CELL OBSERVATION LAB
Objectives: Understand the cell as the basis unit of life by observing and comparing animal, plant, and protist cells.
Background: The cell theory states that the cell is the structural and functional unit of all living things. Eukaryotic cells contain structures
called organelles. Cells can be classified through the type of organelles they contain.
Materials:
Clear packing tape, slides, water, dropper, iodine/methylene blue, microscope, slide cover, prepared slides of protists, prepared slides of
human blood, prepared slides of onion roots, prepared slides of typical animal cells; onion; tweezers; forceps, iodine solution, methylene blue
General Note:
1) Remember not to use the course adjustment while on high power
2) Never touch the lenses when using your microscope
3) Carry microscopes through neck and base
4) Clean slides and slide covers after use (wash/alcohol)
5) Pack microscopes after use
NOTE: Although cells will appear as 2-dimmensional disks under the microscope, they are 3-dimensional (spherical/boxed/etc) in shape.
Part I. Examining Plant Cells
A. White Onion Epidermis
1) Hold a tiny piece of onion so that concave surface is facing you. A transparent, paper-thin layer of epidermis pulls easily from this
surface, much like your skin after a sunburn
2) Prepare a wet-mount slide:
a. Add a drop of water to the slide.
b. Place the onion skin on the slide.
c. Cover the slide with a cover
3) Find the cells using SCANNING POWER
4) Switch and observe the many cells using medium power. Note that each cell has distinct boundary (composed of visible plasma
membrane and non-visible cell wall)
5) Stain the slide with one or two drops of iodine/methylene blue in the following manner:
a. Place a drop at one edge of the cover glass
b. Draw it under the cover glass by touching a piece of paper towel to the opposite edge
6) Under medium power look at several cells and locate one with a stained nucleus. The lightly stained granular substance between
the nucleus and the membrane is the cytoplasm
7) Switch to high power and observe again (do not use coarse adjustment knob). You may find several cells with one or more small
dark bodies inside the nucleus: nucleolus
8) Draw to scale the cells as seen under high power and label cytoplasm, nucleus, cell membrane, and nucleolus of one of the cells
(next page)
B. Cells of purple onion
1) Repeat the steps 1-3 above, but use a purple onion instead
2) Under medium power, observe an area where the is only one cell layer (it will look like there are not cells pilled on top of each
other vertically, or towards the lenses) and note that all the purple pigmentation you see is confined to the large central vacuole
(Remember that these cells are not stained and what you are seeing is not the nucleus, which is barely visible unless you stain it).
3) Also note that under high power, you can see that the cytoplasm has no purple pigmentation.
4) Try to locate a cell with a darker nucleus visible in addition to the central vacuole.
5) Draw to scale the area that includes this cell as seen under high power and label cytoplasm, nucleus, cell membrane, and central
vacuole of one of them (next page)
C. Elodea cells
Elodea is a common flowering plan which is widely distributed in freshwater lakes and ponds. You can find it in pet shops for your
aquarium
1.
2.
3.
4.
Make a wet mount of a small square piece of an elodea leaf
As before, find cells under SCANNING power and then switch up to medium and high power.
Carefully search many cells looking for movement inside the cell. This movement is not always visible, but it is always present.
Draw cell area under high power and label any structures you see (next page)
White onion epidermis
Purple onion epidermis
Elodea leaf
Questions:
1. Estimate the size of cells in microns (you may need to review the microscope measurements material from the Instruments and
Measurements Unit)
a. White onion
b. Purple onion
c. Elodea leaf
2. Using white onion epidermis cells, estimate the ratio of the size of the nucleus to length of the cell.
3. Is the nucleus in the center of these cells?
4. Where is the nucleolus located?
5. As you move the fine adjustment knob slightly, what do you observe that proves to you that the cell is 3-dimmensional?
6. What is the purpose of adding iodine/methylene blue to the slides?
7. What cell structure or structures in the onion observed the greatest amount of stain?
8. Which occupies the greatest volume in the cells, the cytoplasm with suspended nucleus or the vacuole ?
9. All living cells have an abundance of water. Where in the onion cells is most of the water found?
10. Compare the purple onion cells with the cells of the white onion.
a. What is the obvious difference?
b. What are their similarities?
11. Is the cytoplasm green?
12. In what organelle are the green pigment housed?
13. Where is the organelle located?
14. What is the pigment called?
15. What is the shape of a 3dimensional chloroplast?
16. What causes the chloroplasts to move?
17. Describe their motion
18. What is the difference in function between elodea cells with chloroplasts and the onion epidermis cells?
19. A large central vacuole is present in each Elodea cell. Why is it not always visible?
20. A nucleus is always present in each elodea cell. Why is it not always visible?
21. Compare / contrast onion epidermis cells with elodea mesophyll cells
Part II. Examining Animal Cells
A. Skin Cells
1) Wash the underside of a wrist that will be sample for epidermal cells with soap and water
2) Cut a piece of clear packing tape about 2x2cm or to fit on the slide
3) Place the packing tape on the inside of your wrist. Do not place on the top of your arm as removal of the hair will be painful.
4) Rub the tape while using a tissue to avoid putting fingerprints on the tape. This will help it adhere to your skin skills.
5) Quickly remove the tape (using a forceps might help remove the tape without putting fingerprints in it
6) Place the tape sticky side up on a microscope slide. Place a drop of iodine/methylene blue on the tape (if you have iodine allergy
– please inform your teacher). Be careful as these will stain clothes and skin. Place a coverslip over the on the tape.
Alternative: Use pre-prepared slide instead of doing parts 1-3.
7) Observe the skin cell under SCANNING power to locate cells,
8) Then switch to medium and high power and draw them below to scale!
9) Draw a single cell and label the membrane, cytoplasm, and nucleus as observed.
B. Cheek cells
1) Put a drop of methylene blue on a slide.Caution: methylene blue will stain clothes and skin.
2) Gently scrape the inside of your cheek with the flat side of a toothpick.Scrape lightly.
3) Stir the end of the toothpick int the stain and throw the toothpick away.
4) Place a coverslip onto the slide
5) Use the SCANNING objective to focus.You probably will not see the cells at this power.
6) Switch to medium. Cells should be visible, but they will be small and look like nearly clear purplish blobs.If you are looking at
something dark dark purple, it is probably not a cell
7) Once you think you have located a cell, switch to high power and refocus.(Remember, do NOT use the coarse adjustment knob at
this point)
8) Draw the cells to scale:
Questions:
22. Why was it necessary to add iodine/methylene blue?
23. Although the light microscope used was not powerful enough to see view most organelles in the cells, what parts were visible?
24. How does the boundary of the animal cell differ from the cell boundary of the plant?
25. Estimate the size of one skin cell in microns (you may need to review the microscrope measurments material from the
Instruments and Measurements Unit)
26. Estimate the size of one cheek cell in microns (you may need to review the microscrope measurments material from the
Instruments and Measurements Unit)
27. List the structures you observed in the plant cell that are not present in the skin cell and explain why they are not needed in the
skin cell.
28. Where is the nucleus of the animal cell located? How does this compare to the plant cell?
29. What organelle would be numerous in a skin cell that secreats parts of sweat or mouth cell that secretes components of saliva?
Part III. Blood Cells
(Prepared Slide – For procedures for a blood smear. See separate lab under the Human Anatomy Unit: Cardiovascular System Topic)
1) Examine prepared slide of human blood under low and high power
2) Draw both the red and white blood cells below to scale as seen under high power:
Red Blood Cell
White Blood Cell
Questions:
1. In addition to color, how are red and white blood cells different?
2. Which of the blood cells live longer? Why?
3. Why do red blood cells have a biconcave shape?
Part IV. Protist Cells
1) Examine the pre-prepared slide containing an amoeba and draw it under high power (start with scanning and move your way up
after you locate a cell)
Questions:
1. In what way is the amoeba like the animal cells?
2. Why is the amoeba classified as a protist?
3. Is the amoeba a prokaryote or a eukaryote? Why?
Conclusion
How did this activity help you confirm the cell theory?