Q: If a bacterial culture doubles every 30 minutes, how many cells will there be after 24 hours if you start with 40 cells? Use the formula $N = N_0 \\times 2^n$, where $n$ is the number of generations.

$N = 40 \\times 2^{48} = 11,294,976,640,000$

Q: A thermophile would most likely be found in which environment?

A compost pile with temperatures above 45$^\\circ$C

Question 1

Which of the following best describes a biofilm?

Accepted Answer

A slimy matrix of polysaccharides, DNA, and proteins that allows microbial communities to adhere to surfaces and resist antibiotics.

Question 2

Why is brushing teeth effective in preventing dental caries caused by biofilms?

Accepted Answer

Brushing teeth physically disrupts the biofilm, preventing bacteria from adhering to the tooth surface and forming cavities.

Question 3

A facultative anaerobe is best described as an organism that:

Accepted Answer

Can grow with or without oxygen, using aerobic respiration when O$_2$ is present and switching to anaerobic metabolism when it is not.

Question 4

Which of the following best describes a mesophile?

Accepted Answer

An organism that grows best at moderate temperatures, typically around 37$^\circ$C.

Question 5

If a bacterial culture doubles every 30 minutes, how many cells will there be after 24 hours if you start with 40 cells? Use the formula $N = N_0 \times 2^n$, where $n$ is the number of generations.

Accepted Answer

$N = 40 \times 2^{48} = 11,294,976,640,000$

Question 6

Which of the following is a characteristic of psychrophiles?

Accepted Answer

They grow optimally at cold temperatures, typically below 15$^\circ$C.

Question 7

What is the main difference between selective and differential media?

Accepted Answer

Selective media favor the growth of specific microbes, while differential media distinguish between different types of bacteria based on their biochemical properties.

Question 8

Which term describes bacteria that require low oxygen levels (1-10%) for growth?

Accepted Answer

Microaerophile

Question 9

Nitrogen fixation is important in microbiology because:

Accepted Answer

It allows bacteria to convert nitrogen gas (N$_2$) into ammonia (NH$_3$), which can be used by plants and other organisms.

Question 10

During which phase of bacterial growth is the rate of cell division equal to the rate of cell death?

Accepted Answer

Stationary phase

Question 11

Which of the following best describes the lag phase in a bacterial growth curve?

Accepted Answer

The initial phase where bacteria adapt to new conditions but do not divide rapidly.

Question 12

A thermophile would most likely be found in which environment?

Accepted Answer

A compost pile with temperatures above 45$^\circ$C

Question 13

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are always composed of a single bacterial species.

Question 14

Which of the following best describes an aerotolerant anaerobe?

Accepted Answer

It can survive in the presence of oxygen but does not use it for metabolism.

Question 15

Which of the following is a real-world consequence of biofilm formation in the human body?

Accepted Answer

Chronic infections such as dental caries and persistent wounds.

Question 16

Which of the following best describes the function of differential media?

Accepted Answer

To distinguish between different types of bacteria based on their biochemical reactions.

Question 17

Which of the following is NOT a component of the extracellular polymeric substance (EPS) in biofilms?

Accepted Answer

Lipids

Question 18

A microaerophile would most likely be found in which environment?

Accepted Answer

Soil just below the surface where oxygen levels are low but not absent.

Question 19

Which of the following best explains why antibiotics may be less effective against bacteria in a biofilm?

Accepted Answer

Antibiotics cannot penetrate the slimy matrix of the biofilm, and bacteria within the biofilm may have altered metabolic states that reduce antibiotic susceptibility.

Chpt 6 Microbial Nutrition and Growth: Case Studies and Vocabulary

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