Effects of Osmosis on plant tissue- Practical

• Osmosis


  Diffusion of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Effect of osmosis on plant tissue

  1. Place plant cell in water

  2. Water moves into cell by osmosis, cell expands

  3. Place plant cell in concentrated solution

  4. Water moves out of cell by osmosis, cell shrinks
• Potato


  • Commonly used plant tissue to investigate osmosis
  • Can also use other vegetables like beetroot or parsnip
• Investigating effect of osmosis on plant tissue

  1. Peel potato

  2. Use cork board to produce potato cylinders of same diameter

  3. Trim cylinders to same length (around 3cm)

  4. Measure length and mass of each cylinder

  5. Place cylinders in test tubes with different solutions (0.5M sugar, 2.5M sugar, distilled water)

  6. Leave overnight to allow osmosis

  7. Remove cylinders, gently roll on paper towel to remove surface moisture

  8. Measure length and mass of cylinders again
• Percentage change

  Calculated as: (change in value / original value) x 100
• Calculating percentage change

  • Potato cylinder starting mass 1.56g, increases by 0.25g - percentage increase is 16.03%
  • Potato cylinder starting mass 1.32g, decreases by 0.19g - percentage decrease is 14.39%
• Concentration of sugar solution

  Affects percentage change in mass or length of potato cylinder
• Osmosis practical

  1. Cut potato cylinders

  2. Measure length and mass of cylinders

  3. Add cylinders to solutions

  4. Leave overnight

  5. Measure length and mass again

  6. Calculate percentage changes

  7. Plot graphs
• Discs taken from different parts of the potato may have different water potentials
• Potato discs may have different surface areas which affect the rate of osmosis
• Osmosis


  The movement of water from a dilute solution to a concentrated solution through a partially permeable membrane
• Osmosis investigation

  1. Set up the osmosis required practical

  2. Interpret the results of the osmosis practical
• Transport mechanisms in cells

  • Diffusion
  • Osmosis
  • Active transport
• Osmosis

  • Always the movement of water, not other substances
  • Water moves from a dilute solution to a concentrated solution
• Osmosis occurs across a partially permeable membrane</b>
• Osmosis continues until equilibrium is reached, but this does not mean equal numbers of water molecules on each side
• The difference in the number of water molecules on each side is determined by the difference in solute concentration
• Independent variable


  Sugar (The thing that is changed in the investigation)
• Dependent variable


  Mass (The thing that is observed or measured to see what happens)
• Control variables

  • Same source of plant tissue
  • Same type of solution
  • Same time period
  • Aim for identical starting mass
• Dilute solution outside the cells

  Water moves into the cells, increasing their mass and size
• Concentrated solution outside the cells

  Water moves out of the cells, decreasing their mass and size
• In pure water, the mass of the plant tissue increases due to osmosis
• Osmosis investigation procedure

  1. Prepare solutions of different concentrations

  2. Add one piece of plant tissue to each solution

  3. Measure initial and final mass of each piece

  4. Calculate change in mass and percentage change
• A line of best fit is used to determine the concentration of the fluid inside the plant cells
• Potential sources of error

  • Inaccurate solution concentrations
  • Evaporation from tubes
  • Incomplete drying of plant tissue
  • Inaccurate balance