Osmosis

• What is osmosis?

  The net movement of water from high water potential to low water potential across a selectively permeable membrane
• Why is osmosis considered a passive process?

  It requires no energy from ATP and is unaffected by respiratory inhibitors
• What happens when water potentials are equal on both sides of a membrane?

  Water moves in both directions equally, resulting in no net movement
• How is water potential defined?

  As the tendency of water to leave a system by osmosis
• What factors determine the water potential of a solution?

  Solute concentration (solute potential) and pressure exerted on the solution (pressure potential)
• What are the units for water potential?

  kPa
• How does solute concentration affect water potential?

  The higher the concentration of solute, the lower the water potential
• What happens to the water potential of a cell when glucose or ions diffuse into it?

  The water potential of that cell becomes more negative
• Which cells are commonly used to demonstrate osmosis in animals?

  Red blood cells
• What are the two main issues with using blood products in osmosis experiments?

  Blood may be infected and it clots when removed from an animal
• What do the terms hypotonic, isotonic, and hypertonic refer to?

  • **Hypotonic**: Lower solute concentration, higher water potential
  • **Isotonic**: Same concentration of solute, same water potential
  • **Hypertonic**: Higher solute concentration, lower water potential
• What occurs when blood cells are placed in a hypotonic solution?

  Water moves into the cells, causing them to expand and potentially burst (haemolysis)
• What is haemolysis?

  The bursting of red blood cells due to increased pressure from water intake
• What happens when blood cells are placed in a hypertonic solution?

  Water moves out of the cells, causing them to shrivel (crenating)
• What occurs in an isotonic solution regarding blood cells?


  There is no net movement of water
• How does water potential in plant cells differ from that in animal cells?

  It depends on solute concentration and pressure potential generated by the cell wall
• What happens when plant cells become turgid?

  The cytoplasm pushes against the cell wall, preventing further expansion
• What is the relationship between solute, water, and pressure potentials in plant cells?

  Expressed by the equation: $Ψ =$$Ψ_s +$$Ψ_p$
• What happens to plant cells in a solution with a higher water potential?

  Water enters by osmosis, causing the cells to become turgid
• What is the water potential of a cell when it cannot take in more water?

  It is 0, meaning solute and pressure potentials cancel each other out
• What occurs when plant cells are immersed in solutions with lower water potential?

  Water leaves the cells by osmosis, causing plasmolysis
• What is plasmolysis?

  The shrinking of the vacuole and cytoplasm due to loss of water
• What is incipient plasmolysis?

  The point where 50% of cells are plasmolysed, indicating equal water potential
• What is the pressure potential of cells at incipient plasmolysis?

  It is 0 kPa, with equal water and solute potentials