Electron Microscopes: Videos & Practice Problems

Electron microscopes utilize electrons for imaging, offering magnification up to 10,000,000 times and resolution of 0.3 nanometers, surpassing light microscopes. The transmission electron microscope (TEM) creates 2D images of internal structures, requiring thin specimen slices and vacuum conditions, while the scanning electron microscope (SEM) produces 3D images of external structures. Both types necessitate complex sample preparation, which can introduce artifacts. Understanding these tools is crucial for visualizing cellular components and pathogens, enhancing our grasp of microbiology and cellular biology.

Electron Microscopes

In this video, we're going to begin our lesson on electron microscopes. And so recall from our previous lesson videos that electron microscopes, as their name implies, are going to use electrons instead of using light. These electron microscopes are much more powerful tools than the light microscopes themselves. This is because electron microscopes actually provide greater magnification. In fact, they can provide magnification up to 10,000,000 times. This means that they can make objects appear 10,000,000 times larger than the actual object is. This is in comparison to just the 1,000 times magnification provided in most standard light microscopes. Now electron microscopes, not only do they provide greater magnification, but they also provide greater resolution as well. In fact, electron microscopes can provide resolution up to about 0.3 nanometers, which is incredibly great resolution. This is in comparison to the 10 nanometer resolution provided even in a super resolution light microscope. So the light microscopes in general are not able to provide as high magnification or as great resolution as the electron microscopes are capable of providing.

Now these electron microscopes, because they are such powerful tools, they're really, really complex instruments, and it usually requires complex specimen preparation as well that ultimately limits the observation to only nonliving cells and objects. It's very difficult to be able to visualize living cells with electron microscopes because a lot of times the sample preparation will ultimately end up killing the cells. Now the electron micrographs or the images created by these electron microscopes, are usually going to be just black and white. But they can be falsely colored, in order to create images that have color in them. So the false color is usually done by specialized computers. If you take a look at this image down below, notice it's showing you a little map of the electron microscopes. And really, as we'll see moving forward, there are 2 main types of electron microscopes that we'll talk about. And those are the transmission electron microscope, or the TEM, as well as the scanning electron microscope or the SEM. We'll start off talking about the transmission electron microscope, microscope, and then later in a different video, we'll talk about the scanning electron microscope. So I'll see you all in our next video.

Transmission Electron Microscope (TEM)

In this video, we're going to briefly introduce transmission electron microscopes, or TEMs. Transmission electron microscopes are commonly abbreviated as TEMs, and these are microscopes that form a 2D image from a beam of electrons passing through a specimen. Now, there is a variety of sample preparations that can be used to prepare a specimen for visualization under a transmission electron microscope. Many of these sample preparations are going to be used for visualizing internal cell structures. Usually, you want to associate the transmission electron microscope, or the TEM, with the visualization of internal cell structures. These specimens that are visualized under a TEM must be viewed in a vacuum and have to be in extremely thin slices of just 20 to 100 nanometers. This means that there is some complex specimen preparation needed to be done before they can be visualized under a transmission electron microscope.

One of the drawbacks is that sometimes this complex sample preparation can actually distort the cells and cause artificial artifacts to form. These artificial artifacts are substances that are usually not inside the cells, but after this complex sample preparation, they are introduced into the cells. Experienced scientists who know how to use transmission electron microscopes need to be trained to identify these artificial artifacts so that they don't confuse them with actual cell structures.

Below, we're showing a diagram of the transmission electron microscope, which is once again abbreviated as just the TEM. Notice over here on the left-hand side, we're showing you an actual image of a transmission electron microscope, which is a fancy and expensive piece of equipment hooked up to this computer here. Over here, what we have is a little diagram of this TEM. Notice that at the very top, there is an electron gun, which is going to shoot a beam of electrons. The electron beam is in pink and is going to pass through a condenser lens and then through the actual specimen. The placement of the specimen is right here towards the middle. Then, the electron beams are going to pass through an objective lens and a projector lens, and ultimately onto a viewing screen to create the image. The viewing eyepiece can be used to visualize that image.

These are some of the images that can be created by a transmission electron micrograph. Notice here that we're showing you some green algae cells. Note that the image itself is not green because electron microscopes generate black and white images naturally, and they can be falsely colored using a computer. Here we're showing you some avian coronavirus, the mitochondria in a human lung cell, and the Ebola virus. Transmission electron microscopes and electron microscopes in general are powerful enough to visualize viruses, whereas light microscopes are generally not powerful enough to visualize viruses in this way.

One of the main features you want to remember about the transmission electron microscope is that it can be used to visualize internal cell structures. This here concludes our brief introduction to the transmission electron microscope, and you will be able to get some practice applying these concepts as we move forward. I'll see you all in our next video.

Electron microscopes differ from light microscopes in that:

• A. Electron microscopes use an electron beam instead of a light beam.
• B. Electron microscopes can magnify the specimen significantly more than light microscopes.
• C. Electron microscopes have significantly higher resolution than light microscopes.
• D. All of the above.

Answer: (D)

Scanning Electron Microscope (SEM)

In this video, we're going to begin our lesson on the scanning electron microscope, or the SEM. The scanning electron microscope is commonly abbreviated as the SEM, and this microscope forms a 3-dimensional image. Unlike the TEM, the transmission electron microscope, which only forms 2-dimensional images. The SEM forms 3-dimensional images from a beam of electrons scattering off of a specimen surface. There are a variety of sample preparations that may be used for a scanning electron microscope, mainly used for visualizing external cell structures on the surface of the specimen.

Take a look at the image below, showing you a diagram of the scanning electron microscope or the SEM. Notice over here on the left-hand side, we're showing an actual image of a scanning electron microscope, a very complex and expensive instrument that is hooked up to a computer. We’re also showing a diagram of the scanning electron microscope where an electron gun at the top creates an electron beam (represented by the pink lines). The electron beam passes through electromagnetic lenses and ultimately hits the specimen. Notice the specimen's placement is different from that of the transmission electron microscope. The electrons scatter off the surface of the specimen, detected by an electron collector, with an amplifier in place that projects the image onto a viewing screen.

These are some of the images that can be captured by a scanning electron microscope, important for visualizing external cell structures instead of internal cell structures like the transmission electron microscope. Here’s an image of some melting ice, prairie hollyhock pollen, algae and bacterial cells, and the surface of a butterfly wing. Note that all these images are three-dimensional and focus on observing external cell structures.

This concludes our brief introduction to the scanning electron microscope or the SEM. We'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.

There are two major types of electron microscopes, Transmission Electron Microscopes (TEM) & Scanning Electron Microscopes (SEM). What are the major differences between these types of electron microscopes?

• A. TEM shows 2D images of the specimen while SEM shows 3D images of the specimen.
• B. SEM specimen preparations can damage or distort the microorganism's features, while TEM preparations do not.
• C. TEM shows internal cell structures, while SEM show external cell structures.
• D. Both A and B.
• E. Both B and C.
• F. Both A and C.

Answer: (F)

Here’s what students ask on this topic:

What is the difference between a transmission electron microscope (TEM) and a scanning electron microscope (SEM)?

The primary difference between a transmission electron microscope (TEM) and a scanning electron microscope (SEM) lies in their imaging capabilities and applications. TEMs create 2D images by transmitting a beam of electrons through an ultra-thin specimen, making them ideal for visualizing internal cell structures. In contrast, SEMs produce 3D images by scanning a beam of electrons across the surface of a specimen, which is useful for examining external cell structures. TEMs require specimens to be sliced into thin sections and viewed in a vacuum, while SEMs focus on the surface details and do not require such thin slicing. Both types of microscopes necessitate complex sample preparation, which can introduce artifacts.

How does an electron microscope achieve higher magnification and resolution compared to a light microscope?

Electron microscopes achieve higher magnification and resolution compared to light microscopes by using electrons instead of light for imaging. Electrons have much shorter wavelengths than visible light, allowing electron microscopes to resolve much smaller details. Electron microscopes can magnify objects up to 10,000,000 times, whereas light microscopes typically offer up to 1,000x magnification. Additionally, electron microscopes can achieve a resolution of about 0.3 nanometers, significantly surpassing the 10-nanometer resolution of even the best light microscopes. This enhanced magnification and resolution enable electron microscopes to visualize fine cellular structures and even viruses, which are beyond the capabilities of light microscopes.

What are the limitations of using electron microscopes for studying living cells?

One of the main limitations of using electron microscopes for studying living cells is that the complex sample preparation often kills the cells. Specimens must be placed in a vacuum and, in the case of TEM, sliced into extremely thin sections, which is not conducive to maintaining cell viability. Additionally, the preparation process can introduce artifacts that may distort the true structure of the cells. As a result, electron microscopes are generally limited to observing nonliving cells and objects, making them less suitable for studying dynamic processes in living cells.

Why are electron micrographs typically black and white, and how can they be colored?

Electron micrographs are typically black and white because electron microscopes detect variations in electron density rather than color. The images are generated based on the number of electrons that pass through or scatter off the specimen, resulting in grayscale images. However, these images can be artificially colored using specialized computer software to enhance visual contrast and highlight specific features. This process, known as false coloring, assigns different colors to various shades of gray in the original image, making it easier to distinguish between different structures and components within the specimen.

What are some common applications of transmission electron microscopes (TEMs) in microbiology?

Transmission electron microscopes (TEMs) are widely used in microbiology for visualizing the internal structures of cells and microorganisms. Common applications include studying the ultrastructure of cellular organelles, such as mitochondria, nuclei, and ribosomes, as well as examining the detailed morphology of viruses and bacteria. TEMs are also used to investigate the interactions between pathogens and host cells, providing insights into infection mechanisms. Additionally, TEMs can be employed to analyze the effects of drugs and other treatments on cellular structures, contributing to the development of new therapeutic strategies.