OSMOSIS

• EXAMPLE OF OSMOSIS

  If you wash your clothes by hand for a long time, your finger will get pruned or wrinkled.

  • In this case, the finger skin absorbs water and gets expanded.
• At the cellular level, osmosis is a very common process. It is another passive transport mechanism that requires no energy in order to occur.
• Osmosis is the diffusion of water molecules.

  • Water moves into and out of cells depending on the differences of solute concentration outside and inside the cell.
• Hypertonic - the solution with the higher solute concentration
• Hypotonic - the solution with the lower solute concentration
• Isotonic - solutions of equal solute concentration
• Osmosis - is the diffusion of water molecule across a selectively permeable from an area of higher concentration to an area of lower concentration.

  • Water moves into and out of cells by osmosis.
• If a cell is in a hypertonic solution, the solution has a lower water concentration than the cell cytosol, and water moves out of the cell until both solutions are isotonic.
• Cells placed in a hypotonic solution will take in water across their membrane until both the external solution and the cytosol are isotonic.
• • Cell that does not have a rigid cell wall, such as RBC, will swell and lyse (burst) when placed in a hypotonic solution.
  • Cell with a cell wall will swell when placed in a hypotonic solution, but once the cell is turgid (firm), the tough cell wall prevents any more water from entering the cell.
• When placed in a hypertonic solution, a cell without a cell wall will lose water to the environment, shrivel, and probably die.

  • In a hypertonic solution, a cell with a cell wall will lose water too.
• The plasma membrane pulls away from the cell wall as it shrivels, a process called PLASMOLYSIS.
• Animal cells tend to do best in an isotonic environment, plant cells tend to do best in a hypotonic environment. This is demonstrated in the figure below:

  A) plasmolyzed

  B) flaccid

  C) turgid

  D) hypertonic

  E) isotonic

  F) hypotonic

  
• Unless an animal cell (such as the RBC in the top panel) has an adaptation that allows it to alter the osmotic uptake of water, it will lose too much water and shrivel up in a hypertonic environment.
• If animal cell is placed in a hypotonic solution, water molecules will enter the cell, causing it to swell and burst.
• Plant cells (bottom panel) become plasmolyzed in a hypertonic solution but tend to do best in a hypotonic environment.

  • Water is stored in the central vacuole of the plant cell.
• Imagine you have a cup of 100ml water, and you add 15g of table sugar to the water.

  • Sugar - solute
  • Water - solvent
  • Mixture of solute in a solvent is called SOLUTION.
• In comparing two solutions of unequal solute concentration, it can be:

  • Hypertonic
  • Hypotonic
  • Isotonic