Nameadmin / January 24, 2019
Name: Esther Naa Bortiokor Bortey.
Practical Number: 2
Date: Tuesday, 27th February 2018.
Title: Examination of Living Microorganisms Using the Compound Light Microscope.
Microorganisms are so called because they are so small that they cannot be ordinarily seen using unaided eye. The optical instrument that magnifies the image of these organisms that enables us to view their morphological features is a microscope. Microscopes therefore allow for magnification and visualization of cells and cellular components that cannot be seen with the naked eye. The word microscope is derived from the Latin word micro (small) and the Greek word skopos (to look at) (Totora et al, 2010). Antony Van Leeuwenhoek is often considered as the father of microscopy, although compound microscopes were actually invented much before. According to Totora (2010), the microscope Van Leeuwenhoek made was a single lens like that of a magnifying glass with a magnification of 300X and Joseph Jackson Lister was the one who developed a microscope which was greatly advanced in 1830.
Willey et al (2008), elaborates on the fact that microscopes can be classified in different ways, but one easiest way is by the way they produce their images. Some use light, others use a beam of electrons or sound waves. Also, some produce highly detailed two dimensional images and others produce a low powered magnification of three dimensional image. The types of microscopes are the optical microscopes, electron microscopes and the others.
The optical microscopes are also called the light microscopes, they are microscopes that use visible light from a light source to examine specimens through the use of lenses and the types of optical microscopes are the compound light microscope, darkfield microscope, phase-contrast microscope, differential interface contrast(DIC) microscope, fluorescence microscope and confocal microscopes.
The electron microscopes simply scans with electrons producing very detailed images, this is because the wavelength of light is greater than that of the electrons and hence allows for more details when scanning. Scanning electron microscopes and transmission electron microscopes are the two types of electron microscopes.
Apart from these two types, the others are less common and mostly used by research scientists, they include the scanning probe microscope which scans the sample with a physical probe and generates an image with a computer, and the scanning acoustic microscope employs the use of sound waves to measure the sample, finally the x-ray microscope which uses electromagnetic radiation in the form of x-rays to produce images of tiny objects. ,Additionally, the scanning acoustic microscope is used to find craks and voids, detect counterfeit materials, test for failure and reliability and perform quality control on physical materials and the x-ray is also used on biological research and metallurgy (Murray et al, 2013).
With a compound light microscope, we can examine very small specimens as well as some of their fine detail hence mostly used for lab works. Slides are prepared and placed on the stage of the microscope for examination. Atlas (1946) says that the slides can be prepared by either the wet mount technique or the hanging drop technique to observe living organisms. In a wet mount the specimen is usually suspended in a drop of liquid mostly water located between slide and cover slip and for the hanging drop, a cavity slide is placed over a drop of the water sample on a cover slip and inverted so that the drop is suspended (Jawetz et al, 2013). The wet mount was used for this practical in order to observe the natural shape, size and arrangement of bacteria and yeast cells in living conditions.
1. To demonstrate the correct use of the compound light microscope.
2. To observe wet mount slides of yeast and bacteria cells, and draw diagrams of them.
3. To observe the motility of bacteria and yeast cells.
Yeast Specimen Slide
Bacteria Specimen Cover slip
A wet mount was prepared from bacteria and or yeast cells and placed on the compound light microscope. The stage clip was used to hold the prepared slide of yeast in position onto the stage and adjust the stage so that the sample comes in line with the source of light. The revolving turret was turned so that the lowest power objective which is 4X is in position and then adjusted the eyepieces on the microscope to suit personal measurements in order to see sample clear with both eyes. Then looked at the objective lens and stage from the side and turn the course adjustment knob so the stage moves upwards. The stage was moved up without letting the objective lens touch the coverslip. When it has gotten close enough, the fine adjustment knob was used to bring the image into focus. The objective lens was changed to 40X to obtain a better image as well as the adjustment of the light’s intensity for clearer images. Diagrams were obtained for the sample of yeast cells and the process was repeated for the sample of bacteria cells but this time the objective lens was readjusted to 100X.
Figure 1, the yeast cells under the microscopes were observed to be transparent organisms and they were spherical and round in shape with some being small and others quite large in size.The yeast cells were observed to be motile. No filaments were observed. Fungi, according to Murray et al. ( 2013) are unicellular forms of fungi and are larger than bacteria even though they are bacteria-like structures. An example of yeast cell is the Candida albicans.
Bacteria have three typical morphologies: the cocci (spherical bacteria), the bacilli (rod-shaped bacteria) and the spiral or curved shaped bacteria, such as the spirillum, the spirochetes and the Vibrio sp. (Moore, 2016). Figure 2 shows that the bacteria cells observed looked spherical and at the same spiral. Moore elaborates that bacteria with this type of morphology are coccobacillus.
Additionally, both cell samples were observed to be motile. Totora (2010) states that the structures used for motility are the flagella and the pili also known as fimbrae. Flagella are filamentous appendages that propels the organism and made up of filaments, hooks and a basal body. The pili are short generally and present in large numbers.
Motile organisms move from one place to the other indicating true motility and not Brownian movement. Talora (2008) describes Brownian movement to be movement caused by the molecule in the liquid striking an object and causing the object to shake or bounce at almost the same place maintaining their relative positions.
Answers To Questions
6. The role of fine adjustment is to move the Objective lens with finer movements. The object under observation is brought to the focus by adjusting the distance between the Objective lens and the object. While using higher magnifications, it is this distance is very critical and slight variation makes the image out of focus. Hence, it is very difficult to adjust the distance or in other words ‘focus the image’ using course focus. The fine adjustment option moves the Objective lens to very less distances per turn of the knob allowing the user to bring the object into the focus.
8. The Iodine or alcohol kills them and allows you to look at them and any internal structures they might have.
6. The drop should be hanging in order to view the true true motility of the microbesfrom one plce to the other.
Microscopes are the instruments used to observe and examine microorganisms since they cannot be viewed with the naked eye. The compound light microscope aids in examining the morphology of the yeast and bacterial cells as well as their motility. Observations show that microorganisms come in different sizes and shapes. The flagella and pili are the structures used for movement.
Atlas, M.R. (1946). Principles of Microbiology. Great Britain: Morby.
Jawetz , Melnick and Adelberg. (2013). Medical Microbiology, 26th Ed
Moore, K. (2016). Oriented Microbiology.Murray P. R. , Rosenthalk K.S. , Pfaller M.A. (2013). Medical Microbiology, 7th Ed. Phidadelphia: Sanders Elsevler Inc. Pg. 4.
Totora, G .J. , Funke, B. R. and Case, C.L. (2010) Microbiology: An Introduction, 10th Ed.
Talora, K. P., (2008). Foundation in Microbioology. McGraw- Hill, United States.
Willey JM, Sherwood LM, Woolverton C. J. (2008) Prescott, Harley, and Klein’s Microbiology, 7th Ed. New York, McGraw-Hill: The McGraw-Hill Companies, Inc. Pp. 87-135