osmosis

osmosis is a special case of diffusion that deals with water molecules

water concentration is the amount of water, as compared to other molecules, like sugars or salts, that are dissolved in the water

• is you use two jars full of water and put one molecule of a solute into one jar and then three into the other one, the one with three has a higher concentration of solutes and a lower concentration of water

  • the other one has a higher water concentration and lower solute concentration

in a cell

• inside the cell there is a mix of solutes and water (lower water concentration), while there is mostly water (higher water concentration)

• the water outside of the cell

a liquid with high water concentration is dilute

• low water is concentrated

water potential

• a liquid with low water potential is a concentrated solution

• a high water potential is a dilute solution

osmosis can be defined as the net movement of water molecules from a region of high water potential to low water potential through a semi-permeable membrane

at even concentration, water particles still move, but net movement is zero

roles of osmosis

• controlling guard cells

• uptake of water by roots

• reabsorption in the kidneys

• absorption in the intestines

water balance problems

• tonicity is the differences in solute concentration inside and outside the cell

• examples

  • hypotonic - less solute outside the cell meaning higher water concentration outside the cell

    • water enters the animal cell via osmosis which causes lysis (cell membrane can’t withstand pressure)

    • it is not the same with plant cells sue to the presence of the cell wall and the vacuole

      • the vacuole fills up which exerts pressure on the cell wall, this causes it to become firm and swollen

  • hypertonic - high solute outside the cell meaning higher water concentration inside the sell

    • water leaves the animal cell, causing the cell to shrink

      • this process is called crenation (loose water, become distorted)

    • in a hypertonic environment, the cell might be able to create mechanisms to pump solutes out of the cell

    • as water leaves the plant cells, the vacuole looses water causing it to shrink along with the cell membrane from the wall, which leads to eat losing turgor energy

      • loss of turgidity causes the plant to wilt

      • the shrinking of the cell membrane from the cell wall is called plasmolysis

  • isotonic - the concentration of solutes is equal inside and outside the cell, so there is no net movement of water

    • in an animal cell, it maintain it’s shape and size which allows it to function properly and keep structural integrity

    • in a plant cells, there is no net movement of water so the plant cells becomes flaccid (the cell is no longer turgid)