Pathogen
Exam-ready definition
A disease-causing organism. For example, bacteria, viruses, fungi or protoctists that cause transmissible diseases.
How this is marked
One word, one mark, frequently asked. Pair it with 'transmissible disease' (a disease in which the pathogen can be passed from one host to another). The two definitions appear together in Paper 3 and 4.
In an exam answer
Defining it: 'A pathogen, such as the influenza virus, is a disease-causing organism that can be transmitted from one host to another.'
Full topic guide: Human nutrition