Question 1

Which of the following best explains why most bacteria do not grow in highly salted foods such as pickles or salted fish?

Accepted Answer

The high salt concentration creates a hypertonic environment, causing plasmolysis in bacterial cells.

Question 2

A bacterium is isolated from a hot spring where the temperature is consistently 80°C. Which classification best describes this organism based on its temperature preference?

Accepted Answer

Hyperthermophile

Question 3

A microbiologist is culturing a fastidious bacterium that requires many vitamins and amino acids. Which type of medium should be used to ensure its growth?

Accepted Answer

Chemically defined medium

Question 4

Which of the following best describes the function of superoxide dismutase (SOD) and catalase in aerobic bacteria?

Accepted Answer

They detoxify reactive oxygen species such as $$O_2$$^-$$ and H_2O_2$.

Question 5

A patient with a urinary catheter develops a persistent infection. Which of the following is the most likely explanation?

Accepted Answer

Biofilms have developed on the catheter, protecting bacteria from antibiotics and the immune system.

Question 6

Which of the following best describes a facultative anaerobe?

Accepted Answer

An organism that can grow with or without oxygen, using aerobic respiration when oxygen is present and fermentation when it is absent.

Question 7

A sample of raw milk is diluted in a 1:10 series. $$0.1 mL of $$the third dilution is plated, and after incubation, $$50$$ colonies are counted. What is the original concentration of bacteria in the milk sample?

Accepted Answer

$$50,000$$ cells/mL

Question 8

Which of the following best explains why a bacterial colony does not grow to fill the entire Petri plate?

Accepted Answer

Nutrients become depleted and waste products accumulate, limiting further growth.

Question 9

Which of the following methods is best for culturing obligate anaerobes on Petri plates?

Accepted Answer

Using an anaerobic jar with a chemical catalyst to remove oxygen.

Question 10

A bacterial culture has a generation time of $$30$$ minutes. If you start with $$1$$ cell, how many cells will there be after $$3$$ hours, assuming exponential growth and no lag phase?

Accepted Answer

$$64$$

Question 11

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

Accepted Answer

It is a component of DNA, RNA, ATP, and phospholipids.

Question 12

Which of the following statements about biofilms is FALSE?

Accepted Answer

Biofilms are easily removed by standard disinfectants.

Question 13

Which of the following best describes a selective medium?

Accepted Answer

A medium that suppresses the growth of unwanted microbes while encouraging the growth of desired microbes.

Question 14

Which of the following methods for measuring bacterial growth does NOT distinguish between live and dead cells?

Accepted Answer

Direct microscopic count

Question 15

A microbiologist wants to estimate the number of bacteria in a water sample using a statistical method. Which technique should be used?

Accepted Answer

Most probable number (MPN) method

Question 16

Which of the following best explains why fastidious organisms require enriched media for growth?

Accepted Answer

They lack the enzymes to synthesize many essential organic compounds.

Question 17

Which of the following is a correct description of the lag phase in a bacterial growth curve?

Accepted Answer

Cells are metabolically active but not dividing; they are adapting to new conditions.

Question 18

Which of the following best describes the function of agar in microbiological media?

Accepted Answer

It acts as a solidifying agent that is not metabolized by most bacteria.

Question 19

A microbiologist is working with a pathogen that requires a biosafety level 3 (BSL-3) laboratory. Which of the following precautions is most appropriate?

Accepted Answer

Use of biosafety cabinets to prevent airborne transmission.

Question 20

Which of the following best describes the streak plate method?

Accepted Answer

A technique used to isolate pure colonies from a mixed bacterial sample.

Microbial Growth: Physical and Chemical Requirements

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