Chapter 6

Question 1

What does the term “colony” refer to in microbiology?

Answer 1

In microbiology, “colony” refers to groups of cells that are large enough to be seen without a microscope.

Question 2

Define “population” in microbiology.

Answer 2

In microbiology, a “population” refers to billions of cells of the same species.

Question 3

Name some physical requirements for microbial growth.

Answer 3

Physical requirements for microbial growth include temperature, pH, and osmotic pressure.

Question 4

What are the chemical requirements for microbial growth?

Answer 4

Chemical requirements for microbial growth include sources of CHONPS, trace elements, and organic growth factors. Microbes can also form biofilms.

CHONPS(carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur)

Question 5

What are the three primary temperature groups for microbial growth, and what do they prefer?

Answer 5

The three primary temperature groups for microbial growth are:

1. Psychrophiles: Cold-loving microbes. Grows at 0 but optimum is 15 (0-15 celsius)
2. Mesophiles: Microbes that thrive at moderate temperatures. (25-45 celsius)
3. Thermophiles: Heat-loving microbes. (50-60 celsius)

Other temperatures are:
Psychotrophs Grows at 0 but optoimum is 20-30 celsius.
Hyperthermofiles (80 celsius or higher)

Mesophiles are the most common pathogen found in humans.

Question 6

What pH does bacteria like to grow at?
What pH does mold/yeast like to grow at?
What pH do acidphiles like to grow at?

Answer 6

• Bacteria pH: 6.5-7.5
• Molds/Yeast: 5-6
• Acidphiles: 2 or below

Mold/Yeast grow at a more acidic pH compared to bacteria.

Question 7

What are halophiles and why do other bacteria normally not survive in those conditions?

Answer 7

Halophiles that require salt for growth. They grow in bodies of salt water like oceans.
Other bacteria do no do well in salty environments because water will leave the cell through osmosis and the cell with shrivel up and die (plasmolysis).

Question 8

What nutrients are required for a bacteria cell’s survival?

Answer 8

• Carbon
• Nitrogen
• Sulfur
• Phosphourus
• Trace elements
• Oxygen

Trace elements are small minerals like: Iron, Copper, Zinc. This is essential for enzymes.

Question 9

How can oxygen be toxic in the evironment and how does our body counter the toxic oxygen?

Answer 9

• Oxygen can be toxic because of superoxide radicals or superoxide anions. Superoxide dismustase is an enzyme can counter the toxic oxygen.
• Peroxide anion is a toxic form of hydrogen peroxide, so catalase and peroxidase counter it.

Question 10

There are some microbes that CAN and CAN’T grow in the presence of oxygen, what are they classified as? What are their names?

Answer 10

• Obligate aerobes: Only aerobic growth; oxygen required
• Facultative anaerobes: Both aerobic and anaerobic growth; greater growth in presence of oxygen
• Obligate anaerobes: Only anaerobic growth; growth ceases in presence of oxygen
• Aerotolerant anaerobes: Only anaerobic growth; but growth continues in presence of oxygen
• Microaerophiles: Only aerobic growth; oxygen required in low concentration

Question 11

Most bacteria have the ability to produce their own growth factors. Some bacteria can’t. For those that can’t produce their own growth factors, what essential compounds will they be missing out on?

Answer 11

• Certain vitamins, amino acids, purines & pyrimidines

Question 12

What is biofilm?

Answer 12

Thin slimy layer encasing a bacteria that adheres to a surface. This allows cell to cell communication, sharing of nutrients, shield to antibiotics.

Question 13

How do we measure bacterial growth?

Answer 13

Through generations. Most bacteria take 1-3 hours to split into a new generation. Others can take 24 hours. Log scale is used to measure bacteria because they multiply so much.

Question 14

Microbial growth occurs in four stages, what are they?

Answer 14

1. Lag phase: Little or no cell division
2. Log phase: exponential growth
3. Staionary phase: #new cells = #dead cells
4. Death phase: #deaths > #new cells