Describe briefly the process used in the preparation of wet mounts of plant and animals used in this

exercise. Include stains used in both cells.

Onion cells 1. Peel a translucent piece of tissue from the onion. (The smaller the piece the
better.) Translucent means that you can see light through the specimen, but it is not transparent.
2. Place the piece of onion on a glass slide and add a drop or two of the iodine solution. Cover
the slide with a cover slip using your best wet-mount making techniques. 3. Observe the onion
cell under both low and high power. Make a drawing of one onion cell, labeling all of its parts as
you observe them. (At minimum you should observe the nucleus, cell wall, and cytoplasm.) 

Obtain a small piece of onion skin from teacher and a cup of iodine. Place the onion skin on a clean
slide and use one of the eye droppers to place a small drop of iodine on the onion skin. Do not
drench the onion skin, one drop is plenty. Carefully place the slide cover on the slide trying not to
have any air bubbles under the slide. View the slide under the microscope using low power. Work
your way to higher views. Remember do not use the coarse focus on high power! Draw what you see
under 4x, 10x, and 40x. Pick a cell and label the parts you can see.

Obtain a cup of Bromotyhmol blue from the teacher. One lab member needs a clean toothpick.
Carefully rub the toothpick on the inside of your cheek. These cells are constantly being replaced in
your mouth so what you take would be gone by the end of the day anyway. Do NOT stab your mouth
with the toothpick. It will not look like any cells are on the toothpick, but I promise they are there!
Rub the end of the toothpick over the clean slide. Use the clean dropper to place one drop of
Bromothymol blue on the slide. Cover the slide with a clean slide cover careful not to leave any
bubbles. Do not push the slide cover down on the slide. This may damage your cells and may break
the slide cover, not to mention can leave a nasty finger print on the slide preventing you to see well
when you look at your slide. Place the slide under the microscope starting on low power. Draw what
you see. Then carefully move up to 10x drawing what you see. When you move to 40x make sure
you do NOT use the course focus. Only use the fine focus to get a clear view of the cells. Draw what
you see and label one of the cells.
Cheek cells 1. To view cheek cells, gently scrape the inside lining of your cheek with a toothpick.
DO NOT GOUGE THE INSIDE OF YOUR CHEEK! (We will observe blood cells in a future lab!!)
2. Gently tap the toothpick onto the center of a glass slide. Some of the cheek cells should fall
onto the slide. 3. Add a drop of methylene blue stain (specific for animals) and cover with a cover
slip. 4. Observe the cheek cells under both low and high power of your microscope.

Why do we have to Stain the Cells?

The cell has different parts, and those that can absorb stains or dyes are
referred to as chromatic. Having absorbed the stain, these parts of the
cell become more visible under the microscope and can therefore be
easily distinguished from other parts of the same cell.

Without stains, cells would appear to be almost transparent, making it

difficult to differentiate its parts.
Methylene blue has a string affinity for both DNA and RNA. When it comes
in contact with the two, a darker stain is produced and can be viewed
under the microscope.

The nucleus at the central part of the cheek cell contains DNA. When a
drop of methylene blue is introduced, the nucleus is stained, which makes
it stand out and be clearly seen under the microscope.

Although the entire cell appears light blue in color, the nucleus at the
central part of the cell is much darker, which allows it to be identified.  

1. Add a drop of water at the center of the microscopic slide

2. Having pulled of a thin membrane from the onion layer, lay it at the center of
the microscopic slide (the drop of water will help flatten the membrane)
3. Add a drop of iodine solution on the onion membrane (or methylene blue)
4. Gently lay a microscopic cover slip on the membrane and press it down gently
using a needle to remove air bubbles.
5. Touch a blotting paper on one side of the slide to drain excess iodine/water
solution,
6. Place the slide on the microscope stage under low power to observe.
7. Adjust focus for clarity to observe.

Once the cells have been obtained, the following procedure is used for cheek
cell wet mount preparation:

1. place a drop of physiological saline on a clean microscopic slide (central

part of the slide)
2. smear the cotton swab on to the center (part containing the saline
drop) of the clean slide for about 4 seconds to get the cells on to
the center of the slide
3. add a drop of methylene blue solution on to the smear and gently
place a cover slip on top (to cover the stain and the cells)
4. any excess solution can be removed by touching one side of the
slide with a paper towel or blotting paper.
5. place the slide on the microscope for observation using 4 x or 10 x
objective to find the cells
6. once the cells have been found, they can then be viewed at higher
magnification
Make diagrams showing the epidermal cells of onion and epithelial cheek cells under HPO
objectives. Discuss the major differences between the two cells.

epidermal cells of onion and epithelial cells of cheek at 400 total magnification (high power
objective)

Onion epidermal cells Cheek epithelial cells

cell membrane, cytoplasm, nucleus

cell wall and possibly a central vacuole – present in onion cells but weren’t in cheek cells

cell wall provides rigid support for the cell; central vacuoles serve as a storage compartment
for water in the plant cell

cell wall; diff. shape

cheek

 A large number of flat and irregular-shaped cells are observed.

 The cells do not have a cell wall. However, each cell has a thin cell membrane.
 A deeply stained nucleus is observed at the centre of each cell.
 No prominent vacuoles are observed in the cells.
 As the cells observed do not have a cell wall, nor a prominent vacuole, the cells of
the specimen on the slide are animal cells.
 Large irregularly shaped cells with distinct cell membranes.
 A distinct nucleus at the central part of each individual cell (dark blue in
color).
 A lightly stained cytoplasm in each cell.
onion

 There are a large number of regularly shaped cells lying side by side and each cell
has a distinct cell wall.
 A distinct nucleus is present on the periphery of each cell.
 Lightly stained cytoplasm is observed in each cell.
 A large vacuole is present at the centre of each cell, and is surrounded by the
cytoplasm.
 As cell walls and large vacuoles are clearly observed in all the cells, the cells placed
for observation are plant cells.
 Large, rectangular interlocking cells,
 Clearly visible distinct cell walls surrounding the cells,
 Dark stained nucleus,
 Large vacuoles at the center,
 Small granules may be observed inside the cells (within the cytoplasm)

A cell’s shape often correlates with its function. How do you explain the shape of the onion cells
versus your cheek cells?

The onion cells are rectangular and have a rigid cell wall. This enables the onion cell to
be supported and allows for growth. The cheek cell was roughly circular in shape and had no cell
wall. This cell does not need to function in support of other cells.

An animal cell contains about 10 to 20 Golgi apparatus whereas a plant cell contains several
hundred. Why do you think there is such a difference in the number of these organelles in each
cell?

Plant cells need to make or store food. This would mean more golgi apparatus is needed
to package the food and transport it outside the cell. Animal cells do not make food and therefore
need a smaller amount of golgi apparatus.

Onion Cell

An onion is a multicellular (consisting of many cells) plant organism.As in all plant cells,

the cell of an onion peel consists of a cell wall, cell membrane, cytoplasm, nucleus and
a large vacuole. The nucleus is present at the periphery of the cytoplasm. The vacuole is
prominent and present at the centre of the cell. It is surrounded by cytoplasm. The
presence of a cell wall and a large vacuole are indicators that help identify plant cells, such
as seen in the onion peel.

Human Cheek Cell

As in all animal cells, the cells of the human cheek do not possess a cell wall. A cell
membrane that is semi-permeable surrounds the cytoplasm. Unlike plant cells, the
cytoplasm in an animal cell is denser, granular and occupies a larger space. The vacuole in
an an animal cell is smaller in size, or absent. The nucleus is present at the centre of the
cytoplasm.The absence of a cell wall and a prominent vacuole are indicators that help
identify animal cells, such as cells seen in the human cheek.
http://amrita.olabs.edu.in/?brch=15&cnt=1&sim=125&sub=79
A vacuole is a membrane-bound organelle that stores solid and liquid contents.
Vacuoles are found in both animal and plant cells, but are much larger in plant cells.
Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just
larger forms of these. The organelle has no basic shape or size; its structure varies
according to the needs of the cell.

Cell Wall: Protective Coat in Plant Cells

The presence of a cell wall is what provides the most significant difference between plant
and animal cells, as it is present only in plant cells and covers the cell membrane.The cell
wall is rigid and is composed of cellulose fibre, polysaccharides, and proteins. Despite the
rigidity of the cell wall, chemical signals and cellular excretions are allowed to pass between
cells.

Cell Membrane: Protective Coat in Animal Cells

The cell membrane is found in both plants and animals, and it is the outer most layer in the
animal cell, that separates the contents of the cell from the outside world. It consists of
both lipids and proteins and is selectively permeable, which means it permits only
some molecules to pass through it.

http://amrita.olabs.edu.in/?brch=15&cnt=1&sim=125&sub=79

When observing the onion skin cell, we noticed that the cells took on a brick-like
structure and within the cells, small dots (the nuclei) can be seen. When we first
looked into the microscope, the microscope’s total magnification was 40X so there
were about a hundred rows of rectangular
cells (see diagram provided), but as we changed magnifications, the number of cells
in the field of view decreased.
When we viewed the onion skin cells at 400X total magnification, we noticed the
nuclei of the cells looked clearer and larger and we were able to study the cell with
more understanding than when we used the first magnification.
The organelles that we were able to see in this type of cell were the nucleus, the
cytoplasm, and the cell wall. Unlike the onion skin cells, the cheek cells were more
spread out from each other and they all had a round shape. When we viewed the
cheek cells at 40X total magnification, we noticed that the cells were secluded and
spread out (see diagram provided). At 400X total magnification, we were only able to
view one cell at a time, due to the fact that the cells were separated from each other.
The organelles that were visible in this type of cell were the nucleus, the cytoplasm
and the cell membrane. Aside from the actual cells, we were able to see air bubbles
within both the onion skin cell slide and the cheek cell slide.
the plant cells were together in a large group. The animal cells, however, were secluded
both: The important organelles that can be seen are the cell wall (for the plant cells), the cell
membrane, the nucleus, and the cytoplasm. Those organelles could be seen due to the fact
that they are the largest organelles in the cell and also due to the dye which brought them
out.

The cheek cell, an example of an animal cell, generally has a circular, oval shape.
Due to the fact that the cheek cell was not in groups or clumps, the arrangement of
this type of cell is unknown. From previous labs, the cells were pushed together
completely; each cell fitted beside another cell perfectly, and so on.
The animal cell structure is the most prominent in human cheek cells. The onion skin
cell, an example of a plant cell, generally has a rigid, rectangular shape. The onion
skin cells were positioned beside each other (length touching length, width touching
width) and formed a checkered pattern.
Also, like the cheek cell, the onion skin cells were pushed together so that no spaces
were in between. Two differences between a cheek cell and an onion skin cell are
that the onion skin cells has the chloroplast and cell wall organelles while the cheek
cell doesn’t and the general shape of the onion skin cell is a rectangle and the
general shape of the cheek cell is an oval.
OBSERVATIONS:
A large number of regularly shaped cells are lying side by side.
Each cell has a distinct cell wall.
A distinct nucleus is present on the periphery of each cell.
Lightly stained cytoplasm is observed in each cell.
A large vacuole is present in the centre of each cell, surrounded by the cytoplasm.
CONCLUSION:
As cell walls and large vacuoles are clearly observed in all cells, the cells in the observations
are plant cells.
OBSERVATION
A large number of flat and irregular-shaped cells are observed.
The cells do not have a cell wall.
However, each cell has a thin cell membrane.
A deeply stained nucleus is observed in the centre of each cell.
No prominent vacuole is observed in the cells.
CONCLUSION
If the cells observed do not have cell walls or prominent vacuoles, the cells of the specimen
on the slide are animal cells.