1.3 Transport in Cells

• Diffusion


  Movement of molecules from a region of high concentration to a region of low concentration down their concentration gradient
• Osmosis


  Movement of water molecules from a region of high water potential to a region of low water potential down their water potential gradient
• Active Transport


  Movement of substances from a low concentration to a high concentration against their concentration gradient, requiring energy from respiration
• Transport in organisms


  • Diffusion
  • Osmosis
  • Active Transport
• Factors affecting rate of diffusion

  • Concentration gradient
  • Temperature
  • Surface area
• Diffusion is the movement of molecules from a region of high concentration to a region of low concentration down their concentration gradient
• Osmosis is the movement of water molecules from a region of high water potential to a region of low water potential down their water potential gradient
• Active transport is the movement of substances from a low concentration to a high concentration against their concentration gradient, requiring energy from respiration
• Substances transported in organisms

  • Oxygen
  • Carbon dioxide
  • Urea
• Need for mass transport systems

  • Surface area: volume ratio too small
• Adaptations for mass transport

  • Alveoli and cells of the small intestine have a large surface area
  • Thin cell walls of root cells giving a short diffusion distance
  • Thin membrane giving a short diffusion path
• Plant tissue placed in hypotonic solution

  • Mass increases
• Plant tissue placed in hypertonic solution

  • Mass decreases
• Absorption of sugar in the small intestine requires energy from respiration
• Absorption of ions in plant roots is a passive process
• Diffusion is important for transport of materials in organisms, e.g. O2 diffuses into RBCs
• Good ventilation and blood supply are important for diffusion