Required Practical 6

Question 1

State 6 antiseptic techniques

Answer 1

● Wipe down surfaces with ​antibacterial cleaner,​​ both ​before and after experiment.
● Use a ​Bunsen burner​​ in the work space so that ​convection currents​​ draw microbes away from the culture.
● Flame the wire hoop​​ before using it to transfer bacteria.
● Flame the neck of any bottles​​ before using them to prevent any bacteria entering the vessel (air moves out so unwanted organisms don’t move in).
● Keep all vessels containing bacteria​ ​​open for the minimum amount of time.
● Close windows and doors​​ ​​to limit air currents.

Question 2

Why is bacteria incubated at 25 degrees

Answer 2

To prevent the growth of pathogens which occur at higher temperatures

Question 3

How can you compare the effectiveness of different bacteria applied to to the same bacteria

Answer 3

Measure the diameter and calculate the area of the zone of inhibition on the clear agar

Question 4

What does the zone of inhibition indicate

Answer 4

Indicates the bacteria killed off by the antibiotic

The larger the zone the more effective the antibiotic

Question 5

Why should the lid not be completely taped to the Petri dish

Answer 5

To allow oxygen to enter the Petri dish preventing the growth of harmful anaerobic bacteria

Question 6

Why should he incubator be well below human body temperature

Answer 6

It reduces the risk of growing microbes that are pathogenic to humans

Question 7

What is the reasoning for using aseptic techniques

Answer 7

It minimises the risk of bacteria from the air contaminated the agar plate

Question 8

Why is the temperature not exceeded past 25

Answer 8

A higher temperature could be closer to the optimum temperature for bacteria that cause human disease

Question 9

(b)Give one reason why the student used aseptic technique.

Answer 9

This technique minimises the risk of bacteria from the air contaminating the agar plate.

Question 10

The student incubated the agar plates at 25°C. Suggest one reason why she did not incubate them at a higher temperature.

Answer 10

This technique minimises the risk of bacteria from the air contaminating the agar plate.

Question 11

A higher temperature would be closer to human body temperature. Your answer needs to give a possible reason for the student using a lower temperature.

Answer 11

A higher temperature could be closer to the optimum temperature for bacteria that cause human disease. This would be dangerous for the student.