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Prokaryotic and Eukaryotic Cells: A Laboratory Guide, Lecture notes of Molecular biology

The cells of plants are eukaryotic, containing both a membrane-bounded nucleus and membrane-bounded organelles. A cell wall composed of cellulose surrounds the ...

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Lab 2- Bio 201
1
Name: _____________________
Prokaryotic and
Eukaryotic Cells
OBJECTIVES
To explore cell structure and morphology in prokaryotes and eukaryotes.
To gain more experience using the microscope.
To obtain a better understanding of these terms: prokaryote, eukaryote, cell, cell membrane, cell wall,
nucleus, plastids, et al.
Give two general characteristics of prokaryotic cells.
Distinguish among the three morphological types of bacteria.
Describe the subcellular structure of a typical bacterium.
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 in Bio 201. We will
cover the prokaryotes in much more detail in Bio 203.
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). To view them
with the compound microscope, you must use an oil-immersion lens (100x objective). Even then, not
much more than their basic shapes will be visible. With the aid of the electron microscope, however, you
can study these prokaryotic cells more closely. You can even use special staining techniques to learn about
their structure.
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Lab 2- Bio 201

Name: _____________________

Prokaryotic and

Eukaryotic Cells

OBJECTIVES

  • To explore cell structure and morphology in prokaryotes and eukaryotes.
  • To gain more experience using the microscope.
  • To obtain a better understanding of these terms: prokaryote, eukaryote, cell, cell membrane, cell wall, nucleus, plastids, et al.
  • Give two general characteristics of prokaryotic cells.
  • Distinguish among the three morphological types of bacteria.
  • Describe the subcellular structure of a typical bacterium.
  • 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 in Bio 201. We will cover the prokaryotes in much more detail in Bio 203.

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). To view them with the compound microscope, you must use an oil-immersion lens (100x objective). Even then, not much more than their basic shapes will be visible. With the aid of the electron microscope, however, you can study these prokaryotic cells more closely. You can even use special staining techniques to learn about their structure.

Figure 2-1. The cells of many familiar genera of bacteria include the (a) rod-shaped bacillus, (b) spherical coccus, and (c) helical spirillum.

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.

  1. Examine the oil immersion demonstrations of prepared slides of the bacterial specimens set up at the side of the room.
  2. Draw simple sketches of these prokaryotes focusing on shape of the cells. Make the sketches in the spaces below. For each, note whether the bacterium is spherical (coccus), rod-shaped, (bacilus), or spiral-shaped (spirillum). Don’t forget to write in the magnification.
  3. Now prepare a wet-mount of the dilute yogurt provided. Draw and label the bacteria you see in this sample.

Specimen Magnification Shape

Specimen Magnification Shape

  1. Sketch a representative Elodea cell as observed under high power, and label its parts.

Specimen: ________________________ Magnification: ______________________ Shape and Description: ________________



  1. Do the chloroplasts appear to move? Describe their movement.
  2. 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.
  3. 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.
  4. Observe the onion cells using low power (10X objective) and then high power (40X objective).
  5. If it is difficult to see the cells, add a drop of Lugol's solution (I 2 KI) at the edge of the coverslip. The iodine in the Lugol’s solution will stain starch blue/purple.

Does this solution stain the cells as it reaches them?

  1. Sketch a representative onion cell as observed under high power, and label its parts.

Specimen: ________________________ Magnification: ______________________ Shape and Description: ________________



10. Compare the onion cell 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 conspicuous in Elodea cells.

What is this organelle missing in the onion cells?

List the similarities and differences between Elodea cells and onion cells. Similarities Differences

  1. Prepare a wet mount slide of a potato. Use a razor blade to slice a piece of tissue, as thin as possible, from a potato. Be careful not to cut your fingers. Prepare a wet-mount slide; use a drop of water.
  2. Study the slide at low power (10X objective) and then at high power (40X objective). Add a drop of Lugol's solution (I 2 KI) to the side of the coverslip and observe the cells as the iodine solution makes contact with them.

Specimen: ________________________ Magnification: ______________________ Shape and Description: ________________



How does the reaction of iodine with the potato cells compare with what you observed in your onion epidermis preparation?

What does this tell you about the differences between the storage products in onions and potatoes?

Do you see any chloroplasts? Why or why not?

You will probably see some small oval-shaped blue-black structures. These leucoplasts store starch. Why did they turn blue?

List the similarities and differences between the plant cells and the animal cells you have observed.

Similarities Differences

TO TURN IN: Answer all the questions posed in the proceeding pages. If you need additional space, please use a separate page. Also include all drawings as indicated.

REVIEW: For the lab quiz, be able to recognize, describe, and label the different types of cells we have examined today. Emphasize the similarities and differences between the different cell types.