Download Cytology Lab

Cytology Lab Lab Objectives: After this lab a student should be able to...
1. Identify the various cell organelles either from a model or in the field of view of
the microscope
2. Define the basic function of each cell organelle
3. Describe technique for creating a wet mount slide
4. Define the three type of tonicities and the effects each tonicity has on a cell
5. Identify the various stages and phases of mitosis (on models and underneath the
microscope).
I. Cell Structure Below is a list of cell structures and basic cell organelles that a student should be able to identify them as well as describe their function. 1.
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Smooth endoplasmic reticulum Vesicle Ribosomes Golgi Rough endoplasmic reticulum Mitochondria Cell (plasma) membrane 8. Centriole 9. Nucleus 10. Nucleolus 11. Peroxisome 12. Cytoplasm 13. Lysosome II. Cell Observation (Cheek cell preparation) 1. Prepare your own slide by gently scraping your own inner cheek lining with a
toothpick or wooden applicator stick.
2. Smear the moist substance in the center of a clean glass microscope slide.
3. Flood the smear with 1 drop of the Methylene blue stain provided.
4. Gently place a cover-slip on top of the stain.
5. Place the slide on the stage platform.
6. Beginning with the scanning power, observe the cell preparation.
7. Be able to identify the following cell structures:
a. Nucleus/nuclear membrane
b. Cytoplasm
c. Cell membrane
8. Dispose of the slide as indicated by the instructor or by placing the slide into a
glass disposal box.
III. Cell Physiology (Diffusion, Osmosis, and Tonicity) Diffusion, by definition, is the movement of molecules from an area of higher concentration of those molecules to an area of lower concentration. Osmosis, by definition, is the movement of water from an area of higher concentration of water to an area of lower concentration. Furthermore, movement (i.e. diffusion or osmosis) is regulated by the cell membrane as well as cellular tonicity. Special proteins acting as a channel in the cell membrane enable molecules to diffuse into and out of the cell. These cellular channels are either open continuously or are opened and closed by specific biochemical mechanisms. Water, on the other hand, can move directly through the cell membrane and does not need a protein channel. In addition, the concentration of molecules and osmotic forces influence the movement of water. If a solution has a high osmolarity (measure of solutes in solution), then that solution is considered hypertonic. If a solution has a low osmolarity, then that solution is considered hypotonic. Because water reacts with many compounds and reactions tend toward equilibrium, water will move from one area (e.g. one side of a membrane) to another based on solute concentration. For example, if a cell is placed in a hypertonic environment but its internal environment (i.e. cytoplasm) is hypotonic, then water will move out of the cell until equilibrium can be reached. The instructor may demonstrate these principles using a drop of blood or may ask students to investigate these principles in their textbook. IV. Cell Division (Interphase and Mphase) Multicellular organisms develop from a zygote, which is formed by the fusion of a sperm and an egg (gametes). Each gamete has half a half compliment of chromosomes (haploid number) and when combined gives rise to a zygote with a complete set (diploid number) of chromosomes. In order for the zygote to develop into a multicellular organism, it must repeatedly undergo cellular divisions. The series of events a cell (or zygote) undergoes that ultimately produces a new cell is called the cell cycle. The cell cycle is divided into two major stages: Mitosis and Interphase. Interphase is subdivided into three phases: S, G1, and G2 phases. During the S phase, DNA is duplicated in order to provide a full compliment for the new cell, called a daughter cell. The G phases are periods of growth and differentiation of a cell. The cell spends 90% of its time in interphase. Mitosis, in comparison to interphase, is subdivided into four phases: Prophase, Metaphase, Anaphase, and Telophase. During prophase, chromosomes (consisting of DNA and proteins) become distinguishable in the nucleus. In early prophase, the nuclear membrane breaks down, and the chromosomes condense and become distributed throughout the cytoplasm. At high magnifications, sister chromatids may be detected. Chromatids, which are joined to each other in a region called the centromere, are identical copies made during DNA replication. The chromosomes may be sorted or arranged with the aid of contractile fibers called mitotic spindle fibers. By late prophase the chromosomes are drawn toward the middle of the cell. In metaphase, sister chromatids become arranged toward the center of the cell (equatorial plate) in a plane at right angles to the long axis of the spindle. Once all chromatids are aligned at the equatorial plate, anaphase begins. The pair of chromosomes that comprise the chromatid are separated and transported to the polar (opposite) ends of the cell. Telophase will begin. During this stage in plant cells a cell plate will form and divide the original cell into two daughter cells. In animal cells, the cytoplasm pinches inward forming the cleavage furrow. Towards the end of telophase, in both plant and animal cells, the nuclei begin to reorganize, chromosomes uncoil, and the nuclear membrane reforms. Models of the Cell Cycle Interphase Early Prophase Late Prophase Anaphase Early Telophase Metaphase Late Anaphase Late Telophase Be sure to look at the stages and phases of the cell cycle (Interphase and Mitosis) underneath the microscope!