When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how. (5 marks)

With these 5 and 6 mark questions, one of the main skills required is being able to describe the process in sufficient detail, without wasting time with unnecessary information. For example in this question, the student is asked to describe only how antibodies are produced, not how they act once synthesised or how they contribute to immunity. The answer below sufficiently answers the question, without wasting time which could be used for other parts of the exam:
The vaccine contains the antigen expressed by the pathogen. When the vaccine is injected into the bloodstream, the antigen is taken up by macrophages and these antigens are presented on the surface of the macrophage. From here, a specific T helper cell (with a specific receptor protein) binds to the antigen, which in turn leads to the stimulation of B cells, which have a complementary antibody on their surface. Once stimulated, these B cells undergo rapid mitosis called clonal expansion , to produce many B cells all secreting large amounts of the same antibody.