Osmosis

• What is osmosis

  The net movement of water from an area of high water potential to an area of low water potential, through a partially permeable membrane.
• compare and contrast how water and ions enter cells

  Comparison: both move down concentration gradient; Comparison: both move through protein channels in membrane; Contrast: ions can move against a concentration gradient by active transport
• give two similarities between diffusion and osmosis


  Movement is down a concentration gradient; Both are passive processes;
• what is the highest water potential and what happens when you add a solute 


  pure water has a water potential of 0. When any solute is added the solution becomes more negative.
• when investigating osmosis why do you need blot the potato before weighing it 


  Water will affect the mass, and we only want to measure water taken up or lost; Amount of water on cylinders varies so it ensures same amount of water on outside;
• how do you calculate the volume of stock solution needed

  concentration needed

  ——————-——————- x volume needed

  concentration of stock solution
• why do we calculate the percentage change/a ratio of initial to final mass

  Allows comparison or shows proportional change; As the cylinders have different starting masses;
• why doe repeating the experiment improve reliability 


  A mean can be calculated; the effect of anomalies can be minimised by identifying them and discarding;
• explain why a chipped potato would loss mass in a salty solution

  Water potential of solution is more negative than that of potato tissue; Tissue loses water by osmosis;