Bio

• Diffusion Across Barriers


  1. Erdide can diffuse

  2. Barrier must be permeable to the particles

  3. Pore spaces large enough for the particle to pass through
• A barrier is considered permeable to a substance if it has pore spaces large enough for the particle of that substance to pass through
• AIDS (acquired immune deficiency syndrome)


  Disease caused by a breakdown in the defence system, resulting in the individual being unable to cope with even the mildest infections
• HIV (human immunodeficiency virus)

  Virus that infects lymphocytes, damaging the immune system
• Symptoms of AIDS


  • Fever that goes on for a long time
  • Sudden and severe weight loss without good reason
  • Constant fatigue
  • Swollen glands in neck, armpit or groin
  • Persistent skin rashes or spots
  • Thick, white coating or patches on the tongue
  • Diarrhoea and loss of appetite over periods of longer than a month
  • Cancer of the lymph tissue may develop early
• In most people, symptoms of AIDS do not appear until some time after they've been infected with HIV, because the virus 'lies low' inside their cells at first
• If a person has HIV in their system, they are said to be HIV positive
• HIV infection cycle


  1. Virus gets inside a lymphocyte

  2. Virus reproduces, making thousands of copies of itself

  3. New viruses burst out of the cell, destroying it

  4. Viruses infect other lymphocytes and the cycle continues