Intro To Prokaryotes #3

Question 1

what is the generation (doubling) time ?

Answer 1

time required for the population to double in size

Question 2

how can microbial growth be measured ? (2)

Answer 2

by changes in number of cells in a population, or by measuring the changes in mass of population

Question 3

what is turbidity ?

Answer 3

of a culture, often expressed as optical density at a particular wavelength (OD600nm)

cloudiness of a liquid

Question 4

What are the 2 types of elements of life?

Answer 4

1. Macroelements (macronutrients)
2. Micronutrients (trace elements)

Question 5

What are the micronutrients required in trace amounts?

Answer 5

Mn, Zn, Co, Mo, Ni, Cu (serve as enzymes cofactors)

Question 6

What are the macroelements required in large amounts?

Answer 6

C, H, O, N, P, S (found in organic molecules)
Ca, K, Fe, Mg (cations = enzyme catalysis)

Question 7

What is a prototroph?

Answer 7

a microorganism that requires the same nutrients as most of the naturally-occurring members of its species

Question 8

What is an auxotroph?

Answer 8

a mutated prototroph that is no longer able to synthesise a molecule necessary for growth & reproduction, molecule needs to be supplied, unable to produce growth factors it needs

Question 9

what are growth factors ?

Answer 9

organic compounds, essential cell components that cell can’t synthesise, supplied by env

Question 10

What are the 3 classes of growth factors?

Answer 10

1. Amino Acids
2. Purines & Pyrimidines
3. Vitamins

VAP = classes of growth factors

Question 11

what are two types of media (classified according to chemical composition)

Answer 11

defined (synthetic), complex

Question 12

what are 3 types of media (classified according to physical nature)

Answer 12

• liquid,
• semisolid,
• solid

Question 13

what are 4 types of media (classified according to function)

Answer 13

• supportive (general purpose),
• enriched,
• selective,
• differential

Question 14

what is minimal medium ?

Answer 14

a special kind of defined medium containing minimal nutrient requirements for growth

Question 15

what are peptones ?

Answer 15

protein hydrolysates prepared by partial digestion of various protein sources

Question 16

what are extracts ?

in terms of media

Answer 16

aqueous extracts, usually of beef or yeast

Question 17

what is agar?

Answer 17

sulphated polysaccharide used to solidify liquid media; most microorganisms can’t degrade it

Question 18

what is supportive (general purpose) media ?

(with examples)

Answer 18

support the growth of many types of microorgs

(e.g. tryptic soy agar, nutrient agar)

Question 19

what is enriched media ?

(with an example)

Answer 19

general purpose media supplemented by blood or other special nutrients

e.g. blood agar

Question 20

what is blood agar?

media categories, and what is it used for

Answer 20

• both an enriched & differential medium,
• used to isolate fastidious orgs & detect haemolytic activity

Question 21

what are selective media ?

with an example

Answer 21

• favour the growth of some microorganisms and
• inhibit the growth of others

(e.g. macconkey agar)

Question 22

how does macconkey agar work?

Answer 22

selects for gram- negative bacteria by inhibiting the growth of gram-positive bacteria

Question 23

what is differential media ?

provide 2 examples with explanations

Answer 23

distinguish between different groups of microorganisms based on biological characteristics

e.g. blood agar (haemolytic vs non-haemolytic bacteria)

e.g. macconkey agar (see colour difference between colonies of lactose fermenters vs lactose non fermenters) = is a selective & differential medium (only grows gram-negative)

Question 24

what are microaerophiles ?

Answer 24

requires 2-10% O2

Question 25

what is the difference between facultative anaerobes & aerotolerant anaerobes?

Answer 25

facultative = don’t require O2 but grow better in its presence

aerotolerant = grow with or without O2, not killed by O2

Question 26

what are 2 viable counting methods?

Answer 26

• spread technique
• pour plate technique

Question 27

describe what you would do to get a viable count of a culture

Answer 27

1. spread diluted sample over solid agar surface OR mixed with agar and poured into petri dish
2. incubate
3. determine number of organisms by counting the number of colonies multiplied by the dilution factor

results expressed as CFU (colony forming units)

Question 28

what are 3 methods to measure cell mass?

Answer 28

• dry weight
• quantity of a particular cell constituent (useful if amount of substance in each cell is constant)
• turbidometric methods (light scattering by cells) = best one