BIOL 3201 Final Exam Labs 3&4 Test
Questions and All Correct Answers
2026-2027 Updated.
gamma or non-hemolytic - Answer no hemolysis or discoloration of the media
alpha - Answer incomplete hemolysis or greening of the media
beta - Answer complete hemolysis or clearing of the media
KOH test - Answer confirms Gram stain based on whether 3% KOH can lyse bacterial cell wall
and release DNA
positive - Answer KOH test: strings present, indicating a gram negative organism
negative - Answer KOH test: strings absent, indicating a gram positive organism
MSA - Answer selects for organisms based on their ability to grow with 7.5% NaCl present in
the agar, then differentiates organisms based on their ability to ferment mannitol
positive - Answer MSA: growth +/ acid +, yellow colonies
negative - Answer MSA: growth +/acid - or growth-/acid -; colorless colonies or no growth
nitrate reduction - Answer Differentiates microorganisms based on their ability to reduce
nitrate to nitrite or nitrogen gas
positive - Answer nitrate reduction: Red coloration after the addition Nitrate A and B reagents
OR No color change after the addition of zinc
negative - Answer nitrate reduction: Red coloration after the addition of zinc
oxidase - Answer Differentiates microorganisms based on the presence of the enzyme
cytochrome C oxidase in bacteria.
positive - Answer oxidase: blue to purple color change within 30 seconds
, negative - Answer oxidase: no color change or blue within 30 seconds
phenol red carbohydrate tubes - Answer Differentiates organisms based on carbohydrate
fermentation. This media contains specific carbohydrates and the pH indicator phenol red.
When an organism is able to ferment the carbohydrate present, an acid or an acid and gas are
produced and the indicator changes from red to yellow. If the carbohydrate is not fermented,
the color will remain red.
starch hydrolysis - Answer differentiates microorganisms based on their ability to hydrolyze
starch.
positive: dark agar with clear zone around streak line
negative: dark agar up to the streak line
selective medium - Answer a culture medium with an ingredient that inhibits the growth of
microbes other than the one being sought
Antibiotics, antifungals, dyes, and various inhibitory compounds are incorporated into media to
create selective conditions for growing specific microorganisms.
differential medium - Answer A culture medium with an ingredient that certain
microorganisms change in a recognizable way; used to differentiate microbes based on their
metabolic traits
hydrogen peroxide - Answer a highly reactive oxidizing agent that can damage enzymes,
nucleic acids, and other essential molecules in the bacterial cell. To avoid this damage, aerobes
produce the enzyme catalase, which degrades it into harmless oxygen and water.
carbohydrates - Answer If an organism can breakdown ... by oxidation or fermentation, acid is
usually produced
amylose - Answer a straight chain polymer of 200 to 300 glucose molecules that is a
constituent of the starch macromolecule
amylopectin - Answer a larger branched polymer of glucose that is a constituent of the starch
macromolecule
Gram's iodine - Answer Bacteria that hydrolyze starch produce amylases that degrade the
starch molecule into molecules of maltose, glucose, and dextrins that can enter the bacterial
cell. Starch hydrolysis is detected by adding ... to a starch agar plate (a differential medium, see
definition above).
Questions and All Correct Answers
2026-2027 Updated.
gamma or non-hemolytic - Answer no hemolysis or discoloration of the media
alpha - Answer incomplete hemolysis or greening of the media
beta - Answer complete hemolysis or clearing of the media
KOH test - Answer confirms Gram stain based on whether 3% KOH can lyse bacterial cell wall
and release DNA
positive - Answer KOH test: strings present, indicating a gram negative organism
negative - Answer KOH test: strings absent, indicating a gram positive organism
MSA - Answer selects for organisms based on their ability to grow with 7.5% NaCl present in
the agar, then differentiates organisms based on their ability to ferment mannitol
positive - Answer MSA: growth +/ acid +, yellow colonies
negative - Answer MSA: growth +/acid - or growth-/acid -; colorless colonies or no growth
nitrate reduction - Answer Differentiates microorganisms based on their ability to reduce
nitrate to nitrite or nitrogen gas
positive - Answer nitrate reduction: Red coloration after the addition Nitrate A and B reagents
OR No color change after the addition of zinc
negative - Answer nitrate reduction: Red coloration after the addition of zinc
oxidase - Answer Differentiates microorganisms based on the presence of the enzyme
cytochrome C oxidase in bacteria.
positive - Answer oxidase: blue to purple color change within 30 seconds
, negative - Answer oxidase: no color change or blue within 30 seconds
phenol red carbohydrate tubes - Answer Differentiates organisms based on carbohydrate
fermentation. This media contains specific carbohydrates and the pH indicator phenol red.
When an organism is able to ferment the carbohydrate present, an acid or an acid and gas are
produced and the indicator changes from red to yellow. If the carbohydrate is not fermented,
the color will remain red.
starch hydrolysis - Answer differentiates microorganisms based on their ability to hydrolyze
starch.
positive: dark agar with clear zone around streak line
negative: dark agar up to the streak line
selective medium - Answer a culture medium with an ingredient that inhibits the growth of
microbes other than the one being sought
Antibiotics, antifungals, dyes, and various inhibitory compounds are incorporated into media to
create selective conditions for growing specific microorganisms.
differential medium - Answer A culture medium with an ingredient that certain
microorganisms change in a recognizable way; used to differentiate microbes based on their
metabolic traits
hydrogen peroxide - Answer a highly reactive oxidizing agent that can damage enzymes,
nucleic acids, and other essential molecules in the bacterial cell. To avoid this damage, aerobes
produce the enzyme catalase, which degrades it into harmless oxygen and water.
carbohydrates - Answer If an organism can breakdown ... by oxidation or fermentation, acid is
usually produced
amylose - Answer a straight chain polymer of 200 to 300 glucose molecules that is a
constituent of the starch macromolecule
amylopectin - Answer a larger branched polymer of glucose that is a constituent of the starch
macromolecule
Gram's iodine - Answer Bacteria that hydrolyze starch produce amylases that degrade the
starch molecule into molecules of maltose, glucose, and dextrins that can enter the bacterial
cell. Starch hydrolysis is detected by adding ... to a starch agar plate (a differential medium, see
definition above).
