Question 1

Which type of microorganism is most likely to be found growing in a hot spring with temperatures above 80°C, as shown in the image of deep-sea hydrothermal vents?

Accepted Answer

Hyperthermophiles

Question 2

Refer to the graph showing growth rates of microorganisms at different temperatures. Which group of bacteria is most likely to cause food spoilage in refrigerated foods?

Accepted Answer

Psychrotrophs

Question 3

A bacterial culture is placed in a medium with a high salt concentration. What is the most likely outcome for most bacteria, and which term describes this process?

Accepted Answer

Plasmolysis due to hypertonic environment

Question 4

Which equation represents the conversion of superoxide radicals to hydrogen peroxide and oxygen, a reaction catalyzed by superoxide dismutase?

Accepted Answer

$$O_2$$^- + $$O_2^- + 2H$$^+ \rightarrow H_2O_2 + $$O_2$$

Question 5

Why are hyperthermophiles that grow at temperatures above 100°C seemingly limited to oceanic depths?

Accepted Answer

The high pressure at oceanic depths prevents water from boiling, allowing growth at high temperatures.

Question 6

Which phase of bacterial growth is characterized by intense metabolic activity but no increase in population size?

Accepted Answer

Lag phase

Question 7

A culture medium contains peptone, beef extract, sodium chloride, and agar. Which type of medium is this?

Accepted Answer

Complex medium

Question 8

Which method is best for isolating a pure culture from a mixed bacterial sample?

Accepted Answer

Streak plate method

Question 9

A bacterial population doubles every 30 minutes. If you start with 1 cell, how many cells will there be after 3 hours?

Accepted Answer

64

Question 10

Which type of bacteria would grow only at the bottom of a tube of solid growth medium, as shown in the oxygen effect table?

Accepted Answer

Obligate anaerobes

Question 11

Which of the following is NOT a chemical requirement for microbial growth?

Accepted Answer

Light

Question 12

What is the main advantage of using phosphate salts as buffers in growth media, besides controlling acidity?

Accepted Answer

They supply essential phosphorus for nucleic acids and ATP.

Question 13

Which type of media would you use to encourage the growth of a desired microbe present in very small numbers?

Accepted Answer

Enrichment culture

Question 14

A bacterial suspension is added to a Petroff-Hausser cell counter. If 14 cells are counted in a square with a volume of $$1/1,250,000 ml$$, what is the concentration of cells per ml?

Accepted Answer

17,500,000

Question 15

Which of the following is a reason why primitive civilizations used food preservation techniques that rely on osmotic pressure?

Accepted Answer

To inhibit microbial growth by causing plasmolysis

Question 16

Which equation represents the breakdown of hydrogen peroxide into water and oxygen, a reaction catalyzed by catalase?

Accepted Answer

$$2\ H_2O_2 \rightarrow 2\ H_2O + O_2$

Question 17

Which of the following is NOT a characteristic of biofilms?

Accepted Answer

They always consist of a single species.

Question 18

Which method is best for measuring the dry weight of filamentous bacteria?

Accepted Answer

Dry weight method

Question 19

Which biosafety level requires sealed, negative pressure laboratories and double HEPA filtration of exhaust air?

Accepted Answer

BSL-4

Question 20

Which term describes bacteria that can grow via fermentation or anaerobic respiration when oxygen is not available, but prefer aerobic conditions?

Accepted Answer

Facultative anaerobes

Fundamentals of Microbial Growth: Physical and Chemical Requirements, Culture Methods, and Growth Measurement

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