Substances that require transport

  • Nutrients
    • glucose—provide energy
    • protein—growth and repair
    • amino acids, fatty acids, glycerol
  • Water
  • Carbon Dioxide—removal post respiration
  • Lactic acid—removal of waste
  • Urea—removal of waste
  • Hormones—chemical messaging
  • Enzymes

Open circulatory system

  • Haemolymph instead of blood
  • No veins, arteries or vessels, the haemolymph moves freely around the body
  • Haemocoel—a central cavity that handles digestive and circulatory functions
  • Organisms with an open circulatory system may still have a heart, or some form of pumping mechanism
  • Low pressure
  • Eg
    • ant
    • grasshopper
    • stick insect

Closed circulatory system

  • Structured with veins, arteries and capillaries.
  • High pressure
  • Eg
    • human
    • frog
    • bird

Single circulatory system

  • Blood passes the heart ONCE per cycle.
  • Flow rate/pressure falls when blood leaves the gills or lungs.
  • Low pressure blood inefficient for kidney function.

Double circulatory system

  • Blood passes the heart TWICE per cycle.
  • Higher pressure.
  • Kidney function is optimal.


  • Systemic Circulation
    • heart to body
  • Pulmonary Circulation
    • heart to lungs

See Structure of Heart for more details on transport