AQA A Level Biology Test

AQA A Level Biology Test 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 define 'microorganism' - Answer- organism that is too small to be seen without a microscope define 'pathogen' - Answer- microorganism that causes disease outline phagocytosis - Answer- 1. phagocyte follows conc gradient of chemoattractants 2. phagocyte attaches to pathogen 3. pathogen engulfed and placed in a vesicle (phagosome) 4. lysosomes migrate to phagosome and bind with it to form a phagolysosome -- lytic enzymes released from lysosome 5. pathogen digested 6. useful parts absorbed 7. all waste products released by exocytosis 8. non-self antigens of the pathogen displayed on the phagocytes surface (antigen-presenting) where are t-cells made? - Answer- thymus gland where do b-cells mature? - Answer- bone marrow what do b-cells do? - Answer- - humoral response - release antibodies - complementary to a specific antigen what response are plasma cells? - Answer- primary what response are memory b-cells? - Answer- secondary outline the humoral response - Answer- 1. antigen attaches to complementary antibody on b-cell 2. antigen taken into cell (endocytosis) 3. presented on cell surface membrane 4. t-helper cells bind to antigen and stimulate b-cell to divide what does mitosis do in humoral response? - Answer- - forms clones of b-cells (plasma and memory) - clonal response what do clones do? - Answer- each clone can produce one type of antibody (monoclonal) which can be used in medicine outline plasma cells - Answer- - primary response - secrete antibodies - only survive for a few day - slow response = person gets ill before pathogen is killed outline memory cells - Answer- - secondary response - circulated in blood and tissue fluid - divide rapidly - rapid response so person doesn't get ill what is an antibody? - Answer- y-shaped globular protein produced by b-cells where are antibodies produced? - Answer- plasma b-cells what are antibodies made of? - Answer- 4 polypeptide chains -- 2 heavy, 2 light what are the two regions an antigen is made of? - Answer- - variable - constant