B2

• a communicable disease is a disease that can be spread from person to person
• what is the role of the immune system?

  to detect and destroy pathogens
• if your immune system is weakened, which type of diseases do you become more susceptible to?

  communicable diseases
• what is a pathogen?

  a micro-organism which can cause disease.
• four ways pathogens can be spread

  through the air

  by direct contact

  contaminated water

  contaminated food
• what diseases can you get through the air?

  influenza

  measles

  cold
• what diseases can you get from contaminated water?

  cholera
• what diseases can you get from contaminated food?

  salmonella
• what diseases can you get from direct contact?

  athletes foot
• how can we reduce the spread of infectious diseases?

  vaccination

  improving hygiene

  killing vectors that carry pathogens

  isolation
• how viruses spread and multiply

  Viruses pass between humans via the air, contaminated food or water, or by direct contact. As they can't reproduce themselves, viruses have to enter one of our cells, and then use it to create multiple copies of the virus itself. Once there are a lot of copies, the viruses cause the cell to burst, and then go on to infect the neighbouring cells.
• how can HIV be spread?

  sexual contact

  exchange of bodily fluids
• what is AIDS

  where the immune system is so weak the person can catch unusual infections
• what is the main symptom of TMV

  patches of leaves get discoloured
• what are the consequences of TMV photosynthesising less?

  the plant won't be able to grow as well

  the plant won't be able to produce as many sugars
• Bacteria release small proteins called toxins. These can damage our cells and are responsible for many symptoms of bacterial diseases
• bacterial diseases

  salmonella

  gonorrhoea
• ash dieback

  pathogen - fungus

  transmission - airborne spores often through the wind

  symptoms - wilting, dieback of leaves, wounds on the bark

  treatment - none

  prevention - removing infected trees, biodiversity in tree populations, restricting movement of ash trees
• eukaryotic organisms

  animals

  fungi

  plants

  protoctists
• Rose black spot is a fungal disease that causes purple or black spots on the leaves, which often turn yellow and fall off. This reduces photosynthesis and therefore the growth of the plant. It can be spread by water or the wind. Treatment involved spraying the plant with fungicide or destroying the affected leaves.
• Protists are considered parasites. This means they live in a host organism and get their food at the expense of the host.
• how can we reduce the spread of malaria

  mosquito repellent

  mosquito nets

  destroy mosquito breeding sites
• three main causes of plant disease

  infection by micro-organisms

  attack by insects

  lack of essential minerals
• how does the pathogen that causes crown gall disease enter the plant?

  through wounds on the plant
• why do plants require nitrates?

  to make proteins
• what is a symptom of nitrate deficiency (lack of nitrates) in a plant?

  stunted growth
• why do plants require magnesium?

  to make chlorophyll
• what is the main symptom of magnesium deficiency (lack of magnesium) for a plant?

  chlorosis - yellow leaves
• three physical changes that indicate a plant has a disease

  stunted growth

  spots of leaves

  discolouration
• three ways a plant disease can be identified

  compare symptoms to a gardening manual

  use testing kits that contain monoclonal antibodies

  test the DNA of the pathogens
• what's a physical defence

  defences that physically prevent the entry of pathogens
• what are physical defences of plants?

  strong cellulose cell walls

  waxy cuticle on stems and leaves

  layers of dead cells around the trunk
• whats a chemical defence

  chemicals that plants secrete to destroy pathogens
• what are chemical defences of plants?

  production of antimicrobial substances

  production of poison that kills insects
• whats a mechanical defence

  structures that reduce the chance of being attacked
• what are mechanical defences of plants

  hairs and thorns

  leaves that droop or curl when insects land on them

  mimicking other organisms to trick animals
• An antigen is any substance that your body sees as foreign, which then causes your immune system to produce antibodies against it. For example, the toxins and cell walls of pathogens would be considered antigens.
• An antibody is a protein produced by our white blood cells that binds to specific antigens. This acts as a signal to our immune system to destroy the antigen or the pathogen it is a part of.
• The first time you're infected with a new pathogen, you normally get quite ill as it takes your body time to identify and destroy the pathogens. 

  However, in the process, you also develop memory cells, which are a special type of white blood cells that remember the pathogen for next time. 

  This means that if you're infected again your immune system can respond more quickly and powerfully - and so you don't get as ill
• barriers that reduce the entry of pathogens

  enzymes in tears

  skin

  nose hair