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Immunity, pathogen evolution and antibiotics
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Pathogens, antigens and the two layers of defence

Pathogens, antigens and the two layers of defence

Flow diagram of immunity after bacteria enter through a cut, showing clotting, inflammation, phagocytosis, B cells, T cells, antibodies and memory cells

A pathogen is a disease-causing organism or particle, and an antigen is a molecule whose shape can be recognised by the immune system. Immunity depends on specific recognition because only receptors or antibodies with a complementary shape will bind that antigen.

Immunity, pathogen evolution and antibiotics Lesson

  1. A Level
  2. /Biology
  3. /Immunity, pathogen evolution and antibiotics

Step-by-step lessons on Edexcel A A Level Biology Immunity, pathogen evolution and antibiotics. Each one builds up to exam-style questions. Build a strong foundation in cell biology and biochemistry early on, since later topics on genetics, ecology and physiology all draw on these core concepts.

Lessons