Title: Mastering the Microscopic World

Author: Lori Morin, Waterville Junior High School

Overview: Students need to independently use microscopes to study the many aspects of the microscopic world. The flex camera allows a class to view through the same microscopeís eyepiece with teacher direction. Modeling the correct use of a compound microscope while demonstrating common errors using the flex camera television projection is a very effective method to ensure student success with this instrument. The three lab activities described follow the scientific method and meet many of the Maine Learning Results. It is important to note that to ensure cognitive growth, these labs are part of the studentís yearlong growth. Students must gradually enter omitted portions of labs with the year-end goal of having the student design and write their own lab following the scientific method. Use the student worksheets accordingly.

Materials: Video Camera System for Microscope (Flex Camera), television, prepared slides, plain slides, plastic coverslips, stain, toothpicks, eyedroppers, tweezers, scissors, water, classroom set of microscopes, video: The Invisible World by National Geographic, and video: Magic of Cells by Library Video.

Grade Levels: 7-9 Life Science

Time: 9-11 Classes (45 minute periods)

Students Grouping: The demonstration of microscope usage with the Flex camera projecting images on the television screen involves the entire class. The independent practice with the compound microscopes should be in groups no larger than two. Monitor for equal microscope use by each partner. The independent use of the microscope is required for each student to observe the parts and processes of cells.

Maine Learning Results:

Science and Technology

  1. Classifying Life Forms (Middle Grades 5-8)
  2. #3. Describe some structural and behavioral adaptations that allow organisms to survive in a changing environment.

  3. Cells (Middle Grades 5-8)

#2. Prepare and examine microscope slides of single-celled and multi-celled organisms.

  1. Cells (Secondary Grades)

#1. Relate the parts of a cell to its function.

J. Inquiry and Problem Solving (Middle Grade 5-8 and Secondary Grades)

#1. Make accurate observations using appropriate tools and units of measure.

  1. Communication (Middle Grades 5-8)

#4. Make and use scale drawings, maps, and three-dimensional models to represent real objects, find locations, and describe relationships.

#6. Identify and perform roles necessary to accomplish group tasks.

Lesson Descriptions:

Part I. Introducing the invisible world.

Anticipatory Activity: Introduce students to a world we often miss with a video such as National Geographicís "The Invisible World". It does cover many other forms of technology, but has great microscope footage. The age of the video leads to great discussion about how the field of technology changed history and also how it has changed since the release of this video in the late 1970ís. This correlates with many texts like Glencoeís Life Science because they describe the development of the microscope from its simplest forms of AntonVan Leeuwenhookís and Robert Hookeís times.

Input of Information: Give students the following lab format to follow for the use of a microscope. This follows the scientific method. Use the Flex Cam to demonstrate the step by step procedure to view a slide with the compound microscope. The Teacherís Guide allows the teacher to model both correct and incorrect procedure.

 

Practice: Students will complete all twelve steps to view a slide. Students will complete both a low power and high power color sketch in the data portion of the lab for at least two separate slides. Students will complete the lab by reflecting on and answering the conclusion questions.

 

 

Teacherís Guide

Pose the problem to the students "How can we see the microscopic things we have been studying such as cells?" and a student will suggest the use of a microscope usually within the first couple of answers. Review the equipment to be used and where to find it. It is a good idea to discuss with students the equal partnership that must take place if a microscope is to be shared. Both partners will need to be able to independently use a microscope without assistance. It is also a good time to give a speech to middle level students about their graduation to a level of science where they will become capable of some very impressive skills, such as using a microscope with minimal adult assistance. Adult help is made available, but students should gain the confidence to successfully use the microscope, especially for the labs that follow. Emphasize that procedure is essential to success. Model and explain the proper way to carry a microscope, with one hand on the arm and the other under the base. Use the flex camera connected to a compound microscope and television to demonstrate the following steps to the class.

Procedure-

Step 1. Identify all parts of the microscope. Parts should include the eyepiece, arm, body, light source, objective lens, course adjustment knob, fine adjustment knob, revolving nosepiece, base, stage, and stage clips. (Point to the parts of the microscope and see if students can name them. Inform students that many microscopes are built differently. For example, a course adjustment knob may be in a different location or may move the stage while another does the same job by moving the lenses. Using the wrong knob or lens because of lack of knowledge can cause a student to experience a lack of success and become frustrated.)

Step 2. Sketch the microscope and label the parts on a piece of drawing paper. (Make

students aware that they do not have to be great artists, they are just proving that they

can find the correct part to address when given instructions.)

Step 3. Use the coarse adjustment knob to either raise the body tube or lower the stage

creating a wide space between the lens and the stage. (A coarse adjustment knob brings a

specimen either closer or farther from the lens. Even if the coarse adjustment knob

moves different parts, it still does the same thing.)

Step 4. Turn the nosepiece until the lowest powered objective lens is in place. (10x)

(Students often want to start with a high powered lens or do not check to see which lens

they are using. Show the students where to find the power of the lens, and make it clear

that they must always start with the low power lens. This is where you can demonstrate

how inefficient the use of the wrong lens can be if you model it on the television using the

flexcam).

Step 5. Turn on the light. (Additional instructions will be needed for microscopes using

mirrors and diaphragms.)

Step 6. Center the slide on the stage with the stage clips. (Students will really need to see

that the teacher does not just put the slide on the stage, but looks at it first to see where

the specimen is in relationship to the glass slide.)

Step 7. Looking from the side, bring the stage to the lens by either lowering the body or

raising the stage with the coarse adjustment knob. (Stress to students a couple reasons for

doing this. First, looking from the side allows us to make sure the lens does not crush the

slide. Also, to look at a slide, it should start out as close to the lens as possible.

Using the flex camera, you can show the class what would happen if you left out this

step.)

Step 8. Looking through the eyepiece, slowly turn the coarse adjustment knob in the

opposite direction until the specimen is in focus. (Demonstrate on the flex camera

projection what would happen if you turned the knob too fast or used the wrong knob.)

Step 9. Draw and label what you see.

Step 10. Revolve the nosepiece to the high powered lens. (40x) (Make sure it does not hit

the slide)

Step 11. Looking through the eyepiece slowly turn the fine adjustment knob until the

specimen is in focus. (The biggest mistake I see is often made during this step. Students will use the wrong adjustment knob. A student will realize this, and then use the correct knob, but it is too late. The student will need to refocus it under low power with the coarse adjustment knob once again. This is frustrating to the student and they do not often recognize this mistake. Use the flex camera projection to demonstrate this mistake and the proper way to correct it.)

Step 12. Draw and label what you see.

Step 13. Complete steps 3-12 for another slide.

 

 

 

Student Lab

 

 

Title: Using a Microscope

Problem: How can we look at the microscopic things (like cells) that we are going to study?

Hypothesis: We can magnify microorganisms and cells using a microscope.

Experiment:

Materials-Electric compound microscope

Prepared slides

Colored pencils

Procedure-

Step 1. Identify all parts of the microscope. Parts should include the eyepiece, arm, body, light source, objective lens, course adjustment knob, fine adjustment knob, revolving nosepiece, base, stage, and stage clips

Step 2. Sketch the microscope and label the parts on a piece of drawing paper.

Step 3. Use the coarse adjustment knob to either raise the body tube or lower the stage

creating a wide space between the lens and the stage.

Step 4. Turn the nosepiece until the lowest powered objective lens is in place. (10x)

Step 5. Turn on the light.

Step 6. Center the slide on the stage with the stage clips.

Step 7. Looking from the side, bring the stage to the lens by either lowering the body or

raising the stage with the coarse adjustment knob.

Step 8. Looking through the eyepiece, slowly turn the coarse adjustment knob in the

opposite direction until the specimen is in focus.

Step 9. Draw and label what you see.

Step 10. Revolve the nosepiece to the high powered lens. (40x)

Step 11. Looking through the eyepiece slowly turn the fine adjustment knob until the

specimen is in focus.

Step 12. Draw and label what you see.

Step 13. Complete steps 3-12 for another slide.

 

 

Data:

 

 

 

 

 

Specimen A (10x) Specimen A (40x)

 

 

 

 

Specimen B (10x) Specimen B (40x)

 

Conclusion:

  1. How should you carry a microscope?
  2. What do you need to be careful of when moving the lens close to the slide with the coarse adjustment knob?
  3. What is another easy mistake that people commonly make while trying to use a microscope?
  4. Did you meet your hypothesis on the first try? Why or why not?
  5. While looking through the eyepiece move the slide to the left. What direction does the sample on the slide appear to move from the view of the eyepiece?

 

 

Part II. Animal Cells, Up Close and Very Personal.

 

Anticipatory Set. A computerized animation traveling through a cell in the video, Magic of Cells, is a great way to help students visualize the organelles presented in a typical life science text.

Input of information: The flex camera connected to a compound microscope is once again a great way to guide students through the study of an animal cell. Use the flex camera to project a prepared slide of any animal cell. It is good to choose a slide that has easy to see organelles. Frog blood is an excellent sample to use. Model the appropriate steps to using a microscope from part I of this unit. When the slide is focused, clearly point out the organelles that are easy to view. Common organelles that most slides easily show would be the nucleus, nuclear membrane, cell membrane, and cytoplasm.

Practice: Instead of viewing prepared slides, students will take a cell from their cheek and prepare a wet-mount to view. Model the steps in the cheek cell lab below using the teacherís guide before students attempt to perform this lab. Students will complete drawings of a cheek cell and itís labeled organelles under both high and low power as well as the conclusion questions.

 

 

 

Teacherís Guide

 

After the class looks at the prepared slide of an animal cell ask the class if there are any animals in the room that could donate some cells to look at. Some students may suggest to donate some blood or skin from a recent scrape. This next lesson involves looking at our cheek cells. The process the students will use is the creation of a wet-mount. It is very important to refer to the previous lab when given the direction to view the sample under the microscope. Assume that students can use microscopes independently, but watch for errors that commonly occur.

 

Procedure-

Step 1. Place a drop of water on a clean slide. (Students need to know that more is not

better, demonstrate how to limit the amount of water that comes out of an eye dropper.)

Step 2. Carefully scrape the inside of your cheek with a toothpick. (It is very important

that students see how to do this without causing pain or injury.)

Step 3. Swirl the toothpick into the drop of water. (It is good to throw away

dirty toothpicks immediately.)

Step 4. Add one small drop of blue dye. (Using a separate toothpick dipped in the dye

helps to control the amount applied.) (Again, more is not better because too much dye

will make the cells too dark to discriminate. Use just enough to turn the liquid a medium

blue.)

Step 5. Wait one minute for the dye to set.

Step 6. Place the coverslip on the sample dropping from an angle to avoid air bubbles.

(It would be good to show students what air bubbles look like on the flex cam. Students

often mistake them for cells because they are round.)

Step 7. Remove any excess liquid. (Show students how to blot excess liquid with a tissue,

but without disturbing the coverslip or sample)

Step 8. View under low power. (Since an animal cellís organelles where already pointed out once with a prepared slide it is good to leave this step out during the demonstration. Students should have had enough of the procedure modeled to experience success. Review the following steps before the students proceed.)

Step 9. Draw and label one cheek cell and the organelles that are visible.

Step 10. View under high power.

Step 11. Draw and label one cheek cell and the organelles that are visible.

Step 12. Dispose of slides and toothpicks.

 

 

 

Student Lab

 

Title: Cheek Cell Lab

Problem: How can we see one of our cells and itís organelles?

Hypothesis: Magnifying a stained sample of our cheek cells with a microscope will allow us to find many human cells and their organelles.

Experiment:

Materials-

Compound microscope

Slide

Plastic coverslip

Blue stain

Toothpick

Water

Eyedropper

Colored pencils

Procedure-

Step 1. Place a drop of water on a clean slide.

Step 2. Carefully scrape the inside of your cheek with a toothpick.

Step 3. Swirl the toothpick into the drop of water.

Step 4. Add one small drop of blue dye. (Using a separate toothpick dipped in the dye

helps to control the amount applied)

Step 5. Wait one minute for the dye to set.

Step 6. Place the coverslip on the sample dropping from an angle to avoid air bubbles.

Step 7. Remove any excess liquid.

Step 8. View under low power.

Step 9. Draw and label one cheek cell and the organelles that are visible.

Step 10. View under high power.

Step 11. Draw and label one cheek cell and the organelles that are visible.

Step 12. Dispose of slides and toothpicks.

Data:

 

 

 

 

 

 

 

Cheek Cell Low Power (10x) Cheek Cell High Power (40x)

 

 

Conclusion:

 

  1. What organelles did you see and what did each one look like?
  2. For the organelles that you did not see, what were some reasons they could not be viewed? Did you have any sources of error, or did you meet your hypothesis the first time?
  3. What shapes were your cheek cells?

 

 

 

Part III. Plants Have Cells Too!

Anticipatory Set: Plants cells are similar to animal cells in many ways, yet a few organelles differ. A great way to have students review the similar cell parts and be exposed to the additional organelles in a plant cell is by a virtual dissection. The following web site allows students to take apart a computer animated plant cell and locate different organelles: http://ampere.scale.uiuc.edu/~m-lexa/cell/cell.html.

Input of Information: The exposure to plant cells in both the textual and computerized format should be followed by hands on samples. Once again, model the use of the compound microscope to look at a plant cell and its organelles by using the flex camera. A prepared slide of a plant sampling should easily allow you to point out the following organelles: cell wall, cell membrane, cytoplasm, nucleus, nuclear membrane, and chloroplasts. A prepared slide of a bean root tip or onion rind works very well.

Practice: Instead of viewing prepared slides, students will prepare a wet-mount of a plant called elodea (commonly found in pet stores under the name anacharis) to view plant cells and the corresponding organelles. Model the steps in the plant cell lab below using the teacherís guide before students attempt to perform this lab. Students will complete drawings of a plant cell and its labeled organelles under both high and low power as well as the conclusion questions.

Teacherís Guide

Elodea, also known as Anacharis, can be purchased inexpensively at a pet store. It is an aquatic plant often used in fish tanks. A pet store may need to place a special order, so plan ahead. The plant can be kept alive in a container of fresh water in the classroom, but it is best to use fresh samples. Again, model the correct use of the microscope and review the common errors that may occur.

 

Procedure-

Step 1. Place one drop of water on a clean slide.

Step 2. Use the scissors to snip a very small piece of elodea from its leaf tip.

(The sample should also be thin, watch out for accidental folding of the leaf sample.)

Step 3. Lay leaf piece flat on drop of water. (Use the tweezers to manipulate the leaf.)

Step 4. Place the coverslip on the sample dropping from an angle to avoid air bubbles.

Step 5. Remove any excess liquid. (Be aware that the leaf will dry out if the moisture

immediately surrounding the leaf is removed. This will affect the results.)

Step 6. View under low power. (Since a prepared slide of a plant was previously shown

and the organelles pointed out, let the student complete the following steps without a

demonstration on the flex camera.)

Step 7. Draw and label one elodea cell and the organelles that are visible.

Step 8. View under high power.

Step 9. Draw and label one elodea cell and the organelles that are visible.

Step 10. Dispose of elodea leaf sample.

Step 11. Rinse and dry slide.

 

 

 

Student Lab

 

Title: Plant Cell Lab

Problem: How can we view plant cells and their organelles?

Hypothesis: Magnifying a piece of leaf from an elodea plant with a compound microscope will display the plantís cells and organelles.

Experiment:

Materials-

Compound microscope

Slides

Plastic coverslip

Elodea plant

Water

Eye dropper

Scissors

Tweezers

Procedure-

Step 1. Place one drop of water on a clean slide.

Step 2. Use the scissors to snip a very small piece of elodea from its leaf tip

Step 3. Lay leaf piece flat on drop of water.

Step 4. Place the coverslip on the sample dropping from an angle to avoid air bubbles.

Step 5. Remove any excess liquid.

Step 6. View under low power.

Step 7. Draw and label one elodea cell and the organelles that are visible.

Step 8. View under high power.

Step 9. Draw and label one elodea cell and the organelles that are visible.

Step 10. Dispose of elodea leaf sample.

Step 11. Rinse and dry slide.

Data-

 

 

 

 

 

Elodea Cell Low Power (10x) Elodea Cell High Power (40x)

 

 

Conclusion:

  1. What organelles did you see and what did each one look like?
  2. For the organelles that you did not see, what were some reasons they could not be viewed? Did you have any sources of error, or did you meet your hypothesis the first time?
  3. The animal cell in the previous lab did not have a cell wall, but the plant did? Why would plants in particular need cell walls?
  4. You also saw the organelle called chloroplasts that looked like green dots. What makes these organelles green? Why does a plant cell have chloroplasts and an animal cell does not?
  5. What shapes were the plant cells?

 

WWW Links: http://ampere.scale.uiuc.edu/~m-lexa/cell/cell.html

References:

Daniel, Ortleb, Biggs, 1999. Life Science. Glencoe/McGraw-Hill: New York, New York.

Wright, Coble, Hopkins, Johnson, LaHart, 1988. Life Science. Prentice Hall, Inc.: New Jersey.

 

 

This curriculum project was funded by the Colby Partnership for Science Education, the Howard Hughes Medical Institute, and the Bell Atlantic Foundation.