Infection and response

• Pathogens are microorganisms that enter the body and cause disease.
• Four types of pathogen are bacteria, viruses, fungi and protists.
• Bacteria make you feel ill by releasing toxins that damage your cells and tissue.
• Viruses are not cells.
• Viruses live inside your cells and replicate themselves using the cell's machinery. The cell then bursts and the virus is released. The cell damage makes you feel ill.
• All protists are eukaryotes.
• Some protists are parasites, and are often transferred by a vector that doesn't get the disease.
• Some fungi are single celled, while others are made up of hyphae which can penetrate human skin or the surface of plants.
• Fungi release spores which can spread to other organisms.
• Pathogens can be spread in many ways:

  • water - e.g. cholera
  • air - e.g. the influenza virus
  • direct contact - e.g. athlete's foot
• Measles is a viral disease.
• Measles causes a red skin rash and a fever. If there are complications, it can lead to pneumonia or brain inflammation.
• Most people are vaccinated against measles when they are young.
• HIV is a virus spread by sexual contact, or exchanging bodily fluids like blood e.g. sharing needles.
• HIV can be controlled with antiretroviral drugs, which stop the virus from replicating.
• HIV attacks the immune cells.
• If HIV is left untreated, it can develop into AIDS.
• Tobacco mosaic virus (TMV) is a plant virus that causes discolouration on leaves.
• TMV makes it so that the plant cannot carry out photosynthesis very well, affecting growth.
• Rose black spot is a fungal disease.
• Rose black spot causes purple or black spots to develop of the leaves of rose plants. The leaves can then turn yellow and fall off.
• Rose black spot spreads through water or wind.
• Rose black spot can be treated by using fungicides and removing affected leaves. These leaves then need to be destroyed to prevent the spread of the disease.
• Malaria is caused by a protist.
• Mosquitoes are the vectors for malaria. They pick up the protist from feeding on infected animals.
• Every time a mosquito feeds on another animal, it infects it by inserting the protist into the animal's blood vessels.
• Malaria causes repeating episodes of fever. It can be fatal.
• The spread of malaria can be stopped by destroying mosquito breeding sites, and using insecticides and mosquito nets.
• Salmonella is a bacterial infection that causes food poisoning. This includes fever, vomiting, stomach cramps and diarrhoea.
• You can get salmonella from eating food that's been contaminated e.g. a chicken that caught the disease while alive, or food prepared in unhygienic conditions.
• In the UK, most poultry is vaccinated against salmonella.
• Gonorrhoea is an STD caused by bacteria.
• Gonorrhoea causes pain when urinating and a thick yellow/green discharge from the penis or vagina.
• Gonorrhoea was originally treated with penicillin, but there are now resistant strains of the bacteria.
• To prevent the spread of gonorrhoea, people can be treated with antibiotics and should use barrier methods of contraception like condoms.
• The spread of disease can be reduced by being hygienic (like washing hands), destroying vectors, isolating infected individuals, and vaccinating people.
• The skin acts as a barrier to pathogens. It also secretes antimicrobial substances.
• Hairs and mucus in your nose trap particles that could contain pathogens.
• The trachea and bronchi secrete mucus and are lined with cilia that move the mucus up to the throat where it is swallowed.
• The stomach produces hydrochloric acid that kills pathogens.