Lab assignment 1: Microbiology and microorganisms
Answer the questions directly in the space provided. Do not attach additional pages.
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When your assignment is complete, please submit it to the assignment one dropbox on UM Learn. This assignment is due at the end of Lab 1.
Exercise 1: Getting to know your microscope
How should you position the condenser on the Nikon E100 bright field microscope? What does the condenser do? (1 mark)
The condenser is used in its highest position or just slightly lower. While working with high-dry and immersion objectives, the diaphragm should be closed slowly while looking at a sharply focused section until the illumination level is just slightly adjusted.
How should you position the iris diaphragm when viewing a colored specimen, like stained bacteria? Explain why. (1 marks)
The light source should be adjusted to medium intensity, the condenser about three-fourths of the way up, and the iris should be almost closed. Rotate the low power objective into place over the specimen and, while looking from the side, crank the representative up as close as it can get to the purpose.
When should immersion oil be used? Explain why we need immersion oil. (2 marks)
Oil immersion is required whenviewing individual bacteria strands or details of striations in skeletal muscle. Immersion oil should be used anytime you want to consider a more precise image at 1000x.
The objectives on our laboratory microscopes are parfocal. What does that mean? (1 mark)
Parfocal means thatthe microscope is binocular. Parfocal means that when one objective lens is in focus, the other objectives will also be in direction.
Explain, in your own words, how you should go to the 100x objective, after youve already found your specimen with the 10x objective. (1 mark)
You place a drop of immersion oil on the top of your coverslip and another drop directly on your 100px oil objective lens. Slowly rotate your 100px oil objective lens into place and adjust the fine focus until you get a crisp and clear image.
Exercise 2: How can you tell the difference between prokaryotes and eukaryotes
Examine the picture showing the mixed bacteria (3 types) slide in the online Lab 1. What three cell shapes are shown on this slide? (1 mark)
Rods, cocci, and Spirilla.
Explain why we almost always use the 100x objective when viewing bacteria with the microscope in the lab (rather than using lower-powered objectives, like the 40x). (1 mark)
Bacteria are very small of course, so it is necessary toview them at the highest magnification possible with the best resolution possible. In a light microscope this is about 1000x due to optical limitations. The Oil immersion technique is used in order to enhance resolution. This requires a special 100x objective.
Examine the picture of the Halobacterium salinarum What shape are the cells of Halobacterium salinarum? (0.5 marks)
Halobacterium species are obligate aerobic,rod-shaped, archaea enveloped by a single lipid bilayer membrane surrounded by an S-layer made from the cell-surface glycoprotein.
How does the cell size of Archaea compare to that of the cells in the mixed bacteria (3 types) slide? (Look carefully at all of the bacterial cells, including the largest cells on the slide.) Can you tell the difference between Archaea and Bacteria by size? (1 mark)
Individual archaea range from 0.1 micrometers to over 15 micrometers in diameter and occur in various shapes, commonly as spheres, rods, spirals or plates.
Examine the picture of Anabaena. Are any special structures shown? If so, which one(s)? (1 mark)
Anabaena, genus of nitrogen-fixing blue-green algae with beadlikeor barrel-like cells and interspersed enlarged spores (heterocysts), found as plankton in shallow water and on moist soil.
Examine the short video of Euglena. In the cells in the video there is a red spot clearly visible. What is this red spot? (0.5 marks)
The surface of the flagellum is coated with about 30,000 extremely fine filaments called mastigonemes.
Is Euglena a prokaryote or a eukaryote? (0.5 marks)
Examine the picture of Saccharomyces cerevisiae. How was the iris diaphragm positioned to take this picture? Explain why. (1 mark)
The iris diaphragm is placed just above the condenser and below the juncture. That is because of high eminence microscopes include an Abbe condenser with an iris diaphragm.
How do the cells of cerevisiae compare to the cells of prokaryotes that you observed on previous slides? (1 mark)
Eukaryotic cells contain a discrete nucleus comprehending the cells chromosomal material while the prokaryotic cells do not incorporate a nucleus and contain a free- detached genetic material.
Examine the picture of What are the structures shown at the end of the branched hyphae? (0.5 marks)
Exercise 3: Where can I find a good bacterium when I need one?
Describe the characteristics of the following colonies using the terms on pages 18-19 of the lab manual. Make sure you are describing the colonies labeled on the pictures with red arrows. (4 marks)
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