Blood Buffer Essay

Objectives: After completing this exercise and reading the corresponding material in your text, you should be able to 1. Prepare a wet mount slide 2. Identify structures described in this lab on slides 3. Cite examples of the wide diversity of cell types 4. Relate differences in structure among cells to functional differences Introduction Structurally and functionally, all living things share one common feature: all living organisms are composed of cells. The development of this concept began with Robert Hooke’s seventeenth-century observation that slices of cork were made up of small units he called â€Å"cells.† Over the next 100 years, the cell theory emerged. It was formally (and independently) presented by Schleiden and Schwann in 1839, and clarified by Virchow a few years later. This theory has three principles: (1) All organisms are composed of one or more cells. (2) All life processes derive from the activities of cells. (3) All cells arise from preexisting cells. Living organisms are composed of one or many cells, and every activity that occurs in a living organism is ultimately related to metabolic processes in cells. Understanding the processes of life requires an understanding of the structure and function of the cell. Although cells vary in organization, size, and function, all share certain structural features. All are enclosed within a plasma membrane, defining the boundary of the living material. All contain a region of DNA (deoxyribonucleic acid), which forms the genetic code. Inside of the plasma membrane is watery cytoplasm, and the chemical processes inside the cell occur within this watery medium. Upon microscopic examination, we see there are two basic types of cells, prokaryotic and eukaryotic, see the table below to see a comparison of the two cell types. For these following exercise you should use the highest magnification possible, because you will be able to see more detail, and you should record your observations at this magnification. Always begin with the lower magnifications, once you have found your specimen center it and focus it before increasing the magnification. We will not be using the 100X objective because it requires special handling and immersion oil, so you should use the 40X objective for most observations. What is the total magnification of a sample view with the 40X objective? Remember there is a lens in the ocular that magnifies the image 10x, so the total magnification will be 40 x 10 = 400X. Exercise 1: Examining Prokaryotic cells 1. What types of organisms are prokaryotic? 2. What structures are found in a Eukaryotic cell that will not be visible in a Prokayotic cell? 3. Examine the specimens available at the back of the classroom. Locate a prokaryotic cell and bring it back to your microscope. Name of specimen: ____________________ 4. Examine your specimen under the microscope. Sketch your specimen under 40x magnification below. Be sure to label any internal or external structures visible. Exercise 2: Examining Eukaryotic cells The cells on which we focus most of our attention are relatively large and complex, although many details of their structure are only evident with electron microscopy. The word eukaryote derives from the visible nucleus found in most of these cells. No one cell will show all of the features that a cell might have, so you will be observing a variety of eukaryotic cells. Protist cells: The protist kingdom includes eukaryotic unicellular forms (e.g., protozoans, algae, slime molds) as well as some simple multicellular forms. Many are mobile; some are photosynthetic; others are animal-like, ingesting food particles, or fungi-like, secreting digestive chemicals into the environment. Protists are diverse, often having complex cells. 1. What structures do you expect to see in these cells that was not evident in the prokaryotes you saw? Cultures of mixed protists and/or pond water are available in lab. Many different forms may be found in these cultures, including amoebas, flagellates and ciliates. (Many classifications of protists are based on how they move – with flagella, or cilia, or neither of these.) 2. Examine the specimens available at the back of the classroom. Locate the cultures of protist cells. You will examine two separate cultures. One of the cultures you’ll examine is the â€Å"Mixed Pond Protists,† you can pick which specimen you’ll examine for your second sample from the other cultures present in class. Make a wet mount of each culture, drawing material from the debris at the bottom of the culture jar. Name of specimen #1: Mixed Pond Protists Name of specimen #2: ____________________ 3. Observe first with scanning power (4X objective), looking for movement. If you don’t see anything, wash the material back into the jar and get another drop. Once you have located organisms, observe on higher power (40X objective). If the protists are moving very rapidly, they may swim out of the field of view. In this case, remove the coverslip and add a small drop of Detain. Detain is a thick solution that will help slow down the protists. REMEMBER THAT THE MICROSCOPE LIGHT IS HOT. Turn it off when you are not looking at the slide. 4. Examine your specimen under the microscope. Sketch each specimen under 40x magnification below. Be sure to label any internal or external structures visible. 5. What evidence do you see that protists are eukaryotes? 6. Attempt to identify the protists you have observed. There are several keys to protists available. Your instructor can help you use the keys if you’re not familiar with how they work. Write the name of your protists and your rationale for identification based on the characteristics in the key into your notes. When you have finished looking at your slide, place the slide in the bleach water. Plant cells: Plant cells are different from animal cells in many ways. 1. Name three ways plant cells differ from animal cells below. As in animals, cells of plants are organized into tissues, aggregations of similar cells performing a common function in a multicellular organism. In this part of the lab, you will look at several types of plant cells. Onion epidermal cells: 1. Make a wet mount of a colorless scale of an onion bulb by peeling the thin, membranous layer from the inside of one of the bulb scales and placing it on a slide in a drop of water. This usually works best if you partially slice through a ring, allowing the thin layer of tissue on the inner surface of the leaf to be pulled off. Use forceps to arrange the tissue in a drop of Iodine on a slide and cover with a cover slip. 2. Observe your preparation with the microscope, focusing first with the scanning power objective. Continue your study, switching to the low power (10 X) and finally the high power objective (40 X). 3. What shape do most of these cells have? What structure maintains this shape? 4. What structure is stained by the iodine? 5. Examine your specimen under the microscope. Sketch each specimen under 40x magnification below. Be sure to label any internal or external structures visible. 6. Which cellular components present in most leaf cells are absent from onion leaf cells? Elodea leaf cells: 1. Remove a single young leaf and prepare a wet mount. Examine the leaf first on scanning power, then on low power. 2. Examine your specimen under the microscope. Sketch each specimen under 40x magnification below. Be sure to label any internal or external structures visible. 3. After the cells have warmed a bit from the light of the microscope, you may see cytoplasmic streaming. Microfilaments in the cytoplasm are thought to be responsible for this intracellular movement. What cellular structure do you see moving around the cytoplasm? Animal cells: Human epithelial (cheek) cells: 1. Using the broad end of a clean toothpick, gently scrape the inside of your cheek. Stir the scrapings into a drop of saline and a drop of Methylene Blue on a clean microscope slide and add a cover slip. Do not reuse your toothpick. DO NOT PUT IT BACK WITH THE CLEAN TOOTHPICKS AND DON’T LAY IT ON THE TABLE. Discard it in the BIOHAZARD bag. 2. Because the cells are almost transparent, decrease the amount of light entering the objective lens to increase the contrast. Find the cells using the low power objective of your microscope, then switch to the high power objective for detailed study. Find the nucleus of a cell. Many of the cells will be folded or wrinkled due to their thin, flexible nature. 3. Examine your specimen under the microscope. Sketch each specimen under 40x magnification below. Be sure to label any internal or external structures visible. 4. Dark specs on the cells are bacteria, similar to the E. coli you looked at earlier. How big are these bacterial cells relative to your cheek cells? Discard this slide into the bowl containing the bleach water. Sheep’s blood (wet mount): Blood consists of two parts – a liquid portion (water + proteins) called plasma, and a cellular portion, containing many different cell types, including erythrocytes or red blood cells (RBCs), and leukocytes or white blood cells (WBCs). Red blood cells are red because they contain a lot of the oxygen-carrying molecule hemoglobin. The blood sample we have has been treated chemically to prevent clotting. 1. Prepare a wet mount by placing a drop of saline and a small drop of blood on the slide. Add a cover slip. Examine a portion of the slide in which the blood is diluted. 2. Examine your specimen under the microscope. Sketch each specimen under 40x magnification below. Be sure to label any internal or external structures visible. 3. What is missing from these cells that is found in eukaryotic cells? 4. How do the red blood cells compare to your cheek cells in size? What shapes are the cells? Discard this slide into the bowl containing the bleach water. Cells Review Questions Your answers should be specific and to the level of the lecture, book and lab manual. You may need to use outside sources. 1. What characteristics do all cells have in common? 2. What characteristics are common to all eukaryotic cells but not found in prokaryotic cells? 3. Would you expect that all the living cells you saw in lab contain mitochondria? Explain. 4. Did all living plant cells you observed contain chloroplasts? Explain. 5. Describe as many differences as you can between plant and animal cells at a cellular level. Do any of these differences relate to the organismic differences we see between plants and animals? Explain. 6. How do prokaryotic and eukaryotic cells compare in size? 7. How would you compare a protist cell to a cell from your body, a cheek cell for example, in terms of complexity at the cellular level?