Life Science: Cells, Tissues, Organs, and Systems
Ashley Clayton
Lesson 11: Using a Microscope to View a Cheek Cell
Outcome 8.2 - Demonstrate proficiency in the use of a compound light microscope to observe
plant and animal cells. [SI]
Indicator b. - Prepare samples of plant and animal cells for viewing by wet mounting and
staining when necessary.
Objectives:
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Students will learn how to prepare a slide
Students will properly handle a microscope
Materials:
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Microscope
Glass slide
Tweezers
Iodine or methylene blue
Onion
Cover-slip
Toothpick
Science notebook
Lab Worksheet
Procedure:
1. Warm up (5 min)
2. Lab – (35 min)
3. Clean up (5 min)
Evaluation:
-
Exit slip
Life Science: Cells, Tissues, Organs, and Systems
Warm up:
Taking out the microscope for the lab
Step 1: Make sure all backpacks are out of the aisles before you get a microscope! Always carry
the microscope with one hand on the Arm and one hand on the Base. Carry it close to your
body.
Step 2: Remove the cover, plug the microscope in, and place the excess cord on the table! If
you let the excess cord dangle over the edge, your knee could get caught on it, and the next
sound you hear will be a very expensive crash. I will bill you later!
*When using the microscope REMEMBER:
Step 1: Always start and end with Low Power!
Step 2: Place the slide on the microscope stage, with the specimen directly over the center of the
glass circle on the stage (directly over the light). Then you have a 9 out of 10 chance of finding
the specimen as soon as you look through the eyepiece!
NOTE: If you wear glasses, take them off; if you see only your eyelashes, move closer. Be sure to close, or cover
your other eye!!
NOTE: If you see a dark line that goes part way accross the field of view, try turning the eyepiece. That dark line
is a pointer that will be very valuable when you want to point out something to your lab partner, or your teacher!
Step 3: If, and ONLY if, you are on LOW POWER, lower the objective lens to the lowest point,
then focus using first the coarse knob, then the fine focus knob. The specimen will be in focus
when the LOW POWER objective is close to the lowest point, so start there and focus by
slowly raising the lens. If you can’t get it at all into focus using the coarse knob, then switch to
the fine focus knob.
Step 4: Adjust the Diaphragm as you look through the Eyepiece, and you will see that MORE
detail is visible when you allow in LESS light! Too much light will give the specimen a
washed-out appearance.
Step 5: Once you have found the specimen on Low Power (100x), unless specifically asked to
draw it on low power, center the specimen in your field of view, then, without changing the
focus knobs, switch it to High Power. If you don’t center the specimen you will lose it when you
switch to High Power.
Step 6: Once you have it on High Power remember that you only use the fine focus knob! The High Power Objective (430x) is very close to the slide. Use of the coarse focus knob will
scratch the lens, and crack the slide.
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Step 7: Never use the oil immersion lens. Without the oil to lubricate the lens, you will destroy
it! Also, the oil is needed to help gather enough light to actually see through the lens!
Life Science: Cells, Tissues, Organs, and Systems
Lab worksheet:
*Depending on the number of microscopes available, students will work in pairs or groups to do
this lab.
Seeing Cells Lab
Today we will make slides of 2 different cells and look at them under the microscope:
1. Onion skin cells
2. Human cheek cells
Microscope rules
1. Always carry or move a microscope with two hands, one on the arm, and one on the
bottom.
2. Always use the lowest power lens (the shortest lens) when you take a slide on and off
the stage.
3. Always start with the lowest power lens (the shortest lens). Get the slide in focus there,
first using the coarse focus knob (the large knob) to get it close, THEN using the fine
focus knob (the small knob) to get it perfectly in focus. From there, you can switch to a
higher power lens.
4. Always look from the SIDE of the microscope, not through the eyepiece, when switching
lenses to avoid hitting the lens on the slide.
5. Only use the coarse focus knob (the large knob) when you are using the lowest power
lens (the shortest lens). Using the coarse focus knob on a higher power can crack the
lens!
6. Please turn off the light and cover the microscope when you are finished.
Onion skin cells
2 drops iodine
1. Add 2 drops of iodine to the center of a glass
slide. Be careful! Iodine can stain your
onion skin
clothes.
2 drops iodine
2. Take a small piece of onion. Use tweezers to
peel off the skin from the underside (the
glass slide
rough, white side) of the onion. Throw the
rest of the onion piece away.
3. Carefully lay the onion skin flat in the center of the slide on top of the iodine.
4. Add 2 drops of iodine to the top of the onion skin.
5. Stand a thin glass cover slip on its edge near the onion skin, next to the drop of iodine.
6. Slowly lower the other side of the cover slip
until it covers the onion skin completely. If
cover slip
there are air bubbles, gently tap on the glass
to “chase” them out.
7. Make sure the lowest power lens (the
shortest lens) is in place over the stage and
the microscope light is turned on. Place the slide onto the stage of the microscope.
8. Look through the eyepiece and turn the coarse focus knob (the largest knob) until an
image comes into focus. It should look like a brick wall or like lizard skin.
9. Now use the fine focus knob (the smallest knob) to make the image as focused as
Life Science: Cells, Tissues, Organs, and Systems
possible.
10. In your lab notebook, draw a picture of what you see. Label the picture “Onion skin cells
40x”. Label as many parts of the cell as you can see.
11. Looking from the SIDE of the microscope, NOT through the eyepiece, rotate the lenses
to the next highest powered lens (100x). If you need to, use the fine focus knob (the
smallest knob) to get the image into focus. DO NOT USE THE LARGE KNOB!! You may
see a small dot in the middle of each cell.
12. Again, looking from the SIDE of the microscope, rotate the lenses to the highest
powered lens (400x). If you need to, use the fine focus knob (the smallest knob) to get
the image into focus. You should see a dark blob in the middle of each cell.
13. In your lab notebook, draw a picture of what you see. Label the picture “Onion skin cells
400x”. Label as many parts of the cell as you can see.
14. Switch to the lowest power lens and THEN remove the slide. Set it aside for now.
Human cheek cells
1. Add one drop of methylene blue to the middle of a clean slide. Be careful! Methylene
blue will stain your clothes and skin.
2. Use the flat side of a toothpick to gently scratch the inside of your cheek. DO NOT
GOUGE YOUR CHEEK - you don’t need chunks of skin and definitely don’t want to draw
blood.
3. Gently touch the toothpick to the drop of dye on the slide. Some of your cheek cells
should drift off into the dye.
4. Throw the toothpick away.
5. Stand a thin glass cover slip on its edge near the drop of dye.
6. Slowly lower the other side of the cover slip until it covers the dye completely. Make
sure there are no air bubbles.
7. Make sure the lowest power lens (the shortest lens) is in place over the stage. Place the
slide onto the stage of the microscope.
8. Look through the eyepiece and turn the coarse focus knob (the largest knob) until an
image comes into focus. It should look like scattered blobs. Move the slide around until
a nice cluster of blobs moves into the center of your image.
9. Use the fine focus knob (the smallest knob) to make the image as focused as possible.
10. In your lab notebook, draw a picture of what you see. Label the picture “Human cheek
cells 40x”. Label as many parts of the cell as you can see.
11. Looking from the SIDE of the microscope, NOT through the eyepiece, rotate the lenses
to the 100x lens. If you need to, use the fine focus knob (the smallest knob) to get the
image into focus.
12. Again, looking from the SIDE of the microscope, rotate the lenses to the 400x lens. If
you need to, use the fine focus knob (the smallest knob) to get the image into focus.
13. In your lab notebook, draw a picture of what you see. Label the picture “Human cheek
cells 400x”. Label as many parts of the cell as you can see.
14. Switch to the lowest power lens and THEN remove the slide.
Conclusion questions
Answer the following questions in your lab notebook. Use your pictures to answer the questions
but feel free to look at your slides again if you need to remind yourself what you saw.
Life Science: Cells, Tissues, Organs, and Systems
1. Why do we need to stain some of the cells with a dye like iodine or methylene blue?
What color do you think the cells would be without the dye?
2. What does “100x” magnification mean?
3. List the parts of a cell you could see in the cheek cells at 40x magnification.
4. List the parts of a cell you could see in the cheek cells at 400x magnification.
5. Make a table like the one below and fill it in.
Parts we found in all
Parts only found in animal Parts only found in plant
cells
cells (cheek cells)
cells (onion and elodea)
6. Describe the shape of the plant cells. Describe the shape of the animal cells. What
makes them different?
Finally, clean up! Rinse off all your slides in the sink. Set the cover slips on one
paper towel and the slides on another.
After you are finished cleaning, pick up an exit slip and work on it before class is finished.
Life Science: Cells, Tissues, Organs, and Systems
Exit Slip:
What lens power do you start with when using a microscope to view a slide?
When you are finished using the microscope, what lens power do you leave it on?
Lab taken from:
www.mysciencebox.org/files/cells_lab_handout.doc