Requirements for microbial growth – Part 1

Question 1

how is Microbial growth & reproduction
achieved?

Answer 1

Binary fission & the cell cycle

Question 2

what does growth mean?

Answer 2

increase in the number of cells

Question 3

why does multiplication (growth) occur>

Answer 3

occurs as a result of growth – cell grows until it divides into 2 new cells

Question 4

what is generation time?

Answer 4

the time taken for a population to double

Question 5

what are the steps in binary fission?

Answer 5

dna replication
cell elongation
spetum formation
completion of septum with formation of distinct walls
cell seperation

Question 6

what is the cell cycle>

Answer 6

time it takes a newly formed cell to replicate its DNA, elongate & divide

Question 7

what are the 2 phases in the cell cycle?

Answer 7

c phase
d phase

Question 8

what is the c phase

Answer 8

when the cell’s genome undergoes replication to form 2 identical daughter DNAs

Question 9

what is the d phase?

Answer 9

daughters’ DNA separates & moves towards opposite ends of the elongating cell
construction of the cytoplasmic membrane & cell wall at the midpoint of the cell

Question 10

how long does the c phase take?

Answer 10

takes approx. 40 min for the one round of DNA replication

Question 11

how long does the d phase take?

Answer 11

20 min period between the termination of DNA replication & cell division

Question 12

how can a species have a generation time of 20 min if the DNA replication takes 40 min?

Answer 12

Replication of the replicated DNA begins again before the C phase is finished

Question 13

how is population growth measured?

Answer 13

estimated by the change in cell number or biomass per unit time

Question 14

how is species maintained?

Answer 14

through continued growth of the population

Question 15

define growth rate?

Answer 15

change in cell number or cell mass per unit time

Question 16

what are the Four main phases in a typical growth curve:

Answer 16

lag
expoential
stationary
death

Question 17

what do we mean by lag phase?

Answer 17

Cells synthesising essential constituents for growth

Question 18

what do we mean by exponetial phase?

Answer 18

Cell numbers double with each generation
Rate of increase in cell number initially slow but increases at an ever faster rate

Question 19

what do we mean by staionary phase?

Answer 19

Depletion of essential nutrient(s) /or waste product accumulation
No net increase/decrease in cell number (growth & death balanced)

Question 20

what do we mean by death phase?

Answer 20

Death rate > rate of reproduction

Question 21

what is Microbial heterogeneity?

Answer 21

refers to the diversity and variability observed among microorganisms within a given environment.

Question 22

summarise endospore formation:

Answer 22

Resistant to heat & harsh chemicals, can lie dormant
produced inside a cell
endospore-forming bacteria during sporulation
Exhaustion of key nutrient

Question 23

what are extremophiles?

Answer 23

microrganisms that can thrive and survive extreme physical or chemical conditions

Question 24

what are the physhical requirments include for microbial growth

Answer 24

Temperature
pH
Osmotic effects
Oxygen
Pressure

Question 25

which factors can affect bacterial growth?

Answer 25

Extend lag phase
Decrease log phase
Premature stationary/death phase

Question 26

how does temp affect micobial growth?

Answer 26

T rises, reactions proceed more rapidly & growth becomes faster

but above a certain temp proteins denature & cell functions fall sharply to zero

Question 27

how does ph affect microbial growth?

Answer 27

if pH goes out of range then the enzymes start to denature
Enzyme function & nutrient transport into the cell can goes wrong

Question 28

what ph does Acidophiles grow at

Answer 28

Grow at pH 0–5

Question 29

what ph does Neutrophiles grow at?

Answer 29

Grow at pH 5–8

Question 30

what ph does Alkalophiles grow at?

Answer 30

9–11

Question 31

what is a postive water balance?

Answer 31

tendenacy for water to move into the cell

Question 32

the cytoplasm and osmotic effects?

Answer 32

cytoplasm has a higher solute (dissolved substances such as salt, sugar) concentration than the surrounding environment, thus the tendency is for water to move into the cell

Question 33

what happens when a cell is in a an evrionment with a higher external solute concentration

Answer 33

water will flow out unless the cell has a mechanism to prevent this

Question 34

what happens when a cell is an environment with high external solute concetrations (effects)

Answer 34

Cell’s plasma membrane shrinks, growth inhibited

Question 35

what does Osmotolerant mean>

Answer 35

grow over wide range of osmotic concentrations

Question 36

what are Osmophiles

Answer 36

live in environments high in sugar as solute

Question 37

what are Halophiles

Answer 37

– require high salt concentration

Question 38

what are Halotolerant organisms

Answer 38

do not require salt but can grow in its presence

Question 39

what are Nonhalophiles

Answer 39

not able to grow in salty environments

Question 40

what are Xerophiles?

Answer 40

able to grow in very dry environments