Materials Included In Kit

Additional Materials Required

Prelab Preparation

Set up eight lab stations with one microscope at each station. Place one slide at each microscope. Label the microscopes as needed.

Safety Precautions

This laboratory activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Disposal

The materials used in this lab may be saved for future use. Store slides in their original container to prevent breakage.

Lab Hints

• Enough materials are provided in this kit for 8 groups of students. All materials are reusable. All portions of this laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment may be completed before coming to lab, and the Post-lab Questions may be completed the day after the lab.
• Refresh students’ memory on the proper method to focus a microscope before beginning this activity.

Answers to Prelab Questions

1. Describe how the region that contains genetic material is different in prokaryotic versus eukaryotic cells.

   Prokaryotes have one prokaryotic chromosome located in the nucleoid region which is not membrane-bound. Eukaryotes are able to have multiple chromosomes (number dependant upon the species) that are contained in a membrane-bound organelle known as the nucleus.

2. In your own words, describe the proper way to focus a microscope.

   Start by setting the microscope on the lowest objective, usually 4X. Then adjust the coarse focus knob to find the clearest setting. Adjust the fine focus knob as necessary. Repeat at 10X setting. Above 10X, only the fine focus knob should be adjusted.

Sample Data

Answers to Questions

1. Explain three general differences between prokaryotic and eukaryotic cells.

   One major difference is eukaryotic cells have membrane-bound organelles and prokaryotic cells do not. Eukaryotic cells are much larger than prokaryotic cells and have more complex structure.

2. Complete the following chart comparing the specific differences between prokaryotic and eukaryotic cells.

   	Prokaryotes	Eukaryotes
   Approximate size (μm)	1–5 μm	10–100 μm
   Location of genetic material	Nucleoid	Nucleus
   Genetic material membrane-bound	No	Yes
   Replication mechanism	Binary fission	Cell division
   Contain plasmids	Yes	No

3. Based on the information in the Background section and the chart above, which of the observed slides are classified as prokaryotic? Explain your answer.

   The spirulina and stagnant water organisms are prokaryotic. Both exhibited simple cell structure characteristic of prokaryotes. A nucleoid region also appears to be present as a darker stained area toward the center of the cell.

4. Would you predict that the presence of capsules is an advantage or disadvantage in prokaryotes? Explain.

   Capsules would most likely be advantageous for prokaryotes because they increase resistance to pathogens. If bacteria or other microbes did not have capsules they would most likely be taken over by foreign pathogens and no longer exist.

5. Protists were the first known eukaryotes. Why might they be important to the study of eukaryotic evolution?

   Since protists were the first known eukaryotic species, they are ancestral to all other eukaryotes such as plants, fungi, and animals. It is useful to study the most basic eukaryote to observe how they were modified to form other species.

References

Campbell, N. A. Biology, 6th Ed.; Benjamin Cummings: San Francisco; 2002, pp 112–115.

Introduction

Every living organism consists of one of two types of cells—prokaryotic cells or eukaryotic cells. Prokaryotes are bacteria and archaea. All other living things, including protists, plants, fungi and animals, are eukaryotic. Discover the key features that differentiate living things as prokaryotic or eukaryotic and how these features benefit their survival.

Concepts

• Prokaryotes
• Cell structure
• Eukaryotes
• Cell organelles

Background

The incredible diversity of living organisms can be organized into just three domains—Bacteria, Archaea and Eukarya. All organisms in the Bacteria and Archaea domains are considered prokaryotes while members of the Eukarya domain are considered eukaryotes. All cells have certain features in common regardless of whether the organisms are prokaryotes or eukaryotes. Common cell features include a surrounding plasma membrane, a semifluid known as cytosol and genetic material consisting of deoxyribonucleic acid (DNA).

However, there are many differences between prokaryotes and eukaryotes as well. The primary identifiable features to classify something as prokaryotic or eukaryotic are a membrane-enclosed nucleus and membrane-enclosed organelles. If a cell is prokaryotic it is without a nucleus or other membrane-enclosed organelles. If a cell is eukaryotic it has a membrane-enclosed nucleus and other membrane-bound organelles within the cytoplasm. The cytoplasm is the entire region between the nucleus and the plasma membrane. There are several other general characteristics of each category as well.

The majority of prokaryotes are unicellular and range in diameter from 1 to 5 μm. They commonly have a cell wall which maintains the cell shape, provides physical protection, and prevents the cells from lysing or breaking open in a hypotonic environment. Prokaryotes are also often capable of secreting a sticky substance known as a capsule, which provides an additional protective layer against pathogens. Capsules enable prokaryotic cells to adhere to other objects. Most prokaryotes have long cellular appendages known as flagella (see Figure 1). Flagella propel the cell to move via a mechanism known as flagellar action. The flagella may be evenly distributed across the entire body or concentrated at one or both ends.

Prokaryotes also have smaller and less complex genomes than eukaryotic cells. In fact, on average they have one-thousandth as much DNA as the typical eukaryotic cell. Prokaryotic DNA is located in a small cluster of fibers in the nucleoid region—the mass of fibers is known as the prokaryotic chromosome. It is typically one double-stranded DNA molecule in circular form. Remember, there is no membrane separating the nucleoid from the rest of the cell. The entire region within the plasma membrane of the cell is known as the cytoplasm. In addition to their one major chromosome, prokaryotes sometimes contain plasmids. Plasmids are small circles of DNA that contain genes for resistance to naturally occurring antibiotics and may be manipulated to provide resistance to specific autobiotics. Although not essential for prokaryote survival, plasmids do provide benefits to the host cell against foreign DNA.

Eukaryotic cells are typically 10–100 μm in size and exhibit complex genomes. The defining feature of eukaryotic cells is that their chromosomes are located in a membrane-bound organelle called the nucleus. In addition to the nucleus, eukaryotic cells have numerous extensive internal membranes that compartmentalize additional organelles. In general, each organelle provides a unique local environment that specializes in its own metabolic function. Sometimes organelles work independently, other times they work together to achieve a common goal. An example of organelles working together is in the process of genetic control of the cell. The nucleus, which contains the DNA, works with the ribosome that uses the information from the DNA to make proteins.

Reproduction of eukaryotic cells can be either sexual or asexual. Either way, cell division involves the distribution of identical genetic material, DNA, to the resulting cells. The dividing cell replicates its DNA, distributes one copy to each end of the cell, and then divides into two identical daughter cells. In plant and animal cells this process is known as mitosis.

Experiment Overview

Observe and sketch four prepared slides and classify each as prokaryotic or eukaryotic.

Materials

Prelab Questions

1. Describe how the region that contains genetic material is different in prokaryotic versus eukaryotic cells.
2. Read the Procedure section and, in your own words, describe the proper way to focus a microscope.

Safety Precautions

This laboratory activity is considered nonhazardous. Please follow all laboratory safety guidelines.

Procedure

1. You will be assigned to one of the compound microscopes throughout the classroom.
2. Each microscope is labeled with the slide it contains. Note: Microscopes with the same label contain the same slide.
3. Focus the image on the slide using the 4X objective. Adjust the coarse and fine focus knobs as needed to clearly view the cells.
4. Once the image is focused, switch to the 10X objective. Adjust the coarse and fine focus knobs as necessary.
5. Switch to the 40X objective to view the smaller components of each cell and adjust only the fine focus knob to view the image clearly.
6. After viewing with the 40X objective, continue with the oil immersion objective if available. Note: The fine focus knob should be used to clarify the image when the objectives are changed to 40X and 100X.
7. Sketch the appearance of the cells in the data table and observe and record specific features of each cell. Record observations of each slide on the worksheet. Be as specific as possible.
8. Return the microscope to the 4X objective, lower the microscope stage, and, if necessary, wipe clean all objective lenses and the prepared microscope slide using lens paper.
9. Rotate through the workstations as assigned by your instructor. The slides may be viewed in any order. Repeat steps 2–8 at each of the three remaining workstations.

Student Worksheet PDF

11064_Student.pdf