Cell transport system

• Cell membrane

  All cells have a cell membrane
• Functions of cell membrane


  • Controls what enters and exits the cell to maintain an internal balance called homeostasis
  • Provides protection and support for the cell
• Lipid bilayer

  Two layers of phospholipids
• Phospholipid structure

  • Phosphate head is polar (water loving)
  • Fatty acid tails non-polar (water fearing)
• Cell membrane structure

  • Proteins embedded in membrane
  • Carbohydrate cell markers

  
• Fluid mosaic model

  Model of the cell membrane

  
• Cell membrane properties

  • Has pores (holes)
  • Selectively permeable: Allows some molecules in and keeps other molecules out

  
• Types of cellular transport

  • Passive transport
  • Active transport
• Passive transport


  Cell doesn't use energy
• Types of passive transport

  • Diffusion
  • Facilitated diffusion
  • Osmosis
• Diffusion

  Random movement of particles from an area of high concentration to an area of low concentration
• Facilitated diffusion


  Diffusion of specific particles through carrier proteins found in the membrane
• Facilitated diffusion

  • Carrier proteins are specific - they "select" only certain molecules to cross the membrane
  • Transports larger or charged molecules
• Ion channels

  Transport ions from high concentration to low concentration
• Osmosis


  Diffusion of water through a selectively permeable membrane
• Active transport


  Cell uses energy to actively move molecules to where they are needed
• Types of active transport

  • Protein pumps
  • Endocytosis
  • Exocytosis
• Sodium potassium pump

  1. Sodium ions bind to carrier protein on cytoplasm side

  2. Phosphate group binds to carrier protein changing its shape

  3. Carrier protein carries 3 sodium ions across membrane and forces them into environment

  4. Carrier protein now has correct shape to carry 2 potassium ions across membrane and into cell

  5. Phosphate group is released and carrier original shape is restored

  6. Causes potassium ions to be released into cytoplasm
• Endocytosis


  Taking bulky material into a cell, uses energy, cell membrane in-folds around food particle
• Exocytosis


  Forces material out of cell in bulk, membrane surrounding the material fuses with cell membrane, cell changes shape - requires energy
• Hypotonic solution

  Solution has lower concentration of solutes and higher concentration of water than inside the cell, water moves from solution to inside cell causing cell to swell and burst open
• Hypertonic solution

  Solution has higher concentration of solutes and lower concentration of water than inside the cell, water moves from inside cell into solution causing cell to shrink
• Isotonic solution

  Concentration of solutes in solution is equal to concentration of solutes inside cell, water moves equally in both directions and cell remains same size
• How organisms deal with osmotic pressure

  • Bacteria and plants have cell walls that prevent over-expansion
  • Protists like paramecium have contractile vacuoles that collect water flowing in and pump it out
  • Salt water fish pump salt out of specialized gills
  • Animal cells are bathed in blood, kidneys keep blood isotonic by removing excess salt and water