BIO 171 Lab Exam 3
Question 1
2..5 pts
List the four main steps used to prepare a WET mount, and indicate which (if
any) step is optional.
1 – Clean slide
2 – Circle area on slide with wax/hydrophobic
pen 3 – Apply organism to slide
4 – View under microscope
*Note: there are no optional steps in the wet mount.
Question 2
2..5 pts
Why is it important to first clean your slide before applying your sample?
You must first remove any unwanted contaminants from the slide
otherwise it may be difficult to distinguish between the pathogen of
interest and a contaminant.
Question 3
2..5 pts
When performing a wet mount technique, what is the advantage of using a
wax or hydrophobic pen?
pen will keep the water in the ring because the slide will remain wet
Creating a hydrophobic barrier (the circle) helps to keep the water
within the circle so it does not spill off of the slide.
Question 4
2..5 pts
What dye do Gram-negative bacteria primarily retain?
Safranin
Question 5
2..5 pts
Why do Gram-negative bacteria stain red?
Gram-negative bacteria have a thin peptidoglycan layer in their cell
wall. During the alcohol rinse step, the cell wall cannot retain the
crystal violet dye. It will be washed away. The cell wall will then
absorb the counter stain, safranin.
Question 6
.5 pts
Identify the stain and shape of the bacteria pictured below.
Question 1
2..5 pts
List the four main steps used to prepare a WET mount, and indicate which (if
any) step is optional.
1 – Clean slide
2 – Circle area on slide with wax/hydrophobic
pen 3 – Apply organism to slide
4 – View under microscope
*Note: there are no optional steps in the wet mount.
Question 2
2..5 pts
Why is it important to first clean your slide before applying your sample?
You must first remove any unwanted contaminants from the slide
otherwise it may be difficult to distinguish between the pathogen of
interest and a contaminant.
Question 3
2..5 pts
When performing a wet mount technique, what is the advantage of using a
wax or hydrophobic pen?
pen will keep the water in the ring because the slide will remain wet
Creating a hydrophobic barrier (the circle) helps to keep the water
within the circle so it does not spill off of the slide.
Question 4
2..5 pts
What dye do Gram-negative bacteria primarily retain?
Safranin
Question 5
2..5 pts
Why do Gram-negative bacteria stain red?
Gram-negative bacteria have a thin peptidoglycan layer in their cell
wall. During the alcohol rinse step, the cell wall cannot retain the
crystal violet dye. It will be washed away. The cell wall will then
absorb the counter stain, safranin.
Question 6
.5 pts
Identify the stain and shape of the bacteria pictured below.
