Paper 1 - aseptic Techniques Flashcards
Why do scientists require the use of aseptic techniques ?
Help prevent other microorganisms from the air and surfaces from contaminating cultures when they are being prepared.
Aseptic techniques- sterilising dishes and culture media.
sterilisation kills microorganisms.
petri dishes can be sterilised by autoclaving or heating to a high temperature.
Culture media (the substances that the microorganisms grow on, such as nutrient agar)
are sterilised by heating to a high temperature.
Aseptic techniques- sterilising incubating loops.
Hoop sterilised in a hot flame and then cooped, before using it to transfer microorganisms to the growth medium.
Aseptic techniques- sealing petri dishes and viles
The lid is secured to the dish with adhesive tape
to stop microonganinms from the air getting in.
Vials cotaining bacteria must be kept covered
for the same reason.
Why are petri dishes not completely sealed ?
This would encourage the growth of anaerobic bacteria - which are likely pathogens.
Why are bacteria cultured at higher temperatures in industry, than by human hand ?
When microorganisms are grown in industry,t hey are cultured at higher temperatures than 25 “C because they are not handled by people. The microorganisms grow more quickly at these higher temperatures, but
there is no risk that people will get infected by the bacteria.
Describe how you could Prepare a culture of microorganisms so that you could investigate the acton
of a plant exract on the microorganisms
(4marks)
The Petri dish and the growth medium must be sterilised
before use (1). The inoculating loop must be sterilised by
passing it through a fame and allowing it to cool. (1) 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. (1) After
the plant extract is added, the lid of the dish is secured with
adhesive tape to prevent contamination from the air. (1)
