Defence Against DiseaseEdexcel GCSE Biology: Revision notes
Section 1
Physical and Chemical Barriers
Physical: skin, mucus, cilia. Chemical: lysozymes (tears/mucus, break bacterial cell walls), hydrochloric acid (stomach, kills pathogens).
Mucus traps pathogens; cilia move the mucus away.
Section 2
Specific Immune Response
- Exposure introduces antigens
- Antigens trigger antibody production and memory lymphocytes
- Secondary response: memory lymphocytes give a faster, larger antibody response.
Secondary response is FASTER and produces MORE antibodies.
Section 3
Immunisation
Inactive/dead pathogen triggers antibody/memory lymphocyte production without disease, protecting against future infection.
Section 4
Advantages, Disadvantages, Herd Immunity
Advantages: controls disease, reduces healthcare pressure, herd immunity. Disadvantages: mild side effects, rare severe reactions, not 100% protection.
Herd immunity: high vaccination rate limits spread, protecting the unvaccinated.
Section 5
Antibiotics
Inhibit specific bacterial cell processes without harming host cells. No effect on viruses (no target processes).
Antibiotics cannot treat viral infections.
Section 6
Aseptic Technique & Core Practical
Autoclave sterilises equipment. Sterile loop flamed before/after use. Petri dishes kept covered.
Practical: discs of antiseptic/antibiotic/plant extract on inoculated agar; measure zone of inhibition (larger = more effective).
Zone diameter 16mm: radius=8mm, area=π×8²=201.1mm².
Must Know
- Physical: skin, mucus, cilia. Chemical: lysozymes, HCl.
- Antigens → antibodies + memory lymphocytes → faster secondary response.
- Immunisation trains immunity without disease; herd immunity protects unvaccinated.
- Antibiotics target bacteria only.
- Aseptic technique + zone of inhibition = πr².
That's the notes covered.
Carry on to the next subtopic.