Q: A bacterial culture has a generation time of 30 minutes. If you start with 1,000 cells, how many cells will there be after 3 hours, assuming unlimited resources and no cell death? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 1,000 \times 2^6$ = 64,000$$

Question 1

A bacterium is isolated from a hot spring with a temperature of $$75^\circC. $$Which classification best describes this organism based on its temperature preference?

Accepted Answer

Thermophile

Question 2

Which of the following best explains why oxygen is toxic to some microorganisms?

Accepted Answer

Oxygen leads to the formation of reactive oxygen species (ROS) that damage cellular components.

Question 3

A bacterial culture has a generation time of 30 minutes. If you start with 1,000 cells, how many cells will there be after 3 hours, assuming unlimited resources and no cell death? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 1,000 	imes 2^6$ = 64,000$$

Question 4

Which of the following best describes a chemoheterotroph?

Accepted Answer

Uses organic compounds as both energy and carbon sources.

Question 5

A scientist wants to isolate a pure culture of a bacterium from a mixed sample. Which method is most appropriate for obtaining isolated colonies?

Accepted Answer

Streak plate method

Question 6

Which of the following statements about plasmids is correct?

Accepted Answer

Plasmids are circular DNA molecules that can carry antibiotic resistance genes.

Question 7

During DNA replication, which enzyme is responsible for synthesizing the RNA primer required to initiate DNA synthesis?

Accepted Answer

Primase

Question 8

A mutation changes a codon from UAU (tyrosine) to UAA (stop codon). What type of mutation is this, and what is its likely effect on the protein?

Accepted Answer

Nonsense mutation; results in premature termination of translation

Question 9

Which of the following best describes the function of restriction enzymes in recombinant DNA technology?

Accepted Answer

They cut DNA at specific nucleotide sequences.

Question 10

A patient is infected with a bacterium that can grow in the presence or absence of oxygen, but grows better when oxygen is available. How would you classify this organism?

Accepted Answer

Facultative anaerobe

Question 11

Which of the following best explains why high concentrations of salt or sugar are effective preservatives?

Accepted Answer

They create a hypertonic environment, causing water to leave microbial cells and inhibiting growth.

Question 12

Which of the following is a correct statement about the lag phase of a bacterial growth curve?

Accepted Answer

Cells are adapting to the new environment and preparing for growth.

Question 13

Which of the following best describes the process of bacterial conjugation?

Accepted Answer

Direct transfer of DNA between bacteria through a pilus

Question 14

A scientist uses PCR to amplify a specific DNA sequence. Which of the following is an advantage of PCR?

Accepted Answer

It can amplify DNA from a single molecule to millions of copies rapidly.

Question 15

Which of the following best describes the role of the CRISPR-Cas system in bacteria?

Accepted Answer

It provides adaptive immunity against foreign genetic elements such as viruses.

Question 16

A bacterial cell is placed in a solution with a much higher solute concentration than the cytoplasm. What is the most likely outcome for the cell?

Accepted Answer

The cell will lose water and shrink (plasmolysis).

Question 17

Which of the following best describes a frameshift mutation?

Accepted Answer

A mutation caused by insertion or deletion of nucleotides, altering the reading frame.

Question 18

Which of the following is a real-world application of recombinant DNA technology?

Accepted Answer

Production of human insulin by genetically engineered bacteria

Question 19

Which of the following best describes the difference between defined (synthetic) and complex media?

Accepted Answer

Defined media contain exact amounts of pure chemicals, while complex media contain extracts with unknown composition.

Question 20

A scientist is analyzing DNA samples using restriction fragment length polymorphism (RFLP). Which step is essential for this technique?

Accepted Answer

Cutting DNA with restriction enzymes and separating fragments by gel electrophoresis

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