Specialised exchange surfaces

• What is the role of root hair cells ?

  To absorb water and mineral ions from the soil
• State and explain 3 features that most exchange surfaces have in common

  • Large surface area : lots of molecules can diffuse across at the same time
  • Surfaces are very thin : substances only have to diffuse a short distance
  • Surfaces are permeable : substances are able to pass through the surface
• What is an exchange surface ?

  A part of an organism over which substances are exchanged with the environment
• Name 4 exchange surfaces

  • Alveoli
  • Villi
  • Root hair cells
  • Leaves
• What is the role of villi ?


  To absorb nutrients from the small intestines and into the bloodstream
• State and explain 5 features of alveoli that make them good exchange surfaces

  Alveoli walls are very thin ; Substances can diffuse a short distance

  
  

  Alveoli walls are permeable ; oxygen and carbon dioxide are able to diffuse through the walls

  
  

  Good supply of blood ; maintains a strong concentration gradient as oxygenated blood is constantly being replaced with deoxygenated blood

  
  

  Good supply of air ; maintains a strong concentration gradient as air in the alveoli is constantly being replaced with oxygen rich-air from the lungs
• What affect does a good supply have on the rate of diffusion across exchange surfaces ?

  Increases the rate of diffusion ; Having a good blood supply helps maintain a strong concentration gradient - A higher concentration gradient increases the rate of diffusion
• State the role of alveoli


  Exchange gases with the environment - Specifically, to absorb oxygen from the atmosphere into the bloodstream , then get rid of carbon dioxide from the bloodstream - releasing it to the atmosphere .