Biology - Culturing Microorganisms

Pathogen

A microorganism that causes disease.

Examples of pathogens

Bacteria, viruses, fungi, and protists.

How does bacteria reproduce?

Asexually through binary fission.

Binary Fission process

The cell doubles its size and organelles exponentially.

What is the independent variable in this experiment?

The type of antiseptic used.

What are the dependent variables in this experiment?

Diameter of inhibition zone, area of inhibition zone.

What is the control variables in this experiment?

Size of petri dish, volume of antiseptic used, size of disk, time taken to incubate, type of bacteria.

Inhibition zone

Area around an antibiotic disc on a culture plant where bacteria is killed.

What are some of the aseptic techniques used in this practical?

1. Sterilise the benches using a Bunsen burner to kill off unwanted microorganisms.

2. Open the Petri dish slightly to prevent microorganisms in the air from coming in.

3. Secure the dish with tape to prevent the culture from dust and moisture, though not fully to let in oxygen, preventing anaerobic bacteria from growing

4. Leave the Petri dish in an incubator for 24 hours at the temperature of 25°C.

Why is the maximum incubation temperature in schools 25°C?

Harmful pathogens will start to grow above this temperature.

Risk Assessment: Bunsen burner

Can set hair or clothes on fire; tie your hair up and ensure your back is not turned at the Bunsen burner.

Risk Assessment: Bacteria

Could grow on person and potentially cause infection; use tweezers and close the Petri dish as soon as possible.

Risk Assessment: Anaerobic bacteria

Could grow if no oxygen is in the Petri dish; ensure Petri dish isn't fully taped down.