Bacterial Growth

Question 1

What is the independent variable?

Answer 1

Concentration of antiseptic or
Type of antiseptic

Question 2

What is the dependant variable?

Answer 2

Zone of inhibition (mm2)

Question 3

What is the first step?

Answer 3

Sterilise the desk, wash your hands and set up a Bunsen burner to reduce the amount of airborne and other bacteria finding their way into the petridish. This reduces contamination that could skew the results.

Question 4

What is the second step?

Answer 4

Label the Petri dish since once the bacteria has grown it will be difficult to identify which concentration it is.

Question 5

What is the third step?

Answer 5

Place forceps in Bunsen flame for a couple seconds to sterilise and reduce the risk of cross contamination.

Question 6

What is the fourth step?

Answer 6

Twist off each antibiotic disc and gently place on corresponding section of agar jelly. Open and close as quickly as possible to reduce the risk of airborne bacteria contaminating the Petri dish.

Question 7

What is the fifth step?

Answer 7

Tape the Petri dish closed leaving some air gaps since bacteria need the oxygen to grow.

Question 8

What is the sixth step?

Answer 8

Incubate at 25-27° for 2 days to allow bacteria to grow

Question 9

What is the seventh step?

Answer 9

Calculate the zone of inhibition of each antibiotic disc using the equation (pi)(radius)2

Question 10

How should the Petri dish be stored?

Answer 10

Upside down so moisture doesn’t drip down and disturb colonies