Osmosis

• What is osmosis?

  The diffusion of water across a membrane
• What does osmosis involve in terms of water potential?

  Water moves from higher to lower water potential
• What is the water potential of pure water?

  Zero
• How does adding solutes affect water potential?

  It lowers the water potential, making it negative
• What are isotonic solutions?

  Solutions with the same water potential
• What happens to cells in an isotonic solution?

  They won't lose or gain water
• What is a hypotonic solution?

  A solution with higher water potential than the cell
• What occurs when a cell is placed in a hypotonic solution?

  The cell swells as water moves in
• What is a hypertonic solution?

  A solution with lower water potential than the cell
• What happens to a cell in a hypertonic solution?

  The cell may shrink as water moves out
• What factors affect the rate of osmosis?

  • Water potential gradient
  • Thickness of the exchange surface
  • Surface area of the exchange surface
• How does the water potential gradient affect osmosis?

  A higher gradient increases the rate of osmosis
• How does the thickness of the exchange surface affect osmosis?

  A thinner surface increases the rate of osmosis
• How does surface area affect the rate of osmosis?

  A larger surface area increases the rate of osmosis
• What are the steps to investigate water potential using potato cylinders?

  1. Make serial dilutions of known concentrations
  2. Measure change in mass of potato chips
  3. Produce a calibration curve
• What is a serial dilution?

  A set of solutions decreasing in concentration
• How do you create a 1 M sucrose solution from a 2 M solution?

  Mix 5 cm³ of 2 M with 5 cm³ water
• What should you do after placing potato chips in sucrose solutions?

  Measure and record their mass after 20 minutes
• What does a calibration curve represent in this experiment?

  Percentage change in mass vs. sucrose concentration
• What will happen to potato chips in solutions with higher water potential?

  They will gain water and mass
• What will happen to potato chips in solutions with lower water potential?

  They will lose water and mass