Chapter 4: Microbial Growth - Influence of Environmental Factors (oxygen, pH, Osmotic pressure)

Question 1

Is oxygen a requirement for growth in all microorganisms?

Answer 1

• no
• only required by some organisms
• can be extremely toxic to others

Question 2

Name the different types of bacteria based on their oxygen consumption requirements (5)

Answer 2

• obligate aerobes
• Facultative anaerobes
• obligate anaerobes
• Microaerophiles
• aerotolerant anaerobes

Question 3

What are obligate aerobes? (2)

Answer 3

• require oxygen for respiration
• for energy generation

Question 4

What are facultative anaerobes?

Answer 4

• can use oxygen for respiration but can also grow in its absence

Question 5

What are obligate anaerobes?

Answer 5

• cannot use oxygen and are killed by it

Question 6

What are microaerophiles?

Answer 6

• require oxygen in low amounts, but killed by high concentrations

Question 7

What are aerotolerant anaerobes?

Answer 7

• cannot use oxygen but are not killed by it

Question 8

What is pH?

Answer 8

• measurement of acidity or alkalinity

Question 9

What pH do most bacteria grow?

Answer 9

• pH 6.5-7.5

Question 10

What are two classifications of bacteria based on pH?

Answer 10

• acidophiles
• alkaliphiles

Question 11

What are acidophiles?

Answer 11

• bacteria that grow at very low pH

Question 12

What are alkaliphiles?

Answer 12

• bacteria that grow at high pH

Question 13

What is osmotic pressure?

Answer 13

• the movement of solvent molecules across a semi-permeable barrier

Question 14

How is water moving through the cytoplasmic membrane an example of osmotic pressure?

Answer 14

• water will move from areas of high concentration to areas of low concentration

Question 15

What is a hypertonic solution, and where will water move if the cell is placed in a hypertonic solution? (3)

Answer 15

• high solute concentration (ex. salt or sugar)
• water flows out of the cell
• cell dries up - plasmolysis

Question 16

What is a hypotonic solution, and where will water move if a cell is placed in it? (3)

Answer 16

• low solute concentration
• water flows into cell
• cell bursts - osmotic lysis

Question 17

What is an isotonic solution?

Answer 17

• condition where solute concentration on outside of cell is equal to that inside the cell

Question 18

What is osmotic pressure important in?

Answer 18

• food preservation
  ex. salted fish, honey

Question 19

Osmotic pressure: What are extreme halophiles? (2)

Answer 19

• bacteria adpated to life in high salt concentrations
• requires up to 30% NaCl
  ex. bacteria in the dead sea