hello and welcome to another complete Cambridge IGCSE biology lesson where you'll learn absolutely everything you need to know on topic 10.1 diseases and Immunity as always we'll be following the Cambridge syllabus exactly and we'll cover absolutely everything you need to know for your final exam the topic 10.1 you need to know about pathogens disease transmission the body's defense systems and control measures used to prevent the spread of disease for extended you also need to understand the terms active and passive immunity the process of vaccination and the bacterial disease cholera so pathogens are disease-causing organisms and include viruses certain bacteria fungi and protoctista and other organisms like parasitic worms they cause damage to the cells and disrupt the normal functioning of tissues giving rise to symptoms and triggering an immune response in the host a transmissible disease is a disease in which the pathogen can be passed on from one host to another either by direct or indirect contact Direct contact refers to the transfer of pathogens through blood or other bodily fluids for example being injected by a needle previously used by an infected individual allows pathogens to enter the bloodstream directly certain diseases are also passed on in bodily fluids during sexual intercourse indirect contact refers to the transmission of pathogens via contaminated surfaces food animals and particles in the air for example raw meat Harbors bacteria that's killed off when cooking if however raw food is prepared using the same knife or cutting board or the chef doesn't wash their hands bacteria from the meat can be transferred and ingested whenever we sneeze cough talk or even breathe we expel a fine spray of liquid particles that remain suspended in the air for some time pathogens in these tiny droplets May then be inhaled by other people or land on exposed food bacteria is also spread by insects like house flies which transfer bacteria from decaying food or feces to fresh food via their feet and mouth parts now humans come into contact with harmful pathogens or the the time but for most of us illness is fairly uncommon this is due to the body's defense mechanisms which include the skin mucus stomach acid and of course white blood cells so glands in the stomach lining secrete gastric juice containing hydrochloric acid which kills the majority of any bacteria ingested with food the outer layer of the skin called the epidermis acts as a physical barrier preventing pathogens from entering the body the hairs in the nasal passages help to filter out bacteria and foreign particles in the air while the lining of the trachea and bronchi produces mucus that traps pathogens and forms a protective layer the mucus is then carried away from the lungs by ciliated cells in the epithelium finally white blood cells attack pathogens that found their way into the blood and tissues many pathogens are highly transmissible so control measures are put in place to limit their spread you need to explain the importance of a clean water supply hygienic food preparation good personal hygiene waste disposal and sewage treatment so water contaminate related with sewage or animal waste contains harmful bacteria and could infect vast numbers of people if used for drinking to prevent this from occurring raw sewage should be treated and kept away from water supplies and drinking water should be purified water treatment involves filtration to remove larger particles and chlorination which kills the pathogens those who don't have access to a treated water supply can boil it instead as bacteria viruses and other pathogens are unable to survive at such high temperatures raw meat carries bacteria that may cause food poisoning if consumed this can be avoided by thoroughly cooking the meat consuming pasteurized milk and eggs washing the hands regularly and ensuring that uncooked meat is prepared separately from any food that's likely to be consumed raw in addition previously cooked food should never be warmed up as raising the temperature may cause bacteria to proliferate a variety of pathogens including the bacteria that cause typhoid are present in the feces of infected people and may be transferred if the sufferer doesn't wash their their hands in particular hands should be washed after using the toilet and before touching food pathogens that breed on rotting food and other waste may be transferred by the bodies of flies and Vermin if improperly stored or disposed of dustbins should be strong and have a closely fitting lid and the waste should be taken away and either burned or buried finally to prevent the harmful bacteria present in human feces from entering the water supply sewage must be treated in a sewage Works before being released into rivers okay so that's everything for core so we'll move on now to the extended content beginning with the term active immunity so active immunity can be defined as the defense against a pathogen by antibody production in the body antibodies produced by lymphocytes bind to antigens that line the surfaces of pathogens this either destroys the pathogens directly or marks them making it easier for phagocytes to locate and ingest them antigens and antibodies have specific shapes that are complementary meaning a particular antibody only binds to one kind of pathogen when an infection has been fought off some of the lymphocytes that produce the specific antibodies become memory cells and stay in the lymph nodes for some time if the same antigen is detected by the body a second time the memory cells quickly divide and make more antibodies to neutralize the threat this is called active immunity and explains why once you've recovered from a disease like chickenpox or measles you're very unlikely to catch the same disease again active immunity can also be gained by vaccination which will return to in just a moment but first a couple of points on passive immunity so passive immunity is a short-term defense against a pathogen by antibodies acquired from another individual newborn babies haven't had the time to build up an active immunity so instead receive antibodies from the mother antibodies are passed on in the last three months of pregnancy through the placenta and after the baby is born in breast milk this protects infants from Contracting diseases while their own immune systems are developing but it only only provide short-term protection as no memory cells are produced now whenever an individual is exposed to a pathogen to which they haven't yet gained an immunity the patient could suffer symptoms or even die before the white blood cells have had time to act to prevent this from happening vaccinations can be used to gain an active immunity beforehand weakened pathogens or their antigens are introduced to the body by injection or swallowing this stimulates an immune response by lymphocytes which produce the appropriate antibodies and then become memory cells if the person is exposed to the pathogen later they already have a long-term active immunity which stops the disease from developing finally you need to know about one specific transmissible disease so cholera is a disease caused by a bacterium which is transmitted in contaminated water when the bacteria are ingested they reproduce and invade the epithelial cells of the small intestine they release toxins that irritate the intestinal lining resulting in the secretion of large quantities of water and salts including chloride ions the ions draw even more water into the gut by osmosis causing serious diarrhea dehydration and even kidney failure treatment of Cholera involves intravenous rehydration and replacement of salts and the use of an antibiotic to kill the bacteria well done you've discovered absolutely everything you need to know on topic 10.1 diseases and Immunity if you enjoyed this video I'd really appreciate your subscription and I'll see you next time topic 11.1 gas exchange in humans