Required practical - osmosis

• What is osmosis?


  The diffusion of water from a region of high concentration solution to region of dilute solution through a partially permeable membrane.
• What happens when a plant cell is placed in water?


  The water will move into the cell by osmosis and the cell will expand.
• What happens if you place a plant cell into a concentrated solution?


  Water moves out of the cell by osmosis which causes the cell to shrink
• Why do we peel the potato we are using for the experiment? (step 1)

  It can affect the rate of osmosis
• What do we use to produce three cylinders of potato to use for the experiment? and why? (step 2)

  a cork borer and so all the cylinders diameters are the same.
• What do we then use to cut the cylinders to the same length? and to what length? ( step 3)

  A scalpel and around 3cm
• if we use cylinders below 3cm in length, what could happen?


  we might not be able to measure the osmosis.
• what do we do before placing the potatoes into test tubes? (step 4)


  measure the length and mass of each cylinder.
• What instruments do we use to measure the length and mass of each cylinder? (step 4)


  a ruler to measure length, a balance to measure mass.
• What goes into the first test tube? (step 5)

  10cm^3 of 0.5 molar sugar solution with one potato cylinder
• What goes in the second test tube? (step 5)

  10cm^3 of 0.25 molar sugar solution with a potato cylinder
• What goes in the third test tube? (step 5)

  10cm^3 of distilled water with a potato cylinder
• Why do we use distilled water instead of tap water?


  because distilled water contains no dissolved substances which could affect the rate of osmosis
• How long do we leave the cylinders in the test tubes? (step 6)

  overnight
• What do we do when we take the cylinders out? (step 7)

  we roll them on a paper towel, careful only to remove surface moisture, not the water in the cells. do not press down on the cylinders
• What do we do once we removed the surface moisture? (step 8)


  we measure the length and mass again. using a ruler and balance
• What do we do once we’ve measure them again? (step 9)


  calculate the percentage change
• How do you calculate percentage change?


  this equation:

  
• What do we do once we’ve calculated the percentage change?


  plot a graph of the percentage changes in mass or length.
• What happens to the potato in water?


  it gains mass as water moves into it through osmosis
• What happens to the potato in concentrated sugar solution?


  the potato looses mass as water moves out of it through osmosis.
• What does it mean where the line crosses the x axis?


  there is no change in mass
• Why is there no change in mass where the line crosses the x axis?


  the concentration outside the cell is the same as inside the cell so no overall osmosis takes place.
• Where is the approximate concentration in the cell?


  where the line crosses the x axis.

  
• whats the difference between a dilute solution and a concentrated solution?

  a dilute solution contains a high concentration of water molecules whereas a concentrated solution contains a low concentration of water molecules.
• what happens in a more concentrated solution?


  the cell contains lose water by osmosis. they shrink and pull away from the cell wall.