BIOL 3201 LAB 6 AND 7 EXAM QUESTIONS WITH VERIFIED SOLUTIONS LATEST UPDATE 2026
KOH test (purpose) - Answers Confirms Gram reaction by lysing Gram-negative cell walls and
releasing DNA
KOH test - reagent - Answers 3% potassium hydroxide (KOH)
KOH test - positive result - Answers DNA strings form (Gram-negative)
KOH test - negative result - Answers No strings (Gram-positive)
EMB agar (purpose) - Answers Selective for Gram-negative bacteria and differential for lactose
fermentation
EMB agar - reagents - Answers Eosin Y, methylene blue, lactose
EMB - positive vigorous lactose fermenter - Answers Metallic green sheen (e.g., E. coli)
EMB - positive moderate lactose fermenter - Answers Purple colonies
EMB - negative result - Answers Colorless, pink, or gray colonies (non-lactose fermenter)
Catalase test (purpose) - Answers Detects catalase enzyme that breaks down hydrogen peroxide
Catalase test - reagent - Answers Hydrogen peroxide (H₂O₂)
Catalase test - positive result - Answers Bubbles form
Catalase test - negative result - Answers No bubbles
Oxidase test (purpose) - Answers Detects cytochrome c oxidase enzyme
Oxidase test - reagent - Answers Oxidase reagent (tetramethyl-p-phenylenediamine)
Oxidase test - positive result - Answers Blue or purple color within 30 seconds
Oxidase test - negative result - Answers No color change
Phenylalanine test (purpose) - Answers Detects phenylalanine deaminase enzyme
Phenylalanine test - reagent - Answers 10% ferric chloride
Phenylalanine test - positive result - Answers Green color
Phenylalanine test - negative result - Answers Yellow/no color change
Urea test (purpose) - Answers Detects urease enzyme that hydrolyzes urea
Urea test - reagents - Answers Urea, phenol red indicator
Urea test - positive result - Answers Bright pink/red color
Urea test - negative result - Answers No color change/orange
O/F glucose test (purpose) - Answers Determines oxidative or fermentative glucose metabolism
O/F glucose test - reagents - Answers Glucose, phenol red, mineral oil (F tube)
O/F glucose - fermentation positive - Answers Both tubes yellow
O/F glucose - oxidation positive - Answers Open tube yellow only
O/F glucose - negative result - Answers Both tubes remain green
Methyl Red test (purpose) - Answers Detects mixed-acid fermentation
Methyl Red test - reagent - Answers Methyl red indicator
Methyl Red test - positive result - Answers Red color
Methyl Red test - negative result - Answers Yellow or orange color
Voges-Proskauer test (purpose) - Answers Detects 2,3-butanediol fermentation (acetoin production)
VP test - reagents - Answers VP-A (alpha-naphthol), VP-B (KOH)
VP test - positive result - Answers Red color within 30 minutes
VP test - negative result - Answers Yellow/brown or no color change
Citrate test (purpose) - Answers Determines ability to use citrate as sole carbon source
Citrate test - indicator - Answers Bromothymol blue
Citrate test - positive result - Answers Blue color with growth
Citrate test - negative result - Answers Green color, no growth
SIM test (purpose) - Answers Tests hydrogen sulfide production, indole production, and motility
SIM H₂S - reagents - Answers Sodium thiosulfate, ferrous ammonium sulfate
SIM H₂S - positive result - Answers Black precipitate
SIM H₂S - negative result - Answers No black color
SIM indole - reagent - Answers Kovac's reagent
SIM indole - positive result - Answers Red layer at top
SIM indole - negative result - Answers No color change
SIM motility - positive result - Answers Diffuse growth away from stab line
SIM motility - negative result - Answers Growth only along stab line
Starch hydrolysis test (purpose) - Answers Detects amylase (starch degradation)
Starch hydrolysis - reagent - Answers Gram's iodine
KOH test (purpose) - Answers Confirms Gram reaction by lysing Gram-negative cell walls and
releasing DNA
KOH test - reagent - Answers 3% potassium hydroxide (KOH)
KOH test - positive result - Answers DNA strings form (Gram-negative)
KOH test - negative result - Answers No strings (Gram-positive)
EMB agar (purpose) - Answers Selective for Gram-negative bacteria and differential for lactose
fermentation
EMB agar - reagents - Answers Eosin Y, methylene blue, lactose
EMB - positive vigorous lactose fermenter - Answers Metallic green sheen (e.g., E. coli)
EMB - positive moderate lactose fermenter - Answers Purple colonies
EMB - negative result - Answers Colorless, pink, or gray colonies (non-lactose fermenter)
Catalase test (purpose) - Answers Detects catalase enzyme that breaks down hydrogen peroxide
Catalase test - reagent - Answers Hydrogen peroxide (H₂O₂)
Catalase test - positive result - Answers Bubbles form
Catalase test - negative result - Answers No bubbles
Oxidase test (purpose) - Answers Detects cytochrome c oxidase enzyme
Oxidase test - reagent - Answers Oxidase reagent (tetramethyl-p-phenylenediamine)
Oxidase test - positive result - Answers Blue or purple color within 30 seconds
Oxidase test - negative result - Answers No color change
Phenylalanine test (purpose) - Answers Detects phenylalanine deaminase enzyme
Phenylalanine test - reagent - Answers 10% ferric chloride
Phenylalanine test - positive result - Answers Green color
Phenylalanine test - negative result - Answers Yellow/no color change
Urea test (purpose) - Answers Detects urease enzyme that hydrolyzes urea
Urea test - reagents - Answers Urea, phenol red indicator
Urea test - positive result - Answers Bright pink/red color
Urea test - negative result - Answers No color change/orange
O/F glucose test (purpose) - Answers Determines oxidative or fermentative glucose metabolism
O/F glucose test - reagents - Answers Glucose, phenol red, mineral oil (F tube)
O/F glucose - fermentation positive - Answers Both tubes yellow
O/F glucose - oxidation positive - Answers Open tube yellow only
O/F glucose - negative result - Answers Both tubes remain green
Methyl Red test (purpose) - Answers Detects mixed-acid fermentation
Methyl Red test - reagent - Answers Methyl red indicator
Methyl Red test - positive result - Answers Red color
Methyl Red test - negative result - Answers Yellow or orange color
Voges-Proskauer test (purpose) - Answers Detects 2,3-butanediol fermentation (acetoin production)
VP test - reagents - Answers VP-A (alpha-naphthol), VP-B (KOH)
VP test - positive result - Answers Red color within 30 minutes
VP test - negative result - Answers Yellow/brown or no color change
Citrate test (purpose) - Answers Determines ability to use citrate as sole carbon source
Citrate test - indicator - Answers Bromothymol blue
Citrate test - positive result - Answers Blue color with growth
Citrate test - negative result - Answers Green color, no growth
SIM test (purpose) - Answers Tests hydrogen sulfide production, indole production, and motility
SIM H₂S - reagents - Answers Sodium thiosulfate, ferrous ammonium sulfate
SIM H₂S - positive result - Answers Black precipitate
SIM H₂S - negative result - Answers No black color
SIM indole - reagent - Answers Kovac's reagent
SIM indole - positive result - Answers Red layer at top
SIM indole - negative result - Answers No color change
SIM motility - positive result - Answers Diffuse growth away from stab line
SIM motility - negative result - Answers Growth only along stab line
Starch hydrolysis test (purpose) - Answers Detects amylase (starch degradation)
Starch hydrolysis - reagent - Answers Gram's iodine
