B2

• Healthy organism


  In a state of well-being, functioning just as it should be, both physically and mentally
• Disease


  A condition that commonly damages cells of the host and disrupts the normal functioning of the organism
• Types of disease and health

  • Organism may become infected by pathogen
  • There may be variations in the organism's genes
  • The organism may be affected by environmental conditions
  • The organism may experience physical injury or emotional shock
  • The organism's lifestyle may affect their health
• Communicable disease


  A disease that can spread between organisms, caused by pathogens infecting the organism
• Non-communicable disease


  A disease that cannot be passed from one organism to another, generally lasting for a long time and progressing slowly, associated with genetic, lifestyle and environmental factors
• Both communicable and non-communicable diseases cause symptoms - changes in the organism that indicate disease is present
• Symptoms may not always be obvious, especially in the early stages of a disease
• Having one disease


  Can make it more or less likely that you will suffer from another disease
• HPV (human papillomavirus) is a virus that can infect the reproductive system
• Some HPV infections can cause cell changes resulting in the development of certain types of cancer
• Helminths are a type of worm, and if certain helminths get inside the human body, they can cause disease
• Trichinosis is a disease caused by infection by the helminth, Trichinella spiralis
• Infection by Trichinella spiralis may reduce the development of some autoimmune diseases, e.g. Crohn's disease
• Pathogens


  Microorganisms that cause communicable diseases
• Types of pathogens


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Ways communicable diseases are transmitted

  • Water
  • Air
  • Surfaces
  • Body fluids
  • Animal vector
  • Soil
  • Food
• Cholera is a bacterial infection that causes diarrhoea and dehydration, and is spread when drinking water is contaminated with the diarrhoea of other sufferers
• Ash dieback disease is caused by the fungus Hymenoscyphus fraxineus, which is transmitted from infected plants through the air
• Tomato mosaic virus affects many species of plants, making the leaves of plants turn yellow and disrupting photosynthesis, and is spread when infected leaves touch healthy leaves
• Athlete's foot is a fungal disease that affects humans, and is most commonly spread by touching the same things as an infected person, like shoes and towels
• HIV/AIDS is a sexually transmitted disease where the virus enters the lymph nodes and attacks the immune system, and if left untreated can progress to late stage HIV/AIDS
• Malaria is caused by a parasite that is transmitted by mosquitoes, which pick up the parasite when feeding on an infected animal and then transmit it to another animal when they feed
• Soil-borne pathogens like Agrobacterium tumefaciens can infect plants, causing galls on the roots, stems and branches, disrupting the flow of water through the plant
• Salmonella bacteria found in some foods like raw meat can cause food poisoning if the food is not cooked properly
• Human physical defences against pathogens

  • Mucus and cilia in the respiratory tract trap particles and waft them up to be swallowed
  • Skin acts as a barrier, with platelets clotting wounds to prevent entry
  • Enzymes in tears and saliva kill pathogens
• Human chemical defences against pathogens

  • Hydrochloric acid in the stomach kills pathogens
  • Gut bacteria compete with pathogens for resources
• Plant physical defences against pathogens

  • Waxy cuticle layer on leaves acts as a waterproof barrier
  • Cell walls made of cellulose form a physical barrier
• Plant chemical defences against pathogens

  • Antimicrobial substances like phytoalexins disrupt pathogen metabolism and cell structure
• Antigens


  Unique molecules on the surface of cells that are recognised by the immune system
• Immune system response to pathogens

  • Phagocytes engulf and digest foreign cells
  • B-cells produce antibodies that bind to and disable pathogens
  • Cells produce antitoxins to counteract pathogen toxins
• Memory cells remain after an infection, triggering a rapid antibody response if the same pathogen is encountered again
• Ways to reduce and prevent the spread of disease

  • Being hygienic - basic hygiene measures (e.g. washing hands regularly to remove pathogens)
  • Sterilising wounds in the skin - this prevents microorganisms (including pathogens) near the wound from entering the blood
  • Living in sanitary conditions - having access to clean drinking water and a good system for disposing of waste
  • Destroying infected animals - to prevent large numbers of other animals from catching the disease
  • Isolating infected individuals - to prevent them from passing it on to anyone else
  • Vaccination - vaccinating people and animals against communicable diseases
  • Using contraception - using condoms prevents sexually transmitted infections from being transmitted between people during sex
• Ways to control the spread of disease in plants


  • Regulating movement of plant material - to make sure infected plants don't come into contact with healthy plants
  • Destroying infected plants - to stop them being sources of infection
  • Using sources of healthy seeds and plants - to stop the disease from being introduced into a population
  • Crop rotation - to stop pathogens becoming established in an area
  • Polyculture - growing different types of plants in a single area to limit the spread of pathogens
  • Chemical control - using fungicides to kill fungal pathogens
  • Biological control - using another organism to control a pest or pathogen
• The spread of disease can result in huge loss of life and food shortages (if animals reared for food are affected)
• The initial cost to society of creating sanitary conditions can be high
• Destroying infected animals is very costly and the disease may still spread if it is present in other individuals without symptoms
• Isolating infected individuals can be difficult for the infected person as they can't be with their loved ones
• Chemical control using fungicides can lead to the evolution of resistant strains of the pathogen
• Biological control using another organism may become a pest itself and cause more problems
• Vaccination


  Injecting dead, inactive or weakened pathogens into the body to trigger an immune response and produce antibodies