partially permeable membranes (membranes that only let some types of particles through) let water move across them
- a dilute solution of sugar contains high conc or water(solvent) and low conc of sugar(solute)
- concentrated sugar solution contains relatively low conc of water and high conc of sugar
Water moves from dilute solution to conc solution across membrane of cell; this type of diffusion as only water moves across partially permeable membrane from dilute to conc solution is osmosis
conc of solutes inside body cells needs to stay same level for them to work properly but conc of solution outside cells maybe be different to conc inside them and this conc gradient can cause water to move into or out of cells by osmosis
- if conc of solutes in solution outside cell is same as internal conc, solution isotonic to cell
- if conc of solutes in solution outside cell higher than internal conc, solution hypertonic to cell
- if conc of solutes in solution outside cell lower than internal conc, solution hypotonic to cell
if cell uses up water in its chemical reactions, cytoplasm becomes more concentrated and surrounding fluid becomes hypotonic to cell and more water immediately moves in by osmosis
if cytoplasm becomes too dilute because more water made in chemical reactions, surrounding fluid crimes hypertonic to cell and water leaves cell by osmosis - osmosis restores the balance in both cases
osmosis can also cause problems as if solution outside cell becomes much more dilute (hypotonic) than cell contents, water will move out of cell by osmosis and cytoplasm will become too concentrated and cell will shrivel up and no longer survive
