Download OBJECTIVES • To explore cell structure and morphology in

Period:_________
OBJECTIVES
• To explore cell structure and morphology in prokaryotes and eukaryotes.
• To gain more experience using the microscope.
• To obtain a better understanding of terms like: prokaryote, eukaryote, cell membrane, cell wall, nucleus, etc.
• Distinguish among the three morphological types of bacteria.
• Identify cellular structures of a typical plant cell.
• Identify cellular structures of a typical animal cell.
Understanding the nature of cell structure and function is important to an understanding of organisms. All
organisms are composed of cells, whether they exist as single cells, colonies of cells, or in multicellular form. Cells
are usually very small, and for this reason, a thorough understanding of subcellular structure and function has been
possible only through advances in electron microscopy and molecular biology.
There are two general types of cells: prokaryotic and eukaryotic. These two words have their root in the Greek word
karyon (nut), which refers to a cell’s nucleus. The prefix pro- means “before” or “prior to.” Thus, prokaryotic
means “before having a nucleus.” Prokaryotic cells do not have a membrane-bound nucleus and their genetic
material (DNA) is only loosely confined to a nuclear area within the cell. Bacteria, including the cyanobacteria
(formerly known as blue-green algae), are prokaryotes. All other organisms are eukaryotes. The prefix eu- means
“true.” The cells of eukaryotes have true, membrane-bound nuclei containing their genetic material.
Prokaryotic and eukaryotic cells also differ in several other ways. Eukaryotic cells are generally larger and contain
additional specialized compartments (membrane-bounded organelles) in which cell functions such as energy
production may occur. Prokaryotic cells lack membrane-bound organelles; their cell functions are carried out in the
cytoplasm.
During this laboratory you will investigate some of the structural of prokaryotic and eukaryotic cells. We are going
to focus on the simple differences between eukaryotes and prokaryotes and plants vs. animals.
PROCEDURE
Part A: Prokaryotic Cells
Part 1: Observing Bacteria
Most prokaryotic cells are extremely small (approximately 1 to 2 µm in diameter). Most are heterotrophic,
depending on preformed food, but some are autotrophic and make their own food. Morphologically, bacteria are
either round (coccus), rod-shaped (bacillus), or spiral-shaped (spirillum).
1 Bifidobacterium animalis
2 Lactobacillus acidophilus
4 Streptococcus thermophilus
5 Staphylococcus
3 Lactobacillus bulgaricus
6 Thodospirillum rubrum
7 Borrelia burgdorferi
You can use the compound microscope to study bacteria, but only their external features will be distinguishable. It
is possible to identify the three morphological types of bacteria (coccus, spirillum, and bacillus) by observing their
shape (Figure 2-1). You will also note that bacteria are often found in clusters or in chains.
STUDENT WHO PREPARED SLIDE = ____________________________
____(1-5pts)
1. Prepare a wet mount slide of bacteria using the yogurt culture.
Use a cotton swab and smear a small thin area on a clean glass slide.
Place a small drop of water on the smear
Drop a cover slip over the area at a 45º angle
2. Draw a simple sketch of one of the different prokaryotes focusing on shape of the cells. Sketch the prokaryotic
cells in the spaces below. Note the shape of the bacteria and the total
magnification.
3. Tell me five things that you know about Prokaryotic cells._____________
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Part B: Eukaryotic Cells
All eukaryotic organisms are composed of cells, whether they exist as single
Specimen
cells, colonies of cells, or in multicellular form. Your body is composed of
Magnification
billions of cells, most of which are very small, with specialized structures that
Shape
allow for a diversity of functions.
All eukaryotic cells have their genetic material enclosed by a nuclear membrane called the nuclear envelope. In
addition, a variety of subcellular membrane-bound organelles are present. These include mitochondria, lysosomes,
and Golgi complexes. Internal membrane systems divide the cell into specialized compartments. Non-membranebound organelles, such as ribosomes and centrioles, and cytoskeleton are also present in eukaryotic cells.
During this laboratory you will investigate the structures of plant and animal cells.
Part 1: Examining Plant Cells
The cells of plants are eukaryotic, containing both a membrane-bounded
nucleus and membrane-bounded organelles. A cell wall composed of
cellulose surrounds the plant cell. A large central vacuole surrounded by a
membrane (the tonoplast) is used for storing water, pigments, and wastes.
STUDENT WHO PREPARED SLIDE =
____________________________ ____(1-5pts)
1. Prepare a wet-mount slide of an Elodea leaf.
a. Place a drop of water on the slide and lay one blade of an elodea
plant in the drop of water.
b. Drop a cover slip over the area at a 45º angle
c. Observe the specimen under low power
d. Observe the thick cell wall, thinner cell membrane, cytoplasm,
nucleus, and chloroplasts.
e. A large central vacuole may be apparent. These structures
characterize a typical plant cell.
Specimen
Magnification
Shape
2. Sketch a representative Elodea cell as observed under high power, and label at least three parts.
3. Do the chloroplasts appear to move? ______ If so, describe their movement.___________________________
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STUDENT WHO PREPARED SLIDE = ____________________________
____(1-5pts)
4. Prepare a wet-mount slide of onion epidermal tissue. Onions (Allium) have layers of modified leaves (scales)
that can easily be separated from one another. Peel off a portion of one layer and examine the concave side of the
piece you have obtained. The surface is covered by a thin layer of cells, the epidermis.
5. Remove a small piece of the epidermis (approximately 3 x 8 mm) by
breaking the scale gently, leaving the epidermis intact. Peel the epidermis
from one of the halves of the scale. Prepare a wet-mount slide of the isolated
epidermis.
6. Observe the onion cells using low power (l0x objective) and then high
power (40x objective).
7. Add a drop of Lugol’s solution (IKI) at the edge of the coverslip. Use a torn
piece of paper to draw the solution under the coverslip and across the
specimen.
8. Sketch a representative of the stained onion cell as observed under high
power, and label at least three parts.
Specimen
9. Compare (at least three similarities and three differences) the onion cell
Magnification
with the Elodea cell. Since they are both plant cells, they should be similar.
You will note that onion cells lack one structure (organelle) that is very
Shape
conspicuous in Elodea cells. What organelle is missing in the onion cells?
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Part 2: Examining Animal Cells
Animal cells can be studied using the light microscope, but most of the cellular organelles within the cytoplasm are
not visible without the use of special staining techniques. The nucleus and nucleolus, where ribosomes are
manufactured, are usually apparent in most cells. To study the structure of animal cells you will prepare a wet
mount slide of your cheek cells.
STUDENT WHO PREPARED SLIDE = ____________________________
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9.
____(1-5pts)
Prepare a wet mount slide of your cheek cells. You will examine cheek cells obtained from your mouth.
Place a drop of water on a microscope slide.
Use the flat edge of a toothpick to gently scrape the inside of your cheek.
Gently swirl that end of the toothpick into the drop of water.
Place a small drop of methylene blue dye onto the drop of water and cheek cells. CAUTION: This will dye
your clothes permanently, and your skin (until the cells shed).
Place a cover slip over the slide by placing the bottom edge in the water drop and holding it at a 45 degree
angle to the slide. Drop the cover slip over the water drop. Try not to trap air bubbles under the coverslip.
Pull excess dye and water out from underneath the cover slip by allowing a paper towel to touch one side of
the cover slip.
Set the magnification of your microscope to 10X.
Focus, and then set your microscope to 40X.
10. Sketch a few cells, and label the plasma membrane, nucleus, and cytoplasm.
List the similarities and differences between the plant cells and the animal cells you have observed.
When instructed, begin the cleanup procedures;
a. throw away the specimen
b. wrap napkin around slide and wipe off cover slip and specimen
c. carefully wash the glass slides
d. return all items to your laboratory bin
e. Note: Tell your teacher at once if equipment is missing or damaged.
Conclusion Questions:
1. Are all prokaryotes harmful? __________ If not explain how they are beneficial? ________________________
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2. What is the advantage of using a wet mount preparation instead of a dry-mount preparation in the study of living
cells? ____________________________________________________________________________________
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3. If you were given a slide containing living cells of an unknown organism, how would you identify the cells as
either plant or animal? ______________________________________________________________________
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4. Why are stains such as Lugol’s Iodine and Mehtylene Blue used when observing cells under the microscope?
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5. Why is it possible to easily collect cells by gently scraping the inside of your cheek? ______________________
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