RP3

• 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?

  To prevent skin affecting osmosis
• What tool is used to produce potato cylinders?

  Cork borer
• What length should the potato cylinders be trimmed to?

  Approximately three centimeters
• What is measured before placing the potato cylinders in the solution?

  Length and mass of each cylinder
• What volume of sugar solution is added to the first test tube?

  10 centimeters cubed
• What concentration of sugar solution is used in the first test tube?

  0.5 molar
• Why is distilled water used instead of tap water?

  Distilled water has no dissolved substances
• How long should the potato cylinders be left in the solution?

  Overnight
• What is done to the potato cylinders after removing them from the solution?

  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 the cells
• What must be calculated after measuring the length and mass again?

  Percentage change in length and mass
• What is the formula for calculating percentage change?

  Percentage change = (change/original) × 100
• If a potato cylinder has a starting mass of 1.56 grams and increases by 0.25 grams, what is the percentage change?

  +16.03 percent
• If a potato cylinder has a starting mass of 1.32 grams and decreases by 0.19 grams, what is the percentage change?

  • 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 at that concentration
• What does the concentration at the x-axis crossing indicate?

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

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

  1. Peel the potato.
  2. Use a cork borer to create cylinders.
  3. Trim cylinders to the same length.
  4. Measure length and mass of cylinders.
  5. Place cylinders in different sugar solutions.
  6. Leave overnight for osmosis to occur.
  7. Roll cylinders on paper towel.
  8. Measure length and mass again.
  9. Calculate percentage change.
• What are the key concepts of osmosis in plant cells?

  • Water moves from dilute to concentrated solutions.
  • Cells expand in dilute solutions.
  • Cells shrink in concentrated solutions.
  • Distilled water is used to avoid impurities.