BioEd Online

Teacher Background

Skin protects inner tissues of the body and provides communication (through the sensory system) with the outside world. The skin also helps maintain a constant temperature within the body by aiding in cooling (through increased blood flow to the surface and  through perspiration) and heating (by reducing blood flow near the surface).

The skin is comprised of different layers. The outermost layer (the epidermis) consists of an inner layer of living cells and a top layer of compacted dead cells. In fact, most skin that is visible on our bodies actually consists of dead cells! Skin color is determined by special cells called melanocytes, located near the base of the epidermis. The lower layer (the dermis) is fibrous and gives strength to skin. Most nerve receptors that capture information from the outside world are located at the top of the dermis or the base of the epidermis.

Skin can be damaged by ultraviolet (UV) radiation from the sun or tanning lights, which can cause premature wrinkling, loss of elasticity of the skin, and skin cancer. Sunburns and suntans are both  evidence that skin has been exposed to too much harmful radiation. Due to ozone depletion in the upper atmosphere, more UV radiation is reaching Earth’s surface. This has increased the risks for damage to skin and eyes (particularly through the development of cataracts).

This activity builds awareness of skin by having students contrast and compare the “skin” of an orange to human skin. Students will also compare the surface area of an orange to the area of a person’s skin.

Objectives and Standards

Concepts

• Skin is a vital part of the body.

• Skin must be protected from sun damage.

Science, Math, and Health Skills

• Predicting

• Estimating

• Calculating

• Graphing

• Drawing conclusions

Materials and Setup

Materials per Group of Students

• 2–3 feet of wax paper

• crayons or colored markers

• metric tape measure

• orange or tangerine

• paper towels

• plastic knife

• roll of tape

• sheet of centimeter-ruled graph paper

• sheet of paper or a notebook for observations

• copy of “Skin Observations” sheet

Setup

1. Begin with a class discussion.

2. Have students conduct the activity in groups of 2–4.

Procedure and Extensions

Time

Two 30-minute (or longer) sessions

Session 1: Estimating surface area of an orange

1. Generate student interest by brainstorming about things that have a skin. List student ideas on the board. Older students may record the list in their science notebooks.

2. Discuss the purposes of skin (tree bark, skin on a banana, lizard skin, bird skin, etc.) based on the list of things with skins.

3. Holding an orange, explain to students that they will be examining the skin of an orange and comparing it with their own skin. Ask, How is the skin of an orange like your skin? How is it different?

4. Have Materials Managers collect materials for the groups.

5. Begin the group activity by having one student (Recorder) list the group’s observations about the skin of the orange. Then place a check next to all observations that also would apply to human skin.

6. Ask students, How much skin does an orange have? How could we find out? Instruct them to estimate the amount of skin on their oranges by coloring a similar area on their graph sheets. They may want to measure their oranges using tape measures. With older students, use this opportunity to investigate the relationships among diameter, circumference, and area.

7. Ask, How could you check your estimates? Have students peel the oranges and, within each group, trace the peelings onto graph paper. Have them color the traced areas orange. Have students calculate the area that is colored by counting or measuring the number of squares filled in and decide how much skin their oranges really have. Let students devise their own methods for counting partially colored squares, or instruct them to count every other partial square. Ask, Are you surprised about the area covered by the skin? Why or why not?

8. Next, have the students examine the peeled oranges. Discuss what might happen if oranges didn’t have skin.

Session 2: Estimating the amount of skin on a person

1. Explain that, just like oranges, our bodies need protection. Mention some of the characteristics of skin: it is the body’s largest organ; it provides protection from germs; it houses our cooling and heating systems; it contains receptors for our sense of touch, etc. Refer students to the diagram of skin on page 8 of the Global Atmospheric Change unit's Explorations magazine.

2. Ask, How much skin do you have and how do you protect it? Students can record their estimates in cm² in their science notebooks and list ways they protect their skin.

3. Tell students that the area of skin on the body can be measured with relative accuracy by applying the Law of Nines. This rule of thumb was developed to help doctors estimate the amount of skin damaged on people with burns. Roughly, each of the 11 major sections of skin on the body accounts for 9% (or 1/11) of the total (see illustration, PDF). Using this rule, students can estimate the total surface area of skin on their bodies by measuring the area of one arm.

4. Working in teams of two, have one student wrap another’s arm in wax paper. Have them mark any areas of overlap so that they will not be counted for the estimate of surface area.

5. Have them spread the paper out over two or more sheets of centimeter graph paper and count the number of squares covered (or have older students measure the dimensions of the wax paper and calculate the area as if it were a rectangle, or a rectangle and one or more triangles, showing area calculations).

6. Once students have found the surface area of an arm, have them multiply that figure by 11 to obtain the total surface area of skin on the entire body.

7. Ask students to imagine how they might look and feel without their skin—just like the peeled orange. Mention the importance of protecting skin from damaging UV radiation. Discuss strategies for protecting skin, including wearing clothes with long sleeves, always applying sunscreen, wearing hats, etc.

Extensions

• Wrap the entire body of one or more students in wax paper; then spread the paper out and measure its area. Compare the result to the estimate calculated using the area of only one arm.

• Have students calculate the area covered by a t-shirt, shorts, bathing suit, or other clothing. Challenge them to figure out the amounts of skin that are exposed when wearing short sleeves and shorts instead of long sleeves and trousers.

Handouts and Downloads