4.1.1.6 Culturing Microorganisms

Question 1

How do prokaryotic cells replicate?

Answer 1

• binary fission

Question 2

What happens during binary fission?

Answer 2

• circular DNA and plasmid(s) replicate
• cell gets bigger
• circular DNA strands move to opposite ends of the cell
• cytoplasm behind to divide and new cell walls form
• cytoplasm divided and two daughter cells are produced
• each daughter cell has one copy of the circular DNA but can have variable number of copies of plasmid(s)

Question 3

What are the conditions in which bacteria can divide very quickly?

Answer 3

• warm environment
• lord of nutrients

Question 4

What happens if conditions become unfavourable when cells divide?

Answer 4

• the cells stop dividing
• eventually begin to die

Question 5

What is mean division time?

Answer 5

• average amount of time it takes for one bacterial cell to divide

Question 6

What can you work out from the mean division time?

Answer 6

• how many times it has divided in a certain amount of time
• number of cells produced

Question 7

How to work out number of cells produced?

Answer 7

• make sure both times are in same units
• divide total time that bacteria produced cells by mean division time which gives number of divisions
• multiply 2 by itself for the number of divisions to find how many cells produced

Question 8

Where are bacteria and some microorganisms grown/cultured?

Answer 8

• culture medium

Question 9

What does a culture medium contain?

Answer 9

• carbohydrates
• minerals
• proteins
• vitamins

Question 10

What types of culture medium can be used?

Answer 10

• nutrient broth solution
• solid agar jelly

Question 11

How will grown bacteria form on the surface of agar jelly?

Answer 11

• visible colonies
• spread out to give even covering

Question 12

How do you make an agar plate?

Answer 12

• got agar jelly poured into petri dish
• when cooked and set, inoculating loops/sterile dropping pipette and spread are used to transfer microorganisms evenly
• then they multiply

Question 13

What temperatures should cultures of microorganisms be kept at in schools?

Answer 13

• not above 25°C

Question 14

Why should cultures of microorganisms not be kept at above 25°C?

Answer 14

• harmful pathogens are more likely to grow above this temperature
• grow faster

Question 15

What is the clear area that forms around a disc on an agar plate when bacteria dies?

Answer 15

• zone of inhibition
• inhibition zone