Culturing Microorganisms Quiz

Culturing Microorganisms

Bacteria reproduce through binary fission, which allows them to divide approximately every 20 minutes under optimal conditions. These organisms can be cultured in nutrient broth or on an agar gel plate, forming colonies. It is essential to maintain uncontaminated cultures for reliable studies of disinfectants and antibiotics.

Preparing an Uncontaminated Culture

The aseptic technique is used to prepare uncontaminated cultures. Petri dishes and culture media must be sterilised before use to prevent contamination. Inoculating loops, which transfer bacteria, should be sterilised by passing them through a flame. The Petri dish lid should be secured with adhesive tape and stored upside down to prevent condensation from dripping onto the culture. In school laboratories, cultures should be incubated at 25°C to minimise the risk of growing harmful pathogens.

Example of Calculating Bacterial Growth

Example: If a single bacterium divides every 20 minutes, and you start with one bacterium after 3 hours (180 minutes), the number of divisions can be calculated as follows:
Number of divisions = 180 ÷ 20 = 9
The total population after 3 hours is:
Total population = 2⁹ = 512
Expressing this result in standard form:
Standard form = 5.12 × 10². For more guidance on standard form calculations, check out this page.
You should also learn more about microscopy and practise unit conversions.