topic 3

• Pathogens


  Microorganisms that cause infectious disease
• Examples of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• How bacteria make us ill

  • Reproduce rapidly inside the body
  • Produce toxins (poisons) that damage cells
• How viruses make us ill

  • Live and replicate rapidly inside cells
  • Causing cell damage eg. cell bursts

  
• How pathogens can be spread

  1. Direct contact eg. contact with contaminated surfaces / skin

  2. By water eg. by drinking / cooking with / bathing in

  3. By air eg. inhaling droplets from sneezes / coughs
• Ways to reduce or prevent the spread of diseases

  • Hygiene - eg. regular hand washing before preparing food, disinfecting surfaces
  • Vaccination - to provide immunity
  • Isolation - reduces contact with healthy people
  • Destroy vectors (organisms that transport the pathogen) eg. using insecticides (kills insects)
• Not all microorganisms are pathogens as not all cause disease. Many bacteria live in your body, eg. in your gut, and are important for health.
• Viruses are not cells. They live inside your cells and 'hijack' cell machinery to replicate themselves.
• A pathogen is a microorganism that causes disease.
• How measles is spread

  Inhalation of droplets from sneezes / coughs from infected people
• How HIV is spread

  1. Sexual contact

  2. Exchange of body fluids eg. blood when drug users share needles
• How tobacco mosaic virus (TMV) is spread

  Direct contact between diseased / healthy plants
• Ways to reduce or prevent the spread of measles

  • Most young children vaccinated against measles
  • Isolation

  
• Ways to reduce or prevent the spread of HIV

  • Antiretroviral drugs control HIV (to stop AIDS developing)
  • Avoid sexual intercourse / use a condom
  • Do not share needles
• Ways to reduce or prevent the spread of TMV

  • Remove infected plants / leaves
  • Wash tools in disinfectant after using on infected plant
• HIV is an infection caused by a virus whereas AIDS is the consequences in the body from HIV infection.
• HIV can be controlled with antiretroviral drugs. These stop HIV replicating, so the immune system doesn't get so damaged that AIDS develops. These drugs do not eliminate HIV completely though, so are not considered a cure.
• Antibiotics are only effective against bacteria.

  
• TMV causes restricted growth in plants

  • Less chlorophyll so less photosynthesis
  • So less glucose produced
  • So less energy released for growth as glucose is needed for respiration
  • Less proteins / cellulose for growth as glucose needed for making these
• Antibiotics are only effective against bacteria / do not kill viruses.

  
• Reasons for the decrease in the number of new HIV cases in recent years

  • Better education (into prevention of spread of HIV)
  • Condoms more widely available / easier to source / cheaper
  • New / better drugs / antiretrovirals to prevent HIV spread
  • Better / more testing / identification of people with HIV
• Poultry eg. chickens are vaccinated against Salmonella, not humans.
• Chickens can carry the Salmonella bacteria, but it only causes food poisoning (the disease) in humans.
• Warmer weather


  Bacteria reproduce faster
• Other ways farmers could prevent the transmission of Salmonella from chickens to humans

  • Give chickens antibiotics
  • Don't sell infected chickens / eggs
  • Keep infected chickens isolated
  • Slaughter infected chickens
• Reasons why the number of cases of Salmonella food poisoning has decreased

  • Improved hygiene for food preparation
  • Vaccination of poultry
• Rose black spot


  A fungal disease that causes purple / black spots on leaves, leaves often turn yellow & drop early, affects growth of plant as photosynthesis is reduced
• Malaria


  A protist disease that causes recurrent episodes of fever and can be fatal
• How rose black spot is spread

  In the environment by water or wind
• How malaria is spread

  1. Malarial protist has a life cycle that includes the mosquito, which is a vector

  2. Mosquito feeds on infected blood then bites a human

  
• Ways to reduce or prevent the spread of rose black spot

  • Fungicides (kill fungi)
  • Removing and destroying affected leaves
• Ways to reduce or prevent the spread of malaria

  • Prevent mosquitoes breeding eg. drain water holes → fewer to pass on pathogen
  • Mosquito nets (or insect repellent) → to avoid being bitten
• Malaria is caused by a protist that is carried by mosquitoes, so mosquitoes act as vectors.
• Reasons for the reduced number of deaths from malaria each year

  • Improved health care / new treatments
  • Changing behaviour to avoid being bitten (or give example)
• Bushes infected with rose black spots

  Show reduced growth
• Non-specific defence systems of the body

  • Skin: Tough / dry / dead outer layer / scabs form over cuts → acts as a barrier, Antimicrobial secretions → kill pathogens, Sebum / oil → repels pathogens
  • Nose: Hair and mucus → trap pathogens that enter
  • Trachea & bronchi: Produce mucus → traps pathogens breathed in, Cilia (hair-like structures) → waft mucus up to throat to be swallowed
  • Stomach: Contains hydrochloric acid → kills most pathogens in food / swallowed mucus
• Role of the immune system in defence against disease

  1. Phagocytosis - WBCs engulf and digest / destroy pathogens

  2. WBCs produce / release specific antibodies in response to antigens on surface of a pathogen, Antibodies attach / bind to antigens on the pathogen (with a complementary shape), Making pathogens clump together so more can be engulfed

  3. WBCs produce / release specific antitoxins in response to toxins (poisons) released by bacteria, Antitoxins neutralise / counteract toxins, So less cell damage → don't feel as ill

  4. Memory cells remain in the body after infection and produce antibodies faster & in larger quantities when it recognises the same antigen on reinfection

  
• Cells can't 'eat'. Instead, they engulf and destroy a pathogen.
• Antigens are unique molecules on the surface of pathogens that trigger an immune response. A pathogen is a microorganism that causes disease.

  
• Antibodies are protein molecules released by white blood cells in response to a particular antigen.