3.1.2 features of exchange surfaces

• What do effective exchange surfaces in organisms have?

  Large surface area

  short diffusion distance

  good blood supply

  ventilation mechanism
• Why is a large surface area useful for diffusion?


  Provides more space over which the exchange of substances can occur
• why is a short diffusion distance essential for exchange surfaces 


  so gas exchange is quick and efficient
• how are alveoli specialised to have a short diffusion distance?


  walls of alveoli only one cell thick and cells are flattened
• what are features do alveoli have that makes them good exchange surfaces in the lungs?


  large surface area-large number of alveoli

  extensive capillary network - maintains concentration gradient

  one cell thick and flattened cells- short diffusion distance
• Why is a strong concentration gradient being maintained needed for exchange surfaces?


  -so the diffusion of A substance across the exchange site can be continued for a long period of time
• how does a ventilation system in lungs help maintain a concentration gradient ?


  -helps to ensure there is always a higher concentration of oxygen in the alveoli than in the blood
• where are root hair cells found

  Roots of plants
• what do root hair cells do?

  absorb water and mineral ions from the soil
• how do root hair cells increase their surface area and why do they need a large surface area?

  -have root har

  -so water uptake by osmosis is greater
• How do fish have a good blood supply?

  -extensive capillary system to extract oxygen directly from water
• what is the counter current system in fish?

  -capillary system covering gills ensures blood flows in opposite direction to flow of water for maximum oxygen uptake
• why is maintaining a steep concentration gradient important for fish?

  so diffusion can occur rapidly
• what does each gill on a fish have a good supply of and why?

  Blood to absorb oxygen from water