Exam Focus

Exam Focus

Antibiotic resistance is one of the most consistently examined topics across all GCSE Biology specifications. Edexcel 1BI0 Paper 1 (Topic 5: Health, Disease and Medicine) tests this topic with scenario-based questions — you may be given a table of zone of inhibition data or a passage about antibiotic prescribing rates and asked to "Suggest" or "Evaluate." Natural selection mechanism questions and data interpretation questions both appear regularly. Edexcel mark schemes commonly use "Accept…" and "Allow…" for the natural selection steps, so ensure you know all the key steps.

• Natural selection mechanism (4-5 marks): Random mutation → resistance gene present in a few bacteria → antibiotic kills non-resistant → resistant survive → reproduce → pass on resistance → population dominated by resistant bacteria. Every step is required for full marks. The word "mutation" must appear.
• Why not use antibiotics for viral infections (2 marks): Antibiotics target bacterial structures (cell walls, ribosomes). Viruses do not have these structures. Therefore antibiotics have no target and are ineffective. Also: unnecessary use accelerates resistance.
• Disc diffusion practical (3-4 marks): Measure zone of inhibition, compare sizes, link to antibiotic effectiveness. Know variables, know why 25°C is used, know what a control shows.
• Evaluating measures to reduce resistance (4 marks): Complete antibiotic courses, prescribe only for bacterial infections, reduce agricultural use, develop new antibiotics, better diagnostic tests. For each, explain HOW it reduces resistance (reduces selection pressure, prevents resistant strains surviving, etc.).

Common mark losses: Saying the person becomes resistant (it is the bacteria, not the person). Saying bacteria "learn" to resist (it is random mutation + selection). Not including the word "mutation" in natural selection answers. Forgetting that large zone = more effective (not the other way around).