cellular transport

• Cell membrane


  Arranged as a fluid mosaic model - phospholipid bilayer with various proteins that can move freely
• Components of cell membrane

  • Channel proteins
  • Lipid bilayer
  • Carrier proteins
• Channel proteins


  • Form pores through the hydrophobic interior of the membrane, allowing water soluble molecules to pass by facilitated diffusion
• Lipid bilayer


  • Phosphate head is hydrophilic, fatty acid tail is hydrophobic
• Carrier proteins


  • Permit the passage of specific molecules by facilitated diffusion or active transport, including ion pumps
• What can cross a lipid bilayer

  • Gases (CO2, O2)
  • Hydrophobic molecules
  • Small polar molecules (H2O, ethanol)
  • Large polar molecules (glucose)
  • Charged molecules (Na+, Cl-, Ca2+)
• Fluid mosaic model


  Describes the structure of the cell membrane
• Semi-permeable


  The plasma membrane only allows passage of certain substances
• Substances that can freely diffuse through the membrane

  • Small molecules (O2, CO2)
  • Large molecules (glucose, starch) require active transport
• Passive transport


  1. Diffusion

  2. Facilitated diffusion

  3. Osmosis
• Active transport


  1. Endocytosis

  2. Exocytosis
• Diffusion


  • Passive process, molecules move randomly and become evenly dispersed
  • Affected by concentration gradient, distance, surface area, barriers, temperature
• Facilitated diffusion


  Faster form of passive diffusion with the assistance of carrier proteins and protein channels
• Active transport


  Energy-using process of moving molecules/ions against their concentration gradient, using ATP-powered carrier proteins
• Cytosis


  • Bulk movement of molecules/particles into (endocytosis) and out of (exocytosis) cells
• Pinocytosis is the uptake of liquids, phagocytosis is the uptake of solids
• Active transports


  Benefits: Can transport large molecules, can transport against concentration gradient

  Costs: Require carrier proteins, require energy (ATP)
• Sodium-potassium pump


  Active transport mechanism that maintains high K+ and low Na+ concentrations inside cells