Lecture 18 Microbial Growth

Question 1

Microbial growth

Answer 1

an increase in the number of cells, not cell size

Question 2

What bacterial growth occurs through

Answer 2

binary fission

Question 3

Steps of binary fission

Answer 3

1. cell elongates & DNA is replicated
2. cell wall and plasma membrane constrict; DNA gets pulled to two ends
3. cross-wall forms, completely separating the two DNA copies
4. cells separate

Question 4

True or False: bacterial cells can age

Answer 4

TRUE

Question 5

Four stages of bacterial growth

Answer 5

lag phase, log phase, stationary phase, and death phase

Question 6

Lag phase

Answer 6

intense preparation for population growth with NO increase in population

Question 7

Log phase

Answer 7

exponential/logarithmic increase in population

Question 8

Stationary phase

Answer 8

period of equilibrium; deaths equal to production of new cells

Question 9

Death phase

Answer 9

population decreases at a logarithmic rate

Question 10

Growth phase with a highly variable length

Answer 10

lag phase

Question 11

Growth phase with a short length

Answer 11

log phase

Question 12

Best growth phase for experiments

Answer 12

log phase (cells are most active)

Question 13

What occurs inside the cell during the lag phase

Answer 13

adaption to new medium; re-synthesis of damaged cell constituents; turning genes on/off

Question 14

calculation to determine the number of bacteria in the fifth-generation

Answer 14

2^5 = 32

Question 15

Why do we graph in log instead of exponential?

Answer 15

better representation; fits the graph better as exponential gets too large too quickly

Question 16

During what growth stage are endospores produced?

Answer 16

stationary phase

Question 17

What is growth limited by during the growth stage?

Answer 17

nutrient availability, toxic metabolites, and limited space

Question 18

Dying cells =

Answer 18

dividing cells (viable count doesn’t change)

Question 19

True of False: generation time varies by species of bacteria

Answer 19

TRUE

Question 20

Generation time

Answer 20

the time it takes a bacterium to do one binary fission (aka doubling time)

Question 21

Formula to calculate the number of generations a culture has undergone

Answer 21

log # of cells (end) - log # of cells (start) / 0.301

Question 22

Formula to calculate the generation time for a population

Answer 22

hrs x 60 min/hr / number of generations

Question 23

Three methods used to measure growth

Answer 23

direct microscopic count, turbidity measurement, viable cell count

Question 24

Drawbacks of direct microscopic count

Answer 24

doesn’t distinguish dead and live cells, difficult to see small and unstained cells, labor intensive, difficult to count motile bacteria

Question 25

Turbidity measurement

Answer 25

measures how much light gets through compared to known controls

Question 26

Drawbacks of turbidity measurements

Answer 26

dead cells are counted, sensitivity is limited (must be less than 10^7 cells/ml)

Question 27

Advantages of turbidity measurements

Answer 27

fast, doesn’t destroy cells

Question 28

Instrument used for turbidity measurements

Answer 28

spectrophotometer

Question 29

Drawbacks of viable cell counts

Answer 29

pipetting error, dilution error, viability of culture, poor mixing, clumps appearing as a single colony

Question 30

CFU

Answer 30

colony forming unit; each colony that can be counted on a plate

Question 31

Viable cell counts require between ____ CFU on a plate

Answer 31

30-300

Question 32

Formula for CFU/mL

Answer 32

number of colonies x reciprocal of dilution