3. circulatory systems

• define diffusion?

  net movement of molecules/ions from a region of higher concentration to a region of lower concentration down a concentration gradient
• what type of organisms rey solely on diffusion- why?

  unicellular organisms, sufficient to supply enough

  • cells are close to the body surface allowing a short diffusion distance.
  • small so have a large SA:V ratio
  • low metabolic rate, decreased oxygen demand.
• open circulatory system?

  no blood vessels, blood is held within body cavity with diffusion taking place between blood and organs (low blood pressure)
• closed circulatory system?

  blood held within blood vessels under high pressure
• advantages of double closed circulatory system?

  • maintain constant body temp
  • have a higher metabolic rate
  • be more active
  • develop higher brain functions
• single closed circulatory system?

  • blood flows once through heart in each circuit of body
  • low blood pressure in capillaries

  example of fish, heart pumps deoxygenated blood to gills for gas exchange, oxygenated blood comes from gills and to the rest of the body, then goes to the heart
• double closed circulatory system?

  • blood flows twice through heart during each circuit of body
  • high blood pressure in capillaries

  use humans as example