Requirements for microbial growth – Part 1 Flashcards
how is Microbial growth & reproduction
achieved?
Binary fission & the cell cycle
what does growth mean?
increase in the number of cells
why does multiplication (growth) occur>
occurs as a result of growth – cell grows until it divides into 2 new cells
what is generation time?
the time taken for a population to double
what are the steps in binary fission?
dna replication
cell elongation
spetum formation
completion of septum with formation of distinct walls
cell seperation
what is the cell cycle>
time it takes a newly formed cell to replicate its DNA, elongate & divide
what are the 2 phases in the cell cycle?
c phase
d phase
what is the c phase
when the cell’s genome undergoes replication to form 2 identical daughter DNAs
what is the d phase?
daughters’ DNA separates & moves towards opposite ends of the elongating cell
construction of the cytoplasmic membrane & cell wall at the midpoint of the cell
how long does the c phase take?
takes approx. 40 min for the one round of DNA replication
how long does the d phase take?
20 min period between the termination of DNA replication & cell division
how can a species have a generation time of 20 min if the DNA replication takes 40 min?
Replication of the replicated DNA begins again before the C phase is finished
how is population growth measured?
estimated by the change in cell number or biomass per unit time
how is species maintained?
through continued growth of the population
define growth rate?
change in cell number or cell mass per unit time
what are the Four main phases in a typical growth curve:
lag
expoential
stationary
death
what do we mean by lag phase?
Cells synthesising essential constituents for growth
what do we mean by exponetial phase?
Cell numbers double with each generation
Rate of increase in cell number initially slow but increases at an ever faster rate
what do we mean by staionary phase?
Depletion of essential nutrient(s) /or waste product accumulation
No net increase/decrease in cell number (growth & death balanced)
what do we mean by death phase?
Death rate > rate of reproduction
what is Microbial heterogeneity?
refers to the diversity and variability observed among microorganisms within a given environment.
summarise endospore formation:
Resistant to heat & harsh chemicals, can lie dormant
produced inside a cell
endospore-forming bacteria during sporulation
Exhaustion of key nutrient
what are extremophiles?
microrganisms that can thrive and survive extreme physical or chemical conditions
what are the physhical requirments include for microbial growth
Temperature
pH
Osmotic effects
Oxygen
Pressure
which factors can affect bacterial growth?
Extend lag phase
Decrease log phase
Premature stationary/death phase
how does temp affect micobial growth?
T rises, reactions proceed more rapidly & growth becomes faster
but above a certain temp proteins denature & cell functions fall sharply to zero
how does ph affect microbial growth?
if pH goes out of range then the enzymes start to denature
Enzyme function & nutrient transport into the cell can goes wrong
what ph does Acidophiles grow at
Grow at pH 0–5
what ph does Neutrophiles grow at?
Grow at pH 5–8
what ph does Alkalophiles grow at?
9–11
what is a postive water balance?
tendenacy for water to move into the cell
the cytoplasm and osmotic effects?
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
what happens when a cell is in a an evrionment with a higher external solute concentration
water will flow out unless the cell has a mechanism to prevent this
what happens when a cell is an environment with high external solute concetrations (effects)
Cell’s plasma membrane shrinks, growth inhibited
what does Osmotolerant mean>
grow over wide range of osmotic concentrations
what are Osmophiles
live in environments high in sugar as solute
what are Halophiles
– require high salt concentration
what are Halotolerant organisms
do not require salt but can grow in its presence
what are Nonhalophiles
not able to grow in salty environments
what are Xerophiles?
able to grow in very dry environments
