Diffusion

• Diffusion

  the movement of particles from a high concentration to a low concentration
• Small molecules - diffusion

  can diffuse through cell membranes:

  • oxygen
  • glucose
  • amino acids
  • water
• Surface Area to Volume Ratio - RULES

  smaller objects = larger surface area to volume ratio

  • speeds up diffusion, active transport and osmosis
  • makes it easier to obtain nutrients - water and oxygen
• Single celled organisms

  • gases and substances can diffuse directly into the cell - across membrane ---> THEY HAVE A LARGE SURFACE AREA TO VOLUME RATIO - enough substances can be exchanged across membrane - to supply volume of cell
• Multi cellular organisms

  • HAVE A SMALLER SURFACE AREA TO VOLUME RATIO --> not enough substances can diffuse from outside surface to supply their entire volume

  REQUIRE AN EXCHANGE SURFACE FOR EFFICIENT DIFFUSION - have to allow enough of necessary substances to pass through
• Adaptions of Exchange Surfaces

  • thin membrane - short diffusion pathway
  • large surface area - lots of substances can diffuse at once
  • lots of blood vessels - to get stuff in and out of blood efficiently
  • ventilated - air moves in and out
• Examples of Exchange Surfaces

  • Alveoli - lungs
  • Villi - small intestine
  • Root hair cells - plants
  • Gills - fish
  • Leaves structure - plants
• Alveoli- Adaptions

  
  

  • Large Surface Area (creates short diffusion pathway)
  • Good Blood Supply (surrounded by a network of capillaries)
  • Moist lining (enables gases to dissolve)
  • Thin walls
  • Well Ventilated
• Villi

  • very good blood supply - assist quick absorption (surrounded by network of capillaries)
  • thin walls - single layer of surface cells
  • large surface area
• Gills - Adaptation


  gill - made of thin plates (gill filaments) - provide large surface area for gas exchange

  • large surface area - lamellae
  • good blood supply - speeds up diffusion
  • blood and water flow in opposite direction - maintains large concentration gradient
  • high concentration of oxygen in water than blood - most oxygen diffuses
  • thin walls - creates a short diffusion pathway