Q: Which equation correctly describes the exponential growth of bacteria, given an initial population $$N_0$$ and number of generations $$ng$$?

$$N(ng) = N_0$ \times 2$$^{ng}$$

Question 1

Which of the following best describes the adaptation of psychrophiles to low temperatures?

Accepted Answer

They have membranes with unsaturated fatty acids, increasing fluidity at low temperatures.

Question 2

A bacterium is found growing optimally at pH 9.5 in a soda lake. Which term best describes this organism?

Accepted Answer

Alkaliphile

Question 3

Which of the following organisms would most likely be found growing on human skin, and why?

Accepted Answer

Halotolerant organisms, because human skin is exposed to varying salt concentrations.

Question 4

Which macromolecule requires both carbon and nitrogen for its synthesis?

Accepted Answer

Proteins

Question 5

Iron is an essential trace element in bacteria because it is:

Accepted Answer

A part of cytochrome proteins in the electron transport chain.

Question 6

Which enzyme is responsible for detoxifying superoxide radicals ($$O_2$$^-$$) in bacteria?

Accepted Answer

Superoxide dismutase (SOD)

Question 7

Refer to the first image. Which tube represents the growth pattern of obligate anaerobes in thioglycolate medium?

Accepted Answer

Tube (e)

Question 8

A microorganism grows throughout a thioglycolate tube but shows denser growth at the top. What is the most likely classification?

Accepted Answer

Facultative anaerobe

Question 9

Which of the following best describes a biofilm?

Accepted Answer

A community of sessile microorganisms attached to a surface, sharing nutrients and providing protection.

Question 10

What is the primary function of agar in most culture media?

Accepted Answer

Acts as a solidifying agent without being metabolized by most microbes.

Question 11

Which type of media is both selective and differential, and what makes it selective?

Accepted Answer

MSA (Mannitol Salt Agar); selects for salt-tolerant bacteria due to high NaCl concentration.

Question 12

Which equation correctly describes the exponential growth of bacteria, given an initial population $$N_0$$ and number of generations $$ng$$?

Accepted Answer

$$N(ng) = N_0$ 	imes 2$$^{ng}$$

Question 13

A culture starts with $$2 	imes 10^6$ bacteria per mL. After 1 hour, it reaches 8$$ 	imes $$10^6$$ bacteria per mL. What is the generation time?

Accepted Answer

$$30$$ minutes

Question 14

Which phase of the bacterial growth curve is characterized by equal rates of cell division and cell death?

Accepted Answer

Stationary phase

Question 15

Why is serial dilution often required when determining CFUs in a plate count?

Accepted Answer

To reduce the number of colonies to a countable range.

Question 16

Which method estimates bacterial numbers based on the probability of growth in multiple tubes?

Accepted Answer

Most probable number (MPN) method

Question 17

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity measurement

Question 18

Which adaptation allows thermophiles to survive at high temperatures?

Accepted Answer

Heat-stable proteins and long-chain saturated fatty acids in membranes.

Question 19

Which equation can be used to calculate the number of generations ($$ng) $$during exponential growth, given the total time ($$t) $$and generation time ($$G$$)?

Accepted Answer

$$ng = t / G$$

Microbial Growth: Physical and Chemical Requirements, Culture Techniques, and Quantitative Aspects

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