osmosis

• Osmosis

  The net movement of water molecules across a partially permeable membrane from a region of higher water concentration to a region of lower water concentration
• Water concentration


  The amount of water as compared to the other molecules like sugars or salts that are dissolved in that water
• Solutes are the dissolving molecules in water
• Solutes

  • Sugars
  • Salts
• Osmosis in cells


  Water particles diffuse from the outside of the cell (higher water concentration) down the concentration gradient into the cell (lower water concentration)
• Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration
• Osmosis is a special case of diffusion, specifically the diffusion of water molecules
• Water concentration is determined by the proportion of water compared to solutes, not the volume of water
• The cell's partially permeable membrane separates the inside of the cell from the outside
• During osmosis, water moves down the concentration gradient (from high to low)
• Osmosis is a passive process because it doesn’t require any energy from the cell.
• What happens if you place a plant cell in a very salty solution?

  1. There will be a higher water concentration (water potential) within the plant cell than in the salty solution surrounding it.
  2. So water will move from the inside of the plant cell to the outside, by osmosis.
  3. This will cause the cell to shrink and become plasmolysed.
• What happens if you place a plant cell in a beaker of pure water?

  1. There will be a lower water concentration (water potential) within the plant cell than in the pure water surrounding it.
  2. So water will move from the beaker into the plant cell, by osmosis.
  3. This will cause the cell to expand, and become turgid.
• If you add sugars and salts to a beaker of water, what will happen to the water concentration?

  The water concentration will decrease.