Culturing Microorganisms

Question 1

Why is the “agar” needed for the bacteria practical to work?

Answer 1

• The bacteria use the agar for respiration, releasing energy.

Question 2

Name the equipment used to spread the bacteria.

Answer 2

The equipment used to spread bacteria is known as an inoculating loop.

Question 3

Name the equipment used to grow bacteria on.

Answer 3

The equipment used to grow the bacteria is known as an agar plate.

Question 4

Explain why the bacteria is spread across the dish multiple times.

Answer 4

• The bacteria is spread multiple times to ensure it is spread evenly across the plate.

Question 5

Why don’t you tape the agar plate down all the way around? (2 reasons)

Answer 5

• You don’t tape all of the agar plate down so that oxygen can enter, needed for respiration.
• Anaerobic conditions encourage harmful bacteria.

Question 6

How do you switch on the safety flame on a bunsen burner?

Answer 6

• To switch on the safety flame, you must close the hole.

Question 7

How do you switch on the roaring (blue) flame on a bunsen burner?

Answer 7

• To switch on the roaring flame, you must open the hole.

Question 8

What is the best temperature for bacteria to culture at?

Answer 8

• The best temp for bacteria to culture is 25- 30 degress celcius.

Question 9

What would happen if the bacteria is culturing at a very high temperature?

Answer 9

• Harmful pathogens could be produced.
• Enzymes become denatured, bacteria dies.

Question 10

What does this practical show us?

Answer 10

The aseptic practical shows us how quickly bacteria divide.

Question 11

What would happen if the bacteria is culturing at a very low temperature?

Answer 11

• Bacteria reproduce slower
• Longer to see results

Question 12

What is meant by “aseptic technique?”

Answer 12

• Aseptic technique is steps taken to avoid contamination.

Question 13

What is meant by “sterilisation?”

Answer 13

• Sterilisation is to destroy all microbes.

Question 14

Why is it important that you rinse any excess antispetic from the paper disc?

Answer 14

• It is important that you rinse any antiseptic off to avoid splashing.

Question 15

What is an “incubator”?

Answer 15

• An “incubator” is basically an oven!! where the bacteria is grown.

Question 16

What is the benefit of the petri dish being flat?

Answer 16

• The flat petri dish provides a large surface area for the microbes to grow on.

Question 17

Why do we need uncontaminated cultures?

Answer 17

• We want to see the effect of antibiotics on SPECIFIC bacterias.

Question 18

What temperature are cultures often incubated at in school laboraties?

Answer 18

• In school laboraties, cultures are incubated at 25 degree celcius.

Question 19

Give 2 safety precautions for this practical.

Answer 19

• Keep away from flames
• Wash hands afterwards –> avoid disease.

Question 20

What are the 2 ways to culture bacteria?

Answer 20

• Nutrient broth solution
• Agar gell plate.

Question 21

Why is the agar plate placed upside down in an incubator?

Answer 21

• This is so the moisture doesn’t fall on the bacteria, affecting the distribution.
• Some areas will have less bacteria than others*

Question 21

Why do you need to ensure your surface is clean before you start the practical?

Answer 21

• Kill any unwanted organisms that could contaminate the culture.

Question 22

What are the 8 steps to investigating the effect antibiotics have on bacterial growth?

Answer 22

1.) Clean bench with disinfectant
2.) Draw sections on dish
3.) Sterilize inoculating loop
4.) Open plate near flame and spread bacteria
5.)Place discs containing antibiotic on plate using forecps
6.) Seal with selotape
7.) Incubate at 25 degress celcius for 48 hrs.
8.) Measure the diameters of clear zone

Question 23

How do you calculate the area of the zone of inhibition?

Answer 23

πr²

Question 24

Give 3 ways you can improve results.

Answer 24

• Repeat –> reliable
• Work quicker –> minimse contamination.
• Keep bunsen burner next to plate.

Question 25

Why do you calculate a mean for the diameter of the clear zone?

Answer 25

• Because the clear zone isn’t always perfectly circular.

Question 26

Why is the lid opened at an angle in this practical?

Answer 26

• Lid is opened at angle so no microbes enter.

Question 27

What are the main steps to aseptic technique ?

Answer 27

1.) Clean the bench to avoid contamination
2.) Sterilise agar plate (rid of microbes)
3.) Sterilize incolulating loop with bunsen burner (rid of microbes)
4.) Open lid at angle, avoid microbes from entering
5.) Spread the bacteria on plate EVENLY
6.) Seal shut with selotape
7.) Incubate at 25 degrees

Question 28

Why do we selotape shut the petri dish?

Answer 28

• Stops unwanted microbes from entering.
• Stops microbes from leaving

Question 29

Q.)

Why do some areas on agar plate have no bacteria on them after disinfectant has been placed?

Answer 29

• Bacteria have been killed/ destroyed.