Transport Across the Membrane

• The concentration gradient is the difference between the concentrations of molecules on either side of the cell.
• Plasma membrane


  Semi-permeable barrier surrounding the cell
• Selective permeability


  Property allowing only certain substances to cross based on polarity, size, and concentration
• Cytosol


  Fluid inside the cell preserving a special internal environment
• Semi-permeable membrane


  Allows only small, uncharged, and non-polar molecules to freely diffuse
• Diffusion

  Passive movement of molecules from high to low concentration
• Concentration gradient


  Difference in solute concentration between adjacent areas
• Equilibrium


  Even dispersion of particles in an area over time
• Facilitated diffusion


  Passive movement of large/polar molecules through membrane-bound proteins
• Protein channels


  Pores in the membrane allowing specific substances through
• Carrier proteins


  Bind to substances and undergo conformational change to allow passage
• Aquaporins


  Protein channels specifically designed for the facilitated diffusion of water
• Osmosis


  Passive diffusion of water across a semi-permeable membrane
• Tonicity


  Relative concentration of solute in a solution surrounding the cell
• Hypertonic


  Describes a solution with higher solute concentration, causing water to move towards it
• Isotonic


  Solutions with equal concentrations, resulting in zero net movement of water
• Hypotonic


  Describes a solution with lower solute concentration, causing water to move out of it
• Lyse


  Bursting of animal cells in a hypotonic solution
• Turgid


  State of plant cells in a hypotonic solution, filled with water and rigid
• Flaccid


  State of plant cells in an isotonic solution, lacking water and limp
• Shrivelled


  State of animal cells in a hypertonic solution, lacking water and struggling
• Plasmolysed


  State of plant cells in a hypertonic solution, lacking water and struggling
• exocytosis a type of bulk transport that moves large substances out of the cell
• pinocytosis the process of taking in small amounts of liquid through vesicles formed on the surface of the cell
• endocytosis a type of bulk transport that brings materials into the cell
• phagocytosis endocytosis of solid material or food particles by phagocytes
• active transport movement of molecules across a semipermeable membrane that requires energy