Biology Module 7 Revision

• Disease


  A condition that impairs the normal functioning of an organism (Animals, Plants, Humans)
• Infectious


  Contagious conditionals that impair the functioning of an organism
• They can be transmitted from one organism to another
• Pathogens


  Any organism which is capable of causing disease
• Pathogens


  • Bacteria
  • Viruses
  • Fungi
  • Protists
• Pathogens are bad microbes which are able to grow in other organisms and interrupt normal functioning
• Examples of pathogens


  • Common cold
  • AIDS
  • Malaria
• Pathogen


  An infectious agent that is capable of causing a disease in a host
• Pathogens only cause infectious disease
• To cause disease, the biological agent needs the right conditions to multiply and be transmitted, and different pathogens require different conditions
• Disease is caused when the pathogen releases toxins, damages tissues or competes for nutrients
• Presence of pathogen does not always lead to infection
• Infection


  Requires the pathogen to invade, reproduce and elicit a host response
• Some microorganisms flourish in warm weather


  But die in the cold
• A fungal infection on the skin

  Flares up in the summer when conditions are hot and humid; colder, drier weather doesn't suit for its reproduction and growth
• Certain diseases are known as tropical diseases, originate and flourish in tropical climates → High temperatures and high rainfall
• Examples of pathogens


  • Bacteria
  • Viruses
  • Fungi
  • Protists
• Bacteria


  • Prokaryotic, unicellular organisms, which don't have membrane bound organelles and are each made of one cell
  • They are found everywhere, including the soil, air, water and human body
  • Majority of bacteria benefits health, only small portion are pathogenic
• Pathogenic bacteria


  Can cause disease, usually by releasing toxins or damaging host tissues
• Examples of bacterial diseases

  • Tuberculosis
  • Tetanus (humans)
  • Crown Gall (plants)
• Antibiotics and disinfectants can be used to kill bacteria providing the bacteria has not mutated into resistant forms
• Prevention and control of bacterial diseases

  • Antiseptics and disinfectants
  • Antibiotics e.g. penicillin
  • Control of vectors e.g. flies
  • Personal hygiene e.g. wash hands, sterilisation of equipment e.g. by heat, radiation or chemicals
• Fungi


  • Eukaryotic, non-photosynthetic organisms with a cell wall
  • Can be unicellular e.g. Yeasts
  • Can be multicellular e.g. Mushrooms
  • Moulds are composed of a system of microscopic tubular filaments or threads known as hyphae, which branch and spread to form a structure known as mycelium
• Common causes of skin and lung disease in humans and animals
• The damage caused by fungi mostly arises from the enzymes they produce
• Fungi secrete digestive enzymes and chemicals into their surroundings, to break down organic matter
• They then absorb simple nutrients
• Examples of fungal diseases

  • Athletes foot (humans)
  • Chytridiomycosis (Frog)
  • Stem rust (plants)
• Usually affects superficial surfaces like the skin, hair or lungs
• They can be treated with fungicides
• Protists


  • Eukaryotic, unicellular microorganisms without a cell wall
  • Protists either have cilia, flagella, or pseudopodia structures to allow movement
• Examples of protist diseases


  • Malaria (humans)
  • Phytophthora dieback (plants)
• Malaria


  • Caused by plasmodium
  • Plasmodium pathogen flows freely in the blood of an infected person
  • Feeds on haemoglobin in the red blood cells, causing them to pop
  • Symptoms include: Fever, Muscle pain, Nausea, Headaches, Weakness
• Viruses


  • Non-cellular entities, consisting of a single type of nucleic acid (DNA or RNA) encased in a protein coat (capsid)
  • Need a host cell to reproduce
  • The virus attaches to a host cell, which it then penetrates
  • Hijacks hosts enzymes and nutrients to make its own viral proteins and nucleic acid
  • Viral materials then assemble into new viruses which are released from the host cell and infect other cells
• Lytic cycle


  • Virus attaches to a host cell, often a receptor
  • The virus can inject its DNA or RNA into the cell
  • Cell then makes copies of the virus, which can leave the host cell and affect other cells
• Lysogenic cycle


  • Inject their genetic material however it stays hidden in the host's genetic material
  • When the cell replicates the host replicates virus's genetic material
• Examples of viral diseases


  • Influenza (humans)
  • Ross River fever (humans)
  • Tobacco Mosaic virus disease (plants)
• Prevention and control of viral diseases

  • Chemical known to destroy viruses e.g. bleach
  • Good ventilation in community buildings, behavioural education e.g vaccination
  • Controlling vectors e.g. mosquitos
  • Development of vaccines
• Prions


  • Non-cellular, infectious proteins, which are abnormally folded versions of a protein needed within an organism
  • Prions can lead to serious problems, depending on structure, function and location of the normal protein
  • Prion diseases have a long incubation period and are inevitably fatal once clinical signs occur
  • Usually affect brain and neural tissue, leads to neurodegeneration
• Examples of prion diseases

  • Kuru
  • Creutzfeldt-Jakob disease