Bright Field Microscope - Lab Report Example

 The Microscope Introduction: Microscope is a valuable tool in the field of science, as it is used to magnify the specimens for better understanding of the cells and its structures. Since many cells are too small to be seen through the naked eye, microscope is used for the magnification. The main function of microscope is to increase the resolution. If the magnification is higher then the resolution will be higher. (Bisen and Sharma 2012). Microscopes are of two types namely Light microscope and electron microscope. Light microscopes use visible light for illumination using the glasses. Electron microscopes use a beam of electrons focused by magnets on the specimen for magnification. Light microscopes use visible light which has a long wavelength. Electron microscope uses an electron beam which has very short wavelength than that of the light. (Bisen and Sharma 2012). Hence the resolving power is greater with the electron microscope. Electron microscopes are large and complex. It requires proper training to operate. Electron microscopes are used in the research area. Student microscopes are compound light microscopes. These microscopes magnify the objects using two lenses, the objective lens and the ocular lens. The total magnification is thus the multiple of the magnifying power of the two lenses. (Total magnification = objective magnification x ocular magnification). The light microscopes uses the visible light for observation, hence the specimen should be as thin as possible for better resolution. Light microscope can identify the objects up to 0.2 micro meters clearly. (Bisen and Sharma 2012). The light microscope can be used to study two types of slides. Permanent mounts and wet mounts. Permanent slide is a prepared slide, which is ready to use with pre staining, fixing and sealing. These slides are easier to use. The main drawback of these slides is that live micro organisms cannot be studied. Wet mount are the slides that are prepared at the place and viewed. Wet mounts are very useful to study the live cells. Field of view and depth of focus are the two main characteristics that affect the clarity in the light microscope. When the magnification increases, the depth of focus decreases and the lenses must be moved up or down. In the light microscopes bright field microscope and phase contrast microscopes are used in the lab. Bright field microscope is also called as student microscope. Bright field microscope can be used to study live micro organisms and pre- prepared slides. (Fixed stained smears). (Bain 2008). Bright Field Microscope: In this lab bright field microscope is used. The main parts of the microscope are lens system, revolving nose piece, stage, condenser and Iris diaphragm, light source, course focusing knob and fine focusing knob. The lens system consists of ocular and objectives. Ocular lens is the eye piece lens through which the specimen is viewed. Oculars have a magnifying power of 10 x in student microscope and the level of magnification is marked in the ocular. (Bisen and Sharma 2012). There are three objectives with different magnifying power. The scanning objective has the shortest magnifying power of 4x and it is the lowest magnifying power in a microscope. This lens is used to locate the specimen in the slide and to observe the large structures. The low power objective has the magnifying power of 10 x and used to observe the smaller structures at little detail. The high power objective of the student microscope has the longest objective and magnifying power of this objective is 40 x. fine details about the specimen are studied using this high power objective. (Bisen and Sharma 2012). The revolving nose piece has the objectives. The objectives with different magnifying power are chosen using this revolving nose piece. The stage is the flat surface on present below the objective on which the specimen is mounted. The centre of the stage has an opening through which the light passes on the specimen. (Bain 2008). The stage is mechanical and geared. The mechanical stage can be move to obtain the better resolution. The mechanical stage is moved up and down using the two adjustment knobs. The condenser and iris diaphragm are located to regulate the amount of light passing through the specimen to the eye piece. Iris diaphragm is used to control the amount of light that passes to the condenser. It works on a shutter mechanism. The light source is usually an electric bulb located at the base of the microscope. There are two knobs for focusing the lens system on the specimen. They are coarse focusing knob and fine focusing knob. Coarse focusing knob is used for scanning and low power objectives. Whereas fine focusing knob is used only for high power objectives. (Bisen and Sharma 2012). Figure 1: The Student Microscope (Bisen and Sharma 2012). Materials required: Bright Field Microscope Lens Paper Letter “ e” Methyl Cellulose Glass Slides Glass Cover Slips Toothpicks Pond Water Permanent Slides: Paramecium caudatum, Letter “e”, Human Blood cells, Euglena. Method: 1. The bright field microscope was removed from the storage region and kept on the laboratory bench at a safe distance from edge. 2. The cord was plugged into the electrical outlet and the light source was turned on. 3. The lenses of the microscope were cleaned with lens paper. 4. 4x objective, condenser and iris diaphragm was adjusted till the field of view was clear. 5. The letter “e” slide was kept in the objective position and the microscope was adjusted using the coarse adjusting knob. After the image was obtained, the fine focusing knob was used to adjust to get the clear focus. 6. The size of the object was identified by using the formula. 7. Fraction of diameter covered by the specimen x Diameter of field of view = Size. Thus letter “e “was used to analyse the magnification level of the microscope. 8. After the conformation of the image obtained with the letter “e”, more practice was given using the permanent slides. Prepared Slides: 1. The prepared slide of paramecium was further used to practice focusing. At the 10 x focus, the sketch of paramecium obtained by seeing through the microscope was done. 2. Another prepared slide of Euglena was focused and the practice was continued. As the Euglena cells were very small than that of Paramecium, the light adjustment was done for proper visibility of the structures. (Robert’s and King 1987) 3. The third prepared slide used in the microscope was that of the human blood. The blood cells are very smaller than the Euglena and Paramecium, so again the light should be adjusted. The red and white blood cells are drawn by observing through the microscope. Wet Mount Slides: 1. Wet mount Paramecium Slide preparation: The live Paramecium was taken in a slide with water and to it, a drop of methyl cellulose was added. The Paramecium was observed at 4x, 10 x and 40 x magnification and since the cells were not stained, they had little contrast only (Robert’s and King 1987). 2. Wet mount Pond water slide preparation: Similarly a slide was taken and a drop of pond water was added to it and using the wet mount technique, the slide was made ready for observation. The water was observed at 4x, 10 x and 40 x magnification and the presence of micro organisms in the slide was sketched. 3. Wet mount Cheek cells slide preparation: The cheek cells wet slide was prepared by adding a drop of methylene blue to the clean and dry slide. To this slide the cheek cells which were scraped from the inside of the cheek using a clean tooth pick was added. Using the cover slip, the cells were stained well with the dye. Before the cover slip was kept above the slide, the cheek cells were swirled well in the dye for separate cells. The slide was observed under the microscope. (Bain 2008). The cheek cells were easily identified under the microscope since only a few cells were present. The cells were sketched. Result: Figure 2: Paramecium (Robert’s and King 1987). Figure 3: Euglena (Robert’s and King 1987). Figure 4: Human Blood Cells (Bain 2008). Figure 5: Paramecium, wet mount with methyl cellulose in water. (Bain 2008). Figure 6: Pond water analysis: wet mount: Micro organisms present in water. (Saraswathi’s lab manual Biology) Figure 7: Cheeks cells stained with methylene blue. (King, Reiss and Roberts 2001). Conclusion: The prepared slides of Paramecium, Euglena and Human Blood cells were observed in the three different magnifications. It was found that the paramecium cell was well observed at the 4 x magnification and the euglena which was smaller than the paramecium required light adjustment. When the blood cells were observed, the resolution of the cells was better in the 40x magnification and the white blood cells and red blood cells were clearly visible. The wet mount slides were prepared using the Paramecium, Pond water and Cheek cells. Paramecium was clearly visible with having the cilia and in the shape of the rice grain. Some vacuoles were also seen along with the cilia. The internal organs were less visible. The pond water was found to have living micro organisms. Some other micro organisms were present in the pond water which were clearly visible to the naked eye. The concentration of the micro organisms present in the pond water will determine the quality of the pond water. The cheek cells were very few in number. They looked like irregular cells. The cell was filled up with protoplasm. A prominent nucleus was observed. Thus the microscope was used to visualize the cell. The size of the specimen was identified under the microscope. Wet mount preparation methods were learned and the cells were analyzed and identified. References: Bain, BJ., 2008. Blood Cells: A practical Guide, John Wiley and Sons. Besin, PS and Sharma, A., 2012. Introduction to Instrumentation in Life sciences, CRC Press. King, T., Reiss, M and Roberts, M., 2001. Practical Advanced Biology, Nelson Thornes. Roberts, MBV and King, TJ, 1987. Biology: A Functional Approach, Student s’ Manual, Nelson Thornes. Saraswathi’s Lab manual Biology, Saraswathi House Pvt Limited. Read More