Defences Against Pathogenic Organisms

Defences Against Pathogenic Organisms Bacteria Defined in the dictionary as ‘a bacterium, virus, or other microorganism that can cause disease. Which can then be divided into different categories, bacterium, virus, fungus and finally protozoa. Bacteria can be in the form of many sizes and can cause such things as cholera and typhoid fever. The virus type of pathogens are much smaller than bacteria and have a ‘fragment of genetic material inside a protective protein coat’. They are also especially common of causing influenza. Fungi can look like mould and can cause such things like athlete’s foot. Protozoa can come in the form of contaminated food and some are parasites. They are organisms that live in or on, certain things. A very serious example of this type, is malaria. Features Virus Bacteria Fungus Protozoa Nutrition Do not have or need nutrition and do not eat anything Mostly are heterotrophic, which means they live from and off other organisms. Also ‘At an elementary level, the nutritional requirements of a bacterium such as E. coli are revealed by the cells elemental composition’. Absorbs nutrients like carbohydrates (glucose, fructose, xylose, sucrose) and also starches, cellulose, hemicelluloses and proteins. Require organic materials ‘which may be particulate or in solution’. They are holozoic. Reproduction Rely on host cells for the ‘machinery needed to survive and reproduce.’ Once finding a host, it then looks for host cells to take over and ‘slowly implants its genetic makeup into the cell.’ Reproduce by the process binary fission. Where the cells split into and divides into 2 identical daughter cells and ‘When conditions are favourable such as the right temperature and nutrients are available, some bacteria like Escherichia coli can divide every 20 minutes’. Environmental conditions can influence how this happens and usually sexual or asexual reproduction are the main methods. Some yeasts and funguses thrive in warm environments, and can multiply at an extremely fast pace. Also may be a sexual, and also reproduction by binary fission is very common here. Structure Their structure consists of a strand of nucleic acid, which is either DNA or RNA. Then it has something called a ‘capsid’ which is a protective protein coat. Bacteria have a cell wall with no nucleus and have two types of DNA- plasmid and chromosomal. Some are unicellular but most are multicellular which have cell walls and they are made of chitin. Single celled organisms that have a cell membrane, nucleus, cytoplasm and vacuole. Sources used Bbc bitesize . (2015). Whats in a cell?. Available: http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/cells/cells1.shtml. Last accessed 17th march 2015. Chris Sherwood . (2015). How Do Viruses Reproduce?. Available: http://www.ehow.com/how-does_4567511_viruses-reproduce.html. Last accessed 17th march 2015. Constantine John Alexopoulos . (2015). Fungus . Available: http://www.britannica.com/EBchecked/topic/222357/fungus/57967/Nutrition. Last accessed 17th march 2015. G gingham. (2014). Bacteria. Available: http://www.microbiologyonline.org.uk/about-microbiology/introducing-microbes/bacteria. Last accessed 17th march 2015 Kenneth Todar. (2014). Nutrition and Growth of Bacteria. Available: http://textbookofbacteriology.net/nutgro.html. Last accessed 17th march 2015. Robert G Yaeger . (2015). Protozoa . Available: http://www.ncbi.nlm.nih.gov/books/NBK8325/. Last accessed 17th march 2015. How does the body defend itself against pathogens which cause infectious disease? Pathogens can enter the body by ‘route of transmission’. People can pick up a pathogen by person to person contact with touch, saliva and contaminated blood or bodily fluids. Pathogens can also be transmitted through foods, water, insects and fomites. Food can be contaminated by unclean hands, unclean utensils, and is cross contaminated. Water can be contaminated by human or animal faeces which spreads the infection when drank, and insects can also carry a pathogen for example malaria. Lastly fomites are actually non-living but can spread pathogens by way of bedding, toys and wire for example. A common one is also athlete’s foot. Airborne pathogens enter through the nose and mouth of the body as you breathe, and food pathogens enter through your mouth and then into the digestive system. Also they can also enter into the blood stream through ‘vectors’ which is transmitted by mosquitos, fleas, ticks and contaminated needles. Breaks in the skin are also ways of entering. From the outside of the body the physical defences and barriers we have to help us are the skin which is a physical barrier, clotting which if skin is broken the blood clots to stop any entering, sebaceous and sweet glands that produce chemicals that kill bacteria, lysozyme which is in saliva and tears that kills bacteria, mucous membranes which secretes mucous and traps pathogens, nasal hairs that remove the organisms from the air, cilia force mucus to the pharynx for swallowing, hydrochloric acid kills microorganisms, and the vagina produces lactic acid which stops growth of pathogens and has a low ph and mucous membranes that kill bacteria. If the physical barriers cannot defend against pathogens, then a ‘second defence line’ takes over which is a general defence system. Phagocytes that are white blood cells engulf pathogens and macrophages which are a longer living phagocytes help digest the bacteria and protect the body. Substances that are produced by other proteins called complement defence proteins can help fight pathogens, and are produced in response to knowing the presence of foreign materials in the body and ‘burst or engulf the pathogen.’ Also interferons are proteins that help prevent spread of the virus, and inflammation are infected cells that produce a chemical histamine, and help more white blood cells get to the area to help fight infection. Antibodies play a special part to fight pathogens as they are ‘lymphocytes that produce antibodies as a result of antigens.’ These are proteins in the group called immunoglobulins. Each antigen will only stimulate the production of one specific antibody that will fit into its receptor area. This is called natural active induced immunity. It is protection gained against a particular pathogen by the production of specific antibodies after the antigen on the pathogen has been detected.’ Pathogens are prevented from entering a host cell by antibodies binding to the antigens which are on the surface of the pathogen, and pathogens can be burst by antibodies activating the complement system. -see diagram here T and B cells are lymphocytes, while t cells mature in the thymus gland and b cells mature in the bone marrow. The point of t cells, is that they are defenders that are activated in the thymus gland and do not actually produce antibodies but do help to protect in other ways. They have helper t cells which recognise antigens especially macrophages that multiply and enlarge and form helper t cells that produce chemicals (interferon) that then stimulate the forming of b cells. Then they stimulate the reproduction of killer t cells. Killer t cells produce and destroy abnormal body cells and release a protein named perforin which form pores in the membranes of the cells they attack and ‘Water and ions from the surroundings flow into the cells and burst them. This is called lysis.’ Suppressor t cells inhibit working after the pathogen is destroyed, and memory t cells survive for a long time and stimulate memory b cells to produce antibodies. B cells work in the lymphatic syste m ‘especially the spleen and lymph nodes’ and work on just one specific antigen and comes into contact with an antigen to then reproduce at a rapid pace which are plasma cells. They are very efficient and effective, but do only last a few days. Most b cells die within a few days like said before, but some do stay alive which are referred to as memory b cells and ‘When the same antigen becomes present in the organism these memory B-cells are already there to begin the production of plasma cells and antibodies.’ Which is secondary B cell response. These are more powerful because they are produced faster, more are produced, and they are produced to a smaller amount of antigen. The primary response of the immune system to infection is on the first time it is encountered and ‘Depending on the nature of the antigen and the site of entry this response can take up to 14 days to resolve and leads to the generation of memory cells with a high specificity for the inducing antigen.’ As soon as a foreign antigen is exposed, an even though no antibodies are produced activated b cells differentiate to plasma cells. Secondary response is the response to the antigen where there is a large production of amounts of antibodies. Memory cells help generate what type of antibodies to produce during an immune response. It is like a B cell that keeps a memory of the older lymphocyte that was generated when there was an immune response for a specific antigen. They act as guardians waiting for the return of the same antigen so they can recruit the immune system and mount an attack sooner and more aggressively. Sources used for this TAQ *Alexander A Ademokun. (2015). Immune Responses: Primary and Secondary. Available: http://www.els.net/WileyCDA/ElsArticle/refId-a0000947.html. Last accessed 17th march 2015. *bbc bitesize . (2015). Defending against infection. Available: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/human/defendingagainstinfectionrev1.shtml. Last accessed 17th march 2015. *ico praver . (2015). Routes of Transmission. Available: http://www.microbiologyonline.org.uk/about-microbiology/microbes-and-the-human-body/routes-of-transmission . Last accessed 17th march 2015. * S Detea . (2015). secondary response . Available: http://thesciencedictionary.org/secondary-immune-response/. Last accessed 17th march 2015. Immunity Natural Acquired Similarities Resist a specific disease. ‘Inflammation.’ Resist a specific disease. Inflammation.’ Involve the action of antibodies in the body somehow Involve the action of antibodies in the body somehow Technically use white blood cells to try and fight pathogen/ infection Technically use white blood cells to try and fight pathogen/ infection Differences Natural is from birth, and get it from being born and is ‘genetic’. You acquire this immunity after exposure to a pathogen. Remains throughout your life Can be short lived or life long This immunity has barriers that prevent entry of foreign agents Consists of special t and b cells and also antibodies that are in body fluid Response is immediate Response can take a few days, and is not immediate Sources used *Christopher Hassell. (2014). Acquired Immunity. Available: http://greaterimmunity.com/Files/acquired_immunity.html. Last accessed 18th march 2015 *Garland science . (2015). The immune system in health and disease. Available: http://www.ncbi.nlm.nih.gov/books/NBK27090/. Last accessed 18th march 2015 References and bibliography Alexander A Ademokun. (2015). Immune Responses: Primary and Secondary. Available: http://www.els.net/WileyCDA/ElsArticle/refId-a0000947.html. Last accessed 17th march 2015. Ananya Mandal. (2014). Cholera Transmission. Available: http://www.news-medical.net/health/Cholera-Transmission.aspx. Last accessed 16th march 2015. Arthur Schoenstadt. (2012). Malaria Transmission. Available: http://malaria.emedtv.com/malaria/malaria-transmission.html. Last accessed 16th march 2015. Bbc bitesize. (2015). Defending against infection. Available: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/human/defendingagainstinfectionrev1.shtml. Last accessed 17th march 2015. Bbc bitesize. (2015). Whats in a cell?. 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