AQA A LEVEL BIOLOGY EXAM WITH BEST SOLUTIONS AND CORRECT QUESTIONS AND ANSWERS

AQA A LEVEL BIOLOGY EXAM WITH BEST SOLUTIONS AND CORRECT QUESTIONS AND ANSWERS what are killer t-cells? - ANSWER-- cytotoxic cells - bind to non-self antigens how to killer t-cells work? - ANSWER-1. virus attaches to and enters host cell 2. viral DNA causes host cell to express viral antigens on its surface 3. killer t-cells attaches to viral antigens on infected cells 4. killer t-cells induces death of infected cell (apoptosis) what is apoptosis? - ANSWER-programmed cell death how do killer t-cells destroy cancer? - ANSWER-- cancerous = mutations - mutations = abnormal antigens - killer t-cell binds to abnormal antigens - killer t-cells induces death of cancerous cell What does perforin do? - ANSWER-creates holes in the cell membranes in order to destroy the infected cell what do helper t-cells do? - ANSWER-- produce cytokines - cytokines stimulate b-cells to divide into plasma and memory cells - activate killer t-cells define helper t-cells - ANSWER-help humoral response by involvement in the maturation of b-cells and by triggering the production of antibodies by b-cells what do suppressor t-cells do? - ANSWER-- halt immune response - prevent wastage of energy and resources - prevent overactive immune response - causes reduction of white blood cells after being ill define memory t-cells - ANSWER-work in the same way as memory b-cells, ensuring rapid response on subsequent exposure to the same non-self antigens define suppressor t-cells - ANSWER-regulate the immune response by suppressing activity of killer t-cells and b-cells