EXAM 2- Chapter 7- part 3

Question 1

What does growth refer to?

Answer 1

population growth rather than growth of individual cells

Question 2

Cells can grow in what kinds of systems?

Answer 2

open or closed

Question 3

When is growth curve observed?

Answer 3

When microorganisms are cultivated in batcch culture
Closed system

Question 4

Four phases of growth curve

Answer 4

lag phase
exponential/log phase
stationary phase
death phase

Question 5

What is the growth curve?

Answer 5

graphical representation of the change in bacterial population size over time
Semi-log graph

Question 6

Lag phase

Answer 6

cell synthesizing new components
replenishes spent materials and adapts to new environment

Question 7

Log phase

Answer 7

rate of growth and division is contant and maximal

Question 8

What phase is population most uniform?

Answer 8

log phase

Question 9

Stationary phase

Answer 9

population growth eventually stops in a closed system
rate of division=rate of death

Question 10

What are the reasons for stationary phase?

Answer 10

nutrient limitation
oxygen availability
toxic waste accumulation

Question 11

Death phase

Answer 11

number of viable cells declines exponentially
logrithmic death

Question 12

Starvation response- stationary phase

Answer 12

cells activate survival strategies to remain in stationary phase

Question 13

What are strategies used to remain in stationary phase?

Answer 13

morphological changes
Rpos protein assists RNA polymerase in transcribing genes for starvation proteins

Question 14

starvation proteins

Answer 14

bind to different macromolecules to prevent damage

Question 15

What are morphological changes associated with starvation response?

Answer 15

endospore formation
decreasing in size- smaller cells require less nutrients
express flagella- can move to find new food source

Question 16

What triggers sporulation?

Answer 16

nutrient deprivation

Question 17

What are hypothesis for why some cells do not die in death phase?

Answer 17

Viable but not culturable
programmed cell death

Question 18

Viable but not culturable (VBNC)

Answer 18

cells are alive but dormant
can resuscitate upon change in environment/correct conditions

Question 19

Programmed cell death

Answer 19

fraction of the population is genetically programed to die
When cells die they release things that remaining cells can use

Question 20

Why are VBNC cells problematic?

Answer 20

assays tend to be based on ability to culture
VBNC can be problematic for assays used for food contamination- contamination can go unnoticed

Question 21

Prolonged stationary phase

Answer 21

prolonged decline in cell numbers
takes place after traditional death phase
Get waves of increasingly adapted cells

Question 22

How long can cells hang out in prolonged stationary phase?

Answer 22

months to years

Question 23

Balanced growth

Answer 23

have everything they need in perfect timing
cellular constituents manufactured at constant rates

Question 24

Example of balanced growth

Answer 24

log growth

Question 25

Unbalanced growth

Answer 25

rate of synthesis of cell components vary relative to each other

Question 26

When does unbalanced growth occur?

Answer 26

change in nutrient level

Question 27

T/F cells can shift back to balanced growth

Answer 27

TRUE once cells adjust to change in environmental change they can shift back

Question 28

Unbalanced growth: Shift-up

Answer 28

poor medium to rich medium

Question 29

What happens to growth during a shift up?

Answer 29

undergoes a period of log growth but faster

Question 30

Unbalanced growth: shift-down

Answer 30

rich medium to poor medium

Question 31

What happens to growth during shift down?

Answer 31

undergoes period of log growth but slower

Question 32

What does unbalanced growth demonstrate?

Answer 32

Microbial growth is under precise coordinated control Microorganisms respond quickly to changes in environment

Question 33

What are 3 things we can find using growth curve?

Answer 33

generation time growth rate growth yield

Question 34

Generatio time/ doubling time

Answer 34

the time to double the population during exponential phase

Question 35

Growth rate

Answer 35

number of generations per unit of time slope of the line

Question 36

growth yield

Answer 36

maximum population density/the amount of cellular material produced

Question 37

How to calculate doubling time?

Answer 37

1. look at the number of cells: want to find points where cell count doubles 2. look at time of first number and time of second (doubled) number 3. difference between the two is generation time

Question 38

What is the importance of a semi log scale

Answer 38

linear scale will not make log phase obvious semi-log allows exponential phase to be a straight line makes it easier to find slope

Question 39

What is continuous culture and what does it do?

Answer 39

growth in an open system maintains cells in log phase at a constant biomass concentration for extended periods

Question 40

Two types of continuous culture systems

Answer 40

Chemostat Turbidostat

Question 41

What is the importance of continuous culture?

Answer 41

Can study growth at very low nutrient concetration Study interactions under conditions resembling aquatic environments Food and industrial microbiology- can exploit and harvest byproducts

Question 42

Closed system

Answer 42

nothing else is being added or remove has four phases of growth

Question 43

Open system

Answer 43

maintians log phase for extended periods

Question 44

Chemostat

Answer 44

rate of incoming medium= rate of removal Flow rate is set constant 1 essential nutrient is kept at limited quantity

Question 45

What keeps chemostat system in steady state?

Answer 45

1 essential nutrient kept at limited quantity

Question 46

Turbidostat

Answer 46

photocell- regulates the flow rate of media to maintain a predetermined turbidity No limited nutrients- all in excess Dilution rate varies

Question 47

What keeps turbidostat in log phase?

Answer 47

variation of dilution rate to keep predetermined turbidity

Question 48

T/F turbidostat operates best at low dilution

Answer 48

FALSE- best at high dilution If absorbance is too high machine will increase dilution opposite for low absorbance