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Vignya Dontu
Cytology Formal Lab
Title
The Examination of Different Types of Cells under a Compound Light Microscope
Introduction
The purpose of the lab was to observe what different types of cells look like using a
compound light microscope and different types of slides: wet mount, dry mount, and prepared.
The cells were also diagrammed and labeled to show and learn about the different cell parts that
are in different types of cells.
The major difference between prokaryotic and eukaryotic cells is that eukaryotic cells
have a nucleus and prokaryotic cells do not (Green, 2015). For example, E. coli, a type of
bacteria, is a prokaryotic cell because it does not have a nucleus, like all bacteria and
archaebacteria. Human cells are eukaryotic, like all animals, plants, fungi, and protists.
However, prokaryotic and eukaryotic cells have some structural similarities. Both
prokaryotic and eukaryotic cells have a cell membrane surrounding the cell and cytoplasm within
the cell. Also, they both have DNA, found in the nucleoid region of a prokaryotic cell and in the
nucleus of a eukaryotic cell (Green, 2015).
The Endosymbiotic Theory states that modern cells could have originated from bacteria
living inside a host cell, where the bacteria and host cell were completely dependent on each
other (Genetic Science Learning Center). As bacteria began to photosynthesize, the earth’s
atmosphere changed and oxygen breathing bacteria developed (Genetic Science Learning
Center). Mitochondria and chloroplasts are believed to be the original bacteria, where
chloroplasts would be the photosynthesizing bacteria and mitochondria would be the oxygen
breathing bacteria. This is considered evidence of the theory because mitochondria and
chloroplasts have their own DNA that is separate from the DNA in the nucleus that is used to
reproduce like bacteria. Also, they are both surrounded by membrane like that of a bacteria cell
(Genetic Science Learning Center).
Methods and Materials
To observe onion skin cells, a piece of an onion, microscope slide, cover slip, iodine
bottle, and compound light microscope were used. First, the skin was removed from the inside of
the onion by gently rubbing it off with a finger. Then, the onion skin was laid flat on the
microscope slide. Two drops of iodine were placed on top of the skin and it was covered with the
cover slip. Once the slide was placed on the microscope stage, the cells were located using the
magnification of 100x. The image was focused and the magnification was increased to 430x. The
cell membrane, cell wall, cytoplasm, and nucleus of the cell were examined and the cells were
diagrammed. Refer to Appendix A: Cell Examination Procedure for the explanation of the
remainder of the procedure.
Results
During the lab, human cheek cells were observed and diagrammed. Figure 1: Human
Cheek Cells shows three cells that were in the microscope’s field of view. They were tinted blue
from the blue die that was used to make the cells stand out. The nucleus and cell membrane were
seen as a darker blue than the cytoplasm that was also seen. See Figure 1.
Frog blood cells were also observed and diagrammed. Figure 2: Frog Blood Cells shows
five cells that were seen. The cell was light pink with a dark red center. The light pink was the
cytoplasm and the dark red was the nucleus. A cell membrane was also seen surrounding each
cell. See Figure 2.
Furthermore, human red blood cells were observed and diagrammed. Figure 3: Human
Red Blood Cells shows five cells that were seen through the microscope. They were light red
with a slightly darker outline. The outline was the cell membrane and the inside was the
cytoplasm. See Figure 3.
In addition, cells of the Elodea leaf were examined and diagrammed. Figure 4: Elodea
Leaf Cells shows five plant cells. They were green and had a dark green, rectangular outline and
green circles inside. The circles were the chloroplasts and the outline was the cell wall. Just
inside the cell wall was the cell membrane and the light green inside was the cytoplasm. See
Figure 4.
Cells of the onion skin were also observed and diagrammed. Figure 5: Onion Skin Cells
shows the cells that were in the field of view. They were tinted brown from the iodine that was
used to make the cells stand out. The cell wall was seen as a dark brown outline and the nucleus
was seen as a dark brown circle in the center. The cell membrane was just inside the cell wall
and the cytoplasm was the light brown inside. See Figure 5.
Discussion
As a cell gets larger, the surface area to volume ratio gets smaller. The volume of a cell
can grow quicker than the surface area of the cell, so over time the ratio goes down as the
volume increases in size faster than the surface area (Blamire). Because of this, cells cannot
grow very large. Materials that are important to cell functions are passed through the cell
membrane. Eventually, the volume will get so big that not enough materials are able to get
through the cell membrane to help the larger volume function (Blamire). When this happens, the
cell must stop growing or split into smaller cells.
The bulb of a plant, such as an onion, functions as a place for food storage (Bulb). The
onion skin cells from the bulb were missing chloroplasts, a major cell part that was seen in the
Elodea leaf cells. The onion skin cells were missing these structures because the bulb is
underground and is used for storage, not photosynthesis (Onion Epidermal Cell). The leaf cells
of an onion plant would have chloroplasts.
Human red blood cells, though eukaryotic, are missing a nucleus (How a Red Blood Cell
Loses its Nucleus). The red blood cells are produced in the bone marrow. As they mature, they
undergo a type of cell division in which the nucleus is only in one part that is pinched off. The
part with the nucleus is then eaten by macrophages, part of the immune system (How a Red
Blood Cell Loses its Nucleus). The lack of nucleus gives room to store more hemoglobin, the
protein present in the cytoplasm of RBCs. The hemoglobin allows the red blood cells to transport
oxygen from the lungs to the rest of the body, and transport carbon dioxide from the body to the
lungs to be exhaled (Blood Basics).
Phospholipids in cell membranes are made up of a phosphate group, glycerol, and fatty
acids (Green, 2015). See Figure 6. The phosphate group is polar so it is hydrophilic, or likes
water. The fatty acids are non-polar so they are hydrophobic, or fear water. When in water, the
fatty acids are repelled by the water so they turn in towards other fatty acids and allow the
phosphate group to stay closer to the water. This structure allows only non-polar or small
substances to move across the selectively permeable membrane (Green, 2015). The fatty acids on
the phospholipids are unsaturated, which causes the phospholipids to be liquid at room
temperature because they can’t pack closely together and form a solid (The Kinds of Fats).
Conclusion
Based on observations in the lab, the cells that were seen in the most detail were the
onion skin cells. This was because they were the biggest cells that were being observed, so the
structures could be easily defined.
Literature Cited
Blamire, John. "The Problem of Size." BIOdotEDU. N.p., 2001. Web. 14 Nov. 2015.
<http://www.brooklyn.cuny.edu/bc/ahp/LAD/C5/C5_ProbSize.html>.
"Blood Basics." American Society of Hematology. American Society of Hematology, n.d. Web.
14 Nov. 2015. <http://www.hematology.org/Patients/Basics/>.
"Bulb | Plant Anatomy." Encyclopedia Britannica Online. Encyclopedia Britannica, n.d. Web. 14
Nov. 2015. <http://www.britannica.com/science/bulb>.
Genetic Science Learning Center. "The Evolution of the Cell." Learn. Genetics. University of
Utah Health Sciences, 22 June 2014. Web. 14 Nov. 2015.
<http://learn.genetics.utah.edu/content/cells/organelles/>.
Green, Taylor. 2015. Class Notes on Cells
"How a Red Blood Cell Loses Its Nucleus." News-Medical. News-Medical, 17 Feb. 2008. Web.
14 Nov. 2015. <http://www.news-medical.net/news/2008/02/17/35294.aspx>.
"Onion Epidermal Cell." Wikipedia. Wikimedia Foundation, 21 June 2015. Web. 14 Nov. 2015.
<https://en.wikipedia.org/wiki/Onion_epidermal_cell>.
"The Kinds of Fats." Fat and Why It Matters. Indiana University, n.d. Web. 14 Nov. 2015.
<http://www.indiana.edu/~oso/Fat/SolidNLiquid.html>.