B1.7

• Osmosis is the net movement of water molecules across a partially permeable membrane, from a region of higher water concentration, to a region of lower water concentration
• Osmosis is a special form of diffusion.
• In living organisms, the partially permeable membrane is usually the cell membrane
• Osmosis is the movement of which molecules?

  water
• During osmosis, water moves against the concentration gradient?


  No it goes across.
• What would happen to red blood cells if they were placed in pure water?

  If placed in pure water, then the water concentration would be higher outside the cell (in the pure water) than inside the cell. This means that water would move down its concentration gradient into the cell, causing it to swell and possibly burst.
• Isotonic


  Conc. of solutes outside = Conc. of solutes inside
• Hypertonic


  Conc. of solutes outside cell > internal conc
• Hypotonic


  Conc. of solutes outside < internal conc
• Cell uses water = cytoplasm concentrated = surrounding fluid hypotonic = more water moves in via osmosis
• Cytoplasm too dilute as water is made = surrounding fluid hypertonic = water leaves by osmosis
• Osmosis tries to restore balance
• How can osmosis causr problems

  If solution is too dilute (hypotonic) = water will move in = cell will swell and may burst

  If solution is too concentrated (hypertonic) = water moves out = cytoplasm too concentrated and shrivels and can't survive.