BIOL 2051 Lab Final Worksheets Questions and Answers Latest 2025-2026
Starch and cellulose are both glucose polymers. How do they differ in chemical structure? -
Answers -starch uses 1,4 alpha linkages, and is branched
-cellulose uses 1,4 beta linkages and is rigid and elongated
Dubos broth contains NaNO3, K2HPO4, MgSO4, KCl, FeSO4, and distilled water. Before the
addition of paper squares, is Dubos broth a complex or defined medium? - Answers -defined
because we know exactly what the composition of the broth is
True or false. The growth of C. hutchinsonii in Dubos broth + paper demonstrates that this
organism can use cellulose as a carbon source. - Answers -true, the paper in the dubos broth
was the only source of carbon attainable, so therefore the bacteria was able to grow using
cellulose as a carbon source
Which type of paper was the best source of cellulose for C. hutchinsonii (i.e., showed the best
growth)? Give a possible reason why one type of paper is degraded better than another by C.
hutchinsonii. - Answers -the filter paper or index card paper
-filter paper most likely degraded better than the newspaper because of the higher amount of
cellulose and the ink may have something to do with it
Based on your lab results, which paper is likely made of 100% cellulose? - Answers filter paper
Where do you expect to find Cytophaga growing on the strips of paper in the Dubos broths with
paper? Be very specific. Explain why it would be growing here. - Answers -in the oxic surface of
the water
-it degrades cellulose aerobically and needs oxygen
For day 1 of the MPN technique, each bench had a different sample. Two were samples of
water from natural sources, one was tap water, and the other was a dilution of E. coli prepared
by the culture lab. Which sample served as a positive control? Which sample served as a
negative control? - Answers -positive control was e. coli
-negative control was tap water
According to the EPA, water is considered potable if less than 2.2 coliforms per 100 ml. How
many positive LSL tubes results in less than 2.2 coliforms per 100 ml? - Answers -one
What environmental factors influence the level of coliforms in the MS River? in the University
Lake? in the Gulf of Mexico? - Answers -contamination
ms river: chemicals
uni lake: littering
, gulf: chemicals, oil spills, river run off
How is gas collection in the Durham tube an indication of the presence of coliforms? - Answers -
coliforms ferment lactose which produces CO2 in the durham tubes
What reaction is carried out by an indole-positive organism? - Answers
Escherichia coli and Enterobacter aerogenes colonies look different on EMB. Describe this
difference by explaining the connection between lactose fermentation and dye uptake. If you
lacked an EMB plate, how could you distinguish between E. coli and E. aerogenes? - Answers -on
emb plate e coli has a metallic green appearance because it is a lactose fermenter and
produces a lot of acids and e aerogenes has a fish eye appearance which only the center of the
colonies takes up dyes because it produces much less acid
-if lacking an emb plate, one can distinguish between them by measuring acid production
Methyl red is a pH indicator, turning red under ___________ conditions. What products reduce the
pH of the growth medium and give a positive methyl red test? - Answers -positive
-production of acids reduce the pH of the growth medium
The Voges-Proskauer test uses alpha naphthol and 40% potassium hydroxide to detect the
presence of _________________ made from the fermentation of glucose in organisms like
____________________. - Answers -acetoin (acetyl methyl carbinol)
-E. aerogenes
Simmons' citrate agar contains a pH indicator ________________________. Under what conditions
does the color of this pH indicator change? - Answers -bromothymol blue
-when alkaline products are formed and a rise in the pH takes place, it goes from green to blue
To grow on Simmons' citrate agar, an organism must be able to use sodium citrate as a
_____________ source and ammonia salts as a ________________ source. - Answers -carbon
-nitrogen
Which organism showed the best survival at each time and temperature? Give an explanation
for this. - Answers -bacillus megaterium
-they can produce endospores
Define sterilization. How does this differ from pasteurization? Why does spoilage still occur in
milk that has been pasteurized? - Answers -sterilization is the complete killing of
microorganisms on a surface whereas pasteurization is the gentle heating or killing of
microorganisms that cause food spoilage
Starch and cellulose are both glucose polymers. How do they differ in chemical structure? -
Answers -starch uses 1,4 alpha linkages, and is branched
-cellulose uses 1,4 beta linkages and is rigid and elongated
Dubos broth contains NaNO3, K2HPO4, MgSO4, KCl, FeSO4, and distilled water. Before the
addition of paper squares, is Dubos broth a complex or defined medium? - Answers -defined
because we know exactly what the composition of the broth is
True or false. The growth of C. hutchinsonii in Dubos broth + paper demonstrates that this
organism can use cellulose as a carbon source. - Answers -true, the paper in the dubos broth
was the only source of carbon attainable, so therefore the bacteria was able to grow using
cellulose as a carbon source
Which type of paper was the best source of cellulose for C. hutchinsonii (i.e., showed the best
growth)? Give a possible reason why one type of paper is degraded better than another by C.
hutchinsonii. - Answers -the filter paper or index card paper
-filter paper most likely degraded better than the newspaper because of the higher amount of
cellulose and the ink may have something to do with it
Based on your lab results, which paper is likely made of 100% cellulose? - Answers filter paper
Where do you expect to find Cytophaga growing on the strips of paper in the Dubos broths with
paper? Be very specific. Explain why it would be growing here. - Answers -in the oxic surface of
the water
-it degrades cellulose aerobically and needs oxygen
For day 1 of the MPN technique, each bench had a different sample. Two were samples of
water from natural sources, one was tap water, and the other was a dilution of E. coli prepared
by the culture lab. Which sample served as a positive control? Which sample served as a
negative control? - Answers -positive control was e. coli
-negative control was tap water
According to the EPA, water is considered potable if less than 2.2 coliforms per 100 ml. How
many positive LSL tubes results in less than 2.2 coliforms per 100 ml? - Answers -one
What environmental factors influence the level of coliforms in the MS River? in the University
Lake? in the Gulf of Mexico? - Answers -contamination
ms river: chemicals
uni lake: littering
, gulf: chemicals, oil spills, river run off
How is gas collection in the Durham tube an indication of the presence of coliforms? - Answers -
coliforms ferment lactose which produces CO2 in the durham tubes
What reaction is carried out by an indole-positive organism? - Answers
Escherichia coli and Enterobacter aerogenes colonies look different on EMB. Describe this
difference by explaining the connection between lactose fermentation and dye uptake. If you
lacked an EMB plate, how could you distinguish between E. coli and E. aerogenes? - Answers -on
emb plate e coli has a metallic green appearance because it is a lactose fermenter and
produces a lot of acids and e aerogenes has a fish eye appearance which only the center of the
colonies takes up dyes because it produces much less acid
-if lacking an emb plate, one can distinguish between them by measuring acid production
Methyl red is a pH indicator, turning red under ___________ conditions. What products reduce the
pH of the growth medium and give a positive methyl red test? - Answers -positive
-production of acids reduce the pH of the growth medium
The Voges-Proskauer test uses alpha naphthol and 40% potassium hydroxide to detect the
presence of _________________ made from the fermentation of glucose in organisms like
____________________. - Answers -acetoin (acetyl methyl carbinol)
-E. aerogenes
Simmons' citrate agar contains a pH indicator ________________________. Under what conditions
does the color of this pH indicator change? - Answers -bromothymol blue
-when alkaline products are formed and a rise in the pH takes place, it goes from green to blue
To grow on Simmons' citrate agar, an organism must be able to use sodium citrate as a
_____________ source and ammonia salts as a ________________ source. - Answers -carbon
-nitrogen
Which organism showed the best survival at each time and temperature? Give an explanation
for this. - Answers -bacillus megaterium
-they can produce endospores
Define sterilization. How does this differ from pasteurization? Why does spoilage still occur in
milk that has been pasteurized? - Answers -sterilization is the complete killing of
microorganisms on a surface whereas pasteurization is the gentle heating or killing of
microorganisms that cause food spoilage
