Matric No : 111427
1.1 Setting up and using the microscope
Introduction
In order to be seen, microorganisms need to be magnified. Despite advances in other area of microscopy (for example, the electron microscope), the light microscope is still the instrument most frequently used for viewing microorganisms.
Objective
Learn to use a simple bright-field microscope correctly.
Results
Total magnification = objective lens power x eyepiece lens power(10x)
Salmonella enteritidis under 40x magnification:
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1) Microscope is positioned so that it can be observed through the eyepiece comfortably.
2) We adjust the light intensity using the brightness control.
3) We adjust the mechanical stage being higher or lower by using coarse-focus and fine-focus
knobs so that the objective lens is focused on the specimen.
4) We usually begin with low power (4x objective lens, 10x objective lens) to observe specimen
roughly and with wider view. Then, we switch to high power (40x objective lens) to observe
more detail and a clearer view of specimen.
5) Colony morphology of Salmonella enteritidis:
Shape: circular
Size: tiny (punctiform)
Surface: shiny and smooth in appearance
Color: red
Conclusion
The higher the magnification of objective lens, the clearer the view of specimen that we can be observed. The view is narrower and more specific for higher magnification.
References
http://quizlet.com/370451/microbiology-student-presentations-flash-cards/
http://en.wikipedia.org/wiki/Salmonella
1.2 Examination of cells
Introduction
Because of their extreme minuteness, bacteria are not generally studied with the low-power or high power-power dry objectives. Instead they are stained and observed with the oil immersion objective.
The wet mount methods enables you to study the sizes and shapes of living microorganisms (drying or staining microorganism distort them). It also enables you to determine if cells are motile. The wet mount method is quick and easy, and does not require special equipment.
Objectives
- To provide an experience in the use of microscope.
- To illustrate the diversity of cells and microorganisms.
100x objective lens x 10x eyepiece lens = 1000x magnification (with immersion oil)
Saccharomyces cerivisiae (yeast) under 1000x magnification:
Lactobacillus fermentum under 1000x magnification:
1) The 'oil immersion objective' meaning that a small drop of special immersion oil is placed on the
slide and the front lens of the objective is dipped into it for viewing.
2) The oil immersion fills the space between the objective and the specimen and matches
the refractive index of the glass cover slip and glass objective lens. At a given focal length, this
allows us to achieve a greater numerical aperture (better light collection efficiency, better
resolution).
3) Two different types of microorganisms are observed by using immersion oil:
- Saccharomyces cerivisiae (yeast)
- Lactobacillus fermentum
4) Colony morphology of Saccharomyces cerivisiae (yeast):
Shape: circular
Size: tiny
Surface: smooth
Texture: moist
Color: lemon yellow
5) Colony morphology of Lactobacillus fermentum:
Shape: rod
Size: tiny(smaller than yeast)
Surface: smooth
Texture: moist
Color: violet
Conclusion
100x objective lens immersed in oil can get a clearer view of the specimen. Hence, 1000x magnification with 100x oil immersion objective lens has a good resolution and allow us to observe clearer image.
References
http://microbewiki.kenyon.edu/index.php/Saccharomyces
http://en.wikipedia.org/wiki/Lactobacillus_fermentum
wiki.answer.com/q/Why_is_oil_necessary_when_using_the_90x_to_100x_objective
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