Q: A bacterial culture starts with 1,000 cells. If the generation time is 30 minutes, how many cells will there be after 2 hours of exponential (log) growth? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 1,000 \times 2^4$ = 16,000$$

Question 1

A patient develops a bacterial infection after surgery. The bacteria are found to grow best at 37°C and are sensitive to changes in pH between 6.5 and 7.5. Which of the following best describes the temperature and pH classification of these bacteria?

Accepted Answer

Mesophiles and neutrophiles

Question 2

Which of the following statements about osmotic pressure and microbial growth is correct?

Accepted Answer

Hypertonic environments cause plasmolysis of microbial cells.

Question 3

A microbiologist is culturing a bacterium that requires many growth factors and cannot grow on minimal media. Which type of media should be used?

Accepted Answer

Complex media

Question 4

Which enzyme is responsible for converting superoxide radicals to hydrogen peroxide in bacteria?

Accepted Answer

Superoxide dismutase

Question 5

A culture medium that contains yeast extract and peptone but does not have a precisely known chemical composition is best described as:

Accepted Answer

Complex

Question 6

Which of the following best explains why biofilms are highly resistant to antibiotics?

Accepted Answer

Biofilms have a protective matrix and facilitate quorum sensing.

Question 7

A bacterium that uses light as an energy source and organic compounds as a carbon source is classified as a:

Accepted Answer

Photoheterotroph

Question 8

During which phase of the bacterial growth curve does the rate of cell death equal the rate of new cell formation?

Accepted Answer

Stationary phase

Question 9

A scientist is studying a bacterium that can grow in the presence or absence of oxygen, but grows better when oxygen is present. This organism is best classified as a(n):

Accepted Answer

Facultative anaerobe

Question 10

Which of the following is a correct statement about agar as used in microbiology?

Accepted Answer

Agar liquefies at approximately $$100^\circ C$$ and solidifies at approximately $$40^\circ C.$$

Question 11

Which of the following best describes the process of lyophilization?

Accepted Answer

Freeze-drying cultures for long-term storage

Question 12

A bacterial culture starts with 1,000 cells. If the generation time is 30 minutes, how many cells will there be after 2 hours of exponential (log) growth? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 1,000 	imes 2^4$ = 16,000$$

Question 13

Which of the following trace elements is commonly required as a cofactor for enzymes in bacteria?

Accepted Answer

Iron

Question 14

A bacterium that can only grow in the absence of oxygen and is harmed by its presence is classified as a(n):

Accepted Answer

Obligate anaerobe

Question 15

Which of the following best explains why buffers are added to culture media?

Accepted Answer

To prevent drastic changes in pH

Question 16

A hospital patient develops an infection associated with a catheter. The infection is difficult to treat and is found to be caused by bacteria growing in a biofilm. Which property of biofilms most likely contributes to the persistence of this infection?

Accepted Answer

Biofilms allow bacteria to communicate and resist antimicrobial agents.

Question 17

Which of the following best describes the role of nitrogen in microbial growth?

Accepted Answer

It is needed for proteins, DNA, and RNA synthesis.

Question 18

A scientist is studying a microorganism that grows best at pH 5.0. This organism is most likely a(n):

Accepted Answer

Acidophile

Question 19

Which of the following statements about the bacterial growth curve is correct?

Accepted Answer

During the log phase, the population increases exponentially.

Question 20

Which of the following best describes the carbon source for chemoautotrophs?

Accepted Answer

Carbon dioxide

Microbial Growth: Physical and Chemical Requirements, Culture Media, and Growth Phases

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