diffusion - mov't of molecules from higher to lower concentration 

• continues until concentration is uniform
• allows certain polar molecules to enter through the channels
• inner, polar lining of channels allow polar molecules to enter
• each channel is selectively permeable, only allowing certain molecules to pass through
• ions need transport proteins to move in/out of the cell
• ion channels - have hydrated interiors so that ions never come in contact w/ nonpolar fatty acids
  • voltage and concentration determine direction of ions
• carriers - brings substances across the membrane by binding to them at 1 end and releasing them out the other
  • depends on the concentration gradient of the substance being transported
  • performs facilitated diffusion (either specific, passive, or saturated)
  • certain red blood cell proteins transfers different molecules in different directions
  • glucose transporter - adds phosphate group to glucose to keep internal glucose levels low; used by red blood cells to attract more glucose molecules
• saturation - occurs when all the protein carriers are used up; transport rate can no longer increase

osmosis - both water/solutes move from higher to lower concentrations 

• aquaporins - specialized channels for water
• water moves towards area of more concentrated solutes to form hydration shells
• osmotic concentration - concentration of all solutes in a solution
  • hyperosmotic - solution w/ higher concentration
  • hypoosmotic - solution w/ lower concentration
  • isosmotic - solutions w/ equal concentrations
  • water flows towards hyperosmotic region
• hydrostatic pressure - pressure of cytoplasm pushing out against the cell membrane; tends to drive water out of the cell
• osmotic pressure - pressure needed to stop the mov't of water across the membrane; tends to drive water into a cell

maintaining equilibrium - important to have balance between pressures 

• animals need to keep isosmotic conditions more than plants/fungi due to lack of cell walls
• extrusion - used by single-celled eukaryotes w/ vacuoles
  • vacuole collects water from the cell, pumps it out by contracting rhythmically
• isosmotic solutions - some animals use their environment to adjust internal solute concentration
  • ocean organisms' internal conditions match that of seawater
  • blood contains protein albumin to raise solute concentration of liquid blood to match that of the cells
• turgor pressure - internal hydrostatic pressure
  • makes plants rigid by pressing against the membrane/cell wall
  • maintains shape of plants