Why Organisms need a Heart and Circulatory System

• What is diffusion?


  The transfer of particles from a high to low concentration gradient without energy
• What is metabolism?


  The sum of all chemical reactions in the body
• What is mass flow?


  The movement of particles in one direction by the use of pressure
• What is single circulation?


  Where the deoxygenated blood flows from the heart to the gills, becomes oxygenated, then flows through the body and back to the heart
• What is double circulation?


  Where deoxygenated blood is pumped from the heart to the lungs, is oxygenated, pumped back to the heart, to the body and then back to the heart again
• What is open circulation?


  Where blood is pumped into cavities surrounding internal organs, gases are diffuses in and out of the blood and the blood is brought back to the heart
• What is closed circulation?

  Where blood is carried through narrow blood vessels which causes higher blood pressure
• Why can't larger multi-cellular organisms rely on diffusion to transfer gases in and out of the body?

  They are too large for the particles to be supplied at a rapid enough rate to sustain their metabolism and they have a lower surface are to volume ratio