Water Potential and Osmosis

Water Potential

Osmosis

• Osmosis: the movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane
• Types of osmosis:
  • Isotonic: equal solute concentration on both sides of the membrane
  • Hypotonic: higher solute concentration outside the cell
  • Hypertonic: higher solute concentration inside the cell
• Osmosis affects cell shape and turgor pressure:
  • Hypotonic: cell swells and becomes turgid
  • Hypertonic: cell shrinks and becomes flaccid

Water Uptake

• Water uptake in plants occurs through the roots
• Root hair cells have a large surface area for absorption
• Water enters the root through the process of osmosis
• Water then moves up the xylem through transpiration pull

Transpiration

• Transpiration: the process of water movement through a plant, from the roots to the leaves, and evaporation from the leaves
• Factors affecting transpiration rate:
  • Temperature
  • Humidity
  • Light intensity
  • Wind speed
• Transpiration pull: the suction force created by evaporation from the leaves, which pulls water up the xylem

Plasmolysis

• Plasmolysis: the process by which a cell loses water and shrinks away from the cell wall
• Occurs when a cell is placed in a hypertonic solution
• Steps of plasmolysis:
  1. Water leaves the cell through osmosis
  2. Cell membrane pulls away from the cell wall
  3. Cell shrinks and becomes flaccid
• Plasmolysis can be reversible if the cell is returned to an isotonic solution

Water Potential

Osmosis

• Osmosis is the movement of water molecules from high to low concentration through a selectively permeable membrane
• Isotonic solution: equal solute concentration on both sides of the membrane, no net water movement
• Hypotonic solution: higher solute concentration outside the cell, water enters the cell, and it swells and becomes turgid
• Hypertonic solution: higher solute concentration inside the cell, water leaves the cell, and it shrinks and becomes flaccid

Water Uptake in Plants

• Water uptake occurs through the roots, which have a large surface area for absorption
• Root hair cells are specialized for water absorption
• Osmosis is the process by which water enters the root
• Water then moves up the xylem through transpiration pull

Transpiration

• Transpiration is the process of water movement through a plant, from roots to leaves, and evaporation from the leaves
• Factors affecting transpiration rate: temperature, humidity, light intensity, and wind speed
• Transpiration pull is the suction force created by evaporation from the leaves, which pulls water up the xylem
• Transpiration is essential for plant growth, as it helps to distribute nutrients and sugars

Plasmolysis

• Plasmolysis is the process by which a cell loses water and shrinks away from the cell wall
• Occurs when a cell is placed in a hypertonic solution, causing water to leave the cell through osmosis
• Steps of plasmolysis: water leaves the cell, cell membrane pulls away from the cell wall, and the cell shrinks and becomes flaccid
• Plasmolysis can be reversible if the cell is returned to an isotonic solution