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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
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Exam code:9700

The process of osmosis

  • All cells are surrounded by a cell membrane which is selectively permeable

  • Water can move in and out of cells by osmosis

  • Osmosis is the diffusion or net movement of water molecules from a dilute solution (high water potential) to a more concentrated solution (low water potential) across a selectively permeable membrane

    • The cell membrane is selectively permeable which means it allows certain molecules (like water) through the bilayer

Diagram showing a partially permeable membrane. Large solute molecules are blocked, while small water molecules pass through the membrane.
Osmosis and the selectively permeable membrane
Diagram shows osmosis: water moves from dilute to concentrated sugar solution across a membrane. Key explains symbols for molecules and water movement.
How osmosis works

Examiner Tips and Tricks

Water can pass through the phospholipid bilayer because water molecules are small molecules that can pass between phospholipids in the cell membrane.

Although water molecules are polar, they can still pass through the bilayer because of their small size.

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