10.1.8 Moving water around a plant + transpiration

• Transpiration


  The loss of water vapour from the leaves
• Transpiration


  1. Evaporation of water from the spongy mesophyll cells into air spaces

  2. Diffusion of water vapour through air spaces and out through the open stomata
• Cohesion


  The attraction of water molecules to each other
• Water forms a continuous column from root to leaf
• Transpiration pull


  The force created by the cohesion of water molecules that pulls water up the xylem
• Environmental and physical factors

  Can affect the rate of transpiration
• Wilting


  Cells lose their turgidity and plasmolyse
• Potometer


  Measures the volume of water absorbed by a plant, which might indicate the rate of transpiration
• Using a potometer


  1. Air bubble moves as the plant takes up water

  2. Can time how long it takes the air bubble to move a certain distance
• Uptake does not definitely equal transpiration rates because some water is used to keep cells turgid and some is used in photosynthesis
• Using petroleum jelly to investigate transpiration rates

  Water loss can be measured by rubbing petroleum jelly on leaf surfaces and measuring the difference in mass

  
• Leaves with both upper and lower epidermis covered in petroleum jelly had the smallest % decrease in mass (2%), meaning they had the least transpiration

  
• Leaves with no jelly covering had the highest % decrease in mass (40%), meaning they had the highest transpiration rate