Laboratory Exam I (Example II)
1. Define:
Eye-wash station – The eye-wash station is located at the back of the laboratory attached to the yellow and green striped pole. The eye-wash can be operated either by hand or by stepping on the metal foot-pedal located near the floor (right-hand side). The eye-wash is used to wash toxic chemicals or microorganisms from the eyes in the event of accidental contamination. A second eye-wash station is available in the stockroom to the left of the autoclave (behind the door).
Aseptic technique – (A=without, sepsis=infection) Aseptic technique as it is applied in this laboratory refers to the procedures/methods used by students when manipulating live microbial cultures. These procedures are designed to prevent the infection of students and the contamination of the cultures being used.
Morphology - Morphology may be defined as the science or study of external features. The morphological characteristics of bacteria include their cell sizes, shapes and arrangements and the cultural characteristics of colonies grown on solid media (e.g., form, margin, elevation, surface texture, optical character, pigment production, size, etc.).
2. Laboratory disinfectant
3. These materials could become contaminated with pathogenic microorganisms, and could then be the source of infection. Since it is difficult to effectively remove broth cultures spills from these items, it is advisable to keep them on the floor or on the shelf under the lab bench.
4. Flammable materials such as long hair, fuzzy sweaters, alcohol, paper etc./ Never leave the burners unattended (do not walk away from them).
5. Many of the bacteria used in this laboratory are potentially pathogenic, and several types are gastrointestinal pathogens specifically. If students accidentally ingest these organisms, they are very likely to become ill. Ingestion of Salmonella can lead to infection that may result in hospitalization. The loss of study time and missed lectures/laboratory activities could interfere with successful completion of the class.
6. Disposable items only, e.g., used plastic Petri dishes, cotton swabs, plastic pipettes, toothpicks and other contaminated materials/ large plastic tube racks (50-tube baskets)
7. Ocular/ objective/ 40x, 100x, 450x and 1000x
8. Immersion oil/ refraction (bending or scattering) of light
9. Low power or 10x lens/ prepared slides (specifically the cover-slips)
10. Decrease/ center
11. The answer is variable here. If the material being displayed is lens paper (optical lens wipes), then only microscope lenses should be cleaned with it. If the material being displayed is a box of Kimwipes (or a similar paper product), this should not be used on lenses, but can be used to remove oil from prepared slides and can be used to clean the microscope stage.
12. Sub-stage condenser lens, iris diaphragm
13. Decrease/ eye strain and headache
14. Calibrate/ micrometers or microns
15. The coarse focus knob/ The answer is variable and depends on which objective is being used. Remember that if the 100x objecttive is being used, each small segment of the ocular micrometer is equal to one micrometer, and if the 10x objective is being used, each small segment of the ocular micrometer is equal to ten micrometers.
16. All the nutrients necessary for growing microorganisms in vitro.
17. Agar/ bacteria do not digest it (cannot break it down)
18. Carbon and nitrogen
19. Defined/ complex
20. This answer is variable and depends on the medium type being used. Read the label!
21. Before and after each transfer/ airborne organisms from getting in and contaminating the agar surface
22. They leak!/ Flaming the tube mouth will kill any cells present on the glass and will create convection currents that will help prevent airborne microorganisms from entering the tube while it is open and transfers are being made.
23. Well-isolated colonies/ only one type of organism
24. Up-side down or agar-side up/ Water dripping onto the agar surface will cause the bacteria present there to spread and form a confluent mass rather than isolated colonies. Even non-motile bacteria will spread over the surface if the agar is wet.
25. The answer is variable here. A properly streaked plate will have well-isolated colonies in one or more region and will not contain contaminants from the air.
26. On the bottom-side or agar-side of the plate/ The student's name, the date, the identity of the culture and the medium type being used.
27. This answer is variable. Check to see if there is variation in the colonies present. Remember, a pure culture contains only one type of microorganism, and the colonies present will have consistent cultural characteristics (morphology).
28. This answer will be variable, be sure to review the cultural characteristics of colonies in the lab syllabus and consider describing colony form, margin, elevation, surface texture, optical character, pigment production and size in millimeters.
29. Contrast with their background/ swim out of focus, leave the viewing field, or cause infection
30. Cations (positively charged particles)
31. Heat fixed
32. Indirect or negative stains/ size, shape
33. Eukaryotic/ prokaryotic (bacteria)
34. Differential
35. Peptidoglycan/ N-acetyl-muramic acid/ Some of the amino acids found in peptidoglycan do not occur in proteins (e.g., diaminopimelic and diaminobutyric acid) and some of them are D-form amino acids instead of L-form. Only L-form amino acids occur in the proteins produced by living organisms.
36. Crystal violet/ The decolorizing agent (acetone-alcohol mix) removes the color from the Gram-negative cells, and then they are counter-stained (stained pink) with safranin.
37. The answers are variable here – review cell morphology as presented in the lab syllabus. Remember that Gram-positive cells stain dark purple and Gram-negative cells stain light pink.
38. The 3% potassium hydroxide solution/ Gram-negative
39. The red-colored bacilli/ Mycolic
40. The answers are variable here, but unique structures observed in association with bacteria in this laboratory included flagella (amphitrichous and peritrichous), capsules, endospores, heterocysts and akinetes.
41. The answer is variable here, but endospores were stained with either carbol fuchsin or malachite green. Endospore shape is either spherical or ellipsoidal and if the sporangium is swollen, it will appear larger in diameter than the rest of the cell.
42. The three types of bacteria expected in the soil enrichment samples were Pseudomonas, Azotobacter and Bacillus.
Bacteria in the genus Pseudomonas are unique in their ability to use a wide range of unusual organic compounds as nutrient (sources of energy and carbon). Our enrichment media (broth and agar) contained sodium benzoate as the only carbon source, and this material is toxic to most bacteria (is commonly used as a preservative). Pseudomonas were able to grow in this medium but most other types of bacteria could not.
Bacteria in the genus Azotobacter are able to take molecular nitrogen (N2) from the air and use it to make the organic compounds necessary for growth (they can fix nitrogen). We used nitrogen-free media (broth and solid) to grow Azotobacter, and only nitrogen-fixing bacteria could grow on this.
Bacteria in the genus Bacillus are endospore-formers, and endospores are highly resistant to heat. We placed a small sample of soil into a glass tube with 5 ml of water, mixed the tube contents, and then placed the tube in a beaker of boiling water for 1 minute to Pasteurize the contents. Most vegetative cells were killed by this treatment, but the endospores present survived because they are thermoduric. A small sample of the Pasteurized liquid was then streaked on nutrient agar, the spores germinated, and new Bacillus organisms grew. Note – Bacteria in the genus Clostridium are also capable of forming thermoduric endospores, but most Clostridium are anaerobic and will not grow on media exposed to air.
43. Air/ Micrococcus
44. Cyanobacteria/ Bacteria/ The examples used will be selected from the prepared slides available.
45. Yeasts/ molds
46. Ascomycetes
47. These answers are variable, and apply to fungi
48. These answers are variable and apply to fungi
49. These answers are variable and apply to fungi
50. Phylum is Chlorophyta, the other two answers are variable but apply to algae
51. These answers are variable and apply to algae
52. Kingdom is Protista, unique wall material is glass, and organisms with glass coverings are Diatoms and Radiolarians (their order of placement is variable).
53. These answers are variable and apply to protozoa
54. These answers are variable
55. Phylum is Platyhelminthes, and the other answers are variable
56. Phylum is Aschelminthes, and the other answers are variable
57. The answers are variable
58. The kingdom is Animalia, the phylum is Arthropoda, and the other answers are variable.
59. Eukarya
Copyright 2002 Sierra College Biological Sciences Department
Last updated: 09/25/04.
