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AQA A LEVEL BIOLOGY EXAM QUESTIONS AND EXPERT VERIFIED ANSWERS 2024/2025 ALREADY GRADED A | 3 VERSIONS COMPILATION WITH LATEST VERSION!!$15.49
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AQA A LEVEL BIOLOGY EXAM QUESTIONS AND
EXPERT VERIFIED ANSWERS 2024/2025 ALREADY
GRADED A | 3 VERSIONS COMPILATION WITH
LATEST VERSION!!
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
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
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
why do antibodies have a hinge region?
to allow the antibody to move to bind to more than one antigen
what is 'monoclonal antibody production'
the process by which large quantities of antibodies (targeted against a particular antigen) can be
produced
how are monoclonal antibodies produced?
- mouse immunised by injection of antigen to stimulate production of antibodies
- plasma cells isolated from spleen
- plasma cells fuse with tumor cells to form a hybridoma
- hybridoma produces large amounts of identical antibody molecules
what is the scientific term for a tumor cell?
myeloma
what can be monoclonal antibodies be used as?
specific probe to track down and purify specific protein that induced its transformation
what needs to happen to monoclonal antibodies before human use?
humanisation
why do monoclonal antibodies need to be 'humanised' before used by humans?
to stop the trigger of an immune response
what are monoclonal antibodies used for?
- pregnancy tests
- diagnostic tools for AIDS
- industrial production of interferon
what is a vaccine?
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