Observing Specialized Cells

Transcription

1 Name Class Date Chapter 10 Cell Growth and Division Observing Specialized Cells Introduction The cell is the basic unit of structure and function in all living things. All of the processes necessary for life occur in cells. In single-celled organisms, such as amoebas, all of the functions required by the organism take place within one cell. Multicellular organisms, such as humans and plants, are made up of many cells with different structures and functions. The shape and size of a cell, as well as the structures found inside it, are determined by the functions of the cell. In this investigation, you will observe several different types of cells. You will compare and contrast the structures you see in the cells, and relate the structures to the functions the different cells perform. Problem How are the structures of specialized cells adapted to fit their particular functions? Pre-Lab Discussion Read the entire investigation. Then, work with a partner to answer the following questions. 1. What types of cells have a cell membrane, cytoplasm, and a nucleus? Where would you expect to find the cytoplasm in a cell? All plant and animal cells have these structures. The cytoplasm is found between the cell membrane and the nucleus. 2. In what types of cells would you expect to see a cell wall? Plant cells. 3. Saclike structures called vacuoles are found in many cells. What is the function of vacuoles? Vacuoles store materials such as water, salts, proteins, and carbohydrates. You may want to refer students to Section 7 4 in the textbook for a discussion of tissue and organ formation. Time required: 50 minutes 4. An organelle is a cell structure with a specialized function. Plastids are plant organelles. Which plastid traps the energy of sunlight and converts it into chemical energy? Chloroplast. 5. The outer layer of cells of a leaf is called the epidermis. These cells protect the tissues inside the leaf by slowing down the loss of water through evaporation. Predict what these cells will look like. Students may predict that the cells will be stacked closely together like bricks in a wall. 6. Some functions are exclusive to plants, while others are performed only by animals. Which specialized cells or tissues would you expect to find only in plants? Only in animals? Specialized cells such as guard cells are found only in plants. Bone, connective, and nerve tissues are found only in animals. Biology Laboratory Manual B/Chapter 10 95

2 Materials (per group) compound light microscope lens paper lettuce leaf water plant leaf dropper pipette 2 microscope slides 2 coverslips forceps dissecting probe prepared slides of 3 types of human tissues A common freshwater aquarium plant is Elodea. This plant is generally available from pet stores or can be collected throughout most of the year from ponds and slow-moving streams. To maintain Elodea in the classroom, fill an aquarium or large (4 liter) glass jar with pond or spring water. If pond or spring water is not available, fill the container with tap water and set it aside uncovered for at least 24 hours before introducing the Elodea. Float Elodea sprigs loosely on the surface of the water. If Elodea is banned as a weed in your area, alternative water plants are available from aquarium shops and biological suppliers. Obtain prepared slides of human tissues from biological supply houses. Slides may include the following tissues: skeletal, muscle, blood, nerve, bone, skin. Safety Put on a laboratory apron. Handle all glassware and sharp tools carefully. Always handle the microscope with extreme care. If you are using a microscope with a lamp, follow all safety rules related to electrical equipment. You are responsible for its proper care and use. Use caution when handling microscope slides, as they can break easily and cut you. Note all safety alert symbols and review the meaning of each symbol by referring to Safety Symbols on page 8. Procedure 1. Obtain a microscope and place it about 10 centimeters from the edge of the laboratory table. 2. Carefully clean the eyepiece and the objective lenses with lens paper. 3. Locate a rib in the lettuce leaf. As shown in Figure 1, bend the lettuce leaf against the curve until it snaps. A B Bend leaf against curve Remove lower epidermis Figure 1 96 Biology Laboratory Manual B/Chapter 10

3 Name Class Date 4. With the forceps, carefully remove the thin layer of tissue called the epidermis from the piece of lettuce. Spread out the epidermis as smoothly as possible on a microscope slide. Note: If the epidermis becomes folded on the slide, use a dissecting probe to gently unfold and flatten it. CAUTION: Microscope slides can break easily. 5. To prepare a wet-mount slide, place a drop of water in the center of the slide. Using the dissecting probe, gently lower the coverslip onto the lettuce as shown in Figure 2. CAUTION: Be careful when handling sharp instruments. Microscope slide Coverslip Dissecting probe Figure 2 6. Observe the lettuce epidermis under the low-power objective of the microscope. Note: It may be necessary to adjust the diaphragm so there is sufficient light passing through the cells. Notice the irregular shapes of the epidermal cells. 7. Switch to the high-power objective. CAUTION: When turning to the high-power objective, you should always look at the objective from the side of your microscope so that the objective lens does not hit or damage the slide. 8. In the Data Table on page 98, write the name of the cell that you examined. Describe its general shape and place a check mark in the columns below the structures that you are able to observe under the high-power objective. 9. In the appropriate place on page 98, draw and label what you see under the high-power objective. Record the magnification of the microscope. 10. Repeat steps 5 to 9 using the water plant leaf. 11. Repeat steps 6 to 9 using the 3 prepared slides of human cells and/or tissues. Draw and label what you see in the appropriate place on pages 98 and 99. Biology Laboratory Manual B/Chapter 10 97

4 Data Table Cell Structures Cell Type Shape Cell wall Cell membrane Lettuce epidermis Water plant epidermis Prepared Slide 1 Prepared Slide 2 Nucleus Nuclear envelope Cytoplasm Vacuoles Plastids Answers will depend on slides available. Tissue Tissue 98 Biology Laboratory Manual B/Chapter 10

5 Name Class Date Prepared Slide 3 Tissue Analysis and Conclusions 1. Observing Do all the cells share any common structures? Explain your answer. Students should observe a cell membrane, a nucleus, and cytoplasm in all of the cells. 2. Comparing and Contrasting Compare the shapes of the different cells. Describe any similarities or differences. Answers will depend upon tissue selected. 3. Inferring What factors might affect the size and shape of a cell? The specific function of the given cell; the pressure of adjacent cells. 4. Comparing and Contrasting For each type of tissue that you observed, describe one feature that is not found in any of the others. Some possible answers may include: bone tissue has circular layers; epithelial tissue (human and plant) is flat; blood tissue contains disk-shaped cells without nuclei and large irregularly shaped cells with nuclei; skeletal muscle tissue is striated. 5. Analyzing Data How is each tissue you observed adapted to perform its special function? Answers will depend on the tissues selected. Biology Laboratory Manual B/Chapter 10 99

6 6. Drawing Conclusions Why do the cells that make up the different tissues have different shapes and sizes? Cells with different shapes and sizes have different functions; in other words, cell shape and size are related to cell function. Going Further Obtain additional prepared slides of specialized cells and tissue from your teacher. Prepare labeled sketches of each of these slides. 100 Biology Laboratory Manual B/Chapter 10