1|Page
AQA A LEVEL BIOLOGY QUESTIONS AND ANSWERS BANK
WITH MARKING SCHEME AND DETAILED ANSWERS
2025 VERSION// WITH ANSWERS
what are killer t-cells?
- cytotoxic cells
- bind to non-self antigens
how to killer t-cells work?
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?
programmed cell death
how do killer t-cells destroy cancer?
- cancerous = mutations
- mutations = abnormal antigens
- killer t-cell binds to abnormal antigens
- killer t-cells induces death of cancerous cell
What does perforin do?
creates holes in the cell membranes in order to destroy the infected cell
what do helper t-cells do?
- produce cytokines
- cytokines stimulate b-cells to divide into plasma and memory cells
- activate killer t-cells
define helper t-cells
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?
- halt immune response
- prevent wastage of energy and resources
- prevent overactive immune response
- causes reduction of white blood cells after being ill
,2|Page
define memory t-cells
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
regulate the immune response by suppressing activity of killer t-cells and b-cells
define 'microorganism'
organism that is too small to be seen without a microscope
define 'pathogen'
microorganism that causes disease
outline phagocytosis
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?
thymus gland
where do b-cells mature?
bone marrow
what do b-cells do?
- humoral response
- release antibodies
- complementary to a specific antigen
what response are plasma cells?
primary
what response are memory b-cells?
secondary
outline the humoral response
, 3|Page
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?
- forms clones of b-cells (plasma and memory)
- clonal response
what do clones do?
each clone can produce one type of antibody (monoclonal) which can be used in medicine
outline plasma cells
- primary response
- secrete antibodies
- only survive for a few day
- slow response = person gets ill before pathogen is killed
outline memory cells
- secondary response
- circulated in blood and tissue fluid
- divide rapidly
- rapid response so person doesn't get ill
what is an antibody?
y-shaped globular protein produced by b-cells
where are antibodies produced?
plasma b-cells
what are antibodies made of?
4 polypeptide chains -- 2 heavy, 2 light
what are the two regions an antigen is made of?
- variable
- constant
what is special about the variable region?
complementary and specific to an antigen
what are the chains bonded by?
disulphide bridge
AQA A LEVEL BIOLOGY QUESTIONS AND ANSWERS BANK
WITH MARKING SCHEME AND DETAILED ANSWERS
2025 VERSION// WITH ANSWERS
what are killer t-cells?
- cytotoxic cells
- bind to non-self antigens
how to killer t-cells work?
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?
programmed cell death
how do killer t-cells destroy cancer?
- cancerous = mutations
- mutations = abnormal antigens
- killer t-cell binds to abnormal antigens
- killer t-cells induces death of cancerous cell
What does perforin do?
creates holes in the cell membranes in order to destroy the infected cell
what do helper t-cells do?
- produce cytokines
- cytokines stimulate b-cells to divide into plasma and memory cells
- activate killer t-cells
define helper t-cells
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?
- halt immune response
- prevent wastage of energy and resources
- prevent overactive immune response
- causes reduction of white blood cells after being ill
,2|Page
define memory t-cells
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
regulate the immune response by suppressing activity of killer t-cells and b-cells
define 'microorganism'
organism that is too small to be seen without a microscope
define 'pathogen'
microorganism that causes disease
outline phagocytosis
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?
thymus gland
where do b-cells mature?
bone marrow
what do b-cells do?
- humoral response
- release antibodies
- complementary to a specific antigen
what response are plasma cells?
primary
what response are memory b-cells?
secondary
outline the humoral response
, 3|Page
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?
- forms clones of b-cells (plasma and memory)
- clonal response
what do clones do?
each clone can produce one type of antibody (monoclonal) which can be used in medicine
outline plasma cells
- primary response
- secrete antibodies
- only survive for a few day
- slow response = person gets ill before pathogen is killed
outline memory cells
- secondary response
- circulated in blood and tissue fluid
- divide rapidly
- rapid response so person doesn't get ill
what is an antibody?
y-shaped globular protein produced by b-cells
where are antibodies produced?
plasma b-cells
what are antibodies made of?
4 polypeptide chains -- 2 heavy, 2 light
what are the two regions an antigen is made of?
- variable
- constant
what is special about the variable region?
complementary and specific to an antigen
what are the chains bonded by?
disulphide bridge
