Cell Lab including Cell Theory
Plant, Animal and Bacteria
Cell Theory:
The cell theory has three parts and is fundamental in understanding science,
especially the science of cells. Early evidence of the cell theory was
provided by a German botanist in 1838 who concluded that “all plants are
composed of cells. A year later in 1839, Theodor Schwann came to the
same conclusion about animals. These two ideas gave us the first part of the
three part cell theory. Then in 1855 a doctor who was studying how diseases
affect living things came to the conclusion that cells can only come from
other cells. These ideas along with the research of modern scientists give
us the evidence which supports the cell theory.
1. All living things are composed of one or more cells.
2. Cells are the basic units of structure and function in an organism.
3. Cells come only for the reproduction of existing cells.
Cells come in a variety of sizes and shapes. The internal organization of cells
depends greatly on where they are located in an organism. The organelles of
a cell carry out the life functions of a cell just as the organs of our bodies
carry out functions necessary for life.
Lab:
In this lab we will see differences in cell shape, size and organization. We
will also observed differences between prokaryotic (bacteria) cells and
eukaryotic (plant and animal) cells. We will look at onion, bacteria (2) AND
cheek cells.
Materials:
Onion
Water
Slides
Cover slips
Paper Towels
Dropper
Microscope
Stain IKI/Methylene blue
Toothpicks
Procedure:
Part A Plant Cells
1. Pull a piece of scale from the onion bulb until it cracks. Peel the thin
epidermal layer off of the outer skin.
2. Put a drop of water on a clean slide. Place a piece of the epidermal
tissue in the water and make sure it lies flat.
3. Lay the cover slip on top of the epidermal tissue and water.
4. Make a drawing of the onion cells with 2 parts labeled.
Part B Cheek Cells
1. Place a drop of water on a slide. Use a toothpick to GENTLY scrape
the cells from the inside of your cheek. Dip this end of the toothpick
in the drop of water and stir to mix the cells with the water. Use a
coverslip
2. Examine the cells using the microscope. Identify the parts of the
cells. Draw and label two cheek cells (don’t forget to include the
magnification 40x, 100x, or 400x.)
Now You Will Look at Both Slides Again but With a Stain This Time:
PART C Onion Cells with Stain
1. Pull a piece of scale from the onion bulb until it cracks. Peel the thin
epidermal layer off of the outer skin.
2. Put a drop of water on a clean slide. Place a piece of the epidermal
tissue in the water and make sure it lies flat.
3. Place a drop of stain on the onion tissue. Wait for a minimum of one
minute. Then place a cover slip on the slide. (Be careful with the stain
it will stain your clothing.)
4. Remove the stain from the slide and replace it with clear water. To
do this, place a SMALL piece of paper towel next to one edge of the
cover slip. Place drops of water at the opposite edge of the cover slip
with the dropper. The stained water will be absorbed by the paper
towel as the clear water is drawn under the slide.
5. Place the slide on the microscope stage. (Parts of the tissue will not
have absorbed the stain.)
6. Identify parts of the onion cell. Label the nucleus, nucleoli, cytoplasm,
and cell wall. Make a drawing of HIGH POWER ONLY
Part B Cheek Cells with Stain
3. Place a drop of water on a slide. Use a toothpick to GENTLY scrape
the cells from the inside of your cheek. Dip this end of the toothpick
in the drop of water and stir to mix the cells with the water.
4. Apply ONE drop of methyelene blue stain to the cells. Wait one
minute and add a cover slip. Clear the slide using the technique
described in step 4 of the onion cells.
5. Examine the cells using the microscope. Identify the parts of the
cells. Look for and label the cell membrane, cytoplasm, nucleus,
nuclear membrane. Draw and label a stained cheek cell HIGH POWER
ONLY
Part C Bacteria “Cells”
1. Obtain one prepared bacteria slides from the teacher and observe
them under the microscope starting on low power and working to high
power. Draw and label the bacteria under low and high power. Label
cell membrane, nucleus, nucleolus (if visible), vacuoles and any other
parts you can see.
???Questions???
1. Describe the shape of the onion cells and cheek cells:
____________________________________________________
____________________________________________________
Are they irregular or regular in shape? _______________________
2. What factors could account for the differences in size and shape?
1 Sentence: ___________________________________________
____________________________________________________
____________________________________________________
3. Compare and contrast between onion and cheek cells:
Differences (3)
Similarities (3)
4. Why is it necessary to stain the onion and cheek cells? 1 Sentence
_________________________________________________________
_________________________________________________________
_________________________________________________________
5. What prokaryotic cells did you see today and what eukaryotic cells did
you see today. How are they the same and how were they different?
2 Sentences: __________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
6. How do prokaryotic cells carry their genetic information if they have
no nucleus? (You may need to use your phone to find this answer.)
1 Sentence: ________________________________________________
_________________________________________________________
_________________________________________________________