Cell Lab: The Human Cheek Cell and the Onion Cell

1. List the 3 parts of the Cell Theory

Materials:

*slides              *cover slips                  * onion * toothpicks                 *iodine

*methylene blue                                    *forceps           * microscope

Procedure:

PART 1: ANIMAL CELLS

1. Put a drop of methylene blue on a clean slide. Caution: methylene blue will stain clothes and skin.

2. Gently scrape the inside of your cheek with the flat side of a toothpick.

3. Stir the end of the toothpick in the stain and throw the toothpick away.

4. Place a coverslip onto the slide.

5. Use the LOWEST objective to focus and find cells. 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 and do not move the slide)

---Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane. Draw your cells to scale.

 PART 2: PLANT CELLS
1. Carefully peel off a small piece of the very thin layer of tissue from just under the outside skin of an onion.

2. Unroll the specimine so that it is flat and place it in the middle of a clean slide.

3. Use an eyedropper to add a drop of stain (dye) to the specimen on the slide. The stain will make the cellsof the specimen easier to see.

4. Use the tweezers to place the edge of the slip-cover on the slide besides the specimen. Slowly lower the cover slip over the specimen. This method will reduce the chance of trapping air bubbles between the slide and the cover slip. A slide prepared in this way is called a wet-mount slide.

5. Observe the specimen with the microscope. Use the lower objective first. Keep the stage of the microscope level so that the stain does not drain from the slide. Switch to the medium power, and eventually to the high power. PLEASE BE CAREFUL!!


The picture below is Elodea, a small aquatic plant that commonly grows in lakes and is often placed in fish tanks. Did you know that all of these cells are connected by small pores (plasmodesmata) and the plasma membranes are continuous between all of the cells?
Questions:
1. What organelles are responsible for photosynthesis?
2. What structures are found in these cells but are not present in animal cells?




The image below is also from a plant, but notice the cells do not contain any chloroplasts. This slide is from a very thin slice of an onion. Look closely and you should be able to see a nucleus within each cell.

Cheek Cells

Paramecium

Amoeba

. Plasmolysis: Shrinkage of the protoplast or cell contents due to water loss when a drop of salt water (NaCl) is added to the Elodea slide. Because of all the salt ions (Na+ and Cl- ions) outside the cell membrane of each Elodea cell, water molecules move out of the cell membrane causing the cell membrane and it contents to shrink into a blob in the center of the cell wall. The porous, cellulose wall does not shrink because the salt ions easily pass through the wall but cannot pass through the membrane. Therefore, the cell membrane (not the cell wall) loses water molecules and shrinks.
         

 

 

ALTERNATIVE: (Use Skin cells from your wrist instead)

Procedure:
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. Examine the slide under a microscope. Look for cells with low power first, and then switch to high power for details.

 

 


 

Name:_________________________________

 

Cells Lab

 

PART 1: ANIMAL CELL

---Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane. Draw your cells to scale.

LOW (40x)

MEDIUM (100x)

HIGH (400x)

 

 

PART 2: PLANT CELL

---Sketch the cell at low and high power. Label the nucleus, cytoplasm, and cell membrane. Draw your cells to scale.

LOW (40x)

MEDIUM (100x)

HIGH (400x)

 

QUESTIONS


 

3.Why is methylene blue necessary?

 

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

 

5.The light microscope used in the lab is not powerful enough to view other organelles in the cheek cell.What parts of the cell were visible.

 

6. List 2 organelles that were NOT visible but should have been in the cheek cell.

 

7.Is the cheek cell a eukaryote or prokaryote? How do you know?

 

8. Keeping in mind that the mouth is the first site of chemical digestion in a human.Your saliva starts the provss of breaking down the food you eat.Keeping this in mind, what organelle do you think would bem numerous inside the cells of your mouth?

II.    Why do we stain specimens?

 

III.   Why must the specimen you observe be very thin?