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Looking Good, Feeling Good: From the Inside Out

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Teacher's Guide

Lesson 6—Explain/Elaborate

Shining the Light on Skin

At a Glance

Overview

Lesson 6 has two activities and will take two days to complete. In the first activity, students investigate the relationships between certain environmental factors and levels of exposure to sunlight. Students form hypotheses related to how variables such as location, time of year, time of day, and the weather influence the intensity of sunlight. They test their hypotheses using student- and teacher-generated results in an online database. In the second activity, students design and carry out experiments that test the effectiveness of various items intended to provide protection from the sun.

Major Concepts

Objectives

After completing this lesson, students will be able to

Teacher Background

Consult the following sections in Information about the Musculoskeletal and Skin Systems:

  1. 4.3 Skin
  2. 5.2 Vitamin D
  3. 6.3 Disorders of skin

Additional information about skin cancer can be found at http://cancer.gov/cancerinfo/types/Skin/ and http://www.mskcc.org/mskcc/html/420.cfm. General information about skin and skin problems can be found at http://www.aad.org/.

In Advance

Web-Based Activities
Activity Web Component? Photocopies Materials
1 Yes Master 6.1, Calculating the Shadow Ratio, 1 transparency SunCheck Timers (3 per class)
Meter stick (1 per class)
Object to cast shadow
2 large sheets of paper
2 No Master 6.1, Calculating the Shadow Ratio, 1 copy per team of 3 or 4 (optional) SunCheck Timers
2 or 3 kinds of sunscreen
2 or 3 kinds of sunglasses
T-shirts of different colors
Other materials depending on student investigations (see Preparation)

Note to teachers: The fraction of sunlight that causes damage to the skin is called ultraviolet (UV) light. These activities require students to use disposable UV monitors to measure different levels of exposure to sunlight. The specific products recommended for this activity are sold as SunCheck Monitors and Timers. These products have three different UV-sensitive panels. Each panel is protected by a cover that you peel off before use. The three panels are designed to represent three types of skin sensitivity to UV light: normal, sensitive, and supersensitive. Exposure to sunlight causes the panels to turn from white to blue. When the color of the panel matches that of the reference panel, then the wearer is assumed to have been exposed to enough UV light for that day. In this lesson, we don’t regard the SunCheck products as tools that assess “safe” levels of sun exposure. Instead, they are simply used as inexpensive monitors of UV-light exposure.

To use the SunCheck Monitor or Timer,

SunCheck Monitors and Timers are available from a number of suppliers, including

Preparation

Purchase SunCheck Timers for use in both activities. (Throughout the lesson, the two SunCheck products are collectively called SunCheck Timers.) The timers cost between $0.50 and $1.00 each, depending on the supplier and the quantity purchased. To make sure that SunCheck Timers are available for this lesson, remember to order them well in advance.

Activity 1: Measuring Sunlight

Note to teachers: In Activity 1, students use data obtained from SunCheck Timers to explore different factors that influence exposure to UV light. At the same time, students will encounter data about shadow ratios, where

shadow ratio = length of shadow / height of object casting the shadow

Before beginning this lesson, determine how much time is required for the supersensitive panel on a SunCheck Timer to match its reference color. To do this, take the SunCheck Timer outside (not indoors or behind glass), peel off the protective cover from the supersensitive panel, and place the timer in a location that is exposed to sunlight. You might want to tape the timer in place to prevent the wind from moving it. Ensure that the timer will remain in the sun for the entire exposure and that the location will not become shady. Write down the time the exposure begins and the time when the supersensitive panel matches its reference color. Also determine the shadow ratio when you first expose the timer. Measure the height of an object and the length of its shadow. A meter stick is handy for this task. Record the shadow ratio as the shadow length divided by the object height (see Master 6.1, Calculating the Shadow Ratio). You will need this information for the database used in Activity 1. The time it takes for the supersensitive panel to match its reference color can be less than 30 minutes during warmer months or an hour or more during winter months.

You will also need to collect data (shadow ratios and corresponding times of exposure using SunCheck Timers) at three different times of day. Begin taking measurements when the shadow is longer and will be getting shorter or when the shadow is very short and will be getting longer. For example, you could collect data at 8 a.m., 10 a.m., and 12 p.m., or 12 p.m., 2 p.m., and 4 p.m. These data could be collected on a weekend or by student volunteers during the week.

After you have three shadow ratios and three corresponding times for the supersensitive panel to match its reference color, go to the Web site http://science.education.nih.gov/supplements/bone/student. Under "Teacher Administration," click on “Lesson 6—Database.”

The database includes only times corresponding to the supersensitive panel. The factors that influence these times also work in the same way to influence times for the other two panels. We suggest using the times for only the supersensitive panel because they are the shortest and therefore the easiest to measure. Depending on conditions, the exposure time needed for the normal panel to match its reference can exceed four hours. Using the sensitive and normal panels is optional, but only times corresponding to the supersensitive panel should be entered in the database.

Activity 2: Be Prepared!

Have an adequate number of SunCheck Timers and meter sticks on hand. Also have available two or three sunscreens with different SPFs, two or three different types of sunglasses, and some different articles of clothing, such as T-shirts of different colors. To make this easier, you can ask student volunteers to bring these items to class before the lesson.

Prepare photocopies and transparencies.

Procedure


Activity 1: Measuring Sunlight

Note to teachers: This lesson discusses the benefits and risks associated with exposure to sunlight. For the most part, we’re referring to the ultraviolet part of the light spectrum. If your students are familiar with the light spectrum, you may want to speak of UV light rather than sunlight.

National Science Education Standards icon
Content Standard F:
Safe living involves the development and use of safety precautions and the recognition of risk in personal decisions.
  1. Begin the activity by asking the class, “Is sunlight good for your health?”

Student responses will vary. Some may feel that sunlight is good for health because they associate it with an active lifestyle. You may follow up such a response by asking, “Are people who spend a lot of time outdoors healthy because of exposure to the sun or because they get lots of exercise?” Some students may mention that sunlight is needed to help the body produce vitamin D. Other students may respond that sunlight is bad for one’s health because it can lead to sunburn, skin damage, and increased risk for getting skin cancer.

  1. Explain to students that UV light, which is one part of sunlight, can cause sun damage that increases the risk for getting skin cancer. However, UV light is also needed to allow the body to produce vitamin D. People with too little vitamin D can suffer from a disease called rickets. Only 10 to 15 minutes’ of sunlight on the face and wrists, two to three times a week between 8 a.m. and 4 p.m. in the summer are adequate for the body to make enough vitamin D.

Students should understand that a healthy relationship with sunlight involves a balance between its health benefits and risks. Students may focus on how they would like their skin to look in order for them to “fit in” rather than how to keep their skin and bodies healthy. Explain to students that the National Institutes of Health (NIH) recommends that “the best skin color is the one you were born with.”

Note to teachers: Some students may believe that dark-skinned individuals do not get sunburned and are not at risk for skin cancer. However, dark-skinned individuals do get sunburned and may be at a significant risk for sun-induced skin cancer. Recent research has demonstrated that complex factors, such as skin type, genetics, and melanin distribution, may be as important as race and skin color in determining skin-cancer risk.

In dark-skinned individuals, melanin production is continuous. In light-skinned individuals, exposure to UV light stimulates the production of melanin. Melanin absorbs UV light and provides some protection against the damaging effects of UV light. The skin becomes darker (it tans) as melanin levels increase to protect the skin from UV exposure. A suntan or sunburn actually represents cellular damage from UV exposure. Importantly, UV light causes damage to DNA. The UV light used in tanning booths is no different and increases the risk for getting skin cancer and premature aging of the skin.

  1. Ask students whether they think the amount of UV light is the same during the summer as during the winter. Then ask students, “What factors influence how much UV light you get?”

Student responses will vary. Make sure that the following are mentioned:

  • time of year,
  • time of day,
  • weather conditions,
  • latitude,
  • elevation, and
  • reflections off water, sand, or snow.
  1. Ask students, “How could you measure the amount of UV light?”

Students are unlikely to be familiar with techniques for measuring UV light. A few students might be familiar with products that change color in response to UV light, the UV index, or UV meters.

  1. Explain to students that you have already used two strategies for measuring UV light. One is the shadow ratio. Display a transparency of Master 6.1, Calculating the Shadow Ratio. Explain that the shadow ratio provides an indication of UV light intensity. The shadow ratio is calculated as the length of the shadow, divided by the height of the object casting the shadow.
  2. Write “Time of Day,” “Shadow Ratio,” and “SunCheck Time” on a large sheet of paper. On the sheet, record the time of day when you collected data and the shadow ratios that you entered in the database. Share the information with the class.

You will add the SunCheck times to the paper in Step 8. The paper should look similar to the following:

sample data collection chart with three columns labeled Time of Day, Shadow Ratio, and SunCheck Time
Figure 6.2. Data collection setup.

  1. Explain to students that you also measured UV light using a SunCheck Timer. Take out a SunCheck Timer and pass it around the room as you explain how it works.

tip iconTip from the field test: The SunCheck Timers’ three panels are designated “supersensitive,” “sensitive,” and “normal.” These refer not to skin types but to different sensitivities to the sun. In this activity, the SunCheck Timers are simply used as inexpensive UV monitors. Despite what the packaging materials may say, students should not think of them as tools for assessing safe levels of UV exposure. Refer to the teacher note after this activity’s Step 2.

  1. Explain that you have already determined how long the supersensitive panel on a SunCheck Timer can be exposed to sunlight before the supersensitive panel matches the reference color. Write the times you obtained under “SunCheck Time” on the large sheet of paper.

Display the paper with the shadow ratios and times for the SunCheck Timers. Students will use this information in Activity 2: Be Prepared!

  1. Explain that you have recorded the times and the shadow ratios in a database that includes the same information measured under other conditions. Inform students that they will use the database to develop a question about sunlight exposure, answer it by using the data in the database, and provide a short written summary of their findings.
Web activity icon
  1. Divide students into teams of two or three. Direct each team to a computer and instruct them to proceed to http://science.education.nih.gov/supplements/bone/student and click on “Lesson 6—Shining the Light on Skin.”
  2. Explain to students that each team should ask at least one question that can be answered using the information in the database.

Students have a number of options for generating average exposure times in the database, such as average exposure times for specific

  • latitude ranges,
  • elevation ranges,
  • months,
  • times of day,
  • weather conditions, and
  • combinations of these variables.

The database allows students to formulate and test many different questions by comparing average exposure times for various environments. For example, questions that can be tested by using information in the database include the following:

  • Are exposure times longer for schools at higher latitudes?
  • Are exposure times shorter for schools at higher elevations?
  • Are exposure times longer during winter months and shorter during spring months?
  • Are exposure times shortest during the middle of the day?
  • Are exposure times shorter on clear days?

Students are limited by their imaginations, but their questions must be answerable using the available data.

  1. After teams pose their questions, they should establish a hypothesis.

At the middle school level, converting the question to a statement is an acceptable method for establishing a hypothesis. For the example question, “Are times longer during winter months and shorter during spring months?” a hypothesis can be, “Times during winter months are longer than times during spring months.” Students could then test this hypothesis by comparing the average time during December with the average time during April. The alternative hypothesis, “Times during winter months are similar to times during spring months,” is equally acceptable.

A hypothesis is a statement that predicts an outcome. Hypotheses are testable. The statement is tentative because empirical evidence has not yet been obtained to support or contradict it. However, it is a reasonable statement, because it is based on prior knowledge about the phenomenon. For example, some students may have experienced that the sun is less direct during winter compared with spring. For these students, a reasonable hypothesis would be the first one suggested. Other students may live at lower latitudes and may experience similar amounts of sunlight during different months of the year. For these students, the second hypothesis is a reasonable one.

The validity of either hypothesis is tested using data. The data will either support or not support the hypothesis. Many students think that a good hypothesis is one that the data support. In fact, neither hypothesis (one that the data support or one that the data fail to support) is better. The important point is that students will have engaged in an authentic scientific activity. They will have formulated a hypothesis and used data to determine whether the hypothesis is supported or not supported. Using empirical evidence to draw conclusions about phenomena is a key feature of scientific inquiry.

  1. On the “Generate Report” page, teams must enter their hypotheses (only one hypothesis at a time) and select the variables they need to generate a report or reports that will allow them to test their hypotheses. After they have selected their variables, they should click on “Generate Report.”

To test a hypothesis, such as times are shorter during winter than during summer, a student has to generate two different reports, one for the winter and a second for the summer, and compare them. If possible, allow students to print their reports. Otherwise, instruct students to record the results of their reports on a piece of paper. If time allows, encourage students to ask additional questions and produce the reports necessary to answer those questions.

Note to teachers: The database will not accept an entry if a hypothesis is not entered. Testing some hypotheses will require that students generate more than one report.

Note to teachers: The following information is provided to assist you in answering students’ questions:

  • The angle of the sun relative to Earth’s surface varies with the time of day. When the sun is at its highest point in the sky, the angle is such that sunlight travels the shortest distance through the atmosphere. As a result, less UV light is absorbed by the atmosphere and less is deflected when the sun is high in the sky. Of course, the changing angle of the sun in the sky is the basis of the shadow rule.
  • In temperate climates, UV light can vary in intensity up to 25-fold between winter and summer. Nearer the Equator, UV levels vary much less during the year, since the sun is always relatively high in the sky in the middle of the day.
  • The greater the distance from the tropics, the lower the intensity of UV light. For instance, the average annual exposure of a person in Hawaii is about four times greater than that of a person living near the border between the United States and Canada. This results from the greater distance the UV light travels through Earth’s atmosphere at higher latitudes.
  • The intensity of UV light increases about 4 to 5 percent for every 1,000 feet of increase in altitude. The higher the altitude, the shorter the distance UV light has to travel through the atmosphere.
  • Many people know firsthand that UV light has a significant effect on skin on a cloudy summer day, even though the temperature may feel cool. This is because the water in clouds absorbs heat much better than UV light. Pollution, like clouds, absorbs only a small amount of UV light passing through it. Wind has no effect on the intensity of UV light.
  • Some surfaces reflect UV light better than others. Grass reflects little UV light (only about 3 percent), while a white, sandy beach or rippling water reflects much more (25 and 20 percent, respectively). Fresh snow can reflect up to 85 percent of UV light, which, together with higher altitudes, can account for severe effects on the skin, even in winter.
  1. After teams have posed hypotheses and generated reports to test their hypotheses, they should write a short summary of their findings.

The reports should indicate whether the data supported or did not support the hypothesis and what evidence was used to form a conclusion.

  1. Ask for volunteers to report their findings, including why their team chose their hypothesis or hypotheses.

Make sure that students are testing hypotheses that can be investigated using available data.

  1. If a team is not sure that the data support the hypothesis, ask why and consider what additional data could help address the hypothesis.

Even if the team has written an appropriate hypothesis, there may be too few entries in the database to reach a firm conclusion.

  1. As time permits, ask other teams to report their findings. Try to elicit different hypotheses.
  2. Facilitate a class discussion of the relationship between the shadow ratio and the length of time for a supersensitive panel to match its reference color. Ask for several teams to share the shadow ratios and times they collected in their reports. Record their results on a large sheet of paper.
assessment icon
Assessment:
Step 19 can be assigned individually as homework and used as an assessment for this activity.

Group the shadow ratios and times for locations with similar latitudes and altitudes. Students should notice that the shadow ratio is smaller when the times are shorter. Keep the results posted in the classroom. Students may refer to these results during Activity 2.

  1. Instruct students to write two or three sentences describing what influences the amount of UV light to which they are exposed.

Students should explain that latitude, elevation, time of year, time of day, and weather conditions can all affect the amount of UV light.

 

Activity 2: Be Prepared!

  1. Ask the class, “How could you protect yourself from too much sun exposure?” Write their responses on the board.

If students are uncertain how to respond, suggest that they consider different types of environments such as in and out of the shade or in and out of the water. If not mentioned by a student, bring up the topic of products designed to protect us from sunlight, such as sunscreens, sunglasses, and different types and colors of clothing.

  1. Divide the class into teams of three or four. Instruct the teams to ask a question about protection from sun exposure that can be answered using two or three SunCheck Timers.

To ensure that the class addresses a variety of questions, you may want to refer to the questions written on the board and have different teams volunteer to answer different questions.

Note to teachers: The SunCheck Timers will work when underwater or when covered with sunscreen.

National Science Education Standards icon
Content Standard F:
Scientists formulate and test their explanations of nature using observations, experiments, and theoretical and mathematical models.
  1. After the teams have decided on a question, ask them to establish a hypothesis as they did in the previous activity.
  2. Instruct teams to design an investigation that can test the hypothesis using the materials you provide. Ask each team to bring its design to you for approval.

Note to teachers: Make sure that the teams understand that a proper investigation should include a control where the timer is exposed to sunlight without protection. If necessary, take one question as an example and, in front of the class, go over how to design the investigation for that question. Teams should record the question, the hypothesis, and the design of the investigation on a piece of paper. They can refer to this while they conduct their investigations and again when they write a report of the investigation.

  1. Once you have approved each team’s design, remind students that the shadow ratio can be used to assess the intensity of UV light. Display the paper from Activity 1, Step 8, showing the time of day, shadow ratios, and SunCheck times. Ask teams to predict what the shadow ratio will be for their investigations.

Students should use the data you collected to make their predictions.

  1. Ask teams to predict what the time for each their SunCheck Timers will be in their investigations.

Students should predict that the control timer will have a time similar to the results you obtained. Timers with sun protection such as shade, clothing, or sunscreen should have longer times. For example, students might predict that a SunCheck Timer placed next to the water will have a shorter time than the control.

  1. Distribute the SunCheck Timers and materials needed to complete the investigations. Instruct the teams to go outside and begin their investigations. Students should determine the shadow ratio when they first expose their SunCheck Timers.

If necessary, distribute copies of Master 6.1, Calculating the Shadow Ratio, to each team to help them determine the shadow ratio. Students should write down the time required for the panel that corresponds to supersensitive skin to match its reference color. The time needed to complete the investigations likely will go beyond class time. The time required to reach the maximum safe sun exposure does not have to correspond with your class schedule. If long times are being measured, students from other classes may check the timers. Another option is to have a student expose the timers over the weekend and record the times.

Note to teachers: To conserve the SunCheck Timers, you can use just one as a control for all experiments performed at the same time.

  1. Instruct the teams to write reports of their investigations on a single sheet of paper. Their reports should include
  • the question they asked,
  • the hypothesis,
  • the prediction for the shadow ratios and times for each SunCheck Timer,
  • a description of the experimental design,
  • the results obtained (shadow ratios and times for each SunCheck Timer used),
  • the answer to the question, and
  • recommendations for behaviors that will protect skin from excessive exposure to sunlight.
  1. Have a member of each team take about two minutes to summarize the findings for the class.

If any teams were not able to answer their questions, ask them what additional data they would need to do so. If teams draw conclusions that go beyond their data, guide the discussion to bring this out.

  1. Ask a few of the teams to compare their predictions with the shadow ratios and times they obtained in their investigations. They should explain why they think their predictions did or did not match their results.
  2. Ask students whether they think the shadow ratio is a good indicator of how much UV light they are getting. Explain that the shadow ratio is based on the shadow rule. The shadow rule states, “short shadow, seek shade.” Encourage students to use this rule as a guide for when to protect themselves from the sun and minimize the risks of sun exposure.

The shadow rule is an easy way for anyone to minimize the risks of sun exposure by staying out of the sun when UV light is more intense. Students will not usually have a SunCheck Timer with them, but they can notice how long their shadow is compared with their height.

Note to teachers: More information about the shadow rule is available in an article by T. Downham (see the Reference section, number 18).

assessment icon
Assessment:
Step 12 can be assigned as homework and used as an assessment of students’ understanding of this lesson.
  1. To conclude the lesson, instruct students to write a short paragraph describing the shadow rule and how it can be used to decide when to protect themselves from sun exposure. They should also describe different ways to protect themselves from excessive sun exposure.

Students should explain that the shadow rule directs them to seek shade when they have a short shadow. They should understand that shadows indicate how much UV light is present. They should also explain that when shadows are short, people should protect their skin from the sun by seeking shade or using products such as sunscreen, sunglasses, hats, and other articles of clothing.

Lesson 6 Organizer
Activity 1: Measuring Sunlight
What the Teacher Does Procedure Reference

Ask students, “Is sunlight good for your health?”

Step 1

Explain the following information about UV light, which is one part of sunlight:

  • UV light can cause sun damage that increases the risk for getting skin cancer.
  • UV light is needed for the body to produce vitamin D.
  • Too little vitamin D can cause a disease called rickets.
  • Only 10 to 15 minutes’ of sunlight on the face and wrists, two to three times a week between 8 a.m. and 4 p.m. in the summer are adequate for the body to make enough vitamin D.
Step 2

Ask students whether they think the amount of UV light is the same during the summer and the winter. Ask students,

  • “What factors influence how much UV light you get?”
  • “How could you measure the amount of UV light?”
Step 3 and 4

Display a transparency of Master 6.1, Calculating the Shadow Ratio.

  • Explain that the shadow ratio provides an indication of UV-light intensity.
transparency iconStep 5

Write “Time of Day,” “Shadow Ratio,” and “SunCheck Time” on a large sheet of paper. Record on the paper

  • the time of day when you collected data for the database and
  • the shadow ratios you calculated and entered into the database.
Step 6

Pass around a SunCheck Timer and explain how it works.

  • Explain that you have already determined how long the supersensitive panel can be exposed to sunlight before the panel matches the reference color.
  • Write the times you obtained on the large sheet of paper.
Steps 7 and 8

Explain that you have entered the shadow ratios and the times for the supersensitive panel into a database and that they will use the database to develop a question about sunlight exposure.

  • Divide students into teams of two or three.
  • Instruct teams to go to the supplement Web site and click on the “Lesson 6—Shining the Light on Skin” link.
Web activity iconSteps 9 and 10

Instruct each team to ask at least one question that can be answered using the information in the database.

  • After teams pose their questions, they should enter their hypotheses on the “Generate Report” page and select the variables that will allow them to test their hypotheses.
  • After they have selected variables, they should click on “Generate Report.”
Steps 11–13

Instruct teams to write a summary of their findings.

Step 14

Ask for volunteers to report their findings and explain whether the data supported their hypothesis.

  • Make sure students are testing hypotheses that can be investigated using the available data.
  • If a team is not sure that the data support its hypothesis, ask the team to consider what additional data could help address the hypothesis.
  • As time permits, ask other students to report their findings to elicit different hypotheses.
Steps 15–17

Facilitate a class discussion of the relationship between the shadow ratio and the length of time for a supersensitive panel to match its reference color.

  • Ask several teams to share the shadow ratios and times of day they collected in their reports.
  • Record the teams’ results on a large sheet of paper.
Step 18

As a homework assignment, ask students to write two or three sentences describing what influences the amount of UV light to which they are exposed.

Step 19
Activity 2: Be Prepared!
What the Teacher Does Procedure Reference

Ask the class, “How you could protect yourself from too much sun exposure?”

Step 1

Divide the class into teams of three or four.

  • Instruct teams to ask a question about sun exposure that can be answered using two or three SunCheck Timers.
Step 2

Ask each team to establish a hypothesis based on its question.

  • Instruct teams to design an investigation that can test their hypotheses.
  • Ask each team to bring its design to you for approval.
Steps 3 and 4

Once you have approved each team’s design, remind students that the shadow ratio can be used to assess the intensity of UV light.

  • Display the paper from Activity 1, Step 8, showing the time of day, shadow ratios, and SunCheck times.
  • Ask teams to predict the shadow ratio for their investigation.
Step 5

Ask students to predict what the time for each of their SunCheck Timers will be.

Step 6

Distribute SunCheck Timers and materials needed to complete the investigations.

  • Instruct teams to begin their investigations.
  • Students should determine the shadow ratios when they first expose their SunCheck Timers.
Step 7

Instruct teams to write reports of their investigations on a single sheet of paper.

  • Ask a member of each team to take two minutes to summarize its findings for the class.
Steps 8 and 9

Ask a few teams to compare their predictions with the shadow ratios and times they obtained in their investigations.

Step 10

Ask students whether they think the shadow ratio is a good indicator of how much UV light they are getting. Explain that

  • the shadow ratio is based on the shadow rule and
  • the shadow rule states, “short shadow, seek shade.”
Step 11

As a homework assignment, ask students to write a short paragraph describing

  • the shadow rule and how it can be used to decide when to protect themselves from sun exposure and
  • different ways to protect themselves from excessive sun exposure.
Step 12
transparency icon= Involves making a transparency.
Web activity icon= Involves using the Internet.

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