Q: A bacterial culture is diluted 1:100, then 1:10, and 0.1 mL is plated. If 50 colonies are counted, what is the original concentration of bacteria per mL?

$$ \frac{50}{0.1 \times 1/100 \times 1/10} = 5,000,000 $$

Question 1

Which of the following best describes the effect of pH on microbial growth?

Accepted Answer

Extreme pH levels denature proteins and disrupt membrane integrity, inhibiting growth.

Question 2

A bacterial culture is diluted 1:100, then 1:10, and 0.1 mL is plated. If 50 colonies are counted, what is the original concentration of bacteria per mL?

Accepted Answer

$$ \frac{50}{0.1 	imes 1/100 	imes 1/10} = 5,000,000 $$

Question 3

Which phase of bacterial growth is characterized by rapid cell division and exponential increase in cell number?

Accepted Answer

Log (exponential) phase

Question 4

Which of the following best explains why biofilms are more resistant to antimicrobial agents than planktonic cells?

Accepted Answer

Biofilms produce extracellular polymeric substances that limit penetration of agents.

Question 5

Which chemical element is essential for the synthesis of nucleic acids and ATP in microorganisms?

Accepted Answer

Phosphorus

Question 6

A pure culture is defined as:

Accepted Answer

A culture containing only one species of microorganism.

Question 7

Which of the following is the correct sequence for the central dogma of molecular biology?

Accepted Answer

DNA $$ \rightarrow $$ RNA $$ \rightarrow $$ Protein

Question 8

Which method is most effective for sterilizing heat-sensitive medical equipment?

Accepted Answer

Ionizing radiation

Question 9

In the disk diffusion method, what does a large zone of inhibition indicate?

Accepted Answer

The antimicrobial agent is highly effective against the microorganism.

Question 10

Which of the following statements about mutations is correct?

Accepted Answer

Mutations can be beneficial, neutral, or harmful.

Question 11

Which process involves the transfer of DNA from one bacterium to another via a sex pilus?

Accepted Answer

Conjugation

Question 12

Which of the following is a characteristic unique to archaea compared to bacteria?

Accepted Answer

Ether-linked membrane lipids

Question 13

Which fungal reproductive structure is produced asexually?

Accepted Answer

Conidiospore

Question 14

Which of the following is a vector for disease transmission among arthropods?

Accepted Answer

Mosquito

Question 15

Which of the following best describes the lytic cycle of a bacteriophage?

Accepted Answer

The phage causes immediate destruction of the host cell by producing new viral particles.

Question 16

Which of the following is used to identify bacteria based on their antigen-antibody reactions?

Accepted Answer

Serological tests

Question 17

Which of the following is a method for detecting specific DNA sequences in a sample?

Accepted Answer

Southern blotting

Question 18

Which of the following is true about Mycobacterium tuberculosis?

Accepted Answer

It contains mycolic acid in its cell wall.

Question 19

Which of the following best describes the function of an operon in bacterial gene expression?

Accepted Answer

It is a group of genes regulated together by a single promoter.

Question 20

Which of the following is a correct description of budding in microorganisms?

Accepted Answer

A new cell forms as a small outgrowth from the parent cell.

Microbial Growth, Control, Genetics, Classification, and Diversity: Study Notes

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