Transport of substances

• where do most cells get energy from?

  aerobic respiration
• what are the raw materials for aerobic respiration?

  glucose and oxygen
• why can single cell organisms use diffusion to exchange substances?


  • Have a large SA:Volume ratio
  • Substances diffuse across a very short distance across a cell membrane
  • rate of diffusion is faster
• why are multi-cellular organisms unable to use diffusion to exchange substances?


  • Have a smaller SA: Volume ratio
  • Substances would have to travel a large distance to supply the cells
  • Diffusion would be too slow/insufficient
• what do multi-cellular organisms rely on to exchange substances? using what process?

  a mass transport system to move substances efficiently over long distances by mass flow
• what is mass flow?

  the bulk movement of substances from one area to another due to differences in pressure.
• mass transport systems are used...


  • to carry raw materials from specialised exchange organs to body cells e.g. oxygen or glucose
  •  to remove metabolic waste e.g. carbon dioxide
• what is the mass transport system in mammals?

  the circulatory system
• how is the circulatory system a mass transport system?


  • blood is transported in one direction due to a difference in pressure in a process known as mass flow
  • heart is used to pump blood around the body so it can reach body cells
• Why mammals need a heart and circulatory system

  Mammals have a high surface area to volume ratio, so diffusion is inefficient (too slow and unable to supply the volume of the cell)
• Purpose of the circulatory system

  • Pump oxygen and glucose to body cells which are needed for respiration, producing energy and remove carbon dioxide