Module 4 disease and immune system

• Communicable diseases are diseases that can be spread from one organism to another.
• Tuberculosis is caused by a bacterium and affects Humans and animals
• Ring rot is caused by a bacterium and affects potatoes and tomatoes
• HIV/AIDS is caused by a virus and affects humans
• Influenza is caused by a virus and affects humans and animals
• Tobacco mosaic virus is caused by a virus and affects plants
• Black sigatoka is a fungal disease that affects bananas and plantains.
• Athletes foot is a fungal disease and affects humans
• Malaria is casued by a protoctist and affects humans
• Potato/tomato late blight Is caused by a protoctist and affects tomato/potatoes
• Direct transmission is when disease is transmitted from one organism to another
• Indirect transmission is when disease is transmitted indirectly, such as through a vector

  (air,water,food)
• Potato/tomato late blight is spread by spores carried between plants from the air then water
• Mosquitos act as vectors. They don’t cause malaria but spread the protoctista that causes malaria.
• Climate increases the spread of communicable diseases. Tropical countries which are hot and humid is the ideal temperature for mosquitoes to breed.
• Social factors can Increase transmission of communicable disease. Good health education on HIV means less transmission. Eg condoms
• Plants produce a polysaccharide callose during pathogen invasion which is deposited between cell walls and plasma membranes making it harder for pathogens to enter.
• Plants produce anti microbial chemicals like antibiotics which kill pathogens and inhibit their growth.
• some plants produce chemicals saponins which destroy cell membranes of fungi and other pathogens
• The layer of cells acts as a physical barrier to pathogens.
• Skin acts as a physical barrier to prevent pathogens entering the body.
• skin secretes sebum containing fatty acids which has antimicrobial properties.
• evaporation of sweat leaves salt residue,low ph and lack of moisture inhibits growth of pathogens.
• Mucous membranes are lined in the (nose,mouth,ears) which secrete mucus trapping pathogens and contain antimicrobial enzymes.
• plants increase their production of lignin to prevent pathogen entry
• histamines released by mast cells which detect infection
• arterioles dilate increasing blood flow creating heat and redness. Temperature increase prevents reproduction of pathogens
• capillaries become more leaky producing tissue fluid which swells and brings more white blood cells and more fluid to lymphatic system
• expulsive reflexes like coughing and sneezing expel pathogens from the body
• cells lay down collagen fibers skin cells attach and migrate towards edge of wound. Tissue contracts below wound bringing skin together and preventing the entry of pathogens by providing a barrier.
• cytokines attract more pathogens to infected area so they can dispose pathogens via phagocytosis.
• pathogen engulfed via endocytosis, phagosome is formed which is a membrane bound structure containing the pathogen .
• lysosomes containing hydrolytic enzymes fuses with phagosome and lysosomes hydrolyse pathogens into harmless products (amino acids)
• harmless waste is expelled via exocytosis or reabsorbed by cytoplasm in phagocyte
• phagocyte becomes antigen presenting cell by taking antigens of cell surface of pathogens and presenting them on its surface.
• opsonins bind to antigens on cell surface of pathogens (antibodies) increasing rate of phagocytosis
• The pathogen is broken down into harmless products such as amino acids, which can either be expelled from the cell in a process called exocytosis or reabsorbed back into the cytoplasm of the phagocyte and used to build its own proteins.
• Antigens on the cell surface of pathogens can increase the rate of phagocytosis.
• Neutrophils have lobed nuclei.
• Lymphocytes, a type of white blood cell, have a spherical nucleus.