Biology Y9 B2-B2.8

• Pathogens


  Organisms that cause disease
• Four major types of pathogen

  • Bacteria
  • Fungi
  • Protozoa
  • Virus
• How pathogens cause illness


  • Toxins
  • Reproduction
  • Immune response

  
• How pathogens are spread

  • Direct contact
  • Indirect contact
  • Food and water
  • Airborne droplets
  • Insect bites
• Natural defences


  • Physical and chemical barriers (First Line)
  • Non-specific defences (Second Line)
  • Pathogen-specific defences (Third Line)
• Tuberculosis (TB)


  Infectious disease caused by the bacteria Mycobacterium tuberculosis, attacking the respiratory system
• Infectious diseases usually decline as living conditions and standards of healthcare improve
• Painkillers can relieve the symptoms of an infection but do not kill the pathogen
• Invasion of pathogen


  1. Pathogen enters body

  2. Immune system mounts attack

  3. Pathogen reproduces and makes toxins

  
• Lymphocytes


  Type of white blood cell found in blood or lymph nodes, made by bone marrow, including T-lymphocytes and B-lymphocytes
• Antibodies


  • Special Y-shaped proteins produced by B-lymphocytes in response to antigens, binding to and labelling pathogens for destruction

  
• Delayed response


  It takes a few days to produce enough antibodies to destroy the pathogen
• Active immunity


  Memory cells remain after pathogen is destroyed, recognizing the pathogen if it re-infects and mounting a quicker, more effective immune response
• Vaccines


  Contain a small amount of dead or weakened pathogen particles, stimulating antibody and memory cell production without making the person ill
• MMR vaccination rates used to be high, but fell following a media scare story about a speculative link between MMR and autism
• Independent expert scientists re-examined the original research and found no evidence of a link between the MMR vaccine and autism
• If 95% of children had the MMR jab the diseases could be wiped out in the UK, this is called herd immunity
• Antibiotics


  Drugs used to treat bacterial infections, either bactericidal (kill bacterial cells) or bacteriostatic (slow bacterial growth/reproduction)
• Antibiotics are effective against prokaryotic cells but generally leave human cells unharmed

  
• Antibiotic resistance


  Bacteria with resistance to an antibiotic have an advantage and can survive and reproduce, giving rise to a population of resistant bacteria
• Antibiotic resistance is evolving faster than the development of new antibiotics
• Mutations of bacterial pathogens produce new strains, some of which may become immune to antibiotics
• The evolution of antibiotic resistance is an example of natural selection
• Methicillin-resistant Staphylococcus aureus (MRSA) is becoming common in hospitals and can cause life-threatening infections
• Methods to prevent and control antibiotic resistance

  • Antibiotics should only be prescribed when needed
  • Patients should finish the complete course of antibiotics
  • Introduction of infection control in hospitals
• Pathogen


  A microorganism that can cause a disease
• Pathogens can be passed on from one person to another. Diseases caused by pathogens are known to be COMMUNICABLE DISEASES
• Types of pathogens


  • Viruses
  • Bacteria
  • Fungi
  • Protists
• Viruses


  • Not considered as living organisms as they cannot survive outside a host
• Bacteria


  Prokaryotes that do not contain mitochondria and produce toxins
• Fungi


  Can be single or multicellular, cell wall made from chitin, have thread-like structures called hyphae

  
• Single cellular fungus


  • YEAST
• Multicellular fungus


  • MUSHROOM
• Protists


  Single celled eukaryotic organisms, may be parasitic and can cause malaria

  
• Viruses reproduce rapidly inside host cells until they burst open
• Viruses are too small in size to observe under the light microscope. To see a virus we would need a special microscope called an Electron Microscope

  
• We do not have any slides of viruses under the microscope
• Bacteria and protists can be observed under the light microscope
• Pathogens can cause communicable diseases
• Not all diseases are infectious