22.6 Culturing Microorganisms In The Lab Flashcards
Why do microorganisms need to be cultured
To grow large enough numbers of the microorganism to see them and examine them
What is the nutrient medium
The food that microorganisms need to be cultured
Either broth or agar
Why are nutrients added to the agar or broth when culturing microorganisms
To provide a better medium for microobrial growth
And for them to multiply rapidly
It must be kept sterile
What is the process called when adding bacteria to the prepared agar or nutrient broth
Inoculation
What are teh 4 steps of inoculating broth
Make a suspension of bacteria to be grown
Mix a known vol with sterile nutrient broth in flask
Stopper the flask with cotton wool to prevent air contamination
Incubate at a suitable temperature
Shake regularly to aerate the broth and provide oxygen
What is the first step of inoculating agar
Teh wire inoculating loop needs to be sterilised by holding it in a Bunsen flame until it glows red hot
Make sure it doesn’t touch any surfaces as it cools
What is teh 2nd and last steps of inoculating agar
- Dip the sterilised loop in the bacterial suspension
Remove lid of Petri dish and make a zig zag streak across surface again - Replace the lid of petrol dish and hold it down with tape but not sealed completely so 02 can get in
This prevents anaerobic bacteria growth
What are logs abs why are they used
Used to represent teh bacterial population
The difference in number from the initial organism to the billions of descendants is too great to represent using standard numbers
What is the first stage of the growth curve
The Lag phase
Bacteria are adapting to new environment
They grow but nothing reproducing at max rate
What is the 2nd stage of teh growth curve
Log or exponential phase
Rate of bacteria production is close to max
What is the stationary phase of the growth curve
Total growth rate is zero
Number of new cells formed is cancelled by number of cells dying
What is the decline or death phase of the growth curve
Reproduction has almost ceased abs death rate is increasing
What are the limiting factors which prevent exponential growth in a culture of bacteria
Nutrients available Oxygen levels Temperature Change in pH Build up of waste money
How can you investigate the factors which affect the growth of microorganisms
Set up identical colonies in different temperature conditions
Set up serial solutions of nutrients or pH at a set temp
