Osmosis

• Osmosis


  The movement of water from a dilute solution to a more concentrated solution through a selectively permeable membrane
• Selectively permeable membrane


  • Allows small molecules (water) through but not larger molecules (sugar)
• Turgor


  The state of a plant cell when it has gained enough water by osmosis for the cell membrane to push against the cell wall, making the cell firm
• Plasmolysis


  A plant cell is plasmolysed when it has lost water by osmosis and its membrane separates from the cell wall
• Why plants need water

  1. For support (turgor)

  2. For transpiration - the movement of water up through a plant, its evaporation from leaf cells followed by diffusion out of the stomata

  3. For transport - as the water moves up through the plant it carries minerals

  4. As a raw material in photosynthesis
• Measuring transpiration


  1. The bubble potometer - measures the rate of water uptake by a cut shoot

  2. The weight potometer - compares rates of transpiration by measuring the loss in mass of a pot plant (or shoot in a flask)
• Factors affecting the rate of transpiration

  • Temperature
  • Wind speed
  • Humidity
  • Light/darkness
  • Surface area of leaves (or number of leaves)
• Transpiration - the evaporation of water from mesophyll cells, followed by diffusion through the leaf air spaces and stomata
• Osmosis and plants

  • Water enters through osmosi
• Osmosis and plants

  • Water enters the cell by osmosis
  • The vacuole expands pushing against the cell membrane
  • This causes the turgor necessary for support
  • The cell wall stops the membrane expanding too far to cuase damage
  • Opposite - plasmolysis
• Hypertonic solution


  Concentrated
• Hypotonic solution


  Dilute