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Comparing Cells:
Onions and Cheeks
Student Journal/Notebook
April 12th
Today in biology class we observed two different types of cells. The first sample came from an
onion. The second sample came from the insides of our cheeks. Although we’ve studied the
differences between plant and animal cells, I was excited to see them for myself, especially the
cheek cells.
Before starting the lab procedure, I hypothesized that the onion cells would appear more rigid and
rectangular than the cheek cells. Onions come from plants, so their cells must have a cell wall. Cheek
cells come from animals, so they lack a cell wall.
First, my lab partner and I prepared a wet mount slide of onion cells. We peeled off a thin layer of
membrane with forceps. Then we placed the membrane on a glass slide and added a drop of iodine to
the membrane. The iodine served as a stain, which allowed us to see some of the cell organelles more
clearly. We covered the slide with a glass cover slip. It was important to make sure the membrane was
laying flat on the glass slide and that no air bubbles got trapped between the iodine and the cover slip.
Once the slide was prepared, we placed it on the stage of a
compound microscope and observed the cells under low
magnification. The cells looked pretty small, so we moved
to a higher magnification after we knew the cells were
within view.
The most obvious feature of the onion cells was their
shape. As I had hypothesized, they appeared rigid and
rectangular due to the presence of a thick cell wall. Since
the cell wall is composed of cellulose fiber, it gives a plant
cell most of its support and structure.
A thick cell wall gives each onion cell its rigid
shape.
We were also able to clearly observe the nucleus of each
cell, which looked like a small brown dot. I found it
amazing that such a small organelle is responsible for so much of the cell’s functions. It
contains the hereditary material, or DNA. The nucleus also coordinates the cell’s activities
including protein synthesis, cell division, and growth. We were able to infer that onion plants
are eukaryotes since their cells contain a nucleus.
The image lacked some detail, but we could also see the large central vacuoles of each cell. And,
while they were not visible under the magnification we used, we inferred that the plant cells
contained chloroplasts since onion plants produce their own food through photosynthesis.
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Discovery Education Science
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Comparing Cells:
Onions and Cheeks
After observing the onion cells, we began preparing a wet mount slide of our cheek cells. For
the first step, we placed a drop of methylene blue stain on a glass slide. Similar to the iodine,
methylene blue allowed us to see some of the cell details more clearly. Then, we gently scraped
the insides of our cheeks with the flat end of a toothpick. We then swirled the end of each
toothpick in the methylene blue stain, mixing our cheek cells together on the slide. Next, we
placed a glass cover slip on top of the slide and put the slide on the stage of the microscope. As
with the onion cells, we began our observations using low magnification. We switched to high
magnification once we knew the cells were within view. It was really interesting to see our own
cheek cells under the microscope!
In further support of my hypothesis, we observed that the cheek cells did not have a definitive
shape. This makes sense considering they lack a cell wall. The nucleus of each cell was clearly
visible and looked similar to the nucleus of an onion cell.
Large central vacuoles were not visible, which also makes
sense since animal cells do not contain particularly large
vacuoles. Because animals are consumers and do not
produce their own food, we were able to infer that
chloroplasts were not present in the cheek cells.
In summary, the lab activity demonstrated the similarities
and differences between plant and animal cells. Both the
onion cells and cheek cells contained nuclei. The cheek
cells lacked rigid cell walls and large central vacuoles. Had
the microscopes provided greater magnification, the
Animal cells are irregularly shaped due to the
lack of a rigid cell wall.
chloroplasts would probably have been visible in the onion
cells. Based on what we know about cells, we concluded
that the following major organelles would have been visible in both onion and cheek cells:
•
•
•
•
•
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Golgi apparatus
Mitochondria
Endoplasmic Reticulum
Ribosome
Cell membrane
Microtubules
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Discovery Education Science
 Discovery Communications, LLC