GCSE Biology Required Practical: Effects of Disinfectants and Antibiotics

Key Stage 4

Meaning

Investigate the effect of antiseptics and antibiotics on bacterial colonies.

Method

• Independent Variable - The antiseptic or antibiotic used.
• Dependent Variable - Observe the growth of colonies.
• Control Variables - The same quantity of antiseptic and antibiotic. The same spread of bacteria applied to the growth medium. Incubated for the same length of time. Incubated at the same temperature. Only one type of bacteria used.

1. Agar plates prepared with bacteria will be supplied.
2. Mark the underside of an agar plate into three sections making a dot in the centre of each, labeling them 1,2 and 3 and writing your initials and the date on the agar plate.
3. Spray the work space with disinfectant and wash your hands with antibacterial soap.
4. Take a small circle of filter paper and soak it into one of the three antiseptics/antibiotics.
5. Place the circle onto the dot marked at the centre of a section.
6. Repeat steps 4 and 5 ensuring the antiseptics are not mixed in any way.
7. Use two pieces of sellotape to attach the lid loosely to the top of the agar plate (to ensure oxygen get in).
8. Incubate at 25°C for 48 hours.
9. Measure the diameter of the area in which bacteria did not grow.