Ch.4

Question 1

Pure Culture

Answer 1

• population of cells derived from a single cell
• allows study of a single species
• Organisms may behave differently than in nature
• Only about 1% of microorganisms can be cultured
• Pure culture obtained using aseptic technique: Minimizes accidental introduction of other organisms

Question 2

Which technique is used to isolate bacteria from a mixed culture into a pure culture?

Answer 2

Streak-plate method

Question 3

Which polysaccharide derived from Red Seaweed is used to solidify media for bacterial growth?

Answer 3

• Agar used to solidify medium

Question 4

Why is agar preferred over gelatin?

Answer 4

for its non-nutritive qualities, which allow for bacterial growth without being digested

Question 5

In the growth curve of a bacterial population, at which phase are the bacteria rapidly increasing?

Answer 5

Exponential (log) phase:
- Cells divide at constant rate
– Generation time measured
– Most sensitive to antibiotics

Question 6

During which phase of the bacterial growth curve does the total number of viable (live) cells decline?

Answer 6

Death phase:
- Total number of viable cells decreases at constant rate
- Exponential, but slower than cell growth

Question 7

thermophile

Answer 7

• 45 C to 70 C
• love hot tempertures –> common in hot springs and compost heaps

Question 8

What happens to proteins inside of bacteria that cannot survive these types of conditions?

Answer 8

• Proteins of thermophiles resist denaturing
• Thermostability comes from amino acid sequence
• Number and position of bonds that determine structure

Question 9

obligate aerobe

Answer 9

organism requires O2 to grow

Question 10

Facultative aerobes

Answer 10

use O2, but don’t require it

Question 11

Obligate anaerobes

Answer 11

cannot use O2

Question 12

Aerotolerant anaerobes

Answer 12

obligate fermenters (can grow in O2, but they don’t use it)

Question 13

How do high concentrations of salt and sugar in food help preserve food?

Answer 13

• All microorganisms require water for growth
• Dissolved salts, sugars make water unavailable to cell
• If solute concentration is higher outside of cell, water diffuses out (osmosis)
• Some microbes withstand or even require high salt

Question 14

Which are the 6 major elements that are needed to build organic molecules and biological bodies?

Answer 14

Carbon
Hydrogen
Nitrogen
Oxygen
Phosphorus
Sulfur

Question 15

What is the definition of “growth factors” when it comes to bacterial growth?

Answer 15

organic molecules that an organism cannot synthesize; must be present in the environment
- Growth factor requirements reflect biosynthetic capabilities
– Most E. coli strains synthesize all cellular components from glucose; no growth factors needed

Question 16

What do the prefixes “Photo” and “Chemo” mean when it comes to microbial nutrition?

Answer 16

Photo = use light as an energy source
Chemo = gain energy from inorganic compounds

Question 17

Phototrophs

Answer 17

• Phototrophs obtain energy from sunlight
  – Plants, algae, photosynthetic bacteria

Question 18

Chemotrophs

Answer 18

• Chemotrophs extract energy from chemicals
  – Mammalian cells, fungi, many types of prokaryotes extract energy from organic molecules

Question 19

What do the prefixes “Hetero” and “Auto” mean when it comes to microbial nutrition?

Answer 19

Hetero = organisms incapable of making their own food from light or inorganic compounds
Auto = an organism that is self-nourishing or capable of generating its own food.

Question 20

Photoautotrophs

Answer 20

energy from sunlight; carbon from CO

Question 21

Photoheterotrophs

Answer 21

energy from sunlight; carbon from organic compounds

Question 22

Chemolithoautotrophs

Answer 22

energy from inorganic compounds; carbon from CO2

Question 23

Chemoorganoheterotrophs

Answer 23

energy and carbon from organic compounds

Question 24

What is the function of “selective” media?

Answer 24

• Selective media inhibit growth of certain species in a mixed sample, while allowing growth of species of interest