Evolution

• Pathogen


  Disease-causing agent
• Types of pathogens


  • Bacteria
  • Viruses
  • Protoctista
  • Fungi
• Bacterial diseases


  • Tuberculosis
  • Bacterial meningitis
  • Ring rot
• Viral diseases


  • HIV/AIDS
  • Influenza
  • Tobacco mosaic virus
• Protoctista diseases


  • Malaria
  • Potato blight
• Fungal diseases


  • Black sigatoka
  • Ringworm
  • Athlete's foot
• Communicable diseases are caused by pathogens: bacteria, viruses, protoctista and fungi
• Pathogens cause harm through


  • Directly damaging tissue
  • Releasing toxins
• Bacteria


  Prokaryotic cells that can be classified by shape or cell wall structure
• Bacterial shapes


  • Rod (bacilli)
  • Spherical (cocci)
  • Comma (vibrio)
  • Spiralled (spirilla)
  • Corkscrew (spirochaetes)
• Gram-positive and Gram-negative bacteria


  Determined by cell wall structure
• Tuberculosis


  Caused by Mycobacterium tuberculosis and M. bovis, damages lung tissue and suppresses immune system, can be cured with antibiotics and prevented through vaccination
• Bacterial meningitis


  Caused by Streptococcus pneumoniae or Neisseria meningitidis, infects the brain's protective layer, can be cured with antibiotics if diagnosed early and some forms can be vaccinated against
• Ring rot


  Caused by Clavibacter michiganensis, a Gram-positive bacteria that infects potatoes, tomatoes and aubergines, damages leaves, tubers and fruit
• Viruses


  Non-living, acellular, smaller than bacteria, only contain genetic material, capsid and attachment proteins, replicate inside host cells
• Bacteriophage


  Viruses that infect bacteria
• HIV/AIDS


  HIV consists of a protein capsule, RNA, reverse transcriptase enzyme, and attachment proteins. It attaches to CD4 proteins on helper T cells, injects its RNA and enzymes, and uses the host cell to replicate new viral particles. This destroys the immune system, leading to death from other infections and cancers.
• Influenza


  Orthomyxoviridae virus that infects and kills ciliated cells lining gas exchange surfaces, can lead to secondary bacterial pneumonia infections which can be fatal, especially for vulnerable groups
• Tobacco mosaic virus


  Infects plants, mainly tobacco, causes damage to leaves, flowers and fruit, preventing plant growth, no cure but resistant strains have been developed
• Protoctista


  Eukaryotic single-celled organisms or colonies, some are pathogenic parasites transmitted by vectors
• Malaria


  Caused by Plasmodium, transmitted by mosquitoes, infects red blood cells, liver and brain, no vaccine or cure but preventative medicines exist
• Potato blight


  Caused by the fungus-like protoctista Phytophthora infestans, damages leaves and fruit of potatoes and tomatoes, no cure but resistant strains have been developed
• Fungi


  Eukaryotes that can be multicellular or single-celled, pathogenic fungi are parasitic and release enzymes to digest host tissue
• Black sigatoka


  Caused by the Mycosphaerella fijiensis fungus, infects banana leaves causing them to turn black and prevent plant growth, can be treated with fungicides and resistant strains have been developed
• Ringworm


  Usually caused by Trichophyton verrucosum, infects many mammals including humans, causes white crusty circles on skin, not harmful but can cause itching and discomfort
• Athlete's foot


  Caused by Tinia pedia, a type of ringworm that infects the skin between the toes, causes cracking, scaling and itchiness, can be cured with antifungal creams
• Modes of disease transmission


  • Direct contact
  • Inoculation
  • Ingestion
  • Vectors
  • Droplets
  • Fomites
• Certain living conditions can make disease transmission more likely, such as hot climates, poor infrastructure, poverty and overcrowding
• Plant defences


  Produce antibacterial chemicals and proteins, create physical barriers like callose to prevent pathogen spread
• Animal primary defences


  Skin as physical barrier, skin flora outcompeting pathogens, blood clotting, mucous membranes trapping pathogens, expulsive reflexes, inflammation
• Phagocytosis


  White blood cells like macrophages and neutrophils engulf and digest pathogens, aided by opsonin proteins marking pathogens
• Macrophages


  Type of phagocyte
• Neutrophils


  Type of phagocyte
• Engulf


  To surround and take in
• Damaged cells and pathogens release cell-signalling chemicals (cytokines) that attract the phagocytes to the site of infection
• Opsonin


  Protein that attaches to pathogens to mark them and make it easier for neutrophils and macrophages to engulf them
• Phagocytes


  Cells that engulf and digest pathogens

  
• Phagosome


  Vesicle formed when a phagocyte engulfs a pathogen

  
• Phagocytosis


  1. Phagocytes have receptors which can attach onto chemicals on the surface of pathogens

  2. The phagocyte then engulfs the pathogen into a vesicle to create a phagosome

  3. Within the phagocytes, there are lysosomes which contain hydrolytic lysozyme enzymes

  4. The lysosome fuses with the phagosome to expose the pathogen to the lysozyme

  5. The lysozyme hydrolyses the pathogen and any soluble useful molecules are absorbed into the cytoplasm of the phagocyte

  
• The phagocytes will present the antigen of the digested pathogen on their surface - they are then called antigen-presenting cells