Binary fission & cultivating bacteria
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36 Terms
What is binary fission?
Simple cell division in prokaryotic cells where one cell splits into two identical cells
What type of cells use binary fission?
Prokaryotic cells (e.g. bacteria)
Steps of binary fission
Circular DNA and plasmids replicate
The cell grows and DNA strands move to opposite ends (poles)
The cytoplasm begins to divide and new cell walls form
The cytoplasm divides producing two daughter cells
What do daughter cells contain after binary fission
One copy of circular DNA and possibly different numbers of plasmids
What conditions increase the rate of binary fission
Warm temperature and lots of nutrients
What happens if conditions are unfavourable in bacteria growth
Cells stop dividing and may die
What is mean division time
The average time it takes for one bacterial cell to divide into two
How do you calculate number of bacteria after divisions
Number of cells = 2^number of divisions
How do you find number of divisions
Total time ÷ mean division time
What is a culture medium
A substance containing nutrients used to grow microorganisms
What nutrients are needed in a culture medium
Carbohydrates, minerals, proteins and vitamins
What is agar
A jelly-like substance used to grow bacteria in Petri dishes
What is a colony
A visible group of microorganisms growing on agar
What is an inoculating loop
A tool used to transfer microorganisms
Why must equipment be sterilised
To kill unwanted microorganisms and prevent contamination
How is an inoculating loop sterilised
By passing it through a flame
Why is the lid of a Petri dish taped lightly
To prevent contamination while allowing oxygen in
Why are Petri dishes stored upside down
To stop condensation dripping onto agar
Why are cultures kept below 25°C in schools
To reduce growth of harmful pathogens
Why are higher temperatures used in industry
To increase growth rate of microorganisms
What is an antibiotic
A substance that kills bacteria or inhibits their growth
What is an antiseptic
A substance that kills microorganisms on living tissue
How do you test antibiotics on bacteria growth
Place antibiotic-soaked paper discs on agar with bacteria
What is an inhibition zone
A clear area where bacteria have not grown
What does a larger inhibition zone mean
The antibiotic is more effective
Why is a control disc used
To compare results and ensure validity
What is used as a control in antibiotic testing
A paper disc soaked in sterile water
How long are plates typically incubated for antibiotic tests
Around 48 hours
How do antibiotics spread on agar
They diffuse through the agar
How do resistant bacteria behave
They continue to grow despite the antibiotic
What equation is used to calculate inhibition zone area
Area = πr²
How do you find radius from diameter
Radius = diameter ÷ 2
Why calculate area instead of just diameter
Area gives a more accurate comparison
Units for inhibition zone area
cm² or mm²
How can contamination affect results
It can lead to unreliable or invalid results
How can contamination be prevented
Sterilising equipment, sealing plates, minimising exposure to air