Wednesday, June 22, 2011

Movement of Substance Across the Plasma Membrane ~





THE PLASMA MEMBRANE !

  • The plasma membrane is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell .
FUNCTION OF THE PLASMA MEMBRANE !
  • Protects the cell.
  • Separates the intracellular components from the extracellular environment.
  • Controls what enters and exist the cell.
NECESSITIES FOR THE MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE !
  • To transport nutrients into the cell.
  • For gases exchange.
  • To excrete metabolic waste.
  • To maintain the pH value and ionic concentration of the cell.
SUBSTANCES IN AND OUT THROUGH THE MEMBRANE !
  • SUBSTANCES LEAVING A CELL ~
    • Secretion
    • Nitrogenous waste
    • Oxygen
    • Carbon dioxide
    • Excess water
  • SUBSTANCES ENTERING A CELL ~
    • Nutrients
    • Ionic salts
    • Oxygen
    • Carbon dioxide
    • Water
  • PERMEABILITY OF THE PHOSPHOLIPIDS BILAYER !
    • The permeability of the phospholipids bilayer is determined by :
      • The size.
      • The charge.
      • The polarity.
      • Of substances pass through it.
  • SUBSTANCE CAN MOVE THROUGH :
      • Non-polar molecule : fatty acid, vitamin (A.D.E.K) steroid.
      • Oxygen, carbon dioxide, water.
  • SUBSTANCE CAN'T MOVE THROUGH :
      • Ions : Na+, K+, Ca2+, H+
      • Polar molecule : Polysacharides, amino acid, glucose, nucleic acids.
  • WHAT IS PASSIVE TRANSPORT ??
    • Passive transport is the movement of substances across the cell membrane without the use of energy by the cell.
    • During passive transport, substances move down their concentration gradient, hence no energy is required.
    • Passive transport can happen through three different channels, namely :
      • Lipid bilayer.
      • pore protein.
      • carrie protein.
  • WHAT IS DIFFUSION ??
    • Diffusion is the movement of particles from high density region to a low density region. No energy is needed and no membrane involves in diffusion.
  • THE DYNAMIC EQUILIBRIUM !
    • Diffusion will continue until the concentration in all region is the same. When this happen, we say it has reached the dynamic equilibrium.
  • FACTORS AFFECTING THE RATE OF DIFFUSION ( Hom fast diffusion happen ?? ) 
    • Temperature
      • Higher temperature - Diffuse faster
    • Surface area
      • Large surface - Diffuse faster
    • Concentration gradient
      • Higher gradient - Diffuse faster
    • Size of particles
      • Smaller particles - Diffuse faster
    • Diffusion medium
      • Solid - Slowest
      • Liquid - Faster
      • Gas - Fastest
  • PARTICLES THAT MOVE THROUGH THE PLASMA MEMBRANE THROUGH DIFFUSION !
    • Substances soluble in fat : fatty acid, glycerol, some vitamins (A.D.E.K).
    • Neutral particles : water, oxygen, carbon dioxide.

  • EXAMPLE OF DIFFUSION !
    • Between alveoli and blood capillaries in the lung during gases exchange.

  • WHAT IS OSMOSIS ??
    • Osmosis is the diffusion of a water through a semi-permeable membrane, from a solution of high solute concentration to a solution with low solute concentration.
    • It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane separating two solutions of different concentration.

  • IMPORTANT POINTS !
    • It is a diffusion of water (normally) through a semi-permeable membrane.
    • It is from a dilute solution to a more concentration solution.
  • WHAT IS FACILITATED DIFFUSION ??
    • Facilitated diffusion is the passive transport of substances across the plasma membrane with the help of transport proteins such as the channel protein and the carrier protein.
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