To develop an understanding of the different kinds of cells that make up human skin and how the different skin cells relate to one another.
This lesson is part of the Skin Deep Project, which examines the science behind skin. Skin Deep is developed by AAAS and funded by Neutrogena. For more lessons, activities, and interactives that take a closer look at the science behind skin, be sure to check out the Skin Deep Project page.
In this lesson, students use online resources and perform a lab experiment to learn about the different kinds of cells that make up skin and how the different skin cells relate to one another.
It is important for students at this level to begin to see that all self-replicating life forms are composed of cells, from single-celled bacteria to elephants, with their trillions of cells. A few giant cells, such as hens' eggs, can be seen with the naked eye. It is at the cell level where many of the basic functions of organisms are carried out: protein synthesis, extraction of energy from nutrients, and so forth. All living cells have similar types of complex molecules that are involved in these basic activities of life. This lesson begins to show that, in addition to the basic cellular functions common to all cells, most cells in multi-celled organisms perform some special functions that others do not. (Science for All Americans, pp. 80-82.)
With regard to cells, many students may believe that organisms contain cells rather than being composed of cells. Imagining the large number of cells also can be a problem. Large organisms are composed of about a trillion cells. This large nuimber can be difficult to comprehend, though. To render it less abstract, students may be able to better comprehend a million millions than a trillion.
Students may have even more difficulty with the idea that cells are the basic units in which life processes occur. For these reasons, the story on cells should be kept simple. However, an understanding of basic cell processes is prerequisite knowledge that should be covered prior to this lesson.
Students will use microscopes in this lesson so they should know how to use a microscope and know the parts of a microscope. They also should have knowledge of proper laboratory procedure and proper disposal of laboratory materials, including sharp glass slides and chemicals. With their basic "magnification sense," students can use photomicrographs to extend their observations of cells, which can begin to show students that cells are the fundamental building blocks of their own bodies and of other living things as well. (Benchmarks for Science Literacy, pp. 110-112.) It also may be easier for students to understand that the cell is the basic unit of structure (which they can observe) than that the cell is the basic unit of function (which has to be inferred from experiments). (Benchmarks for Science Literacy, p. 342.)
Note: For prerequisite knowledge, students should complete Cells 2: The Cell as a System covering basic cell structure and systems before beginning this lesson.
To get students interested in and focused on the topic, write the word "skin" on the board and have them brainstorm words, concepts, or processes that come to mind. Record all responses (e.g., hair, wrinkles, sweat) and have the class discuss the list.
Then review what students already know about skin and cells in general by asking questions like these:
- What does the skin do for the body?
- (The skin helps to protect the body from injury; provides a shield against harmful substances and organisms such as bacteria and parasites; helps to keep moisture in the body; helps keep your body temperature constant; and has nerve endings that help you feel sensations.)
- What would happen if you didn't have any skin?
- (Answers may vary but encourage students to understand that the skin is our first line of defense against harm.)
- What is the skin made up of?
- (It is made up of skin cells.)
- What do cells do?
- (Cells perform three main functions: cells grow through the functioning of cellular metabolism; cells create new cells through cell division; and cells are capable of synthesizing new proteins, which are essential for the modulation and maintenance of cellular activities.)
- Are all cells the same?
- (No. Cells vary depending on the job that they perform. Specialized cells [e.g., muscle cells, nerve cells] carry out specialized functions [e.g., produce hormones, carry oxygen].)
- Do cells work alone or together with other cells?
- (Cells usually work with other cells to perform a certain function. Specialized cells group and cooperatively work to form tissues such as muscles or fat. They work together as a system.)
In this part of the lesson, students will learn more about the different kinds of cells that make up human skin.
Divide the class into pairs. Have each pair use their Skin Cells student esheet to visit and read the two-page introduction to cells at The Cells in Your Body. When they have finished reading, check their comprehension with questions like these (students can write their answers to these questions on the Skin Cells student sheet):
- What are all living things made up of?
- (They are made up of cells.)
- What are organisms with more than one cell called?
- (They are called multicellular organisms.)
- How many different types of cells are in the human body?
- (There are about 200 different types of cells.)
- What are some things that all cells have and what do they do?
- (They have a membrane, which holds the cell together; a nucleus, which contains the information that allows a cell to reproduce; and a mitochondrion, where food and oxygen combine to make energy.)
- What do groups of different types of cells create?
- (They make up the organs in your body.)
- What does a group of different organs working together to do a job make up?
- (It makes up a system.)
- Can our cells die? If so, are they replaced?
- (Yes, our cells can die and they are replaced. There is a wide variation in the rate of all death and regeneration known as cell turnover. This variation is cell type and organ dependent. For example, humans shed thousands of skin cells per day and they are quickly replaced. Brain cells, however, do not generally regenerate.)
Also, perform a review of the parts of cells. Make sure students recall and understand the location and function of the nucleus, cytoplasm, and cell membrane (as covered in the prerequisite lesson, Cells 2: The Cell as a System).
Before students do the next activity, provide them with some pre-made slides of human organ cells for them to observe under the microscope. You can obtain these slides from Microscope Slide Kit: Histology, Human Organs, from Microscope World, or you can show students images of various organ cells at Human Anatomy and Bacteriology Prepared Slides. To help students understand what they are seeing, show them an image of magnified Cheek Squamous Epithelial Cells, from Wayne's Word Online Textbook of Natural History. Explain that the structures seen here cannot be seen without magnification. Point out the labeled parts on the image and help students understand that they will look for similar structures in their specimens.
Then have students use their Observing Skin Cells lab sheet to look at their own skin cells under a microscope. They should work with their partners to collect and look at some of their skin cells. Students should have experience with the proper use of microscopes and how to prepare microscope slides. They also should know the proper laboratory safety procedures and the proper disposal of laboratory materials, including sharp glass slides and chemicals. Ask students what the function of methylene blue is. Have them look at their cells without the methylene blue so that they can see the benefit of using a dye.
Note: Make sure your students are aware that methylene blue is a vital stain—it stains nearly everything, including skin and clothing. Students should wear chemical-resistant gloves and avoid contact with eyes and skin. They should wear safety goggles whenever working with chemicals, heat, or glassware in the lab.
Once students have completed the lab, follow up with questions like these:
- What did you notice about your skin cells before you used the methylene blue?
- How did the methylene blue help you see your skin cells more clearly?
- What parts of the cell can you see through the microscope and at what magnification do you see them?
- Compare this slide of skin cells to the slides of the human organ cells you saw earlier. Do they look the same? Do all of the cells from the various organs look the same? Why or why not?
- Do you see the same structures among all of the various organ cells?
- Do you see different structures between the different organ cells?
(Answers may vary. Encourage students to provide explanations for their answers.)
Divide the class into three groups representing these layers or structures of the skin:
- dermis and hypodermis
- sweat and oil glands; hair and nails; and skin color.
Hand out the Getting Under Your Skin student sheet and review it with the class. Have the students in each group read through the parts of their layer or structure and review their notes to make sure they understand each one. Then instruct group members to choose one bulleted part to "become," making sure all parts are represented. Each student should study his or her part and be ready to explain how it functions and interacts with other skin cells.
In addition to explaing how his or her part functions and interacts with other skin cells, student should consider this question: What might happen if a particular type of skin cell was missing or damaged? Students also could find information about skin diseases that might affect the part of the skin they're studying.
Once all participants have finished their research, ask them to present the information to the class. They could do so as a poster presentation, a PowerPoint, etc.
You can extend the ideas about skin and systems in this lesson by leading students through these Science NetLinks lessons:
Students can have fun learning more about cell structure and functions by visiting CELLS Alive!, which features detailed cell diagrams, 3-D models, and animated cell cams.
Cell Project, from Access Excellence, allows students to extend what they have learned about cells, including construction of a giant cell model.