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Cell Lab

Biology I Honors - Mrs. Ackroyd, Mr. Black, Mr. Miller,

Purpose: To learn methods of making simple wet mount slides and using those slides to locate and identify basic cell structures.

Pre lab

Be prepared to answer these items verbally when your teacher comes to your lab group.

  1. A student uses a light microscope with a total magnification of 1500x, but the image is too blurry to be seen clearly. Why might this occur?
  2. Why is it important to locate and center a specimen on low power before attempting to focus it at high power?
  3. A student focuses on a specimen at low power and carefully centers it before changing to high power. At high power, however, he doesn't see the part of the organism he was interested in. What might be the problem?
  4. What is the diameter of the low power field of view of your microscope? High power?

A. ONION CELLS

Separate one layer from a piece of onion. Hold it so the inside of the onion faces you. Snap the piece backwards. Using forceps, peel of a small section of the transparent layer of cells along the outer curve of the onion and lay it flat on a slide. Add a drop of Lugol's iodine and a cover slip. Examine the slide under both low and high power. Your view should be similar to Figure 1 below.  Sketch a few cells as they actually appear under high power. (Remember to use a small beaker to draw a circle on your paper to represent your field of view. Make your sketch inside this circle). Sketch a few cells as they would appear if you could see three dimensions. Identify and label the cell wall, nucleus, nucleolus, and cytoplasm. Estimate and record the cell size.

Figure 1. Onion epidermis,100x.

B. ELODEA CELLS

Remove a leaf from the end of an Elodea stem and make a wet mount slide using the entire leaf. Examine the cells along the midrib of the leaf. Look for and observe cytoplasmic streaming, This will be evidenced by the movement of the chloroplasts. Draw an enlarged view of one cell and label: cell wall, cell membrane, cytoplasm, chloroplasts, nucleus.

Figure 2.  Elodea cells, 400x.  

C. PLASMOLYSIS

Add 2-3 drops of 40% NaCl solution to the edge of your cover slip. Wick the solution under the cover slip. as you did in Part B. Examine the Elodea cells. The cytoplasm should shrink away form the cell walls. Click here for video clips of this process.

D. POTATO

Take a small piece of potato and crush it on a clean slide. (Your teacher will demonstrate this technique). Add a drop of water and a cover slip. to make a wet mount. Examine your slide under both low and high power. Locate the leucoplasts. Add a drop of iodine as you did with the onion cells. draw several stained cells, labeling the leucoplasts in addition to the cell wall, cell membrane, cytoplasm, and nucleus.

E. RED PEPPER                                               

Use a scalpel or razor blade to cut a small amount of red pepper and make a wet mount slide. Examine the specimen under high and low power. Add a small amount of iodine as you did with the onion. Draw several cells, labeling the cell wall, cell membrane, cytoplasm, nucleus, and chromoplasts (these are red organelles).                                               

 

Figure 3. Red pepper chromoplasts

F. LEAF EPIDERMIS

Using a pair of forceps, carefully remove a small piece of the lower epidermis of a Purple Queen leaf. Make a wet mount of this material. Examine your slide under low and high power. Draw several cells, labeling the cell wall, cell membrane, cytoplasm, nucleus, chromoplasts, stomata, and guard cells.

 

 Figure 4. Stoma

Clean, dry, and put away slides and cover slips. Properly put away your microscope. Clean up the slide preparation area. Thoroughly wash and dry your hands. Answer the analysis items.

Analysis Items

  1. What controls the opening and closing of stomata?
  2. What caused the elodea cells to undergo plasmolysis?
  3. Based upon what you have observed in this lab, what can you conclude about the permeability of plasma membranes?
  4. Based upon what you have observed in this lab, what can you conclude about the location of starch storage in potatoes?

Write the correct name and function of the cell organelle indicated by numbers in the diagrams below.