Lab One: Techniques for Better Microscope Use

Transcription

1 Name BioPreAP/GT Purpose: Lab One: Techniques for Better Microscope Use Part A: Microscope Parts and Functions *Refer to Fig. 1 to refresh your memory on the parts of the microscope. *The objectives are located on the revolving nosepiece and can be changed by turning the nosepiece. 1. The eyepiece contains a glass lens which magnifies times ( x). 2. The low power objective (the YELLOW obj.) is x. (which means it magnifies times) 3. The high power objective (the BLUE obj.) is x (which means it magnifies times). Note: The RED (5X) will help you find objects but we consider it beyond low. The YELLOW (10X) will be considered low power. If you multiply the eyepiece by the objective it will give you the total magnification. 4. The total magnification of an object when viewed under low power is x. 5. What is the total magnification of your microscope under high power? x.

2 Refer to the colored direction packets to complete the lab. Part B: Position of Objects When Viewed With a Microscope Part C: Use of the Diaphragm Part D. Depth of Field 12. Yes or No 13. Yes or No Part E: Stains as an Aid to Microscope Work ( X) ( X) Analysis: True or False T or F 1. Total magnification of a microscope is determined by adding the eyepiece lens magnification to the objective lens magnification. T or F 2. Objects viewed under the microscope appear upside down.

3 T or F 3. When moving the slide toward the left, objects viewed through the microscope will move toward the left. T or F 4. The diaphragm is used to adjust the amount of light entering the microscope. T or F 5. All objects in different depths appear in focus at the same time while using high power. T or F 6. Stains are used to help make clear objects appear lighter under the microscope. ONION LAB Two: Comparing Plant and Animal Cells ( X) Yes or No Label: cell membrane, cell wall, nucleus, cytoplasm ( X)

4 Yes or No 8. Yes or No CHEEK CELLS Label: cell membrane, cytoplasm, nucleus ( X) 9. Analysis: 1.How does the outer edge of the onion cells differ from the cheek cell? (describe) 2. a. What is the outer edge of the onion called? b. What is the outer edge of the cheek cell called? 3. What are some structural differences between plant cells and animal cells? (specific organelles) 4. What is the basic unit of structure in all living things? 5. What advantages do plant cells have over animal cells?

5 Part B: Position of Objects When Viewed With a Microscope *Place the prepared slide of the letter e on your stage so that you can read the slide label. Look at the e and notice the position of it. Then observe the letter e using low power (10x) on your microscope. Focus the e with the fine adjustment. 6. What is the position of the e viewed with the microscope compared to its position on the stage? *While looking through the eyepiece, move the slide slowly from left to right. 7. In what direction does the letter move as seen through the microscope? *While looking through the eyepiece, move the slide slowly from right to left. 8. In what direction does the letter move when viewed through the microscope? *While looking through the eyepiece, move the slide toward you. 9. In what direction does the letter move as seen through the microscope as you move the slide toward you?

6 Part C: Use of the Diaphragm All objects viewed under the microscope will require adjustment of light. Many problems associated with microscopic observation can be overcome by adjusting the diaphragm for proper lighting. *Prepare a wet mount of a few strands of cotton. >Add a small drop of water to a slide as shown at your station. >Place the object to be viewed in the water drop. >Hold the cover at a 45 degree angle and let it touch the water. Lower the edge of the cover slip down slowly over the water drop and object. This procedure will prevent trapping air under the cover slip.(tweezers are not necessary) *Observe the cotton fiber with low power. While looking through the microscope, change the amount of light entering the microscope by adjusting the diaphragm. (refer to the diagram of the labeled microscope if needed) 10. Under what diaphragm setting are the cotton fibers sharpest to you? (Circle one) *Change to high power (40x) and observe the cotton fibers. Again readjust the amount of light entering the microscope. 11. Under what diaphragm setting do the cotton fibers appear the sharpest?(circle one)

7 Part D. Depth of Field *Use the prepared slide of the colored threads. Locate the strands under low power. Center the slide so you are looking at the point where the strands cross. Adjust the diaphragm for proper lighting. 12. Can all strands be observed clearly at the same time under low power? *Change to high power and observe all strands at the point where they cross. 13. Can all strands be observed clearly at the same time under high power?

8 Part E: Stains as an Aid to Microscope Work Many objects observed with a microscope are colorless. Thus, they appear almost transparent and are difficult to see. Stains often are used in microscope work to color objects for easier and more detailed observations. Stains can be added to a wet mount without disturbing the slide. *Take your slide to the front of the room. >Pick up a piece of potato and rub it on your slide. You only need the juice, not a slice of potato!! >Add a drop of water to the slide with the potato scrapings. >Add a cover slip. *Go back to your scope and view the wet mount under low power. You are looking at starch grains. *Draw, in pencil, the field of view on your paper. Record the power and what you viewed - UNSTAINED potato under the circle. *Remove the slide from the microscope so that you can now add stain. *DO NOT remove the cover slip. Add a drop of iodine solution to your slide along one edge of the cover slip as shown. Do not get any iodine on top of the cover slip. *Caution: securely replace the dropper on the bottle to avoid spilling. *Now place a piece of paper towel (which is cut for you) along the edge of the cover slip opposite the iodine solution. Allow the tissue paper to touch the water of the wet mount as shown. Water will soak into the paper, drawing the iodine stain under the cover slip and into contact with the starch grains. *Throw away the paper towel in the trash bag at your station. *Observe and draw the field of view. Record the power and STAINED potato under the circle.

9 ONION The epidermis of the onion is ideal for cell study because it is composed of a single layer of cells. * At the teacher desk, >remove a thick scale from an onion and peel the delicate transparent tissue from the inner surface. >Mount it on a slide in a drop of water. Avoid wrinkling the tissue. >Add a cover slip to your wet mount. * Go back to your scope and examine the onion cells under low power (10X) and draw the cells. Record the power and name, and then answer the following questions on your own paper. 1. Describe the shape of the cells. 2. Are all the cells similar in shape? 3. Describe the color of the cytoplasm. *DO NOT remove the cover slip. Stain the onion with iodine using the same staining technique you did with the potato. * First, view the onion under low power. 4. What effect does the stain have on the cells? * Choose one cell that shows the contents clearly, move it to the center of the microscope field, and then switch to high power (40X). Record the power and name. Draw, label the cell, and then answer the following questions. 5. Describe the color of the cytoplasm. 6. What is the appearance of the nucleus? 7. Is the nucleus always in the same position in the cell? 8. Does the onion epidermal cell appear to have depth? (HINT: remember the colored threads) *Throw the onion in the trash and clean the slide with water.

10 CHEEK CELLS Cheek cells, taken from your own mouth, are a good source of animal cells that can be readily observed under a microscope. Note the differences between these animal cells and the previously viewed plant cells. * Bring your clean slide to the teacher desk to prepare the mount. >Place a drop of water on a slide. >Gently scrape the inside of your cheek with the broad end of a toothpick. >Place the toothpick in the drop of water and slightly stir. >Then gently place the cover slip on the slide. >NOTE: Dispose of your toothpick immediately! Do not set it on the counter or leave it in your mouth! >Stain the cheek cells, without viewing them first. Stain it before you leave the teacher desk! >Use the same staining technique as you did with the iodine and onion cells, but this time use methylene blue. *Throw away the paper towel in the trash bag at the teacher desk. * Go back to your scope and examine the cells under low power and high power. NOTE: They may be hard to find- if you are not sure what you are looking at- ASK! * Draw a single cheek cell under high power. Record power and name. Label the cell and then answer the following question. 9. Describe the shape of the cheek cells.