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Exam 5: Microbial Growth and Control

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Question 1

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One laboratory group repeated the same experiment described by others with the identical bacterial isolate and the same growth medium and conditions used but were unable to achieve the same O.D.at 600 nm.What is the LEAST likely cause for this discrepancy of turbidity measured?

A) One lab used 16 mm wide test tubes and the other used 18 mm wide test tubes.
B) One lab subtracted the yellow color of the growth medium away from the final turbidity reported whereas the other lab used colorless water.
C) One lab vigorously dispersed the biofilm-forming bacteria with vortexing and the other did not.
D) The two labs varied with 1000 m elevation and did not consider the influence of pressure.

E) None of the above
F) A) and C)

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Question 2

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A microbe growing in a refrigerator is likely

A) psychrophilic.
B) mesophilic.
C) psychrotolerant or psychrophilic.
D) hyperthermophilic.

E) B) and C)
F) All of the above

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Question 3

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Heterotrophic bacteria will run out of organic growth substrates in batch cultures but chemostats can provide constant nutrient source for them to grow.Chemostats for photoautotrophic bacteria are not necessary to maintain them at a constant growth phase because a light can artificially be turned on constantly.

The time between inoculation and the beginning of growth is usually called the

Consider solution A (pH 6) and solution B (pH 9) .Which of the following statements is CORRECT?

In both lag and stationary phase,there is no net increase or decrease in viable cells.

Which of the following methods to enumerate cells often requires specialized staining to observe non-pigmented bacteria?

Which is most abundant and active in divisome complexes?

Organisms able to live in environments with high sugar concentrations are

Superoxide dismutase and catalase work together to convert superoxide into

To determine the specific growth rate of a bacterial population,it is essential to know

A drug targeting ________ would NOT be an effective antibiotic.

Enumerating cells in a biofilm is especially challenging for

Microbial growth is generally described as the increased number of cells rather than the expanding size of an individual microbial cell.

The lag phase does NOT occur if all the cells in the culture are viable.

The duration of logarithmic growth would increase if bacterial cells divided into three equal daughter cells rather than two.

Explain why a hyperthermophile is unlikely to be a human pathogen.

Counting chambers are used for estimating the number of cells present in a liquid culture.

Enumerating the viable and total cell concentration of a population of a microbial isolate can be a really laborious task for a microbiologist.Especially when a microbiologist studies the same isolate for several years,it often becomes practical to determine the relationship between optical density (OD)and cell concentration.Once this relationship (determined by a standard curve)is determined,the OD of an isolate in a broth can be routinely used to determine the population's concentration.Why must a standard curve be prepared for each isolate when using OD measurements to determine cell concentration? Also describe an experiment that would generate this type of standard curve.

An agar plate for counting colonies and maximizing statistical validity should ideally contain