Cell Lab Update

8/4/2019 Cell Lab Update

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Cell Lab

Purpose:1. To identify the major structures found in plant and animal cells that can be seen using the compound lightmicroscope.

2. To identify the major differences between plant and animal cell structures.

Procedures & Data:Part 1: Onion Cell1. Make a wet mount of a small piece of onion epidermal tissue.

Remove the transparent tissue (epidermis) of the inner surface of a small piece of onion scale.

Mount this tissue in a drop of water on a clean slide, taking care not to fold or wrinkle thetissue.

Cover with a cover slip.2. Examine the cells under low and high power objectives of your microscope. Be sure to use all of yourproper microscope procedures.3. While under low power, note the arrangement and shape of the cells.4. While under high power, note the finer structures of the cells. Careful focusing with the fine adjustmentwill aid in this effort and will also bring out the three-dimensional aspects of the cell.

5. Remove the slide from the microscope. Using your staining techniques learned last lab, add a drop ofiodine to the side of the cover slip. Use a paper towel to draw the stain under the cover slip. The iodine willstain parts of the cells and make them more visible.6. Observe again under low and high powers. Locate the following:

Cell Wall: surrounding each cell

Cell Membrane: you cannot see this organelle. It is the membrane just inside the cell wall andcontains the cell and regulates what goes into and out of the cell.

Cytoplasm: a thin transparent layer, finely granular, completely lining the cell-sides, top and bottom.The center of the cell is occupied by a large vacuole filled with a clear colorless liquid called cell sap.

Nucleus: a rather dense organelle embedded in the cytoplasm at one side of the cell

Nucleolus: smaller organelle inside the nucleus.Analysis:

1. Draw several cells from high power. Label your drawing properly with all of the organelles you cansee. You should be able to identify the cell wall, cell membrane, the nucleus, and possibly the nucleolus.

2. What material is the cell wall composed of?

3. Of what material is the nucleolus composed?

High Power

Part 2: Lettuce Leaf1. Prepare a slide by putting one drop of methylene blue on it (if you have time, you may want to experiment with

different stains. You may get better results or see different things with the iodine stain.)2. Carefully break a lettuce leaf by snapping it so that a broken edge of the leaf is exposed. With your fingernail or

with a razor blade, lift up the very top layer of cells off of the leaf. Once you get it started, you should be able topull on it and lift up a large section that is transparent and only one or two cells thick.

CAUTION: The razor blade is extremely sharp and could cut your finger easily!! Use it only if necessary.Cutting motion should always be away from your body, away from your fingers, and away from anyone else. Iwill help you with this step if necessary.

3. Quickly put the sample of lettuce on top of the methylene stain, because the lettuce has a tendency to curl up.


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4. View the slide under Scanning, 100x and 400x magnification. Draw about 5-7 cells and show how they areconnected to one another. Draw any detail you can see inside of the cell. Label the cell membrane, the cell wall,the chloroplasts, and the nucleus.

5. See if you can find any doughnut shapes interspersed in your sample. Those are two long cells curved towardeach other, and they are called guard cells Draw the guard cells if you find them.

Low power high power

Question: What in the name of the green pigment contained within the chloroplasts?

Part 3: Blood Smear1. Obtain the slide labeled blood smear. Place it on the stage of your microscope.

2. Examine these cells on both low and high powers.3. Draw and label several cells from low power.4. Draw several cells from high power. Label your drawing properly with all

of the organelles you can see. You should be able to identify the cell membrane and the nucleus.


Part 4: Epithelial Cells

1. Wash the underside of a wrist that will be sampled for epidermal cells with soap and water.2. Stick a clean piece of clear tape on the underside of the washed wrist.3. Gently remove the piece of tape from the wrist being careful to avoid getting fingerprints on the tape. A forceps

might help to remove the tape and avoid fingerprinting the tape.4. Place the tape, sticky-side up, on a clean microscope slide.5. Stain the top, sticky side of the tape with 2 or 3 drops of 1% methylene blue solution.6. Use a dissecting needle to gently place a cover slip over the sticky tape. Lower the coverslip down onto the tape

and then remove the dissecting needle. This should help prevent staining your fingers.Caution: Use methylene blue carefully. It will stain most items including skin, clothing, and table tops.

7. Use the SCANNING objective to focus. You probably will not see the cells at this power.8. Switch to low power. 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 cell9. 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)---Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane. Draw your cells to scale.



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Analysis:1. Do these cells have a cell wall?

2. Why is methylene blue necessary?

3. Skin cells do not move on their own, so you will not find two organelles that function for cell movement.Name these organelles.

4. The light microscope used in the lab is not powerful enough to view other organelles in the skin cell. Whatparts of the cell were visible?

5. List 2 organelles that were NOT visible but should have been in the skin cell.

6. Is the skin cell a eukaryote or prokaryote? How do you know?

Part 5: Bacterial cells1. Stick a toothpick into yogurt that has live cultures in it, and wipe the yogurt from the toothpick onto a

slide.2. Dilute the yogurt with a drop of water, and cover with a cover slip. If you do not dilute the yogurt, the

milk particles will be so thick that light cannot pass through them.

3. View slide scanning and find the milk particles. Then view the slide in 400x magnification. Thebacteria are extremely small, so you cant see them under 100x magnification. Look between the milkparticles and search for small worm-shaped bacteria that are moving around. Draw their shape anddescribe their movement.

Movement:


Part 6: Cell Membranes in Yeast1. Prepare a slide of the yeast in the warm water by placing a drop of the solution on a clean slide.2. Place a drop of Methylene blue onto the drop of yeast solution.3. Carefully cover it with your cover slip, remembering to drop it at an angle.4. Look at the slide under the microscope, remembering to start focusing with low power.5. Find a good example of the yeast under high power and draw what you see in the data below.6. Repeat steps 1-5 for the yeast that has been boiled.


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yeast in warm water boiled yeast

Questions:1. Explain how boiling affected the yeast cells.

2. Why does the color of the two groups of cells differ? (remember to consider the role of the plasmamembrane.)

3. Are the plasma membranes selective barriers? Explain.

Conclusion Questions:1. Which of the observed cells were plant cells?

2. Which of the observed cells were animal cells?

3. What 2 structures are present in plant cells which are not in animal cells?

4. What material is the cell wall composed of?

5. What is the name of the green pigment contained within the chloroplasts?

6. Why couldnt you see all of the organelles which are contained within the eukaryotic cells?

7. What kind of microscope would allow you to see all of the intracellular structures clearly?


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Cell Lab Update

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