Today we will make slides of 2 different types cells and look at them under the microscope:
- Onion skin cells
- Human cheek cells
Onion skin cells
1. Add 2 drops of iodine to the center of a glass slide. Be careful! Iodine can stain your clothes.
2. Take a small piece of onion. Use tweezers to peel off the skin from the underside (the 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 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 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.
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