Transcription
Good day, welcome everyone to your first practice of General Biology Laboratory at the National Autonomous University of Honduras. This practice is called "Learning Microscopy." The objective of this practice is for us to learn about the types of microscopes, their parts, how each of their parts works, and above all, the use of the microscopes we work with in the laboratory. As the laboratory develops, do not forget that you have to fill in each of the activities that your manual requests, and you can make use of the applications that will be available and use the video as many times as necessary.
The microscope is an apparatus that magnifies the image of very small objects that cannot be observed with the naked eye. There are two types of microscopes: the optical microscope, which is one that needs a light source to illuminate the object it will observe, and the electronic microscope, which illuminates with electrons. The different types of illumination of these microscopes allow objects of different sizes to be observed. With the optical microscope, the resolution is lower due to the size of the wavelength of the radiation it uses; therefore, objects up to the cellular level can be observed, while with the electrons used in the electronic microscope, we can observe structures down to the atomic level.
There are two types of optical microscopes: the two-dimensional image microscopes, known as compound microscopes, which have a high magnification power to observe microscopic organisms, and there is also the three-dimensional image microscope, known as the stereoscopic microscope. They can be used to observe larger organisms, and their magnification power is lower than the two-dimensional microscope, and they do not require prior preparation techniques to observe these structures.
Regarding the electronic microscope, there are also two types: the transmission electron microscope and the scanning electron microscope. In both, an electron beam is required to illuminate the object to be observed. What makes the difference between them is the way they project the observed image. The transmission electron microscope generates a two-dimensional image of the object, while the scanning electron microscope projects a three-dimensional image of the observed object.
In this first activity, we are going to identify the parts of the compound microscope. Just remember that you have to write down each of the parts I mention in your laboratory guide. This apparatus we have here is the compound microscope. This microscope is formed by different systems: the support system, the illumination system, the adjustment system, and the magnification system, which is the most important.
In the support system, we include the arm, the eyepiece tube, the revolving nosepiece, the stage, and the mechanical stage. Additionally, the base. The eyepiece tube gets its name because it is a structure that looks like or has the shape of a tube; specifically, its function is to hold the eyepiece. The arm is the structure from which we hold the microscope when moving it from one place to another. From the arm and the base, which is where it is supported on the table. The revolving nosepiece holds the objective lenses, which can be three or four depending on the manufacturer of the microscope, and also rotates them so they can be used according to the observer's needs. The stage or observation platform is where we place the sample we are going to observe under the microscope. Also included in this support system is the mechanical stage. It is called that because this structure has movement. The mechanical stage holds the clips and allows us to move the sample to the right or left and forward or backward.
The magnification system is formed by the eyepiece and the objective lenses. The eyepiece has a value of 10x. It is called the eyepiece because it is the place where the observer brings their eyes to be able to see the sample that is placed on the body. The objective lenses are numbered, and each objective lens has a specific value, which allows us to play with different magnifications. The first one we will mention is the scanning objective lens. This is a 4x lens and offers us 40x magnification. The second of the objective lenses is the low-power lens. This is a 10x lens and offers us 100x magnification. The third is a medium-power lens; it offers us 400x magnification in this case because it is a 40x lens. The last of the lenses, the highest power one, is called the high-power lens. It has a value of 7 and offers us magnifications of up to 1000x.
How to determine the magnification in times that each of the lenses offers us? The mathematical formula is very simple; it is just the multiplication of the value of the eyepiece by the value in x of the objective lens. For the case of 10x from the eyepiece multiplied by 4x from an objective, it is 40 times, which is why we determine that this lens gives us a magnification of up to 40 times. 10x from the eyepiece multiplied by 40x from this objective lens, this lens then gives us a value of up to 400 times.
These lenses can be divided into dry objective lenses and immersion objective lenses. The dry objective lens is one that only uses air between the space of the sample and the lens. The dry objective lenses are the 4x, the 10x, and the 40x. The immersion objective lens gets its name because to use it, immersion oil needs to be applied to the sample. This lens is submerged in the immersion oil to prevent light from refracting and to allow us to have completely uniform illumination. These would then be the lenses that make up the magnification system.
The illumination system is formed by the switch, the bulb or light source, and the condenser. In this case, it is a bulb, but there are microscopes that use a mirror as a light source; that mirror reflects light coming from the sun. In this case, we use a bulb, so we have the condenser, which is located exactly above the bulb and is responsible for trapping all the light coming from the lamp and directing it to a single point to illuminate the sample, and the switch, which is responsible for turning the microscope on or off.
The adjustment system is formed by the condenser screw, which is responsible for moving the condenser closer to or farther from the light source; the diaphragm knob, which is responsible for opening or closing the diaphragm to regulate the intensity of the light. We also have another of the screws, which is the mechanical stage screw. This is responsible for moving the mechanical stage forward, backward, right, and left. And the last of the screws, or the last two screws, the coarse adjustment knob, which is the larger one, is responsible for moving the sample closer to or farther from the objective lens used, and the next screw, which is the fine adjustment knob. This fine adjustment knob moves the stage closer to or farther from the objective lens. One focuses the image, and the other refines the image.
In this activity, we are going to describe the parts of the stereoscopic microscope. Remember that you have to label each of the parts as your manual requests. This apparatus you observe is the stereoscopic microscope. It provides us with three-dimensional images. The stereoscopic microscope has lower magnification than the microscope we saw in the previous activity. This one offers us magnifications of up to 40 times, all of which will depend on the manufacturer. It is widely used in entomology, the science that deals with the study of insects, because with this microscope we can observe structures that we can see with the naked eye but cannot see in much detail, such as the eyes of a fern, the venation of a leaf, etc. Therefore, it is widely used for the classification of organisms, taxonomic classification of organisms.
First, the support system, which is formed by the eyepiece tube or eyepiece tubes; in this case, there are two, the arm, the stage or observation platform, and the base of the microscope. The next of the systems is the magnification system. This includes two things: the eyepieces, which are two and have a value of 10x, and the lenses that are placed inside the magnification body. There is also the focusing system. Two knobs are involved here: first, this one we call the focusing knob, which is responsible for moving the magnification body closer to or farther from the sample, and this one, which is the magnification knob. This knob is graduated, and in this way, it allows us to determine the magnification we want to use to observe the sample with greater clarity. The illumination system is formed only by the switch and the bulb. These are responsible for illuminating the sample. Especially with this stereoscopic microscope, we can illuminate the sample from below or from above; these are the advantages offered by this stereoscopic microscope.
For the preparation of fixed slides, I will now describe the materials we will need. We will need a slide, which is a transparent, slightly thick glass slide. It is called that because it is here where the structure of the object, the cell, the tissue we want to observe, is placed. We will also use a coverslip, which will be responsible for covering the sample we want to observe. We place it over the slide. We will use a dropper and water. We apply a drop of water over the sample and cover it with the coverslip. Once this activity is done, the sample is ready to be observed under the compound microscope.
In this activity, we will learn to observe a sample with low-power focus. First, turn on the switch and turn on the microscope. If we observe that the bulb works, it means the sample will be illuminated. Second, take a small piece of lens paper, a special paper for cleaning microscope lenses. We will do a small cleaning of our eyepieces. This will allow us to observe the sample clearly. Then, we place the sample on the stage, and to prevent it from moving, we will secure it with the clips. After this, we rotate the revolving nosepiece until we position the 10x objective lens, as this is the low-power objective lens. After this, we use the coarse adjustment knob and the fine adjustment knob simultaneously. We observe through the eyepieces, always trying to keep our eyes a couple of centimeters away from the eyepiece; otherwise, our vision will be difficult. Once we can see the illumination coming from the bulb, we start moving the coarse adjustment knob to focus the image and the fine adjustment knob to refine the image quality. At this moment, I can observe the paper fibers but cannot find the image. It is then that I use the mechanical stage knobs, which allow me to move the sample forward, backward, left, and right, and with these two knobs, I can perfectly position the sample. Now I turn the knobs to clarify the image again, and thus I can observe an image in low power.
Now that I can observe my sample magnified 100 times, meaning with low-power focus, I will observe it with medium-power focus. What we do is rotate the revolving nosepiece, position the medium-power lens, move the coarse and fine adjustment knobs to focus and refine the image, always being careful with the movements. I perform them very carefully, using the fine adjustment knob, and thus I can observe a sample in medium power.
In this activity, we are going to observe a sewing thread, remembering all the procedures for preparing a fixed slide. We are going to use a slide, a fragment of thread that we will place on the slide, a drop of water, and we will cover it with a coverslip. If we have too much excess water, we will dry it with a piece of paper towel. This way, we will prevent the lenses of our microscope from getting wet, and once this is done, we will be able to observe it under the microscope. Here you will be able to observe it with the different objective lenses, observing all these different magnifications. You determine with which magnification you will work, and do not forget that the image you are observing and have placed under the microscope, you must place it in the laboratory manual.
Now we are going to use the stereoscopic microscope. As we have already learned to use the compound microscope, this one is for much finer use. The first thing we have to do is, well, ensure that the light works well. At this moment, I already have the sample placed; it is an insect that is ready to be observed. So, we turn on the lamp. We look through the eyepieces, and we realize that a slightly blurry image is observed. So, I use the focus knob. In this way, I manage to observe the sample placed on the stage with great clarity, and in this way, I am ready, or you are ready, to make your notes in the laboratory manual.
In this way, we have finished with the practice "Learning Microscopy." It is important to remember that the microscope is an instrument that helps us observe structures that we cannot see with the naked eye. Just remember that you must complete the conclusions you reached at the end of this practice. Thank you.