5.18B **Biology Only** - Core Practical: Investigating the effects of antiseptics and antibiotics and 5.19B **Biology Only** - Calculations with Bacterial Cultures Flashcards
What formula is used to calculate the cross sectional area of a bacterial culture?
The formula used is πr².
Why is calculating the cross sectional area of a bacterial culture useful?
It allows us to determine the effectiveness of the antibiotic.
What is the first step in growing a bacterial culture?
Take a Petri dish pre-poured with agar gel and sterilise it in an autoclave before use.
How should bacteria be applied to the agar?
Use a sterilised inoculating loop to apply the bacteria.
What temperature and duration should the bacterial culture be incubated?
Incubate the culture at 25 degrees C for 3 days.
What should be done after incubating the bacterial culture?
Apply a filter paper disc soaked in antibiotic solution to the centre of the agar plate and wait for 24 hours, or until there is no further change.
What is the next step after applying the antibiotic?
Measure the diameter of the circle taken up by the bacterial culture and the diameter of the clear agar jelly in the centre.
How do you calculate the area of the circles?
Divide both diameters by 2 to get the radius and use the formula πr².
How is the effectiveness of the antibiotic calculated?
Divide the area of the smaller circle by the larger, and multiply by 100 to get the percentage of the bacterial culture destroyed.
What does a higher percentage indicate about the antibiotic?
The higher the percentage, the more effective the antibiotic.
Why is it useful to repeat these calculations for multiple antibiotics and bacteria?
It helps determine the effectiveness of different bacteria/antibiotic combinations for particular bacterial infections.
