Item 4: Students can test the relative abilities of
different colors and thicknesses of cloth to protect the
yeast from UV light.
Tip from the field test. Although students will only be able to test
certain aspects of the claims each media item makes, you may wish to
challenge your students to identify what part(s) of the claim they are
not testing and to describe how they might test those parts of the claim.
6. Conclude Day 1 by asking each group to describe to the class the
claim they are testing and the method they are using to test the claim.
94
DAY 2 (or DAY 3 if yeast are incubated at room temperature)
7. Direct students to collect the plates from their experiments and
record their results. Then, convene a class discussion and ask each
group to report briefly on its experiment. As each group reports,
ask students what additional information they would need to
answer the experimental question more completely or to apply
their findings to humans.
Students should follow the outline provided in Master 4.5 as they
report on their experiments.
8. Acknowledge the value of scientific research in evaluating claims,
then ask students how nonscientists can evaluate similar claims
they encounter in the media or from other sources. List their
ideas on the board or a transparency.
Students should recognize that they do not have the expertise,
equipment, or time to experimentally evaluate each claim they hear
about cancer, but they can carefully consider claims to determine their
source, whether they are supported by evidence, and how reasonable
they are (that is, whether they seem to fit within existing knowledge
or seem outlandish). Sometimes, “outlandish” claims are correct, but
this is usually not the case, and students should understand this.
9. Challenge each group to use the results of its own experiment to
develop a media item similar to the item they used in Step 1. Point