AQA A-LEVEL BIOLOGY PAPERS UNOFFICIAL| MARK SCHEME
(2025)
1.what are killer t-cells? - ANSWER - cytotoxic cells
- bind to non-self antigens
2. 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)
3. what is apoptosis? - ANSWER programmed cell death
4. 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
5. What does perforin do? - ANSWER creates holes in the cell membranes in order to destroy
the infected cell
6. what do helper t-cells do? - ANSWER - produce cytokines
- cytokines stimulate b-cells to divide into plasma and memory cells
- activate killer t-cells
7. 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
,8. 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
9.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
10. define suppressor t-cells - ANSWER regulate the immune response by suppressing activity of
killer t-cells and b-cells
11.define 'microorganism' - ANSWER organism that is too small to be seen without a
microscope
12. define 'pathogen' - ANSWER microorganism that causes disease
13. 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)
14. where are t-cells made? - ANSWER thymus gland
,15. where do b-cells mature? - ANSWER bone marrow
16. what do b-cells do? - ANSWER - humoral response
- release antibodies
- complementary to a specific antigen
17.what response are plasma cells? - ANSWER primary
18. what response are memory b-cells? - ANSWER secondary
19. 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
20. what does mitosis do in humoral response? - ANSWER - forms clones of b-cells (plasma and
memory)
- clonal response
21.what do clones do? - ANSWER each clone can produce one type of antibody (monoclonal)
which can be used in medicine
22.outline plasma cells - ANSWER - primary response
- secrete antibodies
- only survive for a few day
- slow response = person gets ill before pathogen is killed
, 23. outline memory cells - ANSWER - secondary response
- circulated in blood and tissue fluid
- divide rapidly
- rapid response so person doesn't get ill
24. what is an antibody? - ANSWER y-shaped globular protein produced by b-cells
25. where are antibodies produced? - ANSWER plasma b-cells
26. what are antibodies made of? - ANSWER 4 polypeptide chains -- 2 heavy, 2 light
27. what are the two regions an antigen is made of? - ANSWER - variable
- constant
28. what is special about the variable region? - ANSWER complementary and specific to an
antigen
29. what are the chains bonded by? - ANSWER disulphide bridge
30. why do antibodies have a hinge region? - ANSWER to allow the antibody to move to bind to
more than one antigen
what is 'monoclonal antibody production' - ANSWER the process by which large quantities of
antibodies (targeted against a particular antigen) can be produced
how are monoclonal antibodies produced? - ANSWER - mouse immunised by injection of
antigen to stimulate production of antibodies
(2025)
1.what are killer t-cells? - ANSWER - cytotoxic cells
- bind to non-self antigens
2. 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)
3. what is apoptosis? - ANSWER programmed cell death
4. 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
5. What does perforin do? - ANSWER creates holes in the cell membranes in order to destroy
the infected cell
6. what do helper t-cells do? - ANSWER - produce cytokines
- cytokines stimulate b-cells to divide into plasma and memory cells
- activate killer t-cells
7. 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
,8. 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
9.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
10. define suppressor t-cells - ANSWER regulate the immune response by suppressing activity of
killer t-cells and b-cells
11.define 'microorganism' - ANSWER organism that is too small to be seen without a
microscope
12. define 'pathogen' - ANSWER microorganism that causes disease
13. 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)
14. where are t-cells made? - ANSWER thymus gland
,15. where do b-cells mature? - ANSWER bone marrow
16. what do b-cells do? - ANSWER - humoral response
- release antibodies
- complementary to a specific antigen
17.what response are plasma cells? - ANSWER primary
18. what response are memory b-cells? - ANSWER secondary
19. 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
20. what does mitosis do in humoral response? - ANSWER - forms clones of b-cells (plasma and
memory)
- clonal response
21.what do clones do? - ANSWER each clone can produce one type of antibody (monoclonal)
which can be used in medicine
22.outline plasma cells - ANSWER - primary response
- secrete antibodies
- only survive for a few day
- slow response = person gets ill before pathogen is killed
, 23. outline memory cells - ANSWER - secondary response
- circulated in blood and tissue fluid
- divide rapidly
- rapid response so person doesn't get ill
24. what is an antibody? - ANSWER y-shaped globular protein produced by b-cells
25. where are antibodies produced? - ANSWER plasma b-cells
26. what are antibodies made of? - ANSWER 4 polypeptide chains -- 2 heavy, 2 light
27. what are the two regions an antigen is made of? - ANSWER - variable
- constant
28. what is special about the variable region? - ANSWER complementary and specific to an
antigen
29. what are the chains bonded by? - ANSWER disulphide bridge
30. why do antibodies have a hinge region? - ANSWER to allow the antibody to move to bind to
more than one antigen
what is 'monoclonal antibody production' - ANSWER the process by which large quantities of
antibodies (targeted against a particular antigen) can be produced
how are monoclonal antibodies produced? - ANSWER - mouse immunised by injection of
antigen to stimulate production of antibodies
