Aseptic techniques Flashcards
Why are aseptic techniques needed?
to prevent other microorganisms in the air and surfaces from contaminating cultures when they are being prepared
sterilising dishes and culture media
sterilisation kills microorganisms
- petri dishes can be sterilised by heating to a high temperature
- culture media (substances that microorganisms grow on) can be heated as well
sterilising inoculating loops (used to transfer microorganisms)
sterilised in a hot flame and then cooled
sealing petri dishes
the lid is secured to the dish with adhesive tape to stop microorganisms from the air getting in
vials containing bacteria must be kept covered for the same reason
Why is the petri dish not completely sealed?
it would encourage the growth of anaerobic bacteria, which are likely to be pathogens
Cultures of microorganisms should be incubated at a maximum temperature of 25C in school laboratories. Explain why. [2]
temperatures higher than this encourage rapid growth in bacteria
this includes pathogenic bacteria which are harmful to humans
Give three ways in which cultures of microorgansims can easily be contaminated with other microorganisms during preparation [3]
blown in from the air
transferred by touch
in the culture media
on the equipment
Describe fully how you would prepare a culture of microorganisms so that you could investigate the action of a plant extract on the microorganisms [4]
the petri dish and the growth medium must be sterilised before use
the inoculating loop must be sterilised by passing it through a flame and allowing it to cool
the loop is then dipped into the bacterial culture and used to inoculate the growth medium in the petri dish, keeping the dish as well covered as possible to reduce contamination
after the plant extract is added, the lid of the dish is secured with adhesive tape to prevent contamination from the air
