BIO250L EXAM SCRIPT FULL QUESTIONS
AND CORRECT ANSWERS GUARANTEED
TO PASS
●● What color is Mycobacterium smegmatis under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Staphylococcus epidermidis under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Bacillus megaterium under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Escherichia coli under an acid fast stain? Why?
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue.
●● What color is Mycobacterium smegmatis in an acid fast stain? Why?
Answer: It is red because it is acid fast positive. The carbolfuchsin is
more soluble in the cell wall lipids therefore, retains the red color.
, ●● What color is Staphylococcus epidermidis in an acid fast stain? Why
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue
●● What color is Bacillus megaterium in an acid fast stain? Why?
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue
●● Which of the four samples from lab is the only acid fast positive
bacteria?
Answer: Mycobacterium smegmatis
●● Which of the four samples from lab is the only gram negative
bacteria?
Answer: Escherchia coli
●● What is the primary stain in the gram stain?
Answer: Crystal violet
●● What is the mordant in the gram stain?
Answer: iodine
AND CORRECT ANSWERS GUARANTEED
TO PASS
●● What color is Mycobacterium smegmatis under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Staphylococcus epidermidis under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Bacillus megaterium under a gram stain? Why?
Answer: Purple because it is gram postive. It does have a thick
peptidoglycan cell wall and therefore retains the crystal violet stain.
●● What color is Escherichia coli under an acid fast stain? Why?
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue.
●● What color is Mycobacterium smegmatis in an acid fast stain? Why?
Answer: It is red because it is acid fast positive. The carbolfuchsin is
more soluble in the cell wall lipids therefore, retains the red color.
, ●● What color is Staphylococcus epidermidis in an acid fast stain? Why
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue
●● What color is Bacillus megaterium in an acid fast stain? Why?
Answer: It is blue because it is acid fast negative. The carbolfuchsin
washes out and you see the methylene blue
●● Which of the four samples from lab is the only acid fast positive
bacteria?
Answer: Mycobacterium smegmatis
●● Which of the four samples from lab is the only gram negative
bacteria?
Answer: Escherchia coli
●● What is the primary stain in the gram stain?
Answer: Crystal violet
●● What is the mordant in the gram stain?
Answer: iodine
