hi everyone welcome to IGCSE study buddy where you can revise biology topics from the Cambridge IGCSE syllabus if you are enjoying this video so far please don't forget to hit the like button and subscribe to my channel this video summarizes chapter 10 diseases and immunity a pathogen is a disease-causing organism a transmissible disease is a disease in which a pathogen can be passed from one host to another a pathogen is transmitted by direct contact including Through Blood and other body fluids so if a person directly gets in contact with the sufferer they might also get infected and may spread the disease examples include chickenpox that can spread just by touching or HIV that requires sexual contact for spreading a pathogen can also be transmitted indirectly including from contaminated surfaces food animals and Air so indirect contact transmission occurs when there is no direct human to human contact examples include getting infected by eating contaminated food or through a mosquito that may be carrying the pathogen or even by inhaling droplets that are spreading the air through coughs and sneezes from an infected person the body defends itself against disease in several ways kin the skin acts as a physical barrier to prevent pathogens from entering our body if the skin gets wounded it immediately starts healing itself forming a scab s in the nose nose hairs act as a natural filter to prevent the entry of pathogens into the lungs mucus mucus is a sticky substance so it traps pathogens before they can enter the lungs the trapped pathogen may be removed by blowing the nose swallowing Etc stomach acid stomach acid is a chemical barrier against infection stomach acid contains hydrochloric acid which is strong enough to kill pathogens that may have been consumed with food or drink and finally white blood cells white blood cells defend the body against infections they fight off infections by carrying out phagocytosis and antibody production in the previous video we learned that there are two types of white blood cells phagocytes and lymphocytes phagocytes engulf and digest pathogens this is called phagocytosis lymphocytes produce antibodies we will learn more about this shortly the simplest way to prevent disease is to stop pathogens from spreading the following measures play an important role in controlling the spread of disease a clean water supply hygienic food preparation good personal hygiene waste disposal and sewage treatment so a clean water supply would control the spread of disease because contaminated water and poor sanitation are linked to the transmission of diseases such as cholera diarrhea dysentery and typhoid so having clean water means being able to avoid exposure to countless diseases hygienic food preparation washing hands before handling food and making sure the surfaces and utensils are clean before cooking food thoroughly at high temperatures help kill pathogens covering food ensures that flies can't land on it thereby making it difficult for them to transfer the germs they carry good personal hygiene washing hands with soap covering the mouth when sneezing or coughing washing hands after going to the toilet are good personal hygiene practices to follow and helps avoid the spread of disease waste disposal when rubbish is exposed it attracts flies which may carry disease so rubbish must be covered and disposed of in a proper manner sewage treatment homes and other buildings must have a proper sewage disposal method to remove feces from toilets safely sewage should be treated to kill pathogens before being disposed off in the environment let's learn about active immunity active immunity is a defense against a pathogen by antibody production in the body active immunity is gained after an infection by a pathogen or by vaccination so as we know a pathogen is a disease-causing organism each pathogen has a uniquely shaped marker on the surface of their membranes called antigens it is very important to understand that antigens are very specific in shape every pathogen is unique because they have differently shaped antigens on their cell surfaces each pathogen has its own antigens which have specific shapes lymphocytes produce proteins called antibodies which are a complementary shape to the antigens on the surface of pathogens antibodies are proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for Destruction by phagocytes specific antibodies have complementary shapes which fit specific antigens so let's look at an example let's say there's a pathogen with antigen a lymphocyte a has receptors that have a complementary shape to antigen a lymphocyte a gets activated and produces antibodies that have a complementary shape to antigen a these antibodies can lock onto antigen a and Destroy them the antibodies made by lymphocyte B on the other hand will not be able to fit in antigen a so how do the antibodies destroy the pathogen they attach themselves to the antigen and cause them to Clump or be stuck together this makes it difficult for the pathogen to move then they can be killed directly or marked for Destruction by phagocytes the antibody sends a chemical signal for phagocytes to come and engulf the pathogen so how do phagocytes destroy the pathogen we learned in the previous video that phagocytes engulf pathogens by a process called phagocytosis so basically when a phagocyte comes across a germ or pathogen it engulfs or surrounds it completely taking it inwards then it releases digestive enzymes on it which digests the pathogen and destroys it lymphocytes that have made antibodies for a particular pathogen also produce memory cells these are cells that remain in the blood even after the infection is over they are able to quickly produce the original antibodies if they were to come across the same pathogen again this is how people can become immune to certain diseases after only having them once an example is chickenpox most people who have had chickenpox will be immune to the disease for the rest of their lives therefore memory cells give long-term immunity let's move on to vaccination vaccination is a way of protecting the body against harmful diseases before we come into contact with them the process of vaccination is as follows weakened pathogens or their antigens are put into the body since the pathogen is weak it cannot cause illness but it can trigger an immune response the antigens stimulate an immune response by lymphocytes which produce antibodies memory cells are produced that give long-term immunity the memory cells remain in the blood and will quickly respond to the antigen if it is encountered again in an infection by a live pathogen so vaccination is done to stimulate the body's immune response against diseases so once again weakened pathogens are put into the body the antigens stimulate the lymphocytes to produce antibodies and memory cells are produced that give long-term immunity what is the role of vaccination in controlling the spread of diseases the effectiveness of a vaccine in a population depends on the proportion of people vaccinated when the majority of a population is vaccinated against a pathogen it breaks the pathogens Chain of Infection this means that the pathogen will have fewer places to breed and therefore it is unable to pass from person to person hence vaccination prevents the spread of disease this is known as herd immunity now let's learn about passive immunity passive immunity is a short-term defense against a pathogen by antibodies acquired from another individual examples of where these antibodies may be obtained are from across the placenta antibodies from mothers are passed to their unborn babies through the placenta and in breast milk breastfeeding is important for the development of passive immunity in infants antibodies pass from the mother to infant through breast milk this is important because a baby's immune system is not well developed and so the mother's antibodies can protect it against any diseases to which she is immune for the first few months of its life until their immune system is stronger passive immunity is a fast acting short-term defense memory cells are not produced in passive immunity now let's learn about cholera cholera is a disease caused by a bacterium which is transmitted in contaminated water cholera causes diarrhea which is the loss of watery feces from the anus how does this happen the cholera bacteria attached to the wall of the small intestine they produce a toxin the toxin causes the cells lining the intestine to secrete chloride ions into the small intestine this causes the water potential inside the intestine to reduce the water potential in the cells lining the intestine is higher therefore water moves from the cells to inside the small intestine via osmosis large quantities of water are lost from the body in watery feces or diarrhea this also leads to dehydration and loss of ions from the blood diarrhea can be effectively treated by Oral rehydration therapy this is a drink with a small amount of salt and sugar dissolved in it so that concludes chapter 10 diseases and Immunity hope this video helped you thank you for watching and please don't forget to subscribe to IGCSE study buddy for more biology revision videos bye bye