April 08, 2010
COMPARING CELLS 2: PLANTS vs. ANIMALS
In this lab, students use microscopes to compare and contrast plant (onion)
and animal (human cheek) cells
the end of this exercise, you should be able to...
PART A: ONION
Place a drop of water in the center of a clean glass slide.
Remove one of the fleshy leaves from a piece of onion. Bend the piece of onion against the curve until it snaps.
With forceps, carefully remove the thin layer of epidermis from inside
the curved piece of onion. The
piece that you remove should be as thin and flexible as plastic wrap.
Spread the epidermis on the drop of water as smoothly as possible.
If the epidermis becomes folded on the slide, use a probe to gently
flatten and unfold it.
Place a drop of methylene blue stain on the piece of onion. Now gently lower the coverslip.
Focus the slide under the lowest power.
Diagram what you see in your lab notebook. Include the total magnification and label the cell wall, cell
membrane, nucleus, cytoplasm, and chloroplast.
Also, write a description of the general shape of the onion cell and a
description of the nucleus inside of the cell.
Do not move the slide, but switch to medium power and diagram what you
see, and then repeat this process under high power.
Estimate the average length and width in micrometers of an onion cell.
Place a drop of water on a clean glass slide.
Gently rub a toothpick across the inner lining of your cheek.
Swish the toothpick in the drop of water and add a drop of iodine
Focus the slide under low power. The
cells will appear as transparent and grainy lumps.
If the light is too bright, you may need to adjust the diaphragm.
Move the slide around until you find a few isolated cells.
Diagram the cheek cells and label the cell membrane, nucleus, and
cytoplasm. Remember to include the
total magnification. Also, write a
description of the cell.
Switch to medium power and diagram and label what you see. Repeat this step with high power.
Estimate the average diameter of human cheek cells.
Complete the homework questions and write a modified lab report that includes diagrams of cells and observed. Your conclusion compares and contrasts onion (plant) cells with human cheek (animal) cells, and eukaryotic cells (plant & animal cells) with prokaryotic cells (bacteria).