Laboratory Exam I (Example I)
1. Define:
Substage condenser lens – The lens located above the illuminator (light source) and under the stage is called the substage condenser lens. This lens is used to focus light on the object being viewed and can be adjusted (moved up or down) by turning the small silver knob on the lower, left-hand side of the microscope.
Pure Culture – A microbial culture that contains only one type of microorganism is referred to as a pure culture. Pure cultures may be maintained in broth media as well as on solid media (in Petri plates or glass tubes), and are frequently frozen for long term storage.
Anamorph state (fungi) – Fungi that reproduce asexually (form only asexual reproductive structures) are said to be in their anamorph or anamorphic state. Many anamorphs were once thought to be incapable of sexual reproduction, and were referred to as imperfect fungi (fungi imperfecti or deuteromycota/deuteromycetes). Most of these organisms have since been reclassified, but are still identified by their anamorph names.
2. Students are advised to clean their section of the bench top before and after any laboratory session involving the manipulation of live microbial cultures.
3. Bunsen burner/ leave the burner unattended (walk away from the work station)
4. Eating food or snacks, drinking, chewing nails or pencils, pens, etc.
5. Large, plastic, tube racks (50-tube racks or baskets)/ When not in a vertical position, these tubes leak. The plastic caps do not seal and the contents of the tubes will spill out onto the shelves creating a potentially hazardous situation.
6. Ocular/ objective/ Total magnification is 40x, 100x, 450x and 1000x.
7. Immersion oil/ refraction (bending or scattering) of light
8. 10x/ prepared slides (specifically the glass cover-slips over the specimens)
9. Decrease/ center
10. 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.
11. Eye-strain and headaches/ the iris diaphragm
12. The switch on the microscope light should be turned to the off position before the instrument is unplugged to prevent possible electric shock and damage to the bulb (when the plug is engaged by the next student).
13. Calibration/ stage micrometer
14. Micrometers or microns/ cell size is variable and will be influenced by the degree of magnification used. Remember that if the 100x objective is being used, each small division of the ocular micrometer is equal to one micrometer, and that if the 10x objective is being used each small division is equal to ten micrometers.
15. Culture medium (pleural is media)
16. Agar/ Agar is an ideal solidifying agent because most bacteria cannot digest it (therefore it will stay solid), and because it will remain solid when exposed to temperatures commonly used for incubation (25 to 37 degrees C).
17. Carbon and nitrogen
18. Defined/ complex
19. The answer will vary depending on the type of medium being used. Read the label!
20. Aseptic/ Wire loops should be flamed until red hot along their entire length before and after each microbial transfer. Glass culture tube mouths should be passed through (rolled in) the flame of the Bunsen burner after removing the cap, before and after each transfer, and before replacing the cap. Plastic snap-on tube caps should be held by the hand holding the wire loop and not placed on the bench top.
21. Culture plates left open-to-the-air are exposed to organisms suspended in the air and can readily become contaminated (remember what air-plates typically look like). It is difficult to maintain a pure culture when air exposure is a common occurrence.
22. Dilute/ well-isolated or separated from one another
23. Up-side down or agar-side up.
24. This answer is variable, but the properly streaked plate is the one with well-isolated colonies, i.e., colonies that are separated from one another on the medium surface.
25. This answer is variable. The label is in the proper position if it is on the agar-side of the plate or on the plate bottom (not on the lid). This placement insures that the label will stay with the culture at all times (will not be lost if the lid comes off). A label on the plate bottom will be visible during incubation (because plates are incubated agar-side up) and will not obstruct visibility of the culture when it is being viewed through the lid.
26. 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).
27. Morphology/ 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.
28. Dead cells cannot swim/move around (leave the viewing field or move out of focus) and dead cells are no longer able to cause infection (if they were pathogens while alive)/motility
29. Cations (positively charged particles)
30. Heat-fixed
31. Indirect/ size, shape
32. Eukaryotic/ prokaryotic (bacteria)
33. Differential
34. This answer is variable. Smears that are heavy (contain too much cellular material) will not provide observers with a clear view of individual organisms because the cells will be piled on top of each other and will form a solid mass. The best smears are relatively thin and uniform so that individual cells can be observed.
35. Peptidoglycan/ N-acetyl-muramic acid/ Some of the amino acids present are D-form instead of L-form (are mirror images of the amino acids found in proteins) and some are never found in proteins (e.g., diaminobutyric and diaminopimelic acid).
36. Crystal violet (are purple)/ safranin (are pink)
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. Negative
39. Although all of the steps involved are important, the decolorizing step is most critical in a differential stain. If cells are decolorized too much during a Gram stain, they will all appear pink, and if they are decolorized too little, they will all appear purple. Too much decolorizing will leave all the cells blue in an acid-fast stain, and too little will leave them all red. Accurate color separation is dependent on the decolorizing step.
40. Mycolic acid/ Acid-fast
41. 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.
42. 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.
43. Air/ Micrococcus
44. Cyanobacteria/ Bacteria/ The examples used will be selected from the prepared slides available.
45. 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 solid media) 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.
46. Yeasts/ molds
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. The phylum is either Platyhelminthes or Aschelminthes. The other answers are variable depending on the specific organism type being considered.
55. Phylum is Platyhelminthes, and the other answers are variable
56. Phylum is Aschelminthes, and the other answers are variable
57. The answer is 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.
