Immunity AS Biology


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Describe and explain how a secondary immune response differs to a primary immune response.

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A secondary immune response is faster and produces a quicker, stronger response than the primary response. This is because memory cells are produced during the primary response which remember the foreign antigen. During the second infection, memory B-cells can quickly divide to form plasma cells, which secrete the correct antibody to the antigen. Memory T-cells quickly divide into the right type of T -cells to destroy the cell carrying the antigen.

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Describe how monoclonal antibodies can be used to target a drug to cancer cells.

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Monoclonal antibodies are made against antigens specific to cancer cells. An anti-cancer drug is attached to the antibodies. The antibodies bind to tumour markers on cancer cells because their binding sites have a complementary shape. This delivers the anti-cancer drug to the cells.

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What is an antigen?

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Antigens are molecules (usually proteins or polysaccharides) found on the surface of cells. When a pathogen invades the body, the antigens on its cell surface are identified as foreign, which activates cells in the immune system.

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What is phagocytosis?

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What are the functions of T cells and B cells?

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A T cell is another type of white blood cell. Some release substances to activate B cells. Others attach to antigens on a pathogen and destroy the cell.

B cells are also a type of white blood cell. When the antibody on the surface of a B cell meets a complementary shaped antigen, it binds to it. This, together with substance released from T cells , activates the B cell. The activated B cell divides into plasma cells

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Describe the function of antibodies.

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Antibodies coat pathogens, making it easier for phagocytes to engulf them

This prevents pathogens from entering host cells.

They also bind to toxins to neutralise them.

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What are monoclonal antibodies?

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Monoclonal antibodies can be used to target specific substances or cells. Monoclonal antibodies are antibodies produced from a single group of genetically identical B cells (plasma cells). This means they are all identical in structure. Antibodies are very specific because their binding sites have a unique structure that only one particular antigen  (with a complementary shape) will fit into. You can make monoclonal antibodies that bind to anything you want, e.g a cell antigen or other substance, and they will only target and bind to this molecule.

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Explain why it is possible to suffer from the flu more than once.

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The flu virus is able to change its surface antigens/shows antigenic variation. This means that when you're infected for a second time with a different strain, the memory cells produced from the first infection will not recognise the new/different antigens. The immune system has to carry out a primary response against these new antigens. This takes time and meanwhile you show the symptoms of the disease.

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How do vaccines cause immunity?

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Vaccines contain antigens that cause your body to produce memory cells against a particular pathogen, without the pathogen causing disease. This means you become immune without getting any symptoms.

Vaccines always contain antigens - these may be free or attached to a dead or weakened pathogen. Vaccines may be injected or taken orally. The disadvantages of taking a vaccine orally are that it could be broken down by enzymes in the gut or the molecules of the vaccine may be too large to be absorbed into the blood.

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Describe herd immunity

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Vaccines protect individuals that have them and, because they reduce the occurrence of the disease, those not vaccinated are also less likely to catch the disease because there are fewer people to catch it from. This is called herd immunity.

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