4.1.1.6 Culturing Microorganisms
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How do prokaryotic cells replicate?
• binary fission
What happens during binary fission?
• 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)
What are the conditions in which bacteria can divide very quickly?
• warm environment • nutrient high
What happens if conditions become unfavourable when cells divide?
• the cells stop dividing • eventually begin to die
What is mean division time?
• average amount of time it takes for one bacterial cell to divide
What can you work out from the mean division time?
• how many times it has divided in a certain amount of time • number of cells produced
How would you work out the number of cells divided?
• 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
Where are bacteria and some microorganisms grown/cultured?
• culture medium
What does a culture medium contain?
• carbohydrates • minerals • proteins • vitamins
What types of culture medium can be used?
• nutrient broth solution • solid agar jelly
How will grown bacteria form on the surface of agar jelly?
• visible colonies • spread out to give even covering
How will bacteria grow in nutrient broth solution?
• it involves making a suspension of bacteria to be grown • mixing with sterile nutrient brother • stoppering flask with cotton wool to prevent air from contaminating it • shaking regularly to provide oxygen for growing bacteria
How do you make an agar plate?
• 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
What temperatures should cultures of microorganisms be kept at in schools?
• not above 25°C
Why should cultures of microorganisms not be kept at above 25°C?
• harmful pathogens are more likely to grow above this temperature • grow faster
What is the clear area that forms around a disc on an agar plate when bacteria dies?
• zone of inhibition • inhibition zone