Question 1

A bacterium is isolated from a deep-sea hydrothermal vent where the temperature is consistently above 80°C. Which classification best describes its temperature preference, and what adaptation is most likely present in its proteins?

Accepted Answer

Hyperthermophile; proteins with increased stability due to more ionic bonds

Question 2

A microbiologist wants to isolate Staphylococcus aureus from a mixed sample. She uses mannitol salt agar, which contains high salt and a pH indicator. What type of medium is this, and what does each component do?

Accepted Answer

Selective; high salt inhibits non-halophiles, and the pH indicator distinguishes fermenters

Question 3

A culture starts with 200 cells. If the cells divide every 40 minutes, how many cells will there be after 4 hours? Use the formula $$N = N_0$ 	imes 2^n.$$

Accepted Answer

25,600

Question 4

Which of the following best explains why most organisms cannot use atmospheric nitrogen ($$N_2) $$directly for growth?

Accepted Answer

They lack enzymes to break the triple bond in $$N_2$$

Question 5

A patient develops a persistent infection on a catheter despite antibiotic treatment. Which property of biofilms most likely contributes to this persistence?

Accepted Answer

Cells in biofilms grow slowly and are protected by an extracellular matrix

Question 6

Which group of organisms would you expect to find growing evenly throughout a tube of thioglycollate broth, regardless of oxygen presence?

Accepted Answer

Aerotolerant anaerobes

Question 7

A microbiologist is studying a bacterium that uses light for energy and organic compounds for carbon. How should this organism be classified?

Accepted Answer

Photoheterotroph

Question 8

Why does refrigeration preserve food but not sterilize it?

Accepted Answer

Refrigeration slows enzyme activity and membrane transport, delaying growth but not killing all microbes

Question 9

A bacterial culture is in the stationary phase of growth. Which of the following best describes what is happening in the culture?

Accepted Answer

The rate of cell division equals the rate of cell death

Question 10

A scientist wants to estimate the number of viable bacteria in a water sample where bacteria are scarce. Which method is most appropriate?

Accepted Answer

Membrane filtration

Question 11

Which of the following best distinguishes selective media from differential media?

Accepted Answer

Selective media inhibit some microbes; differential media show visible differences among those that grow

Question 12

A bacterium is classified as a facultative anaerobe. Which statement best describes its growth in the presence and absence of oxygen?

Accepted Answer

It grows better with oxygen but can grow without it by switching to fermentation or anaerobic respiration

Question 13

A culture begins with 80 cells and undergoes 4 generations. How many cells are present at the end? Use $$N = N_0$ 	imes 2^n.$$

Accepted Answer

1,280

Question 14

Which of the following is a trace element required by cells, and what is its typical role?

Accepted Answer

Iron; acts as an enzyme cofactor

Question 15

A bacterium is found growing in a highly acidic hot spring (pH 2). Which term best describes its pH preference?

Accepted Answer

Acidophile

Question 16

Why does a viable plate count use the term 'colony-forming unit' (CFU) instead of 'cell'?

Accepted Answer

A colony may arise from a single cell or a cluster of cells

Question 17

A researcher measures the turbidity of a bacterial culture to estimate cell density. Which statement is correct about this method?

Accepted Answer

It is an indirect method and does not distinguish between living and dead cells

Question 18

Which of the following best describes the main effect of a hypertonic environment on a bacterial cell?

Accepted Answer

Water leaves the cell, causing plasmolysis

Question 19

A chemostat is used in a laboratory to maintain a bacterial culture. What is the main advantage of using a chemostat?

Accepted Answer

It maintains cells in a steady physiological state by continuously adding fresh medium and removing used culture

Question 20

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

Accepted Answer

Log (exponential) phase

Microbial Nutrition and Growth: Study Guide and Key Concepts

Guida di studio - Domande di pratica

Study guide - Flashcard