Biology 1 Microscope Lab #2

Background Information

What Is a Microscope?

In the most basic sense, a microscope is a tool that’s used to see objects that are too small to be seen by the eye alone. There are many things happening in the world around us and inside of us that we simply can’t see, although we know that they happen. Blood cells move through the body carrying nutrients and oxygen, but without a microscope, we can’t see those individual blood cells.

Because microscopes are so useful, they’ve become an essential tool in many fields of science and have helped us understand how the world works. But how do microscopes work, and are they all the same?

How Does a Microscope Work?

The very first microscopes weren’t very effective, but they’re a good illustration of how a microscope works. They were created by opticians who were used to grinding glass into lenses for people who needed eyeglasses.

These eyeglass makers realized that if they put one lens at the bottom of a tube and one at the top, they could use the power of both lenses to see tiny objects more clearly. These original microscopes were the first examples of compound microscopes, which are microscopes that use more than one lens to view objects. An even more basic microscope is a single convex lens, which we call a magnifying glass.

In a basic compound microscope, the lens at the bottom of the tube which is closest to the object is the objective lens. This lens takes the light rays that bounce off the object and spreads them apart through a convex lens so they appear bigger. When they appear bigger, we can see them in greater detail than we could without the aid of the lenses.

At the top of the compound microscope is another lens which is called the eyepiece. This lens also magnifies the image coming from the objective lens to give you a more detailed and clearer view of the subject.

While two lenses are necessary for a basic compound microscope to work, a light source is also a key factor. Many microscopes today have their own light sources, but a mirror behind and below the objective lens makes a great light source that can be angled to hit the object precisely.

Detailed Steps of How a Microscope Works

That’s the basic premise behind a microscope; it’s pretty simple with two lenses and a light source. Let’s look at it one step at a time to further understand what’s happening. We’ll use a basic compound microscope with two lenses to continue the explanation.

• The specimen is placed on a glass slide, usually with another piece of glass (called a cover slip) over it to prevent it from moving.
• The specimen slide is slid onto the tray, which typically has metal clips to hold it in place.
• Below the tray is a lamp, and light from the lamp shines up through a hole in the stage, which is now holding your specimen. The light moves through the specimen and through the objective lens at the base of the tube portion of the microscope.
• Once passing through the objective lens, the image has had its first magnification. It should be noted that there may be several lenses working together to form the objective lens. It’s not always just one lens.
• Moving through the objective lens(es), the light then travels up to the eyepiece, which works like a magnifying glass to further increase the visible size of the specimen.
• Finally, you place your eye on or above the eyepiece and view the image.
• Throughout the microscope, there may be focusing adjustment knobs that help you adjust the positioning of the lenses to sharpen your view and fine-tune the focus.

Other Types of Microscopes

The basics of how a compound microscope works are the same ones that are used in other microscopes. Compound microscopes are still a very important and powerful tool, and they’re used regularly, but there are some advances that have occurred in the more than 400 years since the first microscope, and we have some other options available.

• Electron microscope: These microscopes get their illumination from a beam of accelerated electrons. This creates a very high resolution of images that are very minuscule.

• Stereoscopic microscope (or just stereo microscope):  A stereo microscope creates a three-dimensional image by taking advantage of your two eyes. These microscopes are sometimes called dissecting microscopes and they feature one eyepiece and objective lens for each eye, giving you that natural 3D view that you have from your own eyes.

• Inverted microscopes: These microscopes usually have biological or metallurgical uses. Inverted microscopes use a fixed stage for the specimen and then use an objective lens that rests under the stage for illumination and view from below. Some inverted microscopes allow the user to move the objective lens so the specimen can be viewed from many different angles.

• Digital microscopes: Digital microscopes take advantage of digital cameras to take pictures or project the specimen onto a screen for viewing. This allows for a more detailed view that can be seen by multiple people at once. It can also be easily captured for future reference.

• Polarizing microscopes: One popular microscope today is a polarizing microscope which takes advantage of the vibrating effect of light waves and focuses those vibrations for a polarized light source. Manipulating polarized light leads to birefringence or double refraction; this is useful as different objects react differently to birefringence, providing information on what the inner structure of the specimen is.

• Brock Magiscope:  The Brock Magiscope is a microscope designed for educational use, and is used to study a variety of objects, including rocks, slides, and biological specimens.  It is designed to be easy to use and can be used indoors or outdoors.

These are a few of the more common microscopes available, but there are many more to choose from. The field of microscopy has become very specialized, allowing for detailed analysis in a variety of professions.

Part One:  Making Temporary or Wet-Mount Slides

What is a wet-mount slide:

• A temporary mount slide, also known as a wet mount slide, is a microscope slide that is made for short-term observation and is not meant to be stored long-term.

How is a wet-mount slide made:

Materials Needed for Part One:

1. compound light microscope
2. water pipette
3. tweezers
4. clean glass slide
5. scissors
6. cover-slip
7. newspaper print
   
   

Procedure for Part One:

1.  Find the smallest letter "e" in the newsprint like the one below, and using your scissors cut it out of the newspaper. 

2.  Using water, make a temporary or wet-mount slide of this letter "e".  Use your tweezers to manipulate it so that it is in the "reading position" like the diagram below:

3.  View the letter "e" under low power and medium power.   Make your sketches of the letter "e" EXACTLY AS IT LOOKS AS YOU VIEW IT WITH THE MICROSCOPE.

4.  Discard this wet-mount slide in the appropriate trash receptacle.

Part Two:  Making Wet-Mount Slides with Stain

Why use stains: 

Stains are used when viewing cells under a microscope to enhance their visibility by creating contrast between different cell components, allowing for better observation of cell structures and morphology, as most cells are naturally transparent and difficult to see without staining; essentially, stains "color" specific parts of a cell, making them easier to distinguish from their surroundings.

Caution when using stains:

The biological stain that we use is called crystal-violet.  It is made by dissolving the dry powder in a sample of water.  Since this stain affects all biological items you should be careful so as not to get any of this stain on your hands or clothing.  This stain is "semi-permanent" on you skin (usually comes off after a number of hand washings), but will be permanent if it gets on your clothing.

Materials Needed for Part Two:

1. compound light microscope
2. clean microscope slides
3. cover-slips
4. stain pipette
5. crystal-violet stain
6. onion skin
7. toothpick

Procedure:  Onion Skin Observation

1.  Remove some onion skin from the onion as discussed earlier in class, and place it on the clean glass slide.  Be sure to smooth it out as best as possible so there are few to no wrinkles in it.

2. Place a drop of crystal-violet stain on top of the onion skin and cover with a cover slip being careful to avoid air bubbles.

3. View the onion skin slide under low and medium power and make sketches of what you see.  Use colored pencils to make your sketches colorful.

4. This is what stained onion skin should look like under the microscope:

5. Discard the onion skin slide you made into the designated trash receptacle.

Procedure:  Human Cheek Cell Observation

1. With the toothpick provided, gently scrape the inside of your cheek to get some cells on the end of the toothpick.

2. You do not have to scrape very hard, and more than likely you will not even see anything on the end of the toothpick.

3. Swab the end of the toothpick that contains your cheek cells onto a clean slide.  Again, it may not look like much other than a smudge, but cells are there.

4. With the pipette, add a drop of crystal-violet stain to the cells and add a cover-slip on top of the cells that you just stained. 

5. The stain will also bring into view the nucleus of the cell.  The nucleus will appear as the round, darker, middle portion of the cell.  It is these types of cells that the Forensic Scientists (CSI dudes) collect and test for DNA when they take a cotton Q-tip and swab the inside of a suspect's mouth.  Each cell they collect will contain thousands of DNA molecules which can be used to positively identify an individual.  This is what these cells might look like:

6. Use your microscope to view these cells under both low and high power.  Make sketches of what you see.  Use colored pencils to enhance your diagrams.

7. Discard the cheek cell slide you made into the designated trash receptacle.

8. Complete the Microscope Lab #2 Review (Jupiter Ed) assignment.