Microbial Growth

Question 1

What is growth?

Answer 1

Growth is the increase in quantity of cellular components

Question 2

What changes during growth?

Answer 2

Cells increase in size
Number of Ribosomes increase
Duplication of Chromosomes
Partitioning of Chromosomes
Makes cell wall and plasma membrane

Question 3

Asexual reproduction is……..

Answer 3

binary fission

Question 4

Direct physical measurements

Answer 4

For cell mass

Dry/wet weight or volume

Question 5

Direct chemical measurements

Answer 5

For Cell Mass

Number of N or DNA in cell

Question 6

Indirect chemical measurements

Answer 6

For cell mass

Amount of CO2 or O2 produced/consumed

Question 7

Direct microscopic counting

Answer 7

For cell number

Uses slides called counting chambers. It can’t distinguish dead from living. Dense suspensions used but can have concentrated.

Question 8

Electronic counting chamber

Answer 8

For cell number

Counts number and size distribution of cells. Often used in eukaryotic cells eg blood cells.

Question 9

Indirect Counts

Answer 9

For cell number

Also known as plate counts. Spread suitable culture on agar plate. Will form colony forming units which is related to the number of viable bacteria.

Question 10

Indirect Counts

Advantages and Disadvantages

Answer 10

Advantages
- Sensitive so can theoretically detect a single cell

Disadvantages
- Only living cells can form a colony
clumps of colonies can look like just 1 colony
Difficult to categorize and count the number of bacteria in complex eco systems.

Question 11

Lag Phase

Answer 11

microbes are adjusting to the new substrate

Immediately after inoculation of the cells into fresh medium, the population remains temporarily unchanged. Although there is no apparent cell division occurring, the cells may be growing in volume or mass, synthesizing enzymes, proteins, RNA, etc., and increasing in metabolic activity.

Question 12

Exponential Growth Phase

Answer 12

microbes have acclimated to the conditions

Pattern of balanced growth -all the cells are dividing regularly by binary fission.. The Cells divide at a constant rate depending upon the composition of the growth medium and the conditions of incubation. The rate of exponential growth of a bacterial culture is expressed as generation time, also the doubling time of the bacterial population. Generation time (G) is defined as the time (t) per generation (n = number of generations).

Question 13

Stationary Phase

Answer 13

limiting substrate or electron acceptor limits the growth rate

Exponential growth cannot be continued forever in a batch culture
Population growth is limited by one of three factors: 1. exhaustion of available nutrients; 2. accumulation of inhibitory metabolites or end products; 3. exhaustion of space

Question 14

Decay Phase

Answer 14

substrate supply has been exhausted

If incubation continues after the population reaches stationary phase, a death phase follows.
Viable cell population declines. (Note, if counting by turbidimetric measurements or micro-scopic counts, the death phase cannot be observed.)
During the death phase, the number of viable cells decreases geometrically (exponentially), essentially the reverse of growth during the log phase.

Question 15

Closed systems = batch cultures

Answer 15

lack of input and output once inoculated. Discontinuous because environment and organisms changing continually

Question 16

Open Systems = Continuous state

Answer 16

can achieve steady state. Balanced input and output of growth substrates. Can be operated indefinitely.