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

Understand the concept of osmosis, its types, and its effects on cell shape and turgor pressure. Learn about isotonic, hypotonic, and hypertonic solutions.