Tell the Difference Between Prokaryotes and Eukaryotes
Prokaryotes and eukaryotes are terms used to define types of organisms. The main difference between the two is the presence of a “true” nucleus: eukaryotes have one, while prokaryotes do not. Although this is the most easily recognizable difference, there are other important distinctions between the two organisms that can be seen under a microscope.
Contents
Steps
Using a Microscope
- Obtain a specimen slide. Specimen slides of prokaryotes and eukaryotes can be obtained from biological supply companies.
- If you are in school, ask your science teacher if they have access to slides.
- Place your specimen slide on the microscope stage (the platform that holds the slides). Some microscopes will have stage clips that allow you to secure the slide in place to prevent movement during focusing and viewing. If there are clips on the stage, gently push the slide underneath to secure in place. If no clips are provided, place the slide directly under objective.
- Be careful when pushing slides underneath the clips. Too much force can damage the slide.
- You may have to move the slide while looking through the eyepiece to find the desired area of the specimen.
- Ensure the microscope is on the lowest magnification. The part of the microscope that allows for magnification is called an objective. Objectives for compound light microscopes usually range from 4x to 40x. You can move to higher magnifications if necessary, but starting low allows you to easily find the specimen on the slide.
- You can determine the magnification of the objective by looking at the objective itself where it will have a label.
- The lowest magnification objective will also have the shortest length, while the highest magnification will have the longest length.
- Focus the image. Looking at a blurry image makes it difficult to make out small structures and define aspects of the cell. To more clearly see every detail, make sure the image is in focus.
- While looking into the eyepiece, use the focus adjustment knobs found below the stage on the side of the microscope.
- By turning the knobs, you will see the image come into sharper focus.
- Increase the magnification if necessary. At the lowest magnification, you might notice that it's difficult to see smaller features and cellular structures. By increasing the magnification, you will be able to see more details within the cell.
- Never change the objective while looking through the eyepiece. Because higher magnification objectives have longer lengths, changing the objective before lowering the stage can result in damage to the slide, the objective, and the microscope itself.
- Use the focus knobs to lower the stage to the appropriate height.
- Shift the objectives until the desired magnification is over the slide.
- Refocus the image.
Observing the Image
- Identify the features of eukaryotes. Eukaryotic cells are large and have many structural and internal components. The word eukaryote is rooted in the Greek language. "Karyose" means "kernel" which refers to the nucleus, while "eu" means "true" so eukaryotes contain a true nucleus. Eukaryotic cells are complex and contain membrane-bound organelles that perform specific functions to keep the cell alive.
- Look for the nucleus of the cell. The nucleus is the structure of a cell that contains the genetic information encoded by DNA. Although the DNA is linear, the nucleus generally appears as a dense circular mass inside cell.
- See if you can find organelles within the cytoplasm (the jelly-like interior of the cell). Under the microscope you should be able to see distinct masses that are rounded or oblong in shape and smaller than the nucleus.
- All eukaryotes have a plasma membrane and cytoplasm, and some (plants and fungi) have a cell wall. The plasma membrane will not be obvious under the microscope, but the cell wall should appear as a dark line outlining the edge of the cell.
- Although there are single-celled eukaryotes (protozoa), most are multi-cellular (animals and plants).
- Identify the features of prokaryotes. Prokaryotic cells are much smaller and have fewer internal structures. In Greek, "pro" means before, therefore prokaryote means "before a nucleus". Due to the absence of organelles they are simpler cells and perform fewer functions to stay alive.
- Look for the absence of a nucleus. Their genetic material is a small simple circle called a nucleoid. The nucleoid will generally appear lighter in color inside the cell and will be circular.
- Look for the presence of ribosomes. Although prokaryotes do not have complex organelles, they do have simpler structures called ribosomes. With high enough magnification, ribosomes look like black dots within the cell cytoplasm.
- Like eukaryotes, prokaryotes do have a cell wall, a plasma membrane, and cytoplasm. As with eukaryotic cells, the plasma membrane may not be obvious under the microscope, but the cell wall should be visible.
- All bacteria are prokaryotes. Example bacteria include Escherichia coli (E. coli), which lives in your intestines and Staphylococcus aureus, which can cause skin infections.
- Observe the image through the microscope. Look through the microscope and write down the defining characteristics you see from the slide. Based on the specific features of eukaryotes and prokaryotes, you should be able to determine what is on your slide.
- Make a checklist for eukaryotes and prokaryotes and check off the features that apply to the specimen you're looking at.
Tips
- Print this out for reference during your lab.
- Specimens can be stained with a nuclear dye allowing a clear distinction between prokaryotes and eukaryotes.
Related Articles
- Constructively Discuss Science with a Creationist
- Create an Amazing Looking Science Project in 1 Week
- Make a Fairly Easy Science Project
