Health and Disease

• Health


  A state of complete physical, mental and social well-being (as defined by the World Health Organization, WHO)
• Disease


  A disorder of the body or mind that negatively affects an individual's health
• Types of disease

  • Communicable
  • Non-communicable
• Communicable disease


  A disease that is passed directly between individuals, caused by a pathogen
• Pathogen

  A disease-causing organism e.g. virus, fungi, bacteria, protists
• Non-communicable disease


  A disease that cannot be transmitted between individuals, generally long lasting with a slow-onset, caused by lifestyle, environmental conditions, genetic mutations etc.
• Symptom

  A change experienced by an organism that indicates disease
• Having an illness


  Makes an individual more likely to contract another disease (weakens the immune system)
• Cholera

  • Caused by Vibrio cholerae bacterium
  • Spread by drinking water or washing in water that has been contaminated with infectious faeces
  • Symptoms: diarrhoea, vomiting
• Reducing the incidence of cholera

  1. Access to clean water

  2. Improved sanitation (sewage disposal etc.)
• Tuberculosis (TB)

  • Caused by Mycobacterium tuberculosis bacterium
  • It is an airborne bacteria spread by droplet infection
  • Symptoms: lung damage, chesty cough, wheezing
• Reducing the transmission of TB

  1. Improved hygiene (washing hands, sneezing into tissues etc.)

  2. Infected individuals should avoid crowded areas

  3. Increased ventilation in the individual's home
• Chalara ash dieback


  • Caused by a fungus that infects ash trees
  • Spread via airborne spores which are carried by the wind
  • Causes dark lesions on bark and blackened leaves which wilt and eventually die
• Reducing the transmission of Chalara ash dieback disease

  1. Control the movement of ash trees

  2. Kill infected plants

  3. Replant with a different species
• Malaria

  • Caused by plasmodium protist
  • Spread by mosquito vectors which pick up the plasmodium protist when feeding on the blood of an infected organism and transmit malaria to other organisms during feeding
  • Flu-like symptoms, damage to red blood cells, liver damage
• Reducing the incidence of malaria

  1. Mosquito nets

  2. Insect repellant

  3. Cover arms and legs
• How viruses differ from other microorganisms e.g. bacteria, fungi (biology only)

  Viruses are not living organisms. They do not reproduce and can only replicate inside a host cell.
• Physical defence system within plants

  • Waterproof waxy cuticle - surface barrier preventing the entry of pathogens
  • Cellulose cell wall - further barrier against pathogens
• HIV


  • Caused by human immunodeficiency virus
  • Spread by direct contact with infected body fluids e.g. blood, semen, breast milk
  • Destroys white blood cells making the individual immunodeficient and increasingly susceptible to other diseases. Leads to AIDS.
• Reducing the spread of HIV

  1. Use of condoms and protected sex

  2. Needle exchange

  3. Screening blood for HIV

  4. Deterring infected mothers from breastfeeding
• Chemical barriers in plants

  • Secretion of toxins to reduce damage by pests e.g. stinging nettles
  • Production of antibacterial chemicals that kill bacterial pathogens
• Chlamydia


  • Caused by Chlamydia bacterium
  • Spread through sexual contact or direct contact with infected genital fluids
  • Can result in infertility
• Reducing the transmission of Chlamydia

  1. Use of condoms and protected sex

  2. Screening
• Chemicals produced by plants

  They produce physiological effects on the body so can be used in medicines to treat disease
• Medicines derived from plants

  • Quinine - antimalarial, bark of Cinchona sp.
  • Aspirin - painkiller, bark/leaves of Salix alba
• Importance of plant defence systems

  • Plants are producers so all organisms higher up in food chains rely upon their survival and ability to fight disease
  • Important in maintaining human food security
• How plant diseases can be detected and identified in the field

  1. Observation of symptoms

  2. Analysis of the distribution of infected plants

  3. Changing environmental conditions to eliminate other causes
• Many diseases may have similar symptoms, making it difficult to identify a disease using symptoms alone
• How plant diseases can be detected and identified in the lab

  1. Detection of foreign antigens in a sample of plant tissue using monoclonal antibodies

  2. Analysis of DNA to identify any pathogen DNA in a tissue sample
• Non-specific defence


  Always present, same for all organisms, prevents pathogens from entering the body
• Examples of the body's physical defence system

  • Skin - protective surface barrier
  • Blood clotting - platelets seal wounds preventing entry of pathogens into the blood
  • Respiratory tract - mucus traps pathogens, cilia waft mucus to the back of the throat where it is swallowed
• Examples of the body's chemical defence system

  • Tears - contain lysozyme which digests bacterial cell walls, killing bacteria and protecting the eye
  • Hydrochloric acid in stomach - acidic pH kills pathogens that are swallowed
• Immune system


  The body's defence against pathogens once they have entered the body, aims to prevent or minimise disease caused by pathogens
• How white blood cells detect pathogens

  Pathogens have unique antigens on their surface which are detected by specialised receptors on white blood cells
• How the immune system destroys pathogens

  1. B-lymphocytes (type of WBC) produce antibodies in response to a particular antigen

  2. Each antibody is specific to an antigen and binds to it

  3. Antibodies 'tag' pathogens or clump them together, disabling them so that they can be killed by other WBCs
• Memory lymphocytes

  WBCs produced in response to a foreign antigen that remain in the body after a pathogen has been destroyed, provide immunity - if the body is re-infected, antibodies are produced more rapidly and the pathogen is destroyed before it can produce disease symptoms
• Vaccination

  Deliberate exposure of an individual to foreign antigens, triggers an immune response (produces antibodies) and provides immunity (due to memory cells), the individual does not contract the disease that they are being immunised against
• Components of a vaccine

  Dead, weakened or inactivated pathogens with their surface antigens still present
• Benefits of vaccinations

  • Herd immunity - vaccination of a significant proportion of the population gives some protection to individuals who are not immune
  • Helps to prevent epidemics and pandemics
• Antibiotic


  A substance that kills or inhibits the growth of bacteria (no effect on viruses), produced by living organisms e.g. fungi, with no effect on cells in the host organism