CCEA A Level Biology 4.2 Immunity Exam Questions

About CCEA A Level Biology 4.2 Immunity

Section 4.2 of Unit A2 1 covers how the body defends itself and how this knowledge is used in medicine. You need natural barriers, the difference between antibody-mediated and cell-mediated immunity, the roles of plasma cells, memory cells and the different T-cells, and active and passive immunity including vaccination. CCEA also requires transplant rejection and immunosuppression, the ABO and rhesus blood groups and transfusion compatibility, antibiotic resistance and the search for new antibiotics, and ELISA as a way to detect biomarkers such as cytokines. Practical work on aseptic technique and antibiotic testing is assessed too. This section links to viruses (1.3) and proteins (1.1).

What you need to know

• Barriers and terms Natural barriers include skin, stomach acid, tears containing lysozyme, mucus and blood clotting. An antigen is a molecule that triggers an immune response; an antibody is a specific globular protein complementary to an antigen.
• Antibody-mediated immunity B-lymphocytes with complementary receptors divide to form plasma cells, which secrete antibodies, and memory cells. Antibodies cause agglutination and mark pathogens for phagocytosis by polymorphs.
• Cell-mediated immunity T-lymphocytes include helper T-cells (activate B-cells and other T-cells), killer T-cells (destroy infected cells), memory T-cells and suppressor T-cells.
• Active and passive immunity Active immunity involves your own lymphocytes making antibodies and memory cells, so it is long lasting; it can be natural (infection) or artificial (vaccination). Passive immunity is receiving antibodies: naturally across the placenta or in colostrum, or artificially as serum or monoclonal antibodies. It is short-term.
• Transplants and blood groups Donor antigens trigger T- or B-cell rejection; immunosuppressant drugs or irradiation reduce this but increase infection risk. Blood groups depend on A and B antigens and anti-A and anti-B antibodies in plasma; anti-D is not naturally present and rhesus incompatibility can cause haemolytic disease of the newborn.
• Antibiotics and ELISA Antibiotic resistance spreads through selection; new antibiotics are sought in natural environments. ELISA uses enzyme-linked antibodies and a colour change to detect biomarkers such as cytokines.
• Practical Use aseptic technique, streak plates to isolate colonies and antibiotic discs or E-strips to compare effectiveness by measuring zones of inhibition.

Common mistakes in 4.2 Immunity

• Saying antibodies kill pathogens directly. They cause agglutination, neutralise toxins and mark pathogens for phagocytes.
• Saying a vaccine gives passive immunity. Vaccination stimulates your own immune response, so it is artificial active immunity.
• In transfusion questions, matching antibodies in the donor blood. What matters is the donor's antigens and the recipient's plasma antibodies.
• Saying bacteria become resistant because they are exposed to antibiotics. Resistance arises by mutation; antibiotics select for resistant bacteria that survive and reproduce.
• Confusing plasma cells and memory cells. Plasma cells secrete antibodies; memory cells remain to give a faster secondary response.

Try three 4.2 Immunity exam-style questions