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 a single cell nucleus, while prokaryotes have no cell nucleus. While this is the most easily recognizable difference, there are other important differences between the two organisms that can be observed under a microscope.
Step
Part 1 of 2: Using a Microscope
Step 1. Get a specimen slide
Slides of prokaryotic and eukaryotic specimens can be obtained from biological equipment supply companies.
If you're still in school, ask your science teacher if they have access to the slides
Step 2. Place the specimen slide on the microscope table (slide holder table)
Some microscopes have table clamps that allow you to hold the slide in position and prevent it from shifting during viewing. If there is a clamp on the microscope table, gently push the slide under the clamp to secure it. If there is no clamp, place the slide directly under the objective lens.
- Be careful when pushing the slide under the clamp. Too much pressure can ruin the slide.
- You may have to move the slide while looking through the eyepiece to find the desired area of the specimen.
Step 3. Make sure the microscope is on the lowest magnification
The part of the microscope that allows magnification is called the objective lens. Objective lenses for compound light microscopes usually have a magnification of between 4x and 40x. You can increase the magnification if necessary, but starting low will allow you to easily find the specimen on the slide.
- You can determine the magnification of the objective lens by looking at the label of the objective lens itself.
- The objective lens with the lowest magnification will also have the shortest length, while the highest magnification will have the longest length.
Step 4. Focus the image
A blurry image will make it difficult to observe the tiny structures and defining aspects of the cell. To see every detail more clearly, make sure the image is in focus.
- When looking at the eyepiece, use the focus control located under the microscope table.
- By turning the focus knob, you will see the image turn sharper.
Step 5. Increase the magnification if necessary
At the lowest magnification, you may find it difficult to observe the smaller cellular features and structures. By increasing the magnification, you will be able to see more details in the cells.
- Never change the objective lens while looking at the eyepiece. Because the objective lens is higher magnification and longer in length, changing the objective lens before lowering the table can cause damage to the slide, the objective lens, and the microscope itself.
- Use the focus adjuster to lower the table to an appropriate height.
- Slide the objective lens until the desired magnification is above the slide.
- Refocus the image.
Part 2 of 2: Observing Pictures
Step 1. Identify the characteristics of eukaryotes
Eukaryotic cells are large and have many structural and internal components. The word eukaryotes comes from the Greek. "Karyose" means "seed" 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 maintain cell survival.
- Look for the nucleus in the cell. The nucleus is a cell structure that contains the genetic information encoded by DNA. Although DNA is linear, the nucleus generally appears as a tightly coiled mass inside the cell.
- Observe if you can find any organelles in the cytoplasm (the inside of the cell is jelly-shaped). Under the microscope you should be able to see distinct masses that are round or oval in shape and smaller than the cell nucleus.
- All eukaryotic cells have a plasma membrane and cytoplasm, and some (plant and fungal cells) have a cell wall. The plasma membrane will not be clearly visible under a microscope, but the cell wall should appear as a dark, circular line around the edge of the cell.
- Although there are single-celled eukaryotes (protozoa), most are multicellular (animals and plants).
Step 2. Identify the characteristics of prokaryotes
Prokaryotic cells are much smaller and have less internal structure. In Greek, "pro" means before, therefore prokaryotes means "before the nucleus". Due to the absence of organelles, these cells are simpler and perform fewer functions to stay alive.
- Observe the absence of the core. The genetic material of this cell is a simple small circle called the nucleoid. The nucleoid will generally appear lighter in color inside the cell and be circular in shape.
- Look for the presence of ribosomes. Although they do not have complex organelles, prokaryotes do have simple structures called ribosomes. With a sufficiently high magnification, the ribosomes look like black dots in the cytoplasm of the cell.
- Like eukaryotes, prokaryotes have a cell wall, plasma membrane, and cytoplasm. As with eukaryotic cells, the plasma membrane may not be visible under a microscope, but the cell wall should be visible.
- All bacteria are prokaryotes. Examples of bacteria include Escherichia coli (E. coli), which lives in your intestines and Staphylococcus aureus, which can cause skin infections.
Step 3. Observe the image through a microscope
Look through the microscope and write down the characteristics you see on the slide. Based on the characteristics of eukaryotes and prokaryotes, you should be able to determine what's on your slide.
Make a checklist for eukaryotes and prokaryotes and check for traits that match the specimens you observe
Tips
- Print this page for your reference during the laboratory.
- Specimens can be stained with a core dye which allows a clear distinction between prokaryotes and eukaryotes.
