2) steralise the inoculating loop used to transfer microorganisms to the agar by heating it in a red hot bunsen flame , then leave it to cool
3) dip the cool steralised loop into the suspension of bacteria you want to grow then use it to make zig zag streaks across the surface of the agar
4) secure the lid of the petri dish with short pieces of tape
5) label the petri dish clearly and place it in an incubator at no more than 25 °C
6) after a few days . examine the surface of agar
stage 3 involves dipping the cool steralised loop into the bacteria you want to use . We then use the innoculating loop to make zig zag streaks across the surface of the agar . Here we should :
tilt the lid of the petri dish to keep out unwanted microbes
we also have to close the lid as quickly as possible to avoid conatimiantion
stage four involves securing the lif of the petri dish with a short piece of tape to
stop microorganisms from the air contaminating your culture and to stop microbes from your culture from escaping into the air , however we musnt seal all the way around the edge
what equipment do you need for culturing microorganisms
a sterile petri dish containing a layer of sterile nutrient agar jelly
culture of harmless bacteria
inoculating loop
bunsen burner
marker pen or label
sealing tape
explain why agar is suitable as a culture medium for growing bacteria
we can steralise it without affecting it
microbes cannot digest agar so it is not used up as they grow
it supplies nutrients and moist conditions to the microbes to enable them to grow
what temperature does agar melt and why is this an advantage
it melts at 98°C so it can be poured into plates it then solidifies at 44°C
what is meany by aseptic
something that is clear of microorganisms
give 3 ways in which microbiological equipment and media can be steralised
autoclave
ultraviolet
ionising radiation
explain why the agar plates are cultured in the incubator at 25°C
because it is at the lower end of the ideal conditions , this allows bacteria to grow , however harmful bacteria needs a higher temperature so will not grow at this temperature
explain why the loop needs to be cooled before picking up the microbes
the heat from the wire may kill the microbes
suggest why the lid of the petri dish is not removed completly whne introducing the microorganisms