Chapter 9

Question 1

Process of diluting sample several times to prevent overgrowth on plates

Answer 1

Serial dilutions

Question 2

Microbial community that usually forms as slimy layer on surface

Answer 2

Biofilm

Question 3

What are the different ways that prokaryotes reproduce?

Answer 3

• Budding
• Binary fission
• Fragmentation

Question 4

What are the different phases of bacteria growth & what happens during those phases?

Answer 4

• Lag phase: time interval in bacterial growth curve during which there is no growth
• Log phase: period of bacterial growth or logarithmic increase in cell numbers
• Stationary phase: period in bacterial growth curve when number of cells dividing equals numbers of dying
• Death phase: period of logarithmic decrease in bacterial population

Question 5

What are the direct methods to measure growth and how they measure growth?

Answer 5

• Plate counts: method by determining number of bacteria in sample by counting number of CFUs on solid culture medium
• Filtration: bacteria filtered out of culture onto membrane; membrane transferred to media
• Most Probable Number (MPN): statistical determination of number of coliforms per 100 mL of water or 100 g of food
  Direct microscopic count: enumeration of cells by observation through microscope

Question 6

What are the indirect methods to measure growth and how they measure growth?

Answer 6

• Turbidity: cloudiness of suspension; measured using spectrophotometer
• Metabolic activity: assumes certain metabolic products are in proportion with population growth
• Dry weight: Fungus removed from media; filtered & dried in desiccator; then weighed

Question 7

Group of cells large enough to be seen without microscope

Answer 7

Colony

Question 8

Organism that can grow with oxygen

Answer 8

Obligate aerobes

Question 9

Organism that can grow with or without oxygen

Answer 9

Facultative anaerobes

Question 10

Organism that does not use & is killed by oxygen

Answer 10

Obligate anaerobes

Question 11

Organism that does not use oxygen but is not affected by its presence

Answer 11

Areotolerant anaerobes

Question 12

Organism that grows best in environment with less oxygen than us normally found in air

Answer 12

Microaerophiles

Question 13

Grow in acidic environments

Answer 13

Acidophiles

Question 14

Grow in basic environments

Answer 14

Alkaliphiles

Question 15

Cold loving

Answer 15

Psychrophiles

Question 16

Moderate-temperature loving

Answer 16

Mesophiles

Question 17

Heat loving; can grow at 50-60 degrees

Answer 17

Thermophiles

Question 18

Can grow in temperatures 80 degrees & above

Answer 18

Hyperthermophiles

Question 19

Introduction of microbes into medium

Answer 19

Inoculum

Question 20

Exact chemical composition is known

Answer 20

Chemically defined media

Question 21

Extracts & digests of yeasts, meat or plants

Answer 21

Complex media

Question 22

Suppress unwanted microbes & encourage desired microbes

Answer 22

Selective media

Question 23

Make it easy to distinguish colonies of different microbes

Answer 23

Differential media

Question 24

What are the chemical requirements for growth?

Answer 24

• Carbon
• Nitrogen
• Sulfur
• Phosphorus
• Trace elements
• Organic growth factors
• Oxygen

Question 25

What are the physical requirements for growth?

Answer 25

• Temperature
• pH
• Osmotic pressure