B5 - Communicable diseases

• Pathogens


  Microorganisms that cause disease
• Pathogens


  • bacteria
  • fungi
  • protists
  • viruses
• Viruses


  • measles
  • HIV
  • TMV
• Measles


  • Spread by:
  • inhalation of droplets produced by infected people when sneezing or coughing
  • Symptoms
  • fever
  • red skin rash
  • complications can be fatal
  • young children are vaccinated to immunise them
• HIV


  • Human Immunodeficiency Virus
  • Spread by:
  • sexual contact
  • exhange of bodily fluid
  • Symptoms
  • flu-like symptoms at first
  • virus attacks the body's immune system
  • can lead to AIDS
  • the immune system is so damaged that it cannot fight off infections or cancer
• TMV


  • Tobacco mosaic virus
  • Spread by:
  • direct contact of plants with infected plant material
  • animal and plant vectors
  • the pathogen can remian in soil for decades
  • Symptoms:
  • mosaic pattern of discolouration on the leaves
  • chlorophyll is destroyed
  • reduces the plant's ability to photosynthesise
  • affects growth
• Bacteria


  • Reproduce rapidly inside organisms and may produce toxins that damage tissues and cause illness
• Bacteria


  • Salmonella
  • Gohorrohea
• Salmonella


  • Spread by:
  • bacteria in or on food that is being ingested
  • Symptoms
  • fever
  • abdominal cramps
  • vomiting
  • diarrhoea
  • Prevention and treatment
  • poultry are vaccinated against Salmonella bacteria to control spread
• Gonorrhoea 


  • Spread by:
  • direct sexual contact
  • a sexually transmitted disease
  • Symptoms:
  • thick yellow or green discharge from the vagina or penis
  • pain when urinating
  • Prevention and treatment
  • antibiotics
  • however, many antibiotic-resistant strains have appeared
  • barrier methods of contraception
  • e.g. condoms
• Fungi


  • Rose black spot
• Rose black spot


  • Spread by:
  • water and wind
  • Symptoms
  • purple or black spots on leaves, which turn yellow and drop early
  • reduces plant's ability to photosynthesise, affecting growth
  • Prevention and treatment
  • fungicides
  • affected leaves removed and destroyed
• Protists


  • Malaria
• Malaria

  • Spread by:
  • mosquitos feed on the blood of infected people and spread the pathogen when they feed on another person
  • organisms that spread pathogens are called vectors
  • Symptoms
  • recurrent episodes of fever
  • can be fatal
  • Prevention and treatment
  • prevent mosquito vectors breeding
  • mosquiot nets to prevent bites
  • anti-malarial medicine
• Controlling the spread of communicable diseases


  • Hygiene
  • Isolation
  • Controlling vectors
  • Vaccination
• Hygiene


  • hand washing
  • disinfecting surfaces and machinery
  • keeping raw meat separate
  • covering mouth when sneezing / coughing
• Isolation

  • isolation of infected individuals
  • people, animals and plants can be isolated to stop the spread of disease
• Controlling vectors


  • destroying or controlling the population of a vector can limit the spread of disease
• Vaccination


  • Can protect large numbers of individuals against diseases
• Signs that a plant is diseased


  • stunted growth
  • spots on leaves
  • areas of rot or decay
  • growths
  • malformed stems or leaves
  • discolouration
  • pest infestations
• Ways of identifying plant diseases


  • gardening manuals and websites
  • laboratory testing of infected plants
  • testing kits with monoclonal antibodies
• Plant diseases caused by insects


  • Aphids are insects that suck sap from plant stems
  • this results in:
  • reduced rate of growth
  • wilting
  • discolouration of leaves
  • Ladybirds can be used to control aphid infestations as their larvae eat aphids
• Plant defences


  • Physical barriers
  • Chemical barriers
  • Mechanical adaptations
• Physical barriers

  • cellulose cell walls
  • provide a barrier to infection
  • tough waxy cuticle on leaves
  • bark on trees
  • a layer of dead cells that can fall off
• Chemical barriers


  • many plants produce antibacterial chemicals
  • poison production stops animals eating plants
• Mechanical adaptations


  • thorns and hairs stop animals eating plants
  • leaves that droop and curl when touched to scare herbivores or dislodge insects
  • some plants mimic the appearance of unhealthy or poisonous plants to deter insects or herbivores