Osmosis Practical

• What is osmosis?

  Diffusion of water through a membrane
• What happens to plant cells placed in water?

  Water moves in, causing cells to expand
• What occurs when plant cells are placed in a concentrated solution?

  Water moves out, causing cells to shrink
• What vegetable is commonly used to investigate osmosis?

  Potato
• Why do we peel the potato before the experiment?

  The skin can affect osmosis
• How do we ensure all potato cylinders are the same diameter?

  Use a cork board to cut them
• What is a good length for the potato cylinders?

  About three centimeters
• Why is it important to measure the length and mass of each cylinder?

  To assess the effect of osmosis
• How much of a 0.5 molar sugar solution is added to the first test tube?

  10 centimeters cubed
• Why do we use distilled water instead of tap water?

  Distilled water has no dissolved substances
• What should be done after leaving the potato cylinders overnight?

  Gently roll them on paper towel
• Why is it important not to press on the cylinders when drying them?

  To avoid forcing water out of cells
• How do you calculate percentage change?

  Change in value divided by original value
• What is the percentage change if a potato cylinder's mass increases from 1.56 grams by 0.25 grams?

  +16.03 percent
• What is the percentage change if a potato cylinder's mass decreases from 1.32 grams by 0.19 grams?

  -14.39 percent
• What does the graph of percentage changes in mass or length show?

  Mass gain in water, loss in concentrated solution
• What does it mean when the graph crosses the x-axis?

  No change in mass occurs
• What does the concentration at the x-axis crossing indicate?

  Approximate concentration inside the cell
• Where can you find more questions on this practical?

  In the vision workbook
• What are the steps to investigate osmosis on plant tissue?

  1. Peel the potato.
  2. Cut cylinders using a cork board.
  3. Trim to the same length (3 cm).
  4. Measure length and mass of cylinders.
  5. Place in test tubes with different solutions.
  6. Leave overnight for osmosis.
  7. Roll on paper towel to remove moisture.
  8. Measure length and mass again.
  9. Calculate percentage change.
• What are the types of solutions used in the osmosis experiment?

  • 0.5 molar sugar solution
  • 2.5 molar sugar solution
  • Distilled water
• What are the key points to remember about calculating percentage change?

  • Use the formula:

  $\text{Percentage Change} =$$\frac{\text{Change in Value}}{\text{Original Value}} \times 100$

  • Remember to learn this formula for exams.
• What are the effects of osmosis on potato cylinders in different solutions?

  • In distilled water: Gains mass (water enters)
  • In concentrated sugar solution: Loses mass (water exits)
  • At equilibrium: No change in mass