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Cell recognition and the immune system - A-Level Biology notes
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Cell recognition and the immune system - A-Level Biology notes
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Chapter 5: Cell recognition and the immune system5.1 Defence mechanisms
Pathogen a microorganism that can cause an infectious disease
Immunity the ability of an organism to resist a particular infection or toxins by antibodies or white blood cells
Infection process of a pathogen invading and multiplying in the body tissue of the host
Antigen a foreign protein found on the cell surface membrane which triggers and immune response
Phagocytosis mechanisms by which cells engulf particles to form a vesicle or a vacuole
Phagocytes ingest and destroy the pathogen
Lymphocytes cells involved in immune responses
Antigen-presenting cell cells that display foreign antigens on the surface
Monoclonal antibody a collection of identical antibodies cloned from a single antibody
Vaccination introduction of a vaccine containing appropriate disease antigens injected into the body in order to
induce artificial immunity
Antibody a protein produced by lymphocytes (B cells) in response to the presence of a specific antigen which
stimulates an immune response
Recognising your own cells
- If the lymphocytes couldn’t identify self from non-self-molecules then the lymphocytes would destroy the
organism’s own tissue.
- Each cell has specific molecules on its surface to identify it, this is why a transport donor has to be genetically
similar to the recipient or the organ might be rejected and the person will die
Humoral response secrets antibodies; cell-mediated response secretes cytokines (signals cells about a potential
pathogen)
How does the body learn to identify its own molecules?
- In the fetus lymphocytes are always colliding with other cells
- Infections are rare as the fetus is protected by a placenta
- Lymphocytes will collide mostly with own material
- Some lymphocytes will have receptors that fit exactly its own material
- These are there for suppressed or die
- In adults lymphocytes produced in the bone marrow encounter self-antigens at the start
- Any lymphocytes that show an immune response will then undergo programmed cell death (apoptosis) before
they mature
5.2 Phagocytosis
The process of phagocytosis
1. Chemical products of pathogen act as attractants causing phagocytes to follow it
2. Phagocytes have several receptors on their cell surface membrane that
recognize and attach to chemicals on the surface of the pathogen 2 types of white blood cells:
3. The phagocyte engulfs the pathogen to form a vesicle (phagosome) - Phagocytes (inject destroy)
4. Lysosomes move in to fuse with the vesicle - Lymphocytes (involved in immune
5. Lysozymes destroy ingested bacteria by hydrolyzing the pathogen’s cell responses)
walls
6. The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
7. The antigen is then presented on the cell surface membrane of the phagocyte
5.3 T lymphocytes and cell-mediated immunity The stages of T cells in response to a pathogen:
Lymphocytes 1. The pathogens invade body cells or are taken in by phagocytosis
- produced by stem cells in the bone marrow 2. Phagocyte becomes an antigen presenting cell
- B cells mature in the bone marrow 3. Receptors on a specific helper T cell fit exactly onto those antigens
- T cells mature in the thymus gland 4. The attachment activates T cells to divide by mitosis and clone itself
5. The cloned T cells:
o Develop into memory cells
o Stimulate phagocytosis
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