AQA A Level Biology: Cell Recognition and the Immune System Flashcards
What is an antigen?
A molecule (usually a protein) found on the surface of a pathogen that triggers an immune response.
What is the role of antigens in the immune system?
Allow the immune system to identify:
* Pathogens
* Abnormal body cells
* Toxins
* Cells from other organisms (e.g., organ transplants)
What are the two main types of immunity?
- Non-specific immunity: Immediate, same for all pathogens. (phagocytes)
- Specific immunity: Slower but targets specific pathogens.
(lymphocytes)
- Specific immunity: Slower but targets specific pathogens.
What is the first line of defence in the immune system?
- Skin (physical barrier)
- Mucus and cilia
- Stomach acid
- Lysozymes in tears and saliva
What are phagocytes?
White blood cells that engulf and digest pathogens through phagocytosis.
What are the steps of phagocytosis?
- Recognition: Phagocyte binds to antigens on pathogen.
- Engulfment: Pathogen is engulfed into a phagosome.
- Lysosome fusion: Lysosomes fuse with phagosome, releasing digestive enzymes.
- Digestion: Pathogen is broken down.
- Antigen presentation: Phagocyte presents antigens on its surface.
What is an antigen-presenting cell (APC)?
A cell that displays foreign antigens on its surface after engulfing a pathogen, triggering the specific immune response.
What are the two types of lymphocytes involved in the immune response?
- T lymphocytes (T cells)
- B lymphocytes (B cells)
What is the role of T lymphocytes?
Recognize antigens presented by APCs and stimulate other immune cells.
What are the different types of T cells and their functions?
- Helper T cells (TH cells): Activate B cells and cytotoxic T cells.
- Cytotoxic T cells (TC cells): Kill infected cells by releasing perforin.
- Memory T cells: Provide long-term immunity.
What is the role of B lymphocytes?
Produce antibodies in response to antigens.
What are plasma cells?
Clones of activated B cells that produce large amounts of antibodies.
What are memory B cells?
Cells that remain after infection and provide immunity by responding quickly if the same pathogen invades again.
What is the structure of an antibody?
- 4 polypeptide chains (2 heavy, 2 light).
- Variable region: Binds to specific antigens.
- Constant region: Same in all antibodies, binds to immune cells.
What are the functions of antibodies?
- Agglutination: Clump pathogens together for easier engulfment.
- Neutralisation: Block toxins and prevent pathogen entry.
- Opsonisation: Mark pathogens for phagocytosis.
What is the primary immune response?
- First exposure to an antigen.
- Slow response as B cells need to divide and produce antibodies.
What is the secondary immune response?
- Faster and stronger due to memory cells.
- Antibodies produced more quickly to destroy the pathogen.
What is the difference between active and passive immunity?
- Active immunity: Body produces its own antibodies (natural or vaccination).
- Passive immunity: Antibodies are given directly (mother to baby or injection).
What is natural active immunity?
Immunity gained after infection where memory cells provide future protection.
What is artificial active immunity?
Immunity gained after vaccination with weakened or dead pathogens.
What is natural passive immunity?
Antibodies passed from mother to baby through the placenta or breast milk.
What is artificial passive immunity?
Antibodies injected into a person to provide immediate, short-term protection.
What is a vaccine?
A preparation containing antigens that stimulate the immune system to produce memory cells.q
What is herd immunity?
When a high percentage of the population is vaccinated, reducing the spread of the disease and protecting unvaccinated individuals.
What is antigenic variation?
When pathogens change their surface antigens, making existing memory cells ineffective.
What is the role of monoclonal antibodies?
- Targeted treatment: Bind to specific antigens.
- Used in cancer treatment and pregnancy tests.
What is the ELISA test?
A test that uses antibodies to detect the presence of specific antigens or antibodies in a sample.
What are the ethical issues with vaccines?
- Animal testing.
- Side effects.
- Compulsory vaccination concerns.
What is HIV and how does it affect the immune system?
HIV infects and destroys helper T cells, weakening the immune system and leading to AIDS.
How does HIV replicate?
- HIV binds to helper T cells.
- RNA is converted to DNA using reverse transcriptase.
- Viral DNA is inserted into host DNA.
- New viruses are produced and released, killing T cells.
