Question 1

Which of the following best describes the difference between a discrete colony and a biofilm, as shown in the provided images?

Accepted Answer

A discrete colony arises from a single parent cell and is isolated, while a biofilm is a complex community of microbes living together on a surface.

Question 2

Which group of organisms uses light as an energy source and carbon dioxide as a carbon source?

Accepted Answer

Photoautotrophs

Question 3

Which toxic form of oxygen is most likely to cause irreparable damage to cellular components due to its high reactivity?

Accepted Answer

Superoxide radical

Question 4

In a thioglycolate broth tube, which pattern of growth would you expect from a facultative anaerobe?

Accepted Answer

Growth throughout the tube, but denser at the top

Question 5

Which process is essential for making atmospheric nitrogen usable for plants, and which organisms are responsible?

Accepted Answer

Nitrogen fixation by bacteria such as Rhizobium and cyanobacteria

Question 6

Which growth factor is required by mycoplasmas for cell membrane synthesis?

Accepted Answer

Cholesterol

Question 7

A bacterial species shows optimal growth at 37°C, minimal growth at 22°C, and no growth at 50°C. Which category does it belong to?

Accepted Answer

Mesophile

Question 8

Which of the following best explains why most human pathogens are classified as mesophiles?

Accepted Answer

They grow best at temperatures similar to the human body, around 37°C.

Question 9

Which type of microorganism would most likely be found growing in snow fields and cold water, and what is its optimal temperature range?

Accepted Answer

Psychrophile; 0–20°C

Question 10

Which physical effect of water restricts organisms to certain environments, and which type of microbe can tolerate high salt concentrations?

Accepted Answer

Osmotic pressure; obligate halophiles

Question 11

Which type of culture media would you use to distinguish between bacteria based on their ability to ferment lactose, and what visible change would you expect?

Accepted Answer

Differential media; color change in colonies or medium

Question 12

A microbiologist wants to isolate a pure culture from a mixed sample. Which technique should they use, and what is the progenitor cell called?

Accepted Answer

Streak plate method; colony-forming unit (CFU)

Question 13

Which relationship describes two organisms that always live together and are interdependent, such as gut bacteria in humans?

Accepted Answer

Symbiotic

Question 14

What is quorum sensing, and how does it relate to biofilm formation?

Accepted Answer

Quorum sensing is the communication between bacteria using chemical signals, triggering biofilm formation when a threshold is reached.

Question 15

Which equation best represents the logarithmic growth of a bacterial population, where $$N_0 is $$the initial number of cells and $$n is $$the number of generations?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Question 16

Which method would be most appropriate for rapidly estimating the number of microorganisms in a clinical sample without incubation?

Accepted Answer

Microscopic count using a cell counter

Question 17

A culture medium contains peptone, agar, lactose, bile salts, and crystal violet. Which type of medium is this, and what is its primary function?

Accepted Answer

Selective and differential medium; selects for Gram-negative bacteria and differentiates lactose fermenters

Question 18

Which preservation method allows cultures to be stored for decades by removing water under vacuum?

Accepted Answer

Lyophilization

Question 19

A patient sample is collected using a sterile swab brushed across the throat. Which type of specimen is this, and why is aseptic technique important?

Accepted Answer

Skin or accessible membrane specimen; prevents contamination and ensures accurate results

Question 20

Which of the following best describes the effect of temperature on the three-dimensional structure of proteins in microbial cells?

Accepted Answer

Both low and high temperatures can disrupt protein structure, affecting enzyme activity and membrane fluidity.

Microbial Nutrition and Growth: Chapter 6 Notes

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