The general pattern of blood circulation is:

  • Large Surface Area: Decrease in the surface area:volume ratio
  • Suitable median: A method of transporting oxygen around the body i.e. blood
  • A form of mass transport in which the median is moved over a large distance
  • Mechanism for moving the medium around the vessels i.e. hearts in mammals or passive process such as transpiration
  • Mechanisms to maintain the mass flow in one direction
  • Controlling the flow of the transport median

Single Circulation

  • Used in smaller organisms such as fish
  • The heart pumps the blood to the exchange surface, to the cells and back to the heart in one contraction

Double Circulation

  • Used in larger organisms such as mammals
  • The heart is comprised of two pumps, the blood leaves the heart to the lungs and then returns back to the heart. The heart then pumps the blood again for it to journey around rest of the body
  • This is required as blood will lose too much pressure after the lungs alone
  • The high pressure allows the mammals to have warm body temperatures as well as a fast-metabolic rate


Human Circulatory System


  • The transport system is used to move substance large distances, the final part of the journey to the cells is via diffusion.
  • The final exchange from blood vessels into the cells is rapid because of the large surface area, short diffusion pathway and the steep concentration gradient.
  • The main reason for a gas exchange system is to allow for large organisms with large surface areas:volume ratios to have a method of supplying the required gases to all of its cells