ONION AND CHEEK UNDER MICROSCOPE INVESTIGATION
PROBLEM:
What characteristic of living things is observed in this investigation?
MATERIAL PER GROUP:
White onion
Microscope
Microscope slide
Coverslip
Eye Dropper
Toothpick
Methylene Blue
Iodine stain
Cheek sample
PROCEEDURE:
PART A:
1. Obtain a white onion
2. Snap an onion bulb scale in half.
3. Use your fingernail to peel off a thin layer of onion tissue (the thin, transparent
membrane from inner surface).
4. Place the thin onion layer onto a microscope slide.
5. Uncurl or unfold any overlapped portion of the layer. Make sure that the layer is
perfectly flat.
6. Add one drop of water. Add a coverslip to the onion. Tap the coverslip gently
with the eraser end of a pencil to drive out any air bubbles
7. Add iodine stain. To add iodine stain, put a drop of the stain next to the cover slip
on the side and then draw it under the cover slip by placing a piece of paper towel
against the other side of cover slip. The paper towel will soak up the water,
drawing the stain under the cover slip.
8. CAUTION: Iodine is a skin and eye irritant and may stain clothes. Be careful not
to spill or drop the bottle. Call the teacher if spillage occurs. Wash hands or flush
eyes with water for 15 minutes if contamination occurs and call the teacher. Wear
eye goggles when using iodine
9. Observe the onion under both low and high power of your microscope.
10. Record your observations by making drawings using proper drawing procedures
learned previously.
PART B:
1. Place a drop of water on a slide.
2. Gently scrape the inside of your cheek with the end of a toothpick. You will not
be able to see anything on the toothpick when you remove it from your mouth.
3. Dip the toothpick into the drop of water on the slide, mix once or twice, and add a
coverslip.
4. Add methylene blue stain. To add methylene blue stain, put a drop of the stain
next to the cover slip on the side and then draw it under the cover slip by placing a
piece of paper towel against the other side of cover slip. The paper towel will soak
up the water, drawing the stain under the cover slip.
5. CAUTION: Methylene blue is a skin and eye irritant and may stain clothes. Be
careful not to spill or drop the bottle. Call the teacher if spillage occurs. Wash
hands or flush eyes with water for 15 minutes if contamination occurs and call the
teacher. Wear eye goggles when using methylene blue.
6. Examine under low and high power of your microscope.
7. Locate and examine those that are separated from one another rather than those
that are in clumps.
8. Record observations by using proper drawing procedure.
Finally, clean up! Rinse off all your slides in the sink. Set the coverslip on one
paper towel and the slides on another. Make sure slide is removed from
microscope and the low power objective is clicked in place and lowered as
close to stage as possible. Wrap cord around microscope and place plastic
cover over microscope.
ANALYSIS:
CONTENT:
1. What characteristic(s) of living things were demonstrated in this
investigation? Explain why.
2. The onion membrane seemed to be built by smaller units put together.
What are these smaller units?
3. Do you think all living things are made from these units? If so, how
many units will the smallest living thing be made of?
4. Consider what you observed and draw. Would you consider these
structures organized internally or disorganized and random?
5. Why do you suppose the structure of the onion and the cheek are
different? (Hint: Why is an egg carton a different shape than a pizza
box?)
PROCESS OF SCIENCE:
1. Which of the following procedures is better written. Explain why.
a. Mix 15 ml of water with 0.5 grams of salt and 0.25 grams of
sugar in a 50 ml beaker.
b. Mix water with salt and sugar in a container.
c. Mix a quart of water with half an ounce of salt and 2 ounces
of sugar.