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Exam 6: Microbial Growth

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Question 1

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Consider a culture medium on which only gram-positive organisms such as Staphylococcus aureus colonies can grow due to an elevated NaCl level. A yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the pH as a result and changing the color of a pH indicator chemical. This type of medium would be referred to as a(n)

A) selective and differential medium.
B) differential medium.
C) selective medium.
D) enrichment culture.
E) differential and enrichment culture.

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Question 2

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Turbidity is an indirect measurement of bacterial growth that can be measured using a spectrophotometer.

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Question 3

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The addition of which of the following to a culture medium will neutralize acids?

An isolated colony on a streak plate contains millions (or even billions) of identical cells all arising from one initial cell.

Bacterial growth refers to an increase in the numbers of cells in a bacterial culture.

Which of the following is the best definition of generation time?

Which of the following is an organic growth factor?

Salts and sugars work to preserve foods by creating a

Pure cultures can easily be obtained on streak plates, even if the desired bacteria are present in very low concentrations in the initial culture broth.

Three cells with generation times of 60 minutes are inoculated into a culture medium. How many cells are there after 5 hours?

Laboratory cultivation of obligate anaerobes requires reducing media or special growth chambers filled with inert gases.

Figure 6.3 -In Figure 6.3, which tube shows the expected growth pattern for a microaerophile?

Which of the following pairs of microbe classification terms and optimal growth temperatures is mismatched?

Which of the following is NOT a direct method to measure microbial growth?

Agar is used as a solidifying agent in microbiological media since few bacteria can degrade it.

Figure 6.2 -Figure 6.2 shows a typical bacterial growth curve with the y-axis indicating the log of the number of bacteria and the x-axis indicating time in culture. In the figure, which section (or sections) shows a growth phase where the number of cells dying equals the number of cells dividing?

Table 6.2 The following data show growth of two bacteria on different media. $\begin{array}{l}\text { Amount of Growth }\\\begin{array} { | l | c | c | } \hline & \text { Staphylococcus aureus } & \text { Streptococcus pyogenes } \\\hline \text { Nutrient agar } & + + & + + \\\hline \text { Nutrient agar } + 7.5 \% \mathrm { NaCl } & + & - \\\hline\end{array}\end{array}$ The data in Table 6.2 indicate that S. aureus is a(n)

Most bacteria reproduce by

An experiment began with 4 cells and ended with 128 cells. How many generations did the cells go through?

Which group of microorganisms is most likely to spoil a freshwater trout preserved with salt?