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CELLS ALL AROUND
Grades 6 - 8

Overview

This lesson presupposes that the students know what cells are, and that cells are an integral part of tissues, organs and organ systems. The goal of this lesson is to measure the size of an epithelial cell and to estimate the number of epithelial cells in a given area of the body. The students should prepare and observe microscope slides of the human-cheek cells and will use the microscope to estimate the size of these cells for use in their calculations of area and quantity.
ITV Series
"BIOSCOPE #2: Cells"
"MATH WORKS #6: Estimating: Rounding"
Learning Objectives
Students will be able to:
Materials
Each student should have:

Pre-Viewing Activities
Prior to class (perhaps over a weekend) have each student (or pair of the students) create and label The Incredible Edible Cell by making a model of a cell, complete with cell parts from commonly-found foods (grapes for chloroplasts, kidney beans for mitochondria, etc.).

Project a picture of a cell from any life-science textbook or laboratory manual using an overhead or opaque projector, or find a picture of a cell and its structures on laser disc and review the cell structures with the class.
Focus Viewing
The goal of this lesson is to have the students estimate the size and number of cells found in their skin. Accordingly, two videos will be used. The first reviews cell structure and function, while the second presents a specific strategy for estimating, round up to the nearest ten. The students should be given the specific responsibility while viewing Bioscope #2: Cells for: identifying by inspection and noting in writing different colors and shapes of different types of cells; and identifying by inference and by noting in writing other cell characteristics

Viewing Activities
Show the two-minute segment from Bioscope #2: Cells in its entirety that discusses the various types of cells. It begins with the narrator saying, "It all begins with a single cell," and ends at the picture of a hand.

Now REWIND the video to the starting point noted above where the narrator says, "It all begins with the cell."

PAUSE when the word "yucca" appears and ask someone to trace the outline of one of the cells, so that the students understand how these particular cells are shaped.

RESUME the video.
PAUSE when the word "algae" appears and ask the students what cell colors they see here and in previous frames. Discuss why different cells have different colors.

RESUME the video.
PAUSE after the word "tobacco" disappears and ask the students to identify two- or three-different shapes of cells. Ask the students why they think different cells have different shapes.

RESUME the video.
PAUSE after the word "bone" appears and ask the students, "Why do bone cells have to be hard?" to illustrate that the characteristics of some cells depend on their function.

RESUME the video.
PAUSE when muscle cells appear and ask the students, "Why do muscle cells have this particular shape?"

RESUME the video.
PAUSE after the narrator says, "Some are large...." Ask the students, "What kind of a cell is this?" so that the students identify different types of cells.

RESUME the video.
PAUSE after the narrator says, "The cell is the smallest living part...." Ask the students, "How large do you think cells are?"

RESUME the video.
PAUSE after the narrator says, "The skin is made up of trillions of cells" and ask, "Can you show me on the screen where one of those cells is?" so that the students begin identifying epithelial cells.

STOP the video at this point.

Segue from the video to the activity by saying, "Now we will estimate how many epithelial cells are in a particular area of your hand." Ask, "What are some general rules for estimating?" After the students respond, say, "We will now see a segment from a video about estimating. The problem here is figuring out how many hot dogs the students should buy for their hot-dog stand at a fair. Listen to the man's solution for estimating."

The students should be given the specific responsibility while viewing Math Works #6: Estimating: Rounding of: identifying a useful strategy for estimating, rounding up to the nearest ten.

Show the segment from Math Works #6: Estimating: Rounding beginning where the man says, "If you have to make a decision but don't know all the facts...."

PAUSE the video after the man states the problem and ask the students for their ideas.

RESUME the video and stop it when the man says to "...round up to the nearest ten."

STOP the video at this point.
Ask students, "What is the particular estimation solution the man describes? How does this apply to our problem with epithelial cells?" to reinforce the connection in the students' minds between the problem on the video and the epithelial problem they will be exploring.
Post-Viewing Activities
At this point the students should have reviewed cell structures and should have identified a specific rounding skill. They should now integrate both of these ideas as they estimate the number of cells found in an area of their body.

Tell the students that we will now use our knowledge of cells and our estimation experience from the videos we've watched to figure out how many epithelial cells exist on the surface of our hand. But first we need to make some calculations about the diameter of the microscope field.

Ask, " What is the diameter of the microscope field?" Have the students put their ruler on the microscope stage, focus on it, and estimate the diameter in millimeters. How many millimeters wide is the field? The students should write the microscope field diameter in millimeters on their piece of paper. Then ask, "Using this information, how many centimeters long is the field?" The students should write the microscope field diameter in centimeters on their piece of paper.

Tell the students, "An epithelial cell is a cell that covers and protects surfaces of your body. We are going to look at some epithelial cells and estimate their size and number."

Have the students scrape some epithelial cells from the inside of their cheeks by using a toothpick or wood splint. The students should wipe the scrapings across the center of the microscope slide and add one or two drops of the stain on top of the scrapings. They should cover this drop with the cover slip. Then they should focus the 10X objective lens of the microscope on the scraping and locate one or two isolated epithelial cells.

If you have access to a microscope video camera and video screen, it would be best to show the class what the cells look like before they try to locate them on their own. If a camera is not available then show the class pictures of epithelial cells using a book or a laser disk image.

Ask the students, "In your estimation, how many epithelial cells would stretch across the diameter of the microscope field? Explain how you thought out your answer using complete sentences on a piece of paper, then record the number of epithelial cells covering the diameter of the microscope field on your piece of paper."

Tell the students, "Using your answers above, estimate the width of one epithelial cell. Explain in complete sentences on your piece of paper how you got your answer. Then record the length of one epithelial cell in centimeters on your paper."

Ask the students to draw a square one centimeter long and one centimeter wide, on the back of their hands with an erasable pen. Ask them to estimate how many epithelial cells would fill that square. They should show their work and explain their reasoning as well as estimate the answer on their piece of paper.
Extensions
Science:
Have the students write to the oncology department at a local medical school, asking about the differences between normal cells and cancerous cells.

Have the students make posters with the theme "Cells Save Lives" to encourage people to donate blood.

Math:
Have the students ask the school's business manager or dietitian how he/she estimates how much food to order for school lunches or how many pencils to order for the school year.

Language Arts:

Imagine three different types of cells commuting to work in New York City on Metro-North. Write the conversation they might have introducing themselves to each other, telling where they work, and explaining why they are dressed the way they are.

Science:
Send e-mail via the Internet to the American Association of Cell Biologists, asking them for the true sizes of several different types of human cells.

Math:
The students can trace the surface area of their hand (front, back and side views) on butcher paper. They can then use the measurements they derived in the last exercise to estimate how many epithelial cells cover the surface of their hand. More ambitious students might want to derive a method for estimating how many epithelial cells cover the surface area of their entire body. They can use butcher paper to trace their front, back and side body views to help them with their calculations. Again, after this activity the class should discuss the estimation methods that the students used to derive their answers.


Master Teachers: Robert Berwick and Susan Kelseya

Note to Teacher:

Prior to class (perhaps over a weekend) have each student (or pair of the students) create and label The Incredible Edible Cell by making a model of a cell, complete with cell parts from commonly-found foods (grapes for chloroplasts, kidney beans for mitochondria, etc.). Project a picture of a cell from any life-science textbook or laboratory manual using an overhead or opaque projector, or find a picture of a cell and its structures on laser disc and review the cell structures with the class.

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