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B5: Communicable Diseases (Health and Disease (Diseases both communicable…
B5: Communicable Diseases
Health and Disease
Diseases both communicable and noncommunicable are major causes of ill health
Other factors including diet, stress and life situations may have a profound effect on both physical and mental health
Health is a state of both physical and mental wellbeing
Different types of diseases may and often do interact with each other
Pathogens and Disease
Bacteria and viruses reproduce rapidly inside your body- they can produce toxins that make you feel ill
Viruses live and reproduce inside your cells, causing cell damage
Communicable diseases are caused by pathogens, which include viruses, fungi and protists
Pathogens can be spread by direct contact, by air, by vectors and by water
Growing Bacteria
An uncontaminated culture of microorganisms can be grown using sterilised Petri dishes and agar jelly
You can sterilise the inoculating loop before use and fix the lid of the Petri dish to prevent unwanted microorganisms from getting in
Uncontaminated cultures of microorganisms are needed for investigating the action of disinfectants and antibiotics
Cultures should be incubated at a maximum temperature of 25°C in school and colleges to reduce the likelihood of pathogens growing that might be harmful to humans
Preventing Bacterial Growth
Bacteria multiply my simple cell division as often as every 20 minutes if they have enough nutrients and a suitable temperature
You can investigate the effects of disinfectants and antibiotics on bacterial growth using agar plates and calculating the cross sectional area of colonies grown or of clear agar
The spread of disease can be prevented by simple hygiene measures, by destroying vectors, by isolation of infected individuals and vaccination
Viral Diseases
Measles is spread by droplet infections. It causes fever and rashes and it can be fatal. Since there is no cure, isolation of patients and vaccination prevents spread
HIV is spread by sexual contact or exchange of bodily fluids. It initially causes flu-like symptoms but it it isn't controlled with antiretroviral drugs, the virus attacks the body's immune cells. Late-stage HIV (AIDS) occurs when the immune system becomes so badly damaged that it can no longer deal with other infections or cancers
Tobacco Mosaic Virus is spread by contact and vectors. It damages leaves and reduces photosynthesis. Since there is no treatment for it, spread is prevented by field hygine and pest control
Bacterial Diseases
Gonorrhoea is a STD. Symptoms include discharge from the genitals and pain during urination. Treatment includes using antibiotics, however, many strains are becoming resistant. Use of condoms limits spread
There are relatively few bacterial diseases in plants, but
Agrobacterium Tumefaciens
causes galls
Salmonella is spread by undercooked food and poor hygiene. Symptoms include fever, abdominal cramps, diarrhoea and vomiting. In the UK, poultry are vaccinated against salmonella to control the spread of the disease
Diseases Caused by Fungi and Protists
Rose black spot is a fungal disease spread in the environment by wind and water. It damages leaves so they drop off, affecting growth as photosynthesis is reduced. Spread is controlled by removing the affected leaves and by chemical sprays, but they aren't very efffective
Malaria is caused by parasitic protists and is spread by the bite of female mosquitos. It damages the blood and the liver cells, causes fever and shaking, and can be fatal. Some drugs are effective if given early but protists are becoming resistant. Spread is reduced by preventing the vectors from breeding and by using mosquito nets to prevent bites
Human Defence Responses
Your body has several lines of defence against the entry of pathogens. These include the skin (barrier and antimicrobial), the nose, the trachea , the bronchi and the stomach
Your white blood cells help you to defend against pathogens by ingesting them and making antibodies and antitoxins
Plant Diseases
Plants can be damaged by a range of ion deficiency conditions
Plant diseases can be detected by a range of symptoms and identified in a number of ways, including gardening manuals and lab tests, some involving monoclonal antibodies
Plants can be infected by a range of viral, bacterial and fungal pathogens as well as insect pests
Plant Defence Responses
Chemical plant defences include antibacterial chemicals and poisons to deter herbivores
Many plants have mechanical adaptations against herbivores such as thorns or hairs, leaves that droop or curl when touched and mimicry to trick animals
Physical plant dfences include cellulose cell walls, tough waxy cuticles and layers of bark or dead cells/leaves which fall off