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Lesson 3 Microscopy

  Modern Microscopes

Today, there are many different types of microscopes.


Let’s explore the advantages and disadvantages of the different microscope types and techniques


© Giudicelli F, Özbudak EM, Wright GJ, Lewis J, via Wikimedia Commons
A3.7 Zebra Fish embryo in darkfield illumination.
Scientists use different types of light to increase the clarity of the image they are looking at. Different types of light will sharpen different parts of the cell, so depending on the cell that you are looking at, you may want to use a different kind of light. There are four kinds of illumination that scientists currently use: brightfield, phase contrast, darkfield, and differential interference contrast. Each of these types of illumination shows a different part of a cell. Brightfield illumination is the default kind of illumination when using a compound light microscope. Make sure you look at page 256 in your textbook for examples of each of these kinds of illumination.


A3.8 Skin cells stained using fluorescent dye
This is not a type of microscope but a way of attaching a fluorescent molecule to a structure or cell so it can be easily identified under a microscope. Under ultraviolet light, the fluorescent molecule will glow, allowing the observer to easily pinpoint its location. This technique is used when staining the structure or cell does not show the detail that is needed.

The use of green fluorescent protein (GFP) is a continuation of this. This type of protein comes from a specific type of jellyfish and will glow green under ultraviolet light. Scientists attach this protein to the parts of the cell they wish to study, and it acts like a tiny lamp, lighting up that specific part. A huge advantage to this technique is it does not kill the cell, unlike other staining techniques. This means scientists can study the live cell and how it works.

A3.9 Aequorea victoria jellyfish that produces GFP

A3.10 Confocal microscope
This type of microscope uses a laser to concentrate light onto the specimen. The laser scans each layer of the specimen so the scientist sees an image of a very thin section. If multiple images are taken, a computer can take these images and build a 3-D image. This type of microscope is great for specimens that are too large for a compound microscope. It also allows us to see the detail of a 3-D image.


A3.11 Transmission Electron Microscope
This type of microscope uses a beam of electrons instead of a light wave. This allows the microscope to produce an image with lots of fine details. The electrons either bounce off of or are absorbed into the specimen, leaving an image where no electrons are present.

A TEM produces a 2-D image of a very thin slice of the specimen; it is very difficult to produce a 3-D image using this microscope. It can produce detail close to 100 times greater than the traditional compound microscope. It can also magnify up to 1 000 000x.


A3.12 SEM microscope
A SEM works in a similar way to the TEM except it provides detail about the surface of a specimen, rather than a thin slice of it. A beam of electrons is scanned over the specimen, and the microscope picks up the electrons being reflected off the surface to create a 3-D image. A SEM can magnify up to 300 000x and can be used on live specimens. 

A3.13 Red blood cell on cotton strand

  Digging Deeper


A3.14 Clear vs. blurry image

You may know the words “resolution” and “contrast.” They play a big part in image and video quality. But did you also know they play a big part in microscopes too? Just like an image, the higher the resolution and the better the contrast, the more detail we can see. Scientists have played around with light sources and staining techniques for hundreds of years, trying to get a clearer picture of what they are looking at. Read pages 253 to 256 in your textbook for more information.

Did You Know?


A3.15 Coming Soon

Scientists have continued to develop new microscopes. Recently, a new microscope called a triple-view microscope was developed. This microscope increases the resolution without increasing the amount of light used, providing a clearer, more detailed 3-D image. This allows scientists to study even smaller structures and functions, such as what a virus does once it is inside of a cell. https://quick.adlc.ca/learn-more

Learn More





  Read This

Please read pages 256 to 260 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the types of microscopes, how they work, and their advantages and disadvantages. Remember, if you have any questions or you do not understand something, ask your teacher!

  Practice Questions

Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.

  1. Fill in the following chart with information about each type of microscope. The column for the compound light microscope has been filled in for you as an example.

    2.  
    		Compound CLSM TEM SEM
    Image Source
    		light
    Magnification 250x N/A
    Advantage simple to use
    Disadvantage not much detail


     
    		Compound CLSM TEM SEM
    Image Source
    		light laser electron beam
    		electron beam
    Magnification 1500x not mentioned in readings—approx. 2000x 1 000 000x 300 000x
    Advantage simple to use
    		–great for specimens too thick for other microscopes
    –creates 3-D image
    		–very detailed
    –largest magnification
    		–provides detail of surface of specimen
    –can be used on live specimens creates 3-D image
    Disadvantage not much detail
    		–uses extremely small sections of specimen –produces 2-D image
    –uses extremely small sections of specimen
    		–do not see the inside of the cell, only the surface
    –not as high of a magnification as the TEM
  2. How does GFP work? Please explain in your own words.

    3. Always be sure the answers you write are your own, are not copied, and make sense to you. Your answer should be a variation of the following: To use GFP, scientists take a protein from a special jellyfish and attach it to the structure they want to study. This protein glows green under UV light, so scientists can quickly hone in on the structure’s location. It will also give the scientists a great view of what the structure looks like and how it is used.