infection and response

• salmonella

  • type of bacteria, causes food poisoning
  • symptoms: fever, stomach cramps, vomiting, diarrhea (caused by toxins from bacteria)
  • can get it by: eating food with salmonella arlresdy in it or eating food made where bacteria is present
  • most poultry given vaccination to control spresd of salmonella in the uk
• gonorrhoea

  • caused by bacteria, sexually transmitted disease
  • passed on by sexual contact (unprotected sex)
  • symptoms: pain when urinating, thick yellow or green discharge from vagina or penis
  • used to be treated with penicilli, now new strains of gonorrhoea that are resistant to penicillin (antibiotics don’t work anymore)
  • to prevent spread: treated with other antibiotics, use barrier methods eg condoms
• measles

  • viral disease, spread by droplets from infected sneeze or cough
  • develop red skin rash and fever
  • possible death if complications
  • most people are vaccinated
• HIV

  • virus spread by sexual control or bodily fluid exchange (sharing needles when taking drugs)
  • causes flu like symptom for a few week, doesn’t usually have symptoms after that for several years
  • can be controlled by antiretroviral drugs. stop viruses form copying itasks in the body
  • if not controlled, virus attached immune cells so it can’t cope with other infections of cancers = late stage HIV infection or AIDS
• Tobacco Mosaic virus

  • virus that affects plants
  • causes leaves to become discoloured
  • these leaves have less chlorophyll to absorb light
  • means less photosynthesis is happening so plants can’t make enough food to grow
• Rose black spot

  • fungal disease
  • causes purple or black spots on leaves of rose plants, leaves can turn yellow and drop off
  • means less photosynthesis so plant doesn’t grow well
  • spreads through water or wind
  • can treat with fungicides (chemicals that kill fungi)
  • strip affected leaves off plant, then destroyed so fungus can’t spread
• Malaria

  • caused by protist
  • part of protists life cycles take place inside mosquito- mosquitos are vectors which spread malaria
  • mosquiots pick up protist when feed on infected animals
  • they don’t get malaria but they pass on when they bite other animals
  • these animals get malaria
  • causes repeating episodes of fever, people can die
  • can be reduced by stopping mosquito breeding and using mosquito nets
• Pathogens are microorganisms that enter the body and cause disease
• Pathogens cause communicable (infectious) diseases
• Communicable diseases are diseases that can spread
• Both plants and animals can be infected by pathogens
• Main types of pathogens

  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Ways pathogens can be spread

  • Air
  • Direct contact
  • Water
• Reducing or preventing the spread of disease

  1. Being hygienic (clean)

  2. Destroying vectors

  3. Isolating infected individuals
• Viruses

  • They are not cells, they are much smaller
  • They reproduce rapidly inside your body
  • They live inside your cells
  • Inside your cells, they make lots of copies of themselves
  • The cells will usually then burst, releasing all the new viruses
  • This cell damage is what makes you feel ill
• where do viruses live in the human body?

  inside cells
• The human body's defence system

  • Skin slags pathogens getting inside
  • Releases substances that kill pathogens
  • Nose hairs trap particles that could contain pathogens
  • Mucus in trachea and bronchi traps pathogens
  • Cilia in trachea and bronchi move mucus up to be swallowed
  • Stomach acid kills pathogens
• How the immune system attacks pathogens

  1. Phagocytosis - white blood cells engulf and digest pathogens

  2. Producing antibodies - white blood cells make antibodies specific to antigens on pathogens

  3. Producing antitoxins - stop toxins produced by invading bacteria
• Antigen

  Molecules on the surface of a pathogen
• How vaccination works

  1. Injecting small amounts of dead or inactive pathogens

  2. Antigens cause white blood cells to produce antibodies

  3. Antibodies can quickly kill the pathogen if infected later
• Drugs that get rid of symptoms

  Don't kill the pathogens causing the disease
• Drugs that cure the problem

  • Kill the specific pathogens
  • Reduce deaths from communicable diseases caused by bacteria
• Antibiotics are used to treat viruses
• Viruses reproduce using host cell machinery, making them difficult to destroy without killing the host
• Bacteria can become resistant to antibiotics

  • Mutations cause bacteria to become resistant
  • Resistant strains increase due to natural selection
• Many drugs came from plants

  • Plants produce chemicals to defend against pests and pathogens
  • Some of these chemicals can be used as drugs
• Examples of drugs from plants

  • Aspirin from willow
  • Digitalis from foxgloves
• Drugs from microorganisms

  Penicillin from Penicillium mould
• Stages in developing new drugs

  1. Preclinical testing on cells, tissues, animals

  2. Clinical testing on healthy volunteers, then patients

  3. Optimum dose found

  4. Patients divided into drug and placebo groups

  5. Double-blind trials

  6. Results peer reviewed
• skin

  stops pathogens getting inside you and releases substances that kill pathogens
• nose hairs


  trap particles that could contain pathogens
• Mucus


  the trachea and bronchi release mucus to trap pathogens
• cilia


  trachea and bronchi are like with cilia, move up the mucus to the back of the throat where it can be swallowed
• stomach acid


  stomach makes hydrochloride acid that kills pathogens in the stomach
• how do bacteria become resistant to antibiotics

  through mutation, resistant strains of bacteria have increased as result of natural selection
• antibiotic resistance is increasing because people don't finish taking all the tablets even if they feel better
• what is a drug tested on in a clinical trail?

  human volunteers
• what is a double blind trial


  neither the patient of the doctor know who is receiving the drug and who is receiving the placebo