Lecture on Osmosis

Definition

• Osmosis: Net movement of water molecules from a region of high water potential to low water potential through a partially permeable membrane.
• Water Potential: Ability of water to move, influenced by solutes. Pure water has the highest water potential at zero.

Key Points

• Water potential symbol resembles a devil's fork (ψ).
• Adding solutes to pure water makes water potential more negative.

Example: Comparing Cells

• Cell B vs. Cell A: Water Potential

  • Cell B: higher water potential (0) than Cell A.
  • Water moves from Cell B to Cell A down the water potential gradient by osmosis.

• Cell B vs. Cell C: Water Potential

  • Cell B: higher water potential than Cell C.
  • Water moves from Cell B to Cell C down the water potential gradient by osmosis.

• Cell C vs. Cell A: Water Potential

  • Cell C: higher water potential than Cell A.
  • Water moves from Cell C to Cell A down the water potential gradient by osmosis.

Types of Solutions

• Hypotonic Solution: Higher water potential outside the cell, causing water to enter the cell.

  • Plant cells: Water enters the vacuole, making it turgid.

• Hypertonic Solution: Lower water potential outside the cell, causing water to leave the cell.

  • Plant cells: Cells become flaccid and can become plasmolyzed (membrane pulls away from cell wall).

• Isotonic Solution: Same water potential inside and outside the cell.

Special Cases: Animal Cells

• Animal Cells in Lower Water Potential: Lyse

  • Water leaves animal cells down water potential gradient, cells may shrivel.

• Animal Cells in Pure Water: Burst

  • Water enters the cells by osmosis, causing them to burst due to lack of cell wall.