Bacterial Growth Curve

Question 1

The definition of growth

Answer 1

1. increase in cell size

2. increase in cell numbers leading to overall increase in biomass

Question 2

what is the most widely used measure of bacterial growth?

Answer 2

to determine the number of cells at any given moment

Question 3

what two techniques can be used to determine the number of cells?

Answer 3

1. plate count technique

2. spectrophotometric method

Question 4

limits of plate count technique?

Answer 4

is able to measure a very small number of cells per ml

Question 5

when to use spectrophotometric method?

Answer 5

requires >100,000 cells per ml and is easier to use

Question 6

How does growth begin?

Answer 6

begins with a cell adjusting to a new environment and new nutrients

Question 7

What happens to a cell before cell division when it begins adjusting to its new environment?

Answer 7

it expresses enzymes
generates ATP
and increases in size

Question 8

what is a lag phase of growth?

Answer 8

This is the initial growth phase where bacterial concentration is low
There are plenty of nutrients so the bacteria are actively synthesizing proteins and they are growing quickly
The cell divisions occurs a little more rapidly and the next faster yet.

Question 9

What is exponential/log phase?

Answer 9

Bacterial cell density is high and the nutrient levels are still high enough to support rapid growth here.
The division rate here will reach a constant.

Question 10

Why is it called exponential/log phase?

Answer 10

each cell divides into two, thus the number of cells increases exponentially

Question 11

What is stationary phase?

Answer 11

bacteria are at a very high cell density and the nutrients have been mostly used up.
the decline in nutrients/increase of metabolic products results in the division rate slowing down.
This causes the cell number to reach a constant.
this constant number may be the result of an end of division altogether
NUMBER OF CELL DEATHS = NUMBER OF NEW CELLS FORMED
the cell number may remain stable for a long time with only a slow decline

Question 12

What is death phase?

Answer 12

cell number declines exponentially.

Question 13

True or false, cell numbers decline to zero

Answer 13

False, it rarely does

Question 14

why is it useful to calculate teh rate of growth during the exponential phase?

Answer 14

because this is the most reproducible measure of the bacterial response to the environmental conditions

Question 15

What is generation time and which phase is this in?

Answer 15

Cells divide at a constant interval and its in the exponential phase.

Question 16

What does the length of the interval of the generation time depend on?

Answer 16

1. bacterial species
2. type of medium
3. temperature
4. pH

Question 17

What is generation time also known as? why is it called that? give an example

Answer 17

doubling time; because the population of cells doubles over one generation. for example, one cell of E.coli placed in a complex medium will divide every 20 minutes. after 1 hour of growth, (three generations) that one cell will have become Eight. ( 1->2 2->4 4->8).

Question 18

how would a linear increase of division occur?

Answer 18

if the increase in cell number over time rose by a fixed amount after every generation

Question 19

how to calculate for the number of generations that an exponential culture undergoes in a given time period?

Answer 19

n = log10(Nt - No)/0.301
No = number of cells at start of the period
Nt= number of cells at the end of the period

Question 20

Limits of exponential growth?

Answer 20

exponential growth occurs only for a short period when all nutrients are in full supply and the concentration of waste products has not become a limiting factor

Question 21

What can the rate of exponential growth be expressed as

Answer 21

it can be expressed as the mean growth rate constant (k)
Which is the number of generations per unit time
(generations/hour)

Question 22

True or false: we need to know the generation time to calculate the mean growth rate constant

Answer 22

False we dont need to know it

Question 23

What do we need to know to calculate the mean growth rate constant?

Answer 23

1. the number of organisms at time zero (No)

2. number of organisms after incubation time (Nt)

Question 24

Formula to calculate the mean growth rate constant?

Answer 24

k = n/t = (log10Nt - Log10No)/0.301t

Question 25

How to calculate for the mean generation time? (g) in hours

Answer 25

its 1/k

Question 26

what od600 value do we add our antibiotic?

Answer 26

0.4