Transpiration

• What is transpiration defined as?

  The loss of water vapour by evaporation from the aerial parts of a plant
• How do nitrates contribute to root pressure?

  Nitrates are actively pumped from the endodermis into the xylem, causing water to move in via osmosis
• What is the effect of root pressure on water movement in plants?

  It forces water up the xylem, effective up to a couple of metres
• Why is root pressure important for seedlings?

  It is important for seedlings with a low leaf surface area for transpiration
• What theory explains the transpiration pull in plants?

  The Cohesion-Tension Theory
• How do hydrogen bonds contribute to water movement in plants?

  They hold water molecules together, allowing one molecule to pull the rest up the xylem
• What happens to water molecules as they move down a water potential gradient in the xylem?

  A water molecule pulls the rest of the water molecules up the xylem due to cohesion
• What role does capillary action play in water movement in plants?

  It attracts water molecules to the sides of the xylem vessels due to adhesion
• What pathways does water move across the leaf?

  Apoplast, symplast, and vacuolar pathways
• How does water evaporate from the leaf surface?

  Water evaporates from the surface of the mesophyll cells into the air spaces
• What is the function of stomata in plants?

  They allow gas exchange with the atmosphere
• What gas is taken in by plants during photosynthesis?

  Carbon dioxide (CO₂)
• What happens to water when stomata are open?

  Water is lost easily from the plant
• Where are stomata mostly found on leaves?

  On the under surface of leaves
• What happens to guard cells when they are turgid?

  They bend to open the pore of the stoma
• What factors affect the rate of transpiration?

  • Number of leaves
  • Number, size, and position of stomata
  • Presence of cuticle
  • Light
  • Temperature
  • Relative humidity
  • Air movement (wind)
  • Water availability
  • Soil moisture
• What are xerophytes?

  Plants adapted to very arid (dry) conditions
• What are hydrophytes?

  Plants adapted to very wet conditions
• What should you complete regarding xerophytes and hydrophytes?

  • Complete the tables about xerophytes and hydrophytes in the booklet
  • Answer questions on page 209 of the CGP book