b5 - communicable disease

• infection cycle of malaria

  1. mosquitos spread it (as a vector)
  2. mosquitos inject the protists into the humans blood
  3. it bursts the red blood cells and multiplies
  4. another mosquito 'feeds' on the person
• mosquitos breed in standing water
• the mmr vaccine protects against measles, mumps and rubella
• droplet infection


  a cough or sneeze
• infections

  caused whenever a foreign pathogen invades an organism
• methods of transmission

  • air - influenza and measles can spread by small droplets of saliva that are expelled when we cough or sneeze, these droplets can then be inhaled by other organisms
  • water - cholera can spread through water sources contaminated by the diarrhoea (of infected people) or sewage
  • direct contact - athlete's foot is spread by walking barefoot on surfaces contaminated with the fungi
  • vector - mosquitoes can spread the malaria
• tmv

  tobacco mosaic virus
• aids

  occurs when a persons immune system has been badly damaged by hiv
• hyphae


  thread like structures that are able to grow and penetrate tissues
• measles

  • pathogen: virus
  • infects humans (specifically children)
  • method of transmission: air (spread in droplets when an infected person coughs or sneezes it is passed into a different person when the droplets are inhaled)
  • treatment: vaccination
  • symptoms: fever and rash
  • could lead to blindness and brain damage
• hiv

  • pathogen: virus
  • infects humans
  • method of transmission: exchange of fluids (sexual contact or sharing needles)
  • treatment: prevented by barrier methods or antiretrovial drugs
  • symptoms: recognised as a flu (sore throat, fever or headaches)
  • can lead to aids
• tobacco mosaic virus

  • pathogen: virus
  • infects plants
  • method of transmission: direct contact
  • treatment: isolation
  • symptoms: discolouration on leaves and affected growth
  • as the level of tmv infection increases, the rate of photosynthesis and growth decreases because there are less chloroplasts and less chlorophyll, meaning less light will be absorbed and less glucose is made
• salmonella

  • pathogen: bacteria
  • infects humans
  • method of transmission: water (ingesting infected food)
  • treatment: poultry vaccination and antibiotics
  • symptoms: food poisoning (vomiting, fever and stomach pain - due to the bacteria releasing toxins)
  • caused by food not being cooked properly or prepared in unhygienic conditions
  • can be found in chicken, raw meat or eggs
• gonorrhea

  • pathogen: bacteria (std)
  • infects humans
  • method of transmission: direct contact (sexual contact)
  • treatment: antibiotics or contraception
  • prevention: use a condom and limit sexual partners
  • symptoms: as yellow/green discharge or pain when urinating
  • could cause long term pelvic pain and infertility
• malaria

  • pathogen: protist
  • infects humans
  • method of transmission: vector (mosquitos)
  • mostly in tropical countries - suitable climate for mosquitos
  • symptoms: fevers and shaking
  • treatment: use mosquito nets, insecticides and remove standing water (to stop mosquitoes from reproducing) and take antimalarial drugs
  • damages blood and liver cells
• protists

  • type of pathogen
  • damages tissues, making people ill
  • eukaryotic
• rose black spot

  • pathogen: fungus
  • infects plants
  • transmission: direct contact
  • treatment: fungicides and removing effected leaves
  • symptoms: spots on leaves
• fungi

  • unicellular
  • made up of hyphae
• examples of disease in plants

  • rose black spot
  • tobacco mosaic virus (tmv)
• host cell

  a living cell that is capable of being invaded by a pathogen
• cilia

  • tiny hair like structures on the surface of the cell
  • the hairs sweep mucus, trapped dust and bacteria up to the back of the throat where it can be swallowed
• skin

  • covers the whole body - acts as a barrier
  • antimicrobial secretions
  • stops pathogens from entering
• scabs

  • form if you get a cut
  • stop pathogens entering
• stomach acid


  makes (hydrochloric) acid to kill pathogens that enter your food
• eyes

  • tear glands make a liquid that kills pathogens
  • eyelashes trap dirt and pathogens
• trachea

  • secrete mucus to trap pathogens
  • cilia moves mucus up the trachea to be removed
• transmission

  the spreading of pathogenic diseases
• fungicide


  a chemical that kills fungi
• how viruses spread and multiply

  1. they pass between organisms via air, water, or direct contact
  2. as they can't reproduce by themselves, viruses have to enter a cell and use it to replicate itself
  3. once there are lots of copies, the viruses cause the cell to burst, and then go on to infect neighbouring cells
• pathogen

  • a micro organism that can cause an infectious disease
  • exmaples: bacteria, viruses, protists and fungi
• communicable disease

  • a disease caused by a pathogen that can be transmitted from one organism to another
  • examples: measles, hiv and salmonella
• direct contact

  • when an infected organism infects a healthy one
  • examples: sexual contact, exchange of body fluids and mosquito bites
• vector

  • an organism that doesn't cause disease itself but spreads infection by conveying pathogens from one host to another
  • example: mosquitos
• bacteria and virus comparison

  • bacteria: larger and living pathogen, can be killed with antibiotics and damage cells to produce toxins
  • virus: smaller and non living pathogen, can't be killed with antibiotics (only treated) and invade cells, release toxins and stay in the host cell
• bacteria

  • contains: cytoplasm, cell membrane, plasmid, ribosome, cell wall and a loop of dna
  • examples: salmonella and gonorrhoea
  • reproduce in warm, moist areas with a good supply of oxygen
  • rapidly divide (by binary fission), damage cells and produce toxins (making us feel ill)
• virus

  • contains: genetic material, protein and a membrane
  • non living because they aren't made out of cells, don't grow and can't make their own energy (they can only reproduce after infecting a living cell)
  • invade host cells, live and reproduce in them and release toxins (which damages the cell)
  • examples: tmv, measles and hiv
• how to prevent the transmission of communicable disease

  • isolation - less people come into contact with the infected organism and the pathogen is less likely to be passed on
  • vaccination - a weakened, inactive or dead version of a pathogen that can make people immune to infection
  • hygiene - washing hands
  • destroy vector - use insecticide (kills mosquitos)
• how to control the spread of malaria

  • insecticide
  • mosquito nets - prevent bites
  • drain standing water
  • antimalaria drugs - kill the protists
• non specific defence system

  • the human body has developed physical defence systems to prevent pathogens from getting into the body and making us ill
  • examples: eyes, cilia, skin/scabs and stomach (acid)
• immune system

  • the body's defence system against entry of any foreign body (pathogens and agents such as pollen grains)
  • prevents disease