Module 3 - Microbial Growth

Question 1

What are the four basic phases of bacterial growth?

Answer 1

• Lag phase
• Log phase
• Stationary phase
• Death phase

Question 2

What occurs during the lag phase of bacterial growth?

Answer 2

Period of little to no cell division; cells do not immediately reproduce but undergo intense metabolic activity

Question 3

What is another name for the log phase in bacterial growth?

Answer 3

Exponential growth phase

Question 4

What characterizes the log phase of bacterial growth?

Answer 4

Cells divide actively, and generation time reaches a constant minimum

Question 5

What happens during the stationary phase of bacterial growth?

Answer 5

Growth rate slows, number of deaths balances new cells, and population stabilizes

Question 6

What defines the death phase in bacterial growth?

Answer 6

Number of deaths exceeds new cells, leading to a decline until the population diminishes or dies out

Question 7

What is a batch culture?

Answer 7

Method of growing microorganisms in a closed system with nutrients provided only at the start

Question 8

What is a continuous culture?

Answer 8

Also known as open system; continuously supplies nutrients and removes waste products

Question 9

How do bacterial cells reproduce?

Answer 9

By binary fission, where one cell divides into two

Question 10

What is the basic equation for exponential bacterial growth?

Answer 10

N = N₀ * 2^n

Question 11

What does each symbol represent in the equation N = N₀ * 2^n?

Answer 11

• N: Final number of cells
• N₀: Initial number of cells
• n: Number of generations

Question 12

How can generation time be calculated?

Answer 12

Using a semilogarithmic plot where the slope represents the growth rate (k)

Question 13

What is the division rate (v) in microbial growth?

Answer 13

Reciprocal of the generation time; indicates how many generations occur per unit of time

Question 14

What is the optimum temperature for most pathogenic bacteria?

Answer 14

37 degrees Celsius

Question 15

What are psychrophiles?

Answer 15

Cold-loving microbes that grow within a temperature range of 0–20 degrees Celsius

Question 16

What are mesophiles?

Answer 16

Moderate temperature-loving microbes that grow between 25 and 40 degrees Celsius

Question 17

What are thermophiles?

Answer 17

Heat-loving microbes that can grow at temperatures between 55–80 degrees Celsius

Question 18

What role do heat shock proteins (HSPs) play in stress response?

Answer 18

Assist microbes in handling heat stress by refolding damaged proteins

Question 19

What are aerobic bacteria?

Answer 19

Bacteria that require oxygen for growth

Question 20

What are obligate aerobes?

Answer 20

Bacteria that can grow only in the presence of oxygen

Question 21

What are facultative aerobes?

Answer 21

Bacteria that can grow with or without oxygen; most pathogenic bacteria belong to this group

Question 22

What are obligate anaerobes?

Answer 22

Bacteria that can grow only in the absence of oxygen

Question 23

What is the pH range for most pathogenic bacteria?

Answer 23

Between pH 7.2 and 7.6

Question 24

What is osmotic pressure in relation to microbial growth?

Answer 24

Factors such as osmotic pressure and salt concentration affect the growth of bacteria

Question 25

What are osmophilic bacteria?

Answer 25

Organisms requiring high osmotic pressures

Question 26

What happens to bacteria in a hypertonic solution?

Answer 26

Causes osmotic withdrawal of water, leading to plasmolysis

Question 27

What are barophiles?

Answer 27

Microbes that have adapted to high pressures, such as those found at the ocean's bottom

Question 28

What is the effect of radiation on cells?

Answer 28

Causes damage to DNA, leading to mutations and cell destruction

Question 29

How do bacterial endospores respond to ionizing radiation?

Answer 29

They are extremely resistant to the harmful effects

Question 30

What types of radiation cause mutations and destruction of the cell’s DNA?

Answer 30

X-rays and gamma rays ## Footnote These types of ionizing radiation can lead to significant cellular damage.

Question 31

Which type of bacterial cells are extremely resistant to the harmful effects of ionizing radiation?

Answer 31

Bacterial endospores ## Footnote Endospores can withstand extreme environmental conditions, including radiation.

Question 32

What were vegetative cells thought to be in relation to ionizing radiation?

Answer 32

Quite susceptible ## Footnote Vegetative cells are the active form of bacteria, as opposed to dormant endospores.

Question 33

What is the purpose of DNA repair mechanisms in microorganisms?

Answer 33

To repair damage caused by radiation ## Footnote These mechanisms help maintain cellular integrity and functionality.

Question 34

Name one DNA repair mechanism used by microorganisms.

Answer 34

Photoreactivation ## Footnote This mechanism involves the direct reversal of DNA damage caused by UV light.

Question 35

What is another DNA repair mechanism besides photoreactivation?

Answer 35

Excision repair ## Footnote This mechanism removes damaged DNA and replaces it with the correct sequence.

Question 36

What is the SOS response in microorganisms?

Answer 36

A DNA repair mechanism activated in response to extensive DNA damage ## Footnote This mechanism allows cells to repair DNA damage that might otherwise lead to cell death.