How Plant and Animal Cells Differ

Transcription

1 How Plant and Animal Cells Differ DRAWINGS Laboratory drawings can be made using several methods. Some drawings are made in circles that represent the viewing field of a microscope or another type of magnifier. When completing these drawings, be sure to include the magnification at which you viewed the object. Other laboratory drawings represent organisms or parts of organisms. These drawings show the relative size, shape, and location of anatomical structures. When completing representative drawings, make the structures as clear and as accurate as possible. Most laboratory drawings are labeled. Use the following guidelines to help make your laboratory drawings.clear and legible: Use a ruler to draw label lines. Label lines should point to the center of the structure being labeled. Do not write on the label lines. Print all labels horizontally. Label the right-hand side of the drawing, if possible. Do not cross, label lines. EXERCISE 3 The following drawing was made without using the guidelines above. Circle those parts of the drawing that do not follow the guidelines. Then, on the lines provided, explain how the drawing should be done. Figure 2 AVERAGES Occasionally you will be required to find the average of data gathered from an investigation. To find an average, add the items in the group together and then divide the total by the number of items. For example, if there were five students of different ages 12,13,14,17, and 19 how would you find the average age of the group? Add the five ages together and divide the total by 5, which is the number of items (students) in the group. What is the average age of this group of students? Your answer should be 15 years old.

2 How Plant and Animal Cells Differ Background Although plant and animal cells have many structures in common, they also have basic differences. Plant cells have a rigid cell wall, and il they are green, they also have chloroplasts. Animal cells lack both a cell wall and chloroplasts. They- also lack -the central uacuole common to plant cells. You will observe and compare animal cells and plant cells. You will first examine epithelial cells from the inside of your cheek. Epithelium is a type of tissue that covers the surfaces of many organs and cavities of the body. You will \\^o ohirpr^ oni'or\ epidci'imo.! cells. TK^^c Ure. fhe layfs of ^^e oi on. Objectives In this activity you will: 1.Observe human epithelial cells. 2.Observe onion cells. 3.Describe the differences between animal cells and plant cells. Materials microscope slides cover slips toothpick pipette oniol forceps Lugol's iodine solution in dropper bottle methylene blue stain in dropper bottle water Procedures and Observations III PART I. HUMAN EP^THELIAL CELLS 1. Place a drop of water on a clean slide. Obtain epithelial cells by gen tly scraping the inside of your cheek with a clean toothpick as shown in Figure 1. CAUTION: Never reuse a toothpick or put any thing in your mouth which may not be clean. Stir the material from the toothpick in the drop of water on the slide. Then immediately break the toothpick in half and throw it away.

3 Figure 1 2. Add a small drop of methylene blue stain to the slide. CAUTION: Stain can damage clothing and discolor skin. Use a clean toothpick to stir the cells on the slide, then immediately break the toothpick and throw it away. Carefully place a cover slip on tke slide. Examine the slide under low power. When you find some cells that are separate from each other, examine them under high power. Recall that you may have to adjust the diaphragm to reduce the intensity of the a. Make a^^rawing of two or three celb as they appear under high power. Label the nucleus, nuclear membrane, cytoplasm, and cell membrane of one of the cells, (use b. What is the shape of the cells? c. Describe the appearance of the cytoplasm.

4 1.Cut an onion bulb into quarters. 2.-Take an inner layer of the onion and, with a razor blade, cut several l/z-cm squares through the paper-thin epidermis lining the leaf. Then, with a forceps, remove one of the squares of epidermal tissue. Place it in a drop of water on a slide. Add a cover slip. This procedure is shown in Figure 2. Figure 2 3. Examine the wet mount under low power. Adjust the light to provide the best contrast, a. What is the shape of the cells? 3. Explain that the cell mem brane is immediately inside the cell and is sometimes dif ficult to see.

5 Every plant cell is surrounded by a nonliving cell wall composed chiefly of cellulose. Pressed tightly against the cell wall is the cell membrane, which surrounds the granular cytoplasm. The central part of the cell consists of the large, fluid-filled vacuole. The spherical nucleus appears as a dense body in the cytoplasm near the cell wall. It is surrounded by a nuclear membrane. Within the nucleus are nucleoll b. Make a diagram of a single cell. Label only the parts you see. A (use c What structure do you see that indicates these are plant cells? 4. Carefully focus on the cytoplasm near the cell wall. d. Describe the appearance of die cytoplasm and any motion that you observe. Stain will enable you to see many cell structures In more detail. 5. Add a drop of Lugol's iodine solution to one side of the cover slip on your onion slide. CAUTION: Stain can damage clothing and discolor skin. Take a strip of paper towel and touch it to the water at the opposite edge of the cover slip. See Figure 3. This should pull the stain under the cover slip. If more stain is needed, repeat the proce dure. Carefully observe the slide under low power, then high power. e. How many nuclei art present in each cell? f. What structures do you see in the nucleus? Now many are there in each nucleus?

6 Name. Observing Onion Cells (continued) g. How does the cytoplasm in the stained celt differ in appearance from the cytoplasm in the unstained cell?' Remind studentsto add water to the edge of the cover slip if the specimen dries out

7 a. plasma membrane _Ab report Plant and Animal Ceils NAME. CLASS.. DATE. 1. What structures are found in plant cells but not in animal cells?. 2. What is the purpose of staining the onion cells?. 3. Describe hew stain is applied to a slide holding a wet mount preparation.. 4. Typical Plant and Animal Cells Animal cel Plant cell 5. Give the functions of the cell parts listed below, b. cytosol. c nucleus _ d. mitochondrion. Laboratory Investigation 5A 65

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