Microbiology core practical

Question 1

Independent variable

Answer 1

Plant material - type of plant extract

Question 2

Control

Answer 2

(read question) - no plant extract

Question 3

Dependant variable

Answer 3

Zone of Inhibition

Question 4

How do you measure zone of inhibition

Answer 4

Measure diameter of zone of inhibition. Calculate area using pi * radius squared

Question 5

Which organism variables should be controlled

Answer 5

Same species of bacteria, same volume of bacteria - use graduated pipette

Question 6

Which environmental variables should be controlled

Answer 6

Same incubation temperature - 25 degrees celsius

Question 7

Which procedural variables should be controlled

Answer 7

Incubation time - 24 hours
Same surface area of paper disc - use hole punch
Same volume of plant extract - use micro pipette

Question 8

What repeats should be carried out?

Answer 8

5 repeats for each plant extract to find mean and exclude anomalies

Question 9

How is the investigation made reliable?

Answer 9

Repeats

Question 10

How is the investigation made valid?

Answer 10

Control, repeats, large sample size, controlled variables

Question 11

Purpose of aseptic technique

Answer 11

Prevents contamination of plate with microbes from other sources

Question 12

Why are plates incubated upside down?

Answer 12

To stop condensation dripping on bacteria which stops them growing

Question 13

How is the investigation made safe?

Answer 13

Aseptic technique
Incubation at 25 degrees
Allowing oxygen into plates - stops spread of pathogenic anaerobic bacteria