A-Level Biology: The Immune System

The immune system is a favourite of A-level examiners because it chains together cell biology, protein specificity and applied medicine. This quiz covers the full immune-response narrative plus the applications the specification names.

The cellular questions follow the response in order: phagocyte recognition of pathogens, antigen presentation, and the two adaptive arms — T helper cells coordinating the response through cytokine signalling to B cells and cytotoxic T cells, and the humoral response tested through clonal selection: the identification and expansion of the one B-cell clone whose receptor matches the antigen, producing plasma cells and antibodies.

The memory questions cover the primary-versus-secondary response contrast — why memory B cells make re-exposure faster and stronger — and the immunity taxonomy: active versus passive, tested with concrete examples of each, plus vaccination and the threshold logic of herd immunity.

The applied questions are where A-level papers cash the topic out: antigen variability in HIV and influenza as the reason immunity and vaccines fail against them, HIV's replication mechanism with reverse transcriptase converting viral RNA to DNA, why antibiotics — which target bacterial walls and 70S ribosomes — cannot touch viruses, and the ELISA test, tested on what the enzyme-linked antibody actually does: converting a substrate into a detectable signal.

Each explanation names the cells and mechanisms precisely, at the level mark schemes require, making this set an efficient consolidation of one of the specification's densest sections.

• Sequence the immune response from phagocytosis to antibody production
• Distinguish the cell-mediated and humoral arms and their coordination by T helper cells
• Explain clonal selection and the memory basis of the secondary response
• Classify immunity as active or passive with correct examples
• Apply the topic to HIV, antibiotics and the ELISA test mechanism

Topic scope follows the immunity content of the DfE A level biology subject content as delivered in current exam-board specifications: phagocytosis, T and B lymphocytes, antibodies, vaccination, HIV and monoclonal antibody applications.