*Aseptic techniques*

• Step;

  Petri dish and culture media must be sterilised before use. This is done by UV light or autoclave.

  Why this is done;

  If not done then petri dish is likely to be contaminated with other microorganisms. They will compete with desired bacteria for nutrients and space. They could also be/become harmful, through mutations.
• Step;

  inoculating loop is streilised, by passing it through a flame.

  Why this is done;

  It kills unwanted bacteria. Which if they got into petri dish then would compete for space and nutrients.
• Step;

  Lid of petri dish is sealed (not completely) with tape.

  Why this is done;

  It stops airborne microorganisms from contaminating the petri dish. However it should not be sealed fully, because it would cause harmful anaerobic bacteria to grow.
• Step;

  Petri dish is stored upside down.

  Why this is done;

  Prevents the condensation from the lid to land on agar surface, which will disturb growth.
• Step;

  Culture should be incubated at 25 degrees.

  Why this is done;

  If it is incubated at higher temperature, which is closer to the temperature of the human body (37), it could make bacteria more harmful to humans because our body temperature would be their optimum. And lower temperatures they would not be able to grow.
• Step;

  Keep bunsen burner on near area where working

  Why this is done;

  It creates a convection current (hot air rises, cools, condenses and falls, repeat) in the air, which prevents microorganisms from landing on petri dish and contaminating it