Microscopes & cells. 2. arm. 3. ocular lens. 4. objective lenses. 5. stage. 6. slide clamp. 7. stage controls

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1 Microscopes & cells Objectives: At the end of this lab you should be able to: o demonstrate the safe and proper handling of a microscope, including carrying a microscope, slide placement, and storage. o focus and adjust light properly to observe objects clearly under all powers of the microscope. o identify and describe the function of some organelles: plasma membrane, cell wall, nucleus, cytoplasm, chloroplast. Using compound microscopes One of the characteristics of life is organization. Cells are usually too small for observations of structure and organization with our unaided eyes. Microscopes provide the magnification needed to investigate the cellular and molecular structures. Today you ll spend most of the period using this important research tool and becoming familiar with the largest organelles found in plant and animal cells. Microscope Your instructor will identify each of the following structures on your microscope. For each structure, label the appropriate part on the diagram and describe the function in the space provided below. 1. base 2. arm 3. ocular lens 4. objective lenses _ 5. stage 6. slide clamp 7. stage controls _

2 7. coarse focusing knob 8. fine focusing knob _

3 Magnification The total magnification of the microscope equals the magnification of the ocular lens times the magnification of the objective lens being used. 10. What is the magnification of the ocular lens? 11. What is the magnification of the objective lenses?,, and 12. What is the total magnification of an object examined under the lowest power? ( )x( ) = 13. What is the total magnification of an object examined under the highest power? ( )x( ) = 14. A fourth objective lens has been removed from your microscope. This magnification of that lens was 100x. What is the total magnification for your ocular lens when used with a 100x objective lens? ( )x( ) = Field of view 15. Obtain a prepared slide of the letter e. Place it on the stage. Use the coarse adjustment knob to bring the nosepiece and stage as close as possible. 16. Make sure you re using the lowest power objective lens. Look through the ocular lens. Adjust the light intensity to the lowest comfortable setting. Very slowly turn the coarse adjustment knob until the letter e comes into focus. Sketch what you can see. 17. Without changing the focus or your slide position, change to the next objective lens. Adjust the light intensity as needed. Sketch what you see. Image under low power Image under medium power Image under high power

4 18. The field of view is the area you can see while looking through the microscope. What happened to the size of this area when you increased magnification? 19. What happened to the amount of light as you went up in magnification? Orientation of the image 20. Move the prepared slide to the right while viewing it through the low power objective. In which direction does the image move? 21. Move the prepared slide to the left while viewing it through the low power objective. In which direction does the image move? 22. Move the slide away from you. In which direction does the image move? Please return your prepared letter e slide to the appropriate tray. Thanks. Depth of field In the laboratory you will need to examine specimens that are several cells thick. A leaf for example, has different cell types on the surface than it does in the interior. You will need to be able to focus upon each layer separately. The characteristic of the microscope that allows the examination of separate layers is called the depth of field. 23. To illustrate this concept, obtain a prepared slide of silk. These slides contain fibers stacked in three layers. Each layer has a different color. Use a Kimwipe to clean your slide and then place it on the stage. Make sure you are using the low power objective lens. Focus as usual. 24. Change to the medium objective lens. Notice that all three thread colors are no longer in focus. Using the fine focus knob, move the stage upward until all the colors are out of focus. Now focus downward noting the order in which the colors come into focus. Which color came into focus first? Which color thread is at the top? Which color thread is on the bottom? Sketch below what you see: Please return your prepared slide to the appropriate tray. Thanks.

5 Elodea Plant Cells Place a leaf from the Elodea plant on a CLEAN glass slide with a drop of water and cover with a cover slip. Focus on the cells. Progress up to medium; then high power. Focus on a single cell. Try to identify the cell wall, chloroplast, and central vacuole. Notice that you can not really differentiate between the plasma membrane and the cell wall. If you re lucky you may be able to see a clear oval within the cell, usually near a corner. This is the nucleus, often hidden by the abundant chloroplast found in Elodea leafs. Sketch your cell and label the organelles you identified. Entire leaf under high power Sketch just one cell under high power. Draw it large and label the organelles. Using the 40x objective lens, focus on a single cell. Very slowly move the fine focus knob while keeping your attention on this single cell. The cell appears to lose focus and then slightly move and regain focus. The cell has not moved, rather you moved the depth of field. You are looking at a different cell, contained in a different layer of cells. 25. How many layers of cells in your Elodea leaf? Please dispose the entire slide into the appropriate disposal container. Thanks.

6 Using stains Stains are used to improve contrast. This improves viewing with a microscope. The next sections use two different stains. The first stain, methylene blue, stains membranes. The second stain, iodine, stains starch. Methylene blue and cheek cells Gently scrape the inside of your cheek with the tip of a toothpick and smear it on your slide. Add a small drop of methylene blue. Add a cover slip. Start on low power and progress up to high power Focus on a single cell. Try to identify the plasma membrane, cytoplasm, and nucleus. Notice that animal cells do not have a cell wall. Sketch a single cell and label organelles. Find a group of cells clumped together. Sketch this clump of cells. Single cheek cell under high power with organelles labelled Clump of cheek cells under high power 26. Describe the spatial relationship between individual cells in this group of cheek cells: side by side, or overlapping? 27. What might be the advantage to how cheek cells are in relationship to each other? 28. Describe the spatial relationship between individual cells in the Elodea leaf:

7 29. What might be the advantage to how Elodea cells are in relationship to each other? Please put the entire slide (including cover slip) into the discard container for all slides. Thanks. Iodine and potato cells Obtain a small, thin slice of potato (about the same thickness as this piece of paper). Place the potato slice on the slide. Add a small drop of iodine. Add a cover slip. Focus on low power and progress up to high power. If it is too thick (it will be very dark) try moving the slide and observing the cells on the edge. Focus on a single cell. Try to identify the cell wall, starch, and plasma membrane. Sketch what you see. Single potato cell under high power with organelles labelled Section of potato slice under high power 30. What turned purple? 31. What function do you think the starch stored in the potato serves for the potato plant? Please put the entire slide (including cover slip) into the discard container for all slides. Thanks.

8 Explorations Practice what you have learned by viewing a variety of materials under the microscope. There is a great selection on the front bench. Please make sure to replace each slide on its proper tray. 32. What does xs mean on a prepared slide? 33. What does ls mean on a prepared slide? Slide = Pond Water Slide = Slide = Slide = Slide = Slide = Slide = Slide = Slide =