(S3)C7 - Mass transport

Question 1

use the cohesion-tension theory of water movement through a plant and why the diameter of the trunk is smallest at midday (6)

Answer 1

• diameter of trunk minimal at warmest/brightest time of day - (midday is the warmest and brightest)
• Stomata open in light = more water loss
• Water evaporates even more when warm
• Hydrogen bonds occur between water molecules (cohesion)
• Then adhesion between water molecules and walls of xylem vessels
• Xylem is pulled inwards by the faster flow of water and pulled in by tension

Question 2

Three ways in which the leaves of xerophytic plants may be adapted to reduce water loss (3)

Answer 2

• thick cuticle (wax layer)
  ^waterproof and impermeable
• reduced number of stomata
  ^reduced surface area for water loss
• small leaves
  ^reduced surface area for water loss