Applicable for A-Level, IB, DSE, AP-Level Exams

Biological Molecules    Cell Structure    Cell Transport    Immunology    Exchange    Mass Transport    DNA, Genes & Protein Synthesis    Genetic Diversity    Biodiversity    Photosynthesis    Respiration    Energy & Ecosystems    Stimuli and Response    Nervous Coordination & Muscles    Homeostasis    Inheritance    Populations & Evolution    Ecosystems    Gene Expression    Recombinant DNA Technology   

Defence Mechanisms

Our body contains an inate and adaptive immune system. The inate immune system is non-specific and targets all pathogens, an example of such a defence is your skin as a barrier as well as phagocytosis. The adaptive immune system involves the activation of T-cells as well as B-cells differentiating into plasma cells to release antibodies that target specific antigens on pathogens.

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White Blood Cells

There are 5 types of white blood cells: Lymphocytes, Eosinophils, Neutrophils, Monocytes and Basophils.

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In phagocytosis, pathogens are engulfed by phagocytes such as macrophages. Pathogens are fused the phagocyte to form a phagosome. Lysozmes then break down the pathogen and cell debris are excreted by exocytosis.

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Cell Mediated Response

Cell mediated response involves T-Cells. As antigens are presented after antigen presentation in phagocytosis, helper T-cells with complementary receptors bind to the antigens. This activates the T-Cells which go on to activate cytotoxic T-cells or B-cells in the humoral response or divide into memory cells to form a long term secondary response.

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Humoral Response

Humoral response involves B-Cells. The actived B-cells from the cell-mediated response will then under clonal selection and divide by mitosis to either form memory cells or plasma cells. Plasma cells will then release antibodies complementary to the specific antigen.

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Immunity Map

This is an overview poster which includes both the non-specific and specific responses which divide into both the cell-mediated and humoral response.

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Antibodies are proteins specific to an antigen. They are produced by plasma cells which originate from B-cells. They bring about the destruction of pathogens either by agglutination, opsonistaion or neutralisation in the form of antitoxins.

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Immunity and Vaccinations

Vaccinations bring about immunity by stimulating the immune system to develop memory cells so that secondary response is much more rapid. Herd immunity is where a sufficient percentage of a population has become immune, thereby reducing the likelihood of infection for individuals who lack immunity.

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Antigenic Variation

Antigenic variation refers to an infectious agent changing the proteins or carbohydrates (possibly due to mutation) on its surface and thus avoids a host immune response.

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HIV contains a capsid, attachment proteins, RNA genetic material and the enzyme reverse transcriptase which converts RNA into DNA to be integrated into the host cell for further replication of the HIV molecule. HIV binds to CD4+ cells which include T-cells. Hence as more and more T-cells are destroyed, HIV develops into AIDs where the immune system does not have efficient T-cells for the cell-mediated response against pathogens.

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The ELISA Test

The ELISA Test works under the principle of antibodies added to a well which are complemtary to antigens you are detecting for. The antibodies are attached to a enzyme in which when an substrate is added to a well, the immobilised antibodies with the enzyme will cause a colour change due to the formation of enzyme-substrate complexes.

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