THE MICROSCOPE,
AN INVENTION WORTHY OF “CELLABRATION”

MASTER TEACHER  Jeff Duffy

GRADES: 6 – 8

OVERVIEW
Students will make a simple microscope. They will also learn some of the uses for and types of microscopy. Calculating magnification and estimating sizes of objects will also be explained.  Additionally, students will have the opportunity to prepare, observe and describe plant cells.

ETV SERIES
Simply Science #116  - A Close-up View of Growth

LEARNING OBJECTIVES
The student will be able to:
* Calculate magnification of a light microscope
* Estimate size of observed cells/organisms
* Prepare a wet mount slide
* Explain why stains are used in slide preparations
* Demonstrate appropriate microscope use
* Draw observed cells in proportion

MATERIALS
Light microscope (one per student)
Slides (one per student)
Cover slip (one per student)
Dissecting Needle (one per student)
Iodine (20 ml.)
Fresh potato (one)
Razor blade or scalpel
Eyedropper
Ruler with metric scale (one per student)
Standard size, unruled paper
Labels with very fine print (less than 4 picas)
Pond water (100 ml.)
Tooth picks, flat (one per student)

VOCABULARY
Microscope:  a device for enlarging an object’s image
Field of view: the area of an object being viewed
Lens: a device for bending light rays
Micron: one one-thousandth of a millimeter
Refraction:  Bending of light rays

PRE-VIEWING ACTIVITY
Begin the lesson by asking, “Have any of you been reproducing lately? You may not have thought you weren’t,  but you were,  and so have I. We haven’t been making more people, but more cells-lots of them. Everywhere, you look, you see living things, and scientists know now that all living things are made of cells.  They did not always know this, but with the invention of an amazing instrument, they were able to observe and begin to understand this basic unit of all living things, the cell.”

FOCUS FOR VIEWING
To give students a specific responsibility, say, “ Today we are going to be looking at the structures that make you, and me, and everything living thing. You are going to make a simple device to make objects appear larger. You will also use a microscope, calculate the magnification of that microscope, observe individual cells and estimate their size. You will also experiment with ways to make cells easier to observe.”

VIEWING ACTIVITIES
Start the video Simply Science 116 when the #16 appears in the upper left corner of the screen and the title “A Close Up View of Growth” fades in. Pause when Dana says “The physics of a microscope brings the biology of life into new focus” as a paramecium moves to the lower left of the screen. Say, “Do any of you know how a microscope works?” Answers will vary. Most will not deal with bending light or refraction. Say, “Let’s look at something small and then make a microscope to help see it better.” Pass out labels with very fine print. Ask students if the writing is easily read. Then pass out a clean slide to each student. Have them place the slide over the print. With a dropper, place a single drop of water over the print.  Ask the students what has happened to the size of the print and why. (the curved surface of the water has bent (refracted) the light and made the print appear larger). Continue by saying, “You have just made a simple microscope. Where did microscopes first come from and what can you see with one? Let’s find out.” Resume tape: A brief explanation that all life is made of cells is given. Leeuwenhoek is credited with inventing the microscope. Pause when the title “Wet Mount Slides and Staining” slides from the left. Ask “What is the basic unit of life and what do we need to be able to see it?” (cell, a microscope) After noting student’s responses, say, “Let’s see what some students have to say.”  Fast forward through Dr. Shibuya until a student slides from left and “replaces” the doctor. Pause when the girl says, “Now you can prepare a wet mount slide.” Pass out equipment to students. Stress importance of lab safety and understanding vocabulary. Resume when student explains/demonstrates wet mount cell preparation. Pause when the student places a slide on the stage and says, “Just a smear.” Have students duplicate the activity. Ask, “Are you having the same problem seeing cells the girl had? What can be done to see the cells more clearly?” Solicit responses. (use some kind of stain).  Fast forward through Dr. Shibuya’s scene until a student is standing in front of a set of cupboards. She demonstrates how iodine is applied. Pause when the student says, “Others work better with animal cells.” A stained nerve cell is shown.  Have students stain potato cells using demonstrated techniques. After staining/observing say, “You can see them now, but is there a way to estimate cell size?” Fast Forward through Dr. Shibuya until the title says, “Magnification and Field of View.” Pause when a student says, “Multiply the two values.” Say, “Since the eyepiece power is usually 10X, moving the decimal point to the right one place for the objective power will give the total magnification.” Have the students calculate the magnification for all lens combinations. Ask, “What do you think happens to the field of view if the magnification increases (or decreases)?” Answers may vary.
Resume the video where a student uses a metric rule on stage and determines the diameter of the field of view at 40X and 100X. Pause when the girl says, “As magnification increases,  the diameter of the field of view decreases.” Have students duplicate this activity and compare results with each other. Since there will likely be some estimating on how many millimeters are seen, especially on high power, answers will vary. Say, “Now that you have an idea about how large the area is that you are viewing, how do you determine the size of the object you are looking at? Let’s see what the students have to say?” Resume when students explain how to estimate the size of a cell and draw it to scale.  Stop when you see text that says, “Most microscopic objects are measured in microns. There are 1000 microns in one millimeter.” Have students re-examine stained potato cells. Have them draw several cells to scale on high power and estimate the size of the cells.

POST VIEWING ACTIVITIES
Say, “Now that you have looked at some cells using the microscope and drawn them, what other kinds of cells would you like to look at?” Looking at yeast cells, cheek cells, and pond water are a few possibilities. Try different types of stains with different cells.

ACTION PLAN
Collect and observe cells from various common organisms.
Try different stains to determine their effectiveness. 
Compare the structure of plant and animal cells.
Visit a hospital or doctor’s office and inquire how the microscope is used for medical purposes.
Investigate sites on the Internet to observe photomicrographs, investigate the history of the microscope, or  investigate operating techniques of microscopes. The following are a few such sites.
http://www.utmem.edu/personal/thjones/hist/hist_mic.htm
http://www.uq.edu.au/nanoworld/nanohome.html#menu
http://www.anserc.org/virtour/microscope_room.html
http://micro.magnet.fsu.edu/micro/gallery.html

EXTENSIONS
Language arts: Write a descriptive paper on proper microscope use.
History: Investigate the importance of the microscope in the advancement of medicine.
Social Studies: Research the importance of microscopy and its impact on pandemic diseases. 
Mathematics: Compare the magnification powers of light microscopes and electron microscopes. (Maximum of 2000X with a light microscope, >1,000,000X with an electron microscope)
Art: Create three-dimensional models of cell observations. 
Science: Research the uses of microscopy outside the realm of the life sciences.
 

Updated:  April 01, 2008