communicable diseases, disease prevention and immune system

• what are communicable diseases caused by?

  Pathogens; bacteria, viruses, Protoctista and fungi
• what can pathogens lead to?

  damage in tissue and the release of toxins
• Bacteria

  • prokaryotic cells classified by their shape or cell wall structure
  • there are two types of cell wall that are classified as Gram-positive or Gram-negative
• Bacterial Diseases

  Tuberculosis

  • caused by Mycobacterium tuberculosis and M.bovis
  • it can infect humans, deer, cows, pigs and badgers
  • Causes harm by damaging lung tissue and suppressing the immune system
  • cured using antibiotics and prevented through vaccination
• Bacterial Diseases

  Meningitis

  • infects the brain
  • causes septicaemia and death
  • antibiotic can cure it if it is diagnosed before too long
  • it can be vaccinated against
• Bacterial Diseases

  Ring Rot

  • infects potatoes, tomatoes and aubergines
  • this bacteria damages leaves, tubers and fruit
• Viruses

  • non living and acellular
  • consist of genetic material, a capsid and attachment proteins
  • viral replication inside the host cells and involves the injection of nucleic acid into the cell
  • Bacteriophage
• How does HIV result in the symptoms of AIDS?

  1. attachment proteins bind to complementary CD4 receptor on Th cells
  2. HIV particles replicate via reverse transcriptase inside Th cells, killing or damaging them
  3. AIDS develops when there are too few Th cells for the immune system to function
  4. Individuals cannot destroy other pathogens and suffer from other infections = death
• How is HIV transported?

  though the blood
• Virus

  Tobacco mosaic

  • affects plants through sap
  • contains ssRNA which is directly transcribed by host cell to assemble new virions
  • Virions enter other cells via plasmodesmata then enter xylem and phloem
  • cause stunted growth and mottled leaves
• Virus

  Influenza

  • transmitted via droplets and contact with mucus containing virus
  • injects viral RNA into ciliated epithelial cells of throat + lungs
  • Pneumonia caused by a bacterium that infects the airways
  • causes headache, coughing, sneezing, sore throat, vomiting, fever, muscular/joint pain
• Protoctista

  Malaria

  • Female Anopheles mosquito acts as vector for plasmodium.
  • plasmodium spp. Protoctista when transfers saliva to another organism during feeding
  • parasite reproduces asexually in red blood cells in liver
• Protoctista

  • eukaryotes that exist as single-celled organisms or cells grouped into colonies
  • the pathogenic Protoctista are parasites and are usually transmitted via a vector e.g. malaria is transmitted by mosquitos
• Protoctista

  potato blight

  • caused by a phytophthora infestans a fungus-like Protocista
  • causes potato blight and tomato late blight
  • has hyphae which enter the plant and cause damage to the leaves
• Fungi

  • eukaryotes that cause many plant diseases
  • can be multicellular or single celled
  • pathogenic fungi are parasitic, releasing enzymes to digest the host's tissue (animals or plants)
• Fungus

  Black sigatoka

  • caused by the mycosphaerella fijiensis fungus
  • infects bananas
  • fungal hyphae cause damage to leaves = turn them to black preventing plant growth
  • fungicides can kill the fungus and resistant strains have been developed
• Fungus

  Ring Worm

  • infects many mammals including humans
  • causes white, crusty circles on the skin
  • not harmful but it can cause itching and discomfort
• Fungus

  athlete's foot

  • only infects humans
  • a type of ring worm that thrives in warm, damp regions between the toes
  • causes the skin to crack and to become scaly, causing itchiness and soreness
• Describe 3 fungal infections

  • leaf spot disease black sigatoka in banana plants
  • ringworm transmitted by direct contact
  • athletes foot in humans caused by fungi which affects hands or nails
• How are communicable pathogens transmitted directly?

  • inhalation (droplet infection)
  • skin to skin contact or exchange of fluids
  • penetrate skin actively using enzymes
• How are communicable pathogens transmitted indirectly?

  • consumption of contaminated food + drink
  • via vector (mosquitoes transmit)
  • spores
• How do living conditions affect disease transmission?

  • Overcrowding increases direct transmission
  • climate determines which organisms can survive (malaria is more prevalent in hot countries)
  • social factors influence how quickly people are treated
• Name 4 physical barrier to pathogen entry in plants

  • cellulose cell walls
  • lignified layer
  • waxy upper cuticle
  • old vascular tissue is blocked to prevent pathogens from spreading inside the plant
• Describe 2 mechanical response to infection in plants?

  • Guard cells close stomata
  • the thick polysaccharide callose is produced + deposited between the cell wall + plasma membrane to increase entry distance/ limit spread
• what is necrosis?


  injury activates enzymes in plants that kill cells near site of infection to prevent pathogen from spreading

  • necrosis of woody tissue is known as canker
• name chemical defences plants use against pathogens?

  • terpenoids
  • phenols
  • alkaloids
  • defensins
  • hydrolytic enzymes
• Name 5 barrier to infection in animals?

  • skin is tough keratin layer
  • blood clotting prevents pathogens from entering through skin lesions
  • hydrochloric acid in stomach kills bacteria
  • harmless bacteria in gut + on skin surface increase interspecific competition with pathogens
  • mucous membrane trap pathogens and may secrete antimicrobial enzymes
• what are expulsive reflexes?

  Body attempts to force foreign substance out

  • irritation of mucous membranes in nostrils causes sneezing
  • irritation of ciliated epithelium in respiratory tract causes coughing
• Name 4 ways the nonspecific immune system responds to infection?

  • inflammation
  • phagocytosis
  • digestive action of lysozymes
  • production of interferon (antiviral agent)
• Outline the process of inflammation

  1. damaged vessels release histamines causing vasodilation
  2. blood flow + permeability of blood vessels increase
  3. white blood cells + plasma move into the infected tissue
• How does blood clotting occur?

  1. blood platelets form plug + release chemicals that enhance clotting e.g. thromboplastin
  2. Prothrombin changes into thrombin its active form
  3. fibrinogen changes into insoluble fibrin which covers wound
• Name the 2 types of whit blood cells involved in phagocytosis?

  • Neutrophils
  • Macrophages (can become antigen-presenting cells)
• How does phagocytosis destroy pathogens?

  1. phagocyte moves towards pathogen which may have been marked by opsonin's via chemotaxis
  2. Phagocyte engulfs pathogen via endocytosis to form a phagosome
  3. phagosome fuse with lysosome (phagolysosome)
  4. Lysozymes digest pathogen
  5. Phagocyte absorbs the products from pathogen hydrolysis
• explain the role of antigen-presenting cells?

  • macrophage displays from pathogen on its surface (after hydrolysis in phagocytosis)
  • Enhances recognition by T helper cells which cannot directly interface with pathogens/antigens in body fluid
  • secrete cytokines that are involved in stimulating specific immune response
• what are lysozymes?


  digestive enzymes

  • found in lysosomes as well as many secretions e.g. tears + mucus
  • damage bacterial cell walls, causing osmotic lysis
• Outline how to prepare blood to be observed under a microscope?

  1. smear a drop of blood onto a slide using a spreader held at 45
  2. add Leishman stain then a buffer rinse
• Name the 2 types of specific immune response

  • cell-mediated
  • humoral
• Process of a cell mediated response

  1. complementary T helper lymphocytes bind to foreign antigen on APC (antigen presenting cells)
  2. cell signalling via secretion of interleukins stimulates
  3. clonal expansion of complementary T helper cells (rapid mitosis) = memory cells or humoral response
  4. clonal expansion of cytotoxic T cells: secrete enzyme perforin to destroy infected cells
• process of the humoral response

  1. complementary T helper lymphocytes bind to foreign antigen on antigen presenting T cells
  2. release cytokines that stimulate clonal expansion (rapid mitosis) of complementary B lymphocytes
  3. B cells differentiate into plasma cells
  4. plasma cells secrete antibodies with complementary variable region to antigen
• Describe the structure and function of B and T lymphocytes?

  many specific receptors + immunoglobulins on surface

  B cells differentiate into plasma cells to secrete antibodies

  3 types of T cell:

  • T helper (secrete cytokines)
  • T killer (secrete perforin)
  • T regulator (suppress other immune cells to prevent autoimmune disease)