Infection and response

• Pathogens


  Microorganisms that enter the body & cause disease.

  Cause Communicable disease: easily spread

  Can infect both plants and animals
• Bacteria


  cells reproduce rapidly in body

  cause illness by producing toxins; damage cells and tissues.
• Virus

  Not cells, reproduce rapidly

  live in cells to produce copies

  cause illness when the cell burst which release all new viruses
• Protists

  • Eukaryotes, single celled
  • some are parasites, live in organisms and cause damage
• Fungi

  • some are single celled, some are hyphae(Thread-like)
  • Hyphae grow on human skin and plants to cause disease
  • also produce spores, can spread to others
• Ways pathogens are spread:

  • Water: drinking/ bathing in dirty water
  • Air: carried in air and breathed in
  • Direct Contact: touching contaminated surfaces, including skin
• Measles

  • Virus
  • spread by droplets; sneeze or cough
  • Symptoms: fever, red skin rash
  • fatal; leads to inflammation of brain & lung infection
  • Most teens are vaccinated
• HIV

  • Virus
  • Spread by sexual contact & exchanging body fluids (sharing needles)
  • Symptoms: flu-like illness
  • Can be controlled with antiretroviral drugs
  • Can leads to Late stage HIV infection/ AIDs
  • when body'd immune system can deal with infections (badly damaged)
• Tobacco Mosaic Virus (TMV)

  • Virus
  • affects many species of plant
  • Symptoms: mosaic pattern, discolouration
  • discolouration means plant can't carry out photosynthesis, affects growth
• How to reduce or prevent disease?

  • Being hygienic: washing hands
  • Destroying vectors: getting rid of organisms that spread disease
  • Isolating infected individuals: prevent them to pass it on to others
  • Vaccination: vaccine against disease means infection can't be developed.
• Salmonella

  • Bacteria
  • Cause by toxins bacteria produced
  • Cause by eating contaminated food; food poisoning
  • Symptoms: fever, cramps, vomiting, diarrhoea
  • Most poultry have vaccine to control spread
• Gonorrhoea

  • Cause by Bacteria
  • Sexual transmitted disease
  • Symptoms: thick yellow/ green discharge from vagina/ penis, pain when urinating
  • easily treated with antibiotic penicillin
  • Prevent using contraception; ie condoms
• Rose Black Spot

  • Fungus
  • Causes purple/ black spots on leaves of rose plants (turn yellow)
  • affects growth as less photosynthesis
  • spread in water & wind
  • treat with fungicides/ removing affected leaves
• Malaria

  • Protist
  • Causes recurrent episodes of fever, can be fatal
  • spread by mosquito
  • prevent by stoping breeding and using mosquito nets
• Defence system in human body against pathogens

  • Skin: barrier, secretes antimicrobial substances (kill pathogens)
  • Nose: hair & mucus to trap particles containing pathogens
  • Trachea & Bronchi: secrete mucus to trap pathogens. Lied with cilia, waft mucus to back of throat so it can be swallowed.
  • Stomach: hydrochloric acid to kill pathogens.
• How does the immune system destroy pathogen?

  1. Phagocytosis
  2. Antibody production
  3. Antitoxin production

  This protects us incase the same type of pathogen invades us again in the future.
• Phagocytosis

  • White Blood cell detects chemical and moves towards it
  • It then ingest the pathogens
  • WBC uses enzymes to destroy pathogens.
• Antibody production

  • antibodies are proteins produced by White Blood cells.
  • Antibodies are specific to that type of antigen, they find and destroy pathogens
  • Antibodies are produced rapidly
  • If 1 is infected with same pathogen again, WBC produce antibodies to kill it (rapid), person is immune.
• Antitoxin production

  • White Blood Cells produces antitoxins
  • they stick to toxins to prevent them to damage cells.
• How does vaccine works?

  • inject small amount of dead/inactive pathogens
  • these carry antigen to stimulate the white blood cells to produce antibodies
  • WBC can produce correct antibodies quickly, prevents infection.
• Pros and Cons of vaccination:

  • Controls lots of communicable diseases
  • Epidemics (outbreak of disease) can be prevented if large % is vaccinated
  • Some don't give you immunity
  • Bad reaction of vaccine
• Antibiotics (penicillin)

  • cure disease by killing infective bacteria
  • different antibiotics kill different types of bacteria
  • useful, greatly reduced death
  • cannot kill viruses; virus reproduce with body cells, and antibiotics does not destroy body cells
• Painkillers (aspirin) & other drugs

  • relieve pain
  • It only reduce the symptoms, but cannot kill pathogens
• How is bacteria resistant to antibiotics?

  • bacteria mutate (change) and can cause resistance.
  • bacteria might be resistant when infection occurs
• Discovery of drugs

  • Traditionally drugs were extracted fro plant and microorganisms
  • Digitalis (♡ drugs), was found in foxgloves
  • Aspirin, originates from willow
  • Penicillin, Alexander Fleming from the Penicillium mould
  • New drugs are synthesised by chemists in the pharmaceutical industry.
• Development of Drugs:

  • Medical drugs has to be tested and trialled before being used to ensure they are safe and effective.
  • New drugs are tested for toxicity, efficacy, dose.

  1. Preclinical testing: done in lab with cells, tissue and live animals
  2. If test passes on animals, Clinical trials is done.
  3. This uses healthy patients and volunteers
  4. low doses of drug is given
  5. If drug is safe, further clinical trials is carried out to find optimum does
  6. Double blind trials, some are given a placebo(appears real but no effect)
• Monoclonal antibodies:

  • Antibodies; produced by WBC called lymphocytes
  • Lymphocytes produce antibodies against anything body detects foreign (ANTIGEN)
  • Monoclonal antibodies are produced from single clone hybridoma.
  • Antibodies are specific to 1 binding site on 1 protein antigen
  • target specific chemical/ cells
• Process of producing Monoclonal Antibodies:

  1. Inject mouse with Antigen
  2. lymphocytes will produce antibodies against the Antigen
  3. Collect lymphocytes from mouse & fuse with tumour cell
  4. Hybridoma formed: produce Antibodies & divide by mitosis
  5. Hybridoma cells are cloned (single) to get lots of them
  6. These produces antibodies, it's collected and purified
• Uses of Monoclonal Antibodies:

  • Pregnancy test: antibodies binds to specific hormone in urine
  • Measure level of hormones/ chemicals in blood, or detect pathogens
  • locate/identify specific molecules in cell/tissue
  • treat diseases
• How to detect plant diseases?

  • stunted growth
  • spots on leaves
  • areas of decay
  • discolouration
  • malformed stems/leaves
• How to identify plant diseases?

  • reference to gardening manual/website
  • take plants to a lab to identify pathogens
  • testing kits contains monoclonal antibodies
• Deficiency of plants:

  • Nitrate deficiency: causes stunted growth, as less protein synthesis occurs.
  • Magnesium deficiency: causes chlorosis (yellow leaves), not enough chlorophyll is made for photosynthesis
• Physical Defences:

  • response to resist invasion of microorganisms
  • cellulose cell walls; physical barrier against pathogens
  • waxy cuticle; barrier to stop pathogens entering
  • layers of dead cells around stems; barrier
• Chemical defences:

  • Produce antibacterial chemicals; kill bacteria
  • Poisons; deter herbivores (organisms that eats plants)
• Mechanical Defences:

  • Thorn and hair: deter animals
  • Leaves that droop/curl; prevent being eaten by insects
  • Mimic other organisms; trick animals