Pathogens:Pathogens are micro organisms that cause disease.There are four types of pathogens you'll need to know:- Bacteria- Viruses- Protists- FungiBacteria are small, prokaryotic cells that make you feel ill by reproducing rapidly inside your body, and producing harmful toxins that damage cells and tissues.Common examples of bacterial diseases or illnesses are:- Cholera- Typhoid- Food poisoning- GonorrhoeaViruses are not cells. They live inside cells and reproduce rapidly, until the cell bursts. Viruses escape through the airways and bloodstream and can spread through populations. The cell damage is what causes you to feel ill.Common examples of illnesses caused by viruses are:- Flu- Measles- Mumps- Common cold- AIDsSome fungi are single celled while others have a body made up of hyphae (thread like structures).Hyphae can grow and penetrate human skin and the surface of plants, causing diseases. The hyphae can produce spores which can be spread to other plants and animals.The most common fungal infection a human can get is athletes foot.Protists are single celled eukaryotics. Some protists are parisites.Parasites live on or inside other organisms and can cause them damage. They are often transferred to the organism by a vector e.g. an instect that carries the protist. An emaple of this is malaria. The protist lives in the bloodstream and is tranferred by mosquitos.

How can vaccine programmes be made more effective?* If a large proportion of the population is vaccinated i.e. a large percentage of people have been given the vaccine and so are immune. * This is because it reduces the spread of the pathogen. (Do not talk about the spread of disease, only the spread of what causes the disease e.g. pathogens)

* A lot of our current drugs were discovered by studying plants and micro-organisms (This is because plants produce a variety of chemicals to defend themselves against pests and pathogens). * The heart drug digitalis was developed from a chemical found in foxglove plants. * The painkiller aspirin was developed from a chemical found in the plant willow. * Penicillin was discovered by Alexander Fleming from the Penicillium mould. (Fleming was clearing out petri dishes containing bacteria when he noticed there was also mould on the dishes. The area around the mould had no bacteria in it – he found that the mould was making a chemical that killed the bacteria – this chemical was penicillin) * Most new drugs are synthesised (made) by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted (taken) from a plant.

How can an uncontaminated cult of bacteria be produced?*Using sterilised equipment (e.g. petri dish). *The equipment is normally sterilised by heating them to high temperatures. *This is done to kill any bacteria on the equipment. *The inoculating loop, which is used to transfer bacteria from the culture to the agar, is passed through a Bunsen flame to kill any bacteria on the loop. *The loop should be allowed to cool before it is put in to the culture so it doesn’t kill bacteria in the culture you are trying to collect bacteria from. *The loop should not be placed on the bench to cool as it could be contaminated with bacteria from the bench. *The lid of the petri dish is removed as little as possible and replaced quickly to prevent bacteria entering from the air and prevent bacteria from the petri dish escaping in to the air. *The petri dish is sealed with two small pieces of tape so that oxygen can enter the dish, which the bacteria need to grow. If the dish is sealed all the way around and no oxygen can enter then harmful pathogens can grow. *The petri dish is incubated in warm conditions to allow the bacteria to grow.

How are monoclonal antibodies produced?* Antibodies are produced by B-lymphocytes (a type of white blood cell). * Monoclonal antibodies are produced from clones of a single white blood cell (This means all of the antibodies are identical and will only target one specific protein antigen) * However, lymphocytes don’t divide very easily so it is difficult to grow more of them. * Tumour cells, on the other hand, don’t make antibodies but divide lots – so can be grown easily. * It is therefore possible to fuse a mouse B-lymphocyte with a tumour cell to create a cell called a hybridoma. The hybridoma cell can divide and make the antibody. * Hybridoma cells can be cloned to get lots of identical cells. These cloned cells all produce the same antibodies (monoclonal antibodies). * A large amount of the antibody can be collected and purified. * The antibodies are specific to one binding site on one protein antigen and so are able to target a specific chemical or specific cells in the body. You can make monoclonal antibodies that bind to anything you want e.g. an antigen that’s only found on the surface of one type of cell.

How can monoclonal antibodies be used?* For diagnosis such as in pregnancy tests * in laboratories to measure the levels of hormones and other chemicals in blood, or to detect pathogens * in research to locate or identify specific molecules in a cell or tissue by binding to them with a fluorescent dye * to treat some diseases: for cancer the monoclonal antibody can be bound to a radioactive substance, a toxic drug or a chemical which stops cells growing and dividing. It delivers the substance to the cancer cells without harming other cells in the body.

How are monoclonal antibodies used in pregnancy tests?* A hormone called HCG is found in the urine of pregnant women * Pregnancy testing sticks detect this hormone. This is how they work: * The bit of the stick you wee on has some antibodies to the HCG hormone with blue beads attached. * The test strip (which turns blue if you are pregnant) has some more antibodies to the hormone stuck on to it, so they can’t move. * The HCG hormone binds to the antibodies on the bit of the stick where you wee and the antibodies on the test strip. If you’re pregnant and you wee on the stick: * The HCG hormone binds to the antibodies attached to the blue beads. * The urine moves up the stick carrying the HCG hormone and the blue beads with it. * The blue beads and HCG hormone bind to the antibodies on the test strip – so the antibodies get stuck on the test strip turning it blue – showing you are pregnant. If you’re not pregnant and you wee on the stick: * The urine still moves up the stick carrying the blue beads. * But because there is no HCG hormone to bind to the antibodies on the test strip it doesn’t go blue.

How are monoclonal antibodies used to treat diseases?* Different cells in the body have different antigens on their surface – so you can make monoclonal antibodies that will bind to specific cells in the body. * Cancer cells have antigens on their cell membrane that are not found on normal body cells – they’re called tumour markers. * In labs you can make monoclonal antibodies that will bind to these tumour markers. * An anti-cancer drug can be attached to these monoclonal antibodies. This might be a radioactive substance, a toxic drug or a chemical which stops cancer cells growing and dividing. * The antibodies are given to a patient through a drip. * The antibodies target specific cells (the cancer cells) because they only bind to the tumour markers. * The drug kills the cancer cells but doesn’t kill any normal body cells near the tumour

Cancer* Cancer is the result of changes in cells that leads to uncontrolled growth and division. * Benign tumours are growths of abnormal cells which are contained in one area, usually within a membrane. They do not invade other parts of the body. * Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours. * Scientists have identified lifestyle risk factors for various types of cancer e.g. smoking and lung cancer, obesity and cancers of the bowel, liver and kidney. U.V. radiation from the sun can also cause skin cancer. * Viral infections can also be a risk factors for certain cancers e.g. HPV and cervical cancer. * There are also genetic risk factors for some cancers e.g. having certain faulty genes has shown an increased likelihood of developing breast and ovarian cancer.

Natural Immunity* If your white blood cells have made a particular antibody in the past they can remember how to make that particular antibody. * If you have an illness caused by a particular pathogen your white blood cells produce the correct antibody and destroy the pathogen. * If you are infected by exactly the same identical pathogen your white blood cells will remember how to make the correct antibody, produce it quickly and destroy the pathogen before it can make you ill. * If the pathogen is different it will have different antigens on its surface and your white blood cells will need to make a different antibody to destroy it. – You can become ill while you are waiting for your white blood cells to make the correct antibody.