prokaryotes- growth requirements Flashcards
what is growth?
the orderly increase in all the components of a cell, that is going on all of the time
what are the phases of growth?
lag phase, log (exponential) phase, stationary phase, death (decline) phase
what is the lag phase?
no growth occurs. cells are adapting to their new environment.
in this phase of growth enzymes can be synthesised, metabolism is adjusted and damage is repaired.
what is the log (exponential) phase?
rapid cell growth occurs and cell number doubles at regular intervals.
primary metabolites are produced.
what is the stationary phase?
there is no net change in population size as the rate of cell division equals the rate of cell death.
secondary metabolites are produced.
what is the death (decline) phase?
the rate of cell death overtakes the rate of cell division.
cells die due to the build up of toxic waste, lack of nutrients, and in aerobic microbes a lack of oxygen.
what happens to the growth curve in unfavourable conditions?
the log phase is not as steep as the growth rate would slow as there is less energy available for growth and reproduction because cell respiration is reduced.
the stationary phase would begin at a lower level of cells as the maximum size of the population would be less.
the death phase would begin earlier as the numbers of dying bacterial would overtake new cells being produced at an earlier stage.
if bacteria could form endospores it would do so as levels of oxygen are depleted.
what are bacterial endospores?
formed by Bacillus and Clostridium
not reproductive structures
highly resistant structures that allow bacteria to survive periods when the environment is hostile to growth.
temperature for growth
microorganisms can grow in a wide range of temperatures
microorganisms depend on water as a solvent for nutrients, frozen or boiling water inhibits their growth.
psychrophiles, psychrotrophs, mesophiles, and thermophiles.
psychrophiles
grow best at low temperatures
psychrotrophs
grow below 25ºC
able to grow at low temperatures but prefer moderate temperatures
mesophiles
grow best at or near room and body temperature
most bacteria, especially those living in association with warm-blooded animals.
thermophiles
grow above 40ºC
show a wide variation in optimum and maximum temperatures
adaptation in temperature
as temperature increases the membrane becomes more fluid
as temperature decreases, rigidity increases
enzymes will be adapted to operate at each enzymes optimum temperature.
psychrophilic > have a membrane that contains unsaturated fatty acids to increase fluidity at low temperatures
thermophilic > have a membrane with long-chain saturated fatty acids that will be thermostable
pH for growth
most bacteria require near neutral conditions for optimal growth, with a minimum and maximum pH between 4 and 9
some microorganisms change the pH of their environment by producing by-products during growth, they can change conditions such that the environment can no longer tolerate their growth.
