Q: If a bacterial population has a generation time of 30 minutes, how many cells will there be after 3 hours if you start with 100 cells? Use the formula $$N = N_0$ \times 2^n$$, where $$n is $$the number of generations.

$$N = 100 \times 2^6$ = 6400$$ cells

Question 1

A patient’s wound is infected with a bacterium that grows optimally at $$37^\circ C$$, but can also grow at temperatures as low as $$10^\circ C$$ and as high as $$45^\circ C. $$Which category best describes this microorganism?

Accepted Answer

Mesophile

Question 2

Which of the following best explains why refrigeration at $$4^\circ C is $$effective for food preservation?

Accepted Answer

It slows the metabolic rate of most mesophilic bacteria, inhibiting their growth.

Question 3

A culture of bacteria is placed in a solution with a high concentration of salt. After some time, the cells shrink and the plasma membrane pulls away from the cell wall. What is this process called?

Accepted Answer

Plasmolysis

Question 4

Which of the following statements about halophiles is correct?

Accepted Answer

Obligate halophiles require high salt concentrations to grow.

Question 5

Which of the following is NOT considered an essential element required by most microorganisms?

Accepted Answer

Gold

Question 6

Trace elements are required by microorganisms in small amounts. Which of the following is a trace element?

Accepted Answer

Iron

Question 7

A bacterium that can grow in the presence or absence of oxygen, but grows better when oxygen is present, is classified as a(n):

Accepted Answer

Facultative anaerobe

Question 8

Why is molecular oxygen ($$O_2) $$considered toxic to some living cells?

Accepted Answer

It reacts to form toxic oxygen species such as superoxide ($$O_2$$^-$$) and hydrogen peroxide (H_2O_2$).

Question 9

Which enzyme do aerobic bacteria use to detoxify superoxide radicals ($$O_2$$^-$$)?

Accepted Answer

Superoxide dismutase

Question 10

A hospital-acquired infection is traced to a biofilm on a catheter. Which of the following best explains why biofilms are medically significant?

Accepted Answer

Biofilms protect bacteria from the host immune system and increase resistance to antibiotics.

Question 11

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

A bacterium divides into two genetically identical daughter cells after replicating its DNA.

Question 12

If a bacterial population has a generation time of 30 minutes, how many cells will there be after 3 hours if you start with 100 cells? Use the formula $$N = N_0$ 	imes 2^n$$, where $$n is $$the number of generations.

Accepted Answer

$$N = 100 	imes 2^6$ = 6400$$ cells

Question 13

During which phase of the bacterial growth curve are bacteria most susceptible to antibiotics that target cell wall synthesis?

Accepted Answer

Log (exponential) phase

Question 14

A laboratory technician isolates a bacterium that grows only at the bottom of a thioglycollate broth tube. Which term best describes this organism?

Accepted Answer

Obligate anaerobe

Question 15

Which of the following best describes acidophiles?

Accepted Answer

Microorganisms that grow optimally at pH below 5.5

Question 16

A bacterial culture is exposed to a hypertonic environment. What is the most likely effect on the cells?

Accepted Answer

Water will leave the cells, causing plasmolysis.

Question 17

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 18

A microaerophile is best described as an organism that:

Accepted Answer

Grows best at low oxygen concentrations.

Question 19

Which of the following is a real-world example of a biofilm causing a persistent infection?

Accepted Answer

Dental plaque on teeth leading to cavities

Question 20

Which of the following best describes the lag phase of the bacterial growth curve?

Accepted Answer

Cells are metabolically active but not dividing.

Microbial Growth and Environmental Factors – Chapter 6 Study Guide

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