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A level Biology > communicable disease > Flashcards

Flashcards in communicable disease Deck (23):

what are the main disease causing pathogens in humans

bacteria and virus


what type of pathogen causes TB



what pathogen causes TB

Mycobacterium tuberculosis


what does TB infects

phagocytes in the lungs


what does TB lead to

breathing problems, coughing, weight loss, fever and can result in death


what are examples of physical defences against pathogens in plants

cellulose cell walls
a lignin layer that thickens the cell wall
waxy cuticles
old vascular tissue is blocked to stop the pathogen spreading


what mechanisms are activated in plants when a pathogen is detected

closing of the stomata to prevent entry to the leaves
additional thickening of cell walls
callose deposits between cell wall and cell membrane near the site of infection to strengthen cell wall
necrosis which is when cells near the infection are killed by intracellular enzymes


what are the physical barriers against infection in animals

skin consisting of keratin
stomach acid that kills bacteria
gut and skin flora that compete with pathogens for food and space


explain inflammation

histamines released by mast cells in the injured tissue cause vasodilation which increases blood flow to the infected area and increases permeability of blood vessel.
antibodies, white blood cells and plasma leak out into the infected area and destroy the pathogen


explain lysozyme action

lysozymes are enzymes found in secretions such as tears and mucus that kills bacterial cells by damaging their cell walls


what is phagocytosis

a process in which white blood cells engulf pathogens, destroying them by fusing a pathogen enclosed in a phagocytic vacuole with a lysosome


explain blood clotting

reduces the blood loss by temporarily sealing the opening thus preventing the entry of pathogens


what are memory cells

cells that replicate themselves when exposed to an invading pathogen and remain in the lymph nodes searching for the same antigen thus resulting in a much faster immune response.


what are B effector cells

antibody producing cells


what are T helper cells

stimulate B cells and T killer cells to divide


what are T killer cells

destroy pathogen infected cells


explain the humoral response

a B cell is triggered when it encounters its matching antigen
the B cell engulfs the antigen and digest it
it then displays the antigen on its surface
a matching T cell is then attracted
the T cell secretes cytokines which help the B cell multiply and divide into plasma cells
then released into the blood and the antibodies lock onto matching antigens


explain the cell mediated response

macrophage ingests the antigens
processes them
presents them to a T helper cell
produces clones to produce a T helper cell, a T killer cell or a memory cell


what are antibodies

globular proteins produced by lymphocytes


explain antibody action

neutralisation- have a complementary shape to a specific antigen. they attach to the antigen and inhibit its action
agglutination- several antibodies clump the antigens together allowing easier digestion


describe the structure of antibodies

composed of four polypeptide chains which are linked by disulfide bridges
have a constant region and a variable region
contain hinge region responsible for flexibility


what is meant by active immunity

results from the production of antibodies by the immune system in response to the presence of an antigen


what is meant by passive immunity

the introduction of antibodies from another person or animal