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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>.