Transport Across cell Membranes

Transport across cell membrane

Simple diffusion

  • Molecules suspended in gas or liquid are in constant random movement

  • Net movement of molecules from region of high concentration to low concentration

  • Passive process

  • Rate of diffusion = how long to reach equilibrium

    • Equilibrium = concentration is the same in both regions

  • Factors that influence the rate of diffusion 

    • Surface area (increased Surface area will increase the rate of diffusion

    • Concentration gradient (increased concentration gradient will increase the rate)

    • Distance (increased distance will decrease the rate of diffusion)

  • Molecules that move across the membrane by simple diffusion

    • Oxygen

    • Carbion Dioxide

    • Lipids

Facilitated Diffusion

  • Use integral membrane proteins as channels (carrier molecules) to transport material

  • Movement from high to low concentration

  • Passive process

  • Transported molecules dissolved in water

    • Monosaccharides

    • Amino acids

    • Ions (k+, Na+ and Cl-)

Active Transport

  • Move molecules from a region of low concentration to high concentration

  • Require membrane pumps (integral proteins)

  • Require energy (ATP) 

  • Many types of pumps

    • Na+/k+ pumps

    • Cl- pumps

    • Transported molecules dissolved in water

      • Monosaccharides

      • Amino acids

      • Ions (k+, Na+ and Cl-)

Osmosis

  • Diffusion of h20 molecules across a semipermeable barrier

  • Movement from a high to a low concentration, a passive process

  • A major concern for cells

Endocytosis

  • Movement of bulk material into the cell

    • Phagocytosis: cell eating

    • Pinocytosis: cell drinking

    • Depended on ATP and the cytoskeleton

Exocytosis

  • Movement of bulk material out of the cell

  • Requires ATP and the cytoskeleton