Lab Report Questions pgs.
39; 45-46, 50-52, 60-61
Terms in this set (20)
Why are thick or dense smears less It will diminish the amount of light that can pass through
likely to provide a good smear making it difficult to see under the microscope. Also, Causes to
preparation for microscopic many microorganisms clumped together on the slide.
evaluation?
Why is it essential that smears be air- * Overheat will denature and rupture the cell wall.
dried? Why can't they be gently * Excess water on the slides will boil during fixation.
heated over the flame to speed up the
drying process?
Why should you be careful not to Overheating will distort the morphology (form and structure)
overheat the smear during the heat- of cells
fixing process?
* some other microbes from dirt or grease may prevent seeing
Why do you think the presence of
the organism you wanted to see.
grease or dirt on a glass slide will
* dirt may prevent bacteria from staining and heat-fixing
result in a poor smear preparations?
properly.
Why are basic dyes more effective for basic dyes with positive charge bind to negative charge cells.
bacterial staining than acidic dyes? The acidic dyes are only used for acid-fast bacteria.
Can simple staining technique be used Yes, the simple staining shows clear cell form and structure
to identify more than the and allows individual to view arrangement of appearance of
morphological characteristics of cells.
microorganisms? Explain
During the performance of the simple When heat fixing the bacteria, the bacterial proteins are
staining procedure, you failed to heat coagulated and fixed to the glass surface. If fail to heat fix, the
fix your E. coli smear preparation. bacteria will wash away when staining.
Upon microscopic examination, how
would you expect this slide to differ
from the correctly prepared slides?
During a coffee break, your friend The biological stain imparts color to a feature that you want to
spills coffee on your lab coat and the see, like the cell walls or a nucleus. The compound stain might
fabric is discovered. Is this a true bind to something in the cell and you might not be able to see
biological stain or simply a compound the nucleus in the cell.
capable of imparting color? Explain
your rationale.
What are the advantages of Differential staining separates two groups of organisms into
differential staining procedure over gram negative and gram positive. Simple stain is quick, easy,
the simple staining techniques? and allows individual to see size and shape.
* Primary stain (crystal violet): to impart its color to all cells
*Mordant (gram's iodine) : Increases the cells' affinity for a stain
Cite the purpose of each following
and is used as a killing agent.
reagents in the differential staining
*Decolorizing agent (95% ethel alcohol): remove excess dye
procedure: Primary stain, counterstain,
of cell and to be protein dehydrating agent.
decolorizing agent, mordant.
* Counterstain: final reagent - will show gram-positive (retain
the purple color) or gram-negative (retain pink color)
Why is it essential that the primary So it can be distinguished from each other.
stain and the counterstain be of
contrasting color?
Which is the most crucial step in the Decolorizing Step.
performance of the Gram staining Over-decolorizing will result in the lost of primary stain,
procedures? causing gram positive to appear negative.
Because of snowstorm, your regular The bacteria most likely stopped growing for lack of nutrients
laboratory session was canceled and causing break down in cell walls, which caused the stain to be
the Gram staining procedure was washed away and not hold in cell walls properly. This caused
perform on cultures incubated for a variability in the counter staining procedure results.
longer period of time. Examination of
stained Bacillus Cereus slides revealed
a great deal of color variability,
ranging from an intense blue to
shades of pink. Account for this result.
Why is heat necessary in spore the heat will break cell wall and allow the stain to
staining? enter/penetrate the spores; it allows dye to stain spore
Explain the function of water in spore water washes off the excess stain, so that you can see the
staining spore; acts as decolorizer
Assume you made several errors in Now you have decolorized the cells and the stain. You will not
your spore staining procedure. You see anything. You should have used water, which would wash
used acid-alcohol as the decolorizing off excess stain to see spores.
agent
The cells walls will stain green and the spore will stain red. The
Assume you made several errors in
endospores will be harder to distinguish. Key is safranin is heat
your spore staining procedure. You
driven into the sproe but malachite green has a weak affinity.
used safranin as the primary stain and
Malachite green should be primary and safranin as counter
malachite green as the counterstain
stain for gram negative cells.
Assume you made several errors in The stain won't penetrate the spores
your spore staining procedure. You
did not apply heat during the
application o the primary stain
Assume you made several errors in the capsule protects bacteria from phagocytic activities. this
your spore staining procedure. Explain increases the virulence of the bacteria.
the medical significance of a capsule
the copper sulfate is used as a decolorizer instead of water.
Assume you made several errors in
Sulfate washes the purple stain out of capsule material without
your spore staining procedure. Explain
removing the cell wall boundary. At the same time, the
the function of copper sulfate in this
decolorizing capsule absorbs the copper sulfate to give the
procedure
capsule a blue contrast from the deep purple cell.
