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BIOC17 LAB EXAM QUESTIONS AND ANSWERS 2024;(SOLVED 100%)
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BIOC17 LAB EXAM QUESTIONS AND ANSWERS 2024;(SOLVED 100%)
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BIOC17 LAB EXAM QUESTIONS AND ANSWERS 2024;(SOLVED 100%)
What is the stage micrometer used for?
calibrating the ocular micrometer at each objective
increments on the stage micrometer
major divisions: 100 μm
minor divisions: 10 μm
process of calibrating ocular micrometer
1. find two incidences where the gradations on the ocular micrometer match up w. the ones on the stage
micrometer
2. make calculations of the value of one ocular unit (minor division) for both incidences
3. if the values are different, take the mathematical mean
difference between simple staining and negative staining
simple staining: staining the microbe; uses basic stain
negative staining: staining the background; uses acidic stain
basic makeup of a stain
solutions with a solvent and a coloured molecule
- solvent tends to be water or ethanol
- coloured molecule tends to be chromogen
What is a chromogen? (2 components)
coloured component of a stain consisting of:
1. auxochrome: charged portion of the molecule to ionically/covalently bind cell portion or background to be dyed
2. chromophore: portion of the chromogen giving the stain its colour
DEF basic stain stain w. a (+) charged auxochrome in its chromogen; attract bacterial cell b/c cell wall (-) charged
examples of commonly used basic stains (3)
1. crystal violet
2. safranin
3. methylene blue
example of commonly used acidic stains (2)
1. Nigrosine
2. Congo Red
DEF acidic stain
stain w. a (-) charged auxochrome in its chromogen; repels (-) charged bacterial cell walls so that the background is stained, instead
purpose of heat-fixation (3)
1. kills the bacterial cells
2. coagulates the cytoplasmic proteins to make more visible
3. helps cells adhere to the slide to be stained
consequences of heat-fixation
- can distort cell
- can cause cell shrinkage
- not usable if cells need to be alive during observation
For what procedures are heat-fixing prohibited? (3)
1. negative stain
- don't want distorted/shrunken cells
2. capsule stain
- don't want shrunken cells that may appear to have halo
3. hanging drop
- don't want dead cells
methods of determining bacterial motility (3)
1. hanging drop
2. flagellar stain technique 3. motility test
difference between true motility and brownian motion
true motility: single flagellum/flagella to enable directional motion
brownian motion: vibrating on the spot due to bombardment of water molecules in their aqueous environments
What type of slide is used for hanging drop?
depression slide
microbes displaying true motility vs. Brownian motion
motile: Escherichia coli
Brownian (non-motile): Staphylococcus epidermidis
Is the 100X objective used for the hanging drop?
no; if can't focus on the 100X, the drop will no longer be suspended
What stain is used for flagella staining? Why?
Ryu stain mordant to stain in multiple layers to flagella so that the flagella appears thicker to be visible thru bright-field microscopy
types of flagellar arrangements:
monotrichous
amphitrichous
lophotrichous
petritrichous
monotrichous: single flagellum at one end of the cell
amphitrichous: flagella at both ends of the bacteria
lophotrichous: tufts of flagella at the end of the cell
petritrichous: flagella emerging from all over the cell surface
What does flagella staining tell us about the bacteria's motility?
if flagellum present, the organism is motile
What is Wescodyne?
iodine-based anti-germicidal agent for disposal of solid and liquid waste including used tips
What is a bright-field light microscope ?
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