Cell Transport


Facilitated Diffusion

Active Transport


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  • Created by: Ramisha
  • Created on: 05-12-14 11:28
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  • Transport in and out of cells
    • Diffusion
      • The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower
      • Rate of Diffusion
        • Difference Concentration Gradient
        • Area of which diffusion takes place - Surface Area
        • Thickness of exchange surface
        • Temperature: Higher temp, particles bounce and spread more quickly
      • Ficks Law-Proportional to: (Surface area X Difference in Conc) / Length of Diffusion Path
      • Down a concentration gradient
      • Passive
        • Energy requirement: Kinetic energy of particles
      • Types of particles moved across membrane: Lipid soluble, small, non-polar molecules
      • Examples
        • Lungs: O2 diffuses from air into blood, C02 diffuses out
        • Gills: O2 diffuses from water into blood
        • Leaves: CO2 diffuses into palisade cells
    • Active Transport
      • movement of molecules or ions into or out of a cell from a region of lower conc to an area of higher conc using energy and carrier molecules
      • Metabolic energy in the form of ATP needed
      • Carrier proteins act as pumps
      • Selective process - specific substances transported
      • Hydrolysis of ATP: ATP binds protein - split into ADP and phosphate. Protein changes shape
      • Co-transport of glucose, Sodium-potassium pump
        • Na ions removed cell, K ions in cell
      • Ions and medium-sized molecules
      • uses carrier proteins (pumps)
    • Osmosis
      • The net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane
      • solute attracts water
      • Partially permeable plasma only allows water molecules across - not solute
      • Highest water potential=0= pure water
        • lower water potential= more negative
        • units kilopascals (kPa)
          • lower water potential= more negative
      • Down water potential gradient
      • Energy required: Kinetic energy of particles
      • Moves water molecules across membrane
    • Facilitated Diffusion
      • Passive Process - relies on the inbuilt kinetic energy of diffusing molecules
      • Types of particles moved across membrane: Ions and medium sized molecules (e.g) glucose
      • Down concentration gradient
      • Transport proteins at specific points
        • Protein Channels (ions)- hole through middle, some specific/some non-spcific, some open all time/ some gated channels which open and close
        • Carrier proteins (glucose) - medium sized molecules, change in shape
      • Stops when equilibrium reached


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