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Living Cells
I. AIM
The cell theory states that all living things are composed of cells. Cells are the basic structural units of
living things, and cells come from pre-existing cells. This inquiry will provide an opportunity to make
first-hand observations of cells.
PURPOSE: To become familiar with the techniques for making wet mounts and the staining of cells.
These skills will help the student observe plant and animal cells under the microscope.
PROBLEM: What are the differences in structure between plant and animal cells?
II. MATERIALS AND PROCEDURE:
microscope
slides
cover slips
forceps
scalpel
dissecting needle
medicine dropper
flat edged toothpick
iodine stain
methylene blue
onion
Elodea leaves
human cheek cells
Part I: Making a wet mount
1. Obtain a slide, rinse it with water and wipe both sides with a paper towel. Now that the slide is clean
make sure you only hold it by its edges.
2. Obtain a clean coverslip.
3. Using a medicine dropper, place a drop of water in the center of the slide.
4. Cut a small thin piece of the onion and center it in the drop of water on the slide.
5. Place the coverslip at a 45-degree angle over the specimen. Carefully lower the coverslip onto the slide.
6. Check for any air bubbles. Use your finger to gently tap the coverslip to remove them. Sometimes, you
may need to add additional water to the slide.
Part II: Onion: cell wall, nucleus, nucleolus, cytoplasm
1. Obtain a scale of an onion section.
2. Peel the delicate transparent tissue from the inner surface of the scale.
3. Prepare a wet mount with the onion skin. Avoid wrinkling the tissue.
4. Observe the tissue under the microscope. Adjust the amount of light coming through the stage by
changing the diaphragm opening.
5. Add a drop of iodine stain next to the edge of the coverslip of the wet mount.
6. Place a small piece of paper towel next to the coverslip on the side opposite of the iodine stain. As
the paper towel absorbs the water it will pull the iodine stain through the wet mount and stain
the onion.
7. Put the slide onto the microscope stage and examine it under low power and locate a cell that
shows the contents clearly. Move the slide so that this cell will be in the center of the microscope’s
field of view.
8. Looking from the side of the microscope, carefully move the high power objective into position.
Using high power, examine all parts of the cell. Remember, do NOT use the coarse adjustment
knob on high power! You may use the fine adjustment to observe the cell at various depths.
9. Draw the onion cell under high power. Remember to label the cell’s structures and magnification
power.
Part III: Elodea: cell wall, chloroplasts, nucleus
Elodea is common plant that lives in fresh water. The part of the onion where you obtained cells is below
the ground. The elodea plant is found where sunlight strikes the plant.
1. Prepare a wet mount of an Elodea leaf. The whole leaf should be used.
2. Examine the leaf under low power and select a portion of the leaf where the cells are particularly
distinct. Center this portion within the field of view.
3. Switch to high power. Use the fine adjustment to observe the cells and associated parts at various
depths.
4. Observe the chloroplasts in the cells. These are the small oval green structures in the cytoplasm.
As you observe the chloroplasts, watch carefully for chloroplast movement. (HINT: you may
have to look for this in several cells! Try switching to low power to look for movement.)
5. Other structures are present in the cells of elodea, but most of these except the cell wall are
hidden by chloroplasts. With patience and careful observation of many cells you may be able to
find a nucleus in a spike cell. Spike cells are located at the edges of the elodea leaf.
6. Draw and some Elodea leaf cells. Also indicate the magnification power.
Part IV: Cheek cells: cell membrane, nucleus, nucleolus, cytoplasm
1. Gently scrape the inside of your cheek with the broad end of a clean toothpick.
2. Prepare a wet mount of the material you have scrapped.
3. To stain these animal cells, use methylene blue stain instead of the iodine used for plant cells.
4. Examine the cells under low power and locate some isolated cells that are not clumped together.
Center these cells.
5. Switch to high power and look for the various cell structures.
6. Draw a single cheek cell as you observe it under high power and label the following structures:
plasma membrane, cytoplasm, and nucleus.
III. DATA: Draw, label, and color the cells. The drawings should be done in a circle on unlined paper.
Label each cell and their structures and indicate the magnification.
IV. RESULTS:
Part I:
1. Why must the specimen be thin when mounted on a slide?
2. What is the purpose of the coverslip?
3. Why should coarse adjustment not be used with high power?
Part II:
4. Describe the shape of the onion cell.
5. Are all the onion cells similar in shape?
6. When the iodine stain was added, what effect does the stain have on the cells?
7. What is the appearance of the cytoplasm after the stain was added?
8. What is the appearance of the nuclei with the stain added?
9. Describe the shape, size, and location of the nucleus?
10. Where is the nucleolus found?
11. What is the function of the cell’s nucleolus? (Consult text or notes if necessary)
12. Does the onion cells appear to have depth? Explain your answer.
Part III:
13. Describe the shape of the Elodea cell.
14. What cell structures in the Elodea determine if it is a plant or animal cell?
15. Describe the size, shape, color, and location of the chloroplasts.
16. Chloroplasts have no means of independent movement, yet they can be seen moving in the
Elodea’s leaf cells. Explain this observation.
17. What pigment is contained within the chloroplasts?
18. What is the function of the chloroplasts?
19. What do you think the purpose of the movement of the chloroplasts might be?
Part IV:
20. Describe the shape of the cheek cell.
21. How does the outer edge of the cheek cell differ from the Elodea cell?
22. What is the outer edge of the cheek cell called?
23. What is the purpose and effect of adding methylene blue?
24. How would you be able to tell that this cell was from an animal and not a plant?
V. CONCLUSION: Paragraph
1. Do elodea cells have the same function as onion cells? Explain.
2. How are elodea cells similar to onion cells? How are they different?
3. How does the shape of the plant cells compare to the cheek cells?
4. Do your observations support the ideas of Schwann and Schleiden? Explain.
5. What are the structural differences between plant and animals cells?
6. List four organelles that were not seen, but should have been in the 3 cells.