Transcript Class Notes
Transport in flowering plants Transpiration http://croptechnology.unl.edu/animationOut.cgi?anim_name=transpiration.swf Lesson Objectives By the end of this lesson you should be able to: • 1) Define the term transpiration and explain that transpiration is a consequence of gaseous exchange in plants. • 2) Describe the factors that affect transpiration rate Get this right • Water potential= a measure of the tendency of water to move from one place to another. higher water • A dilute solution has a ............... potential than a concentrated one. • Water moves from a solution of higher water potential to a solution of lower water potential Capillary action- cohesion • Each molecule of water consists of 1 oxygen and 2 hydrogen atoms negative • Oxygen carries ............. charge positive • Hydrogen carries ............. charge • Charges results in forces of attraction between water molecules: force of cohesion Capillary action- adhesion • Water also sticks to the inner surface of xylem vessels • The wall of the xylem just above the water surface attracts water molecules upwards: force of adhesion Transpiration- How? • Definition: The loss of water vapour from the aerial parts of a plant Higher water potential open for • Stomata on the surface of leaves Lower water gaseous exchange potential • Air surrounding the leaves are “drier” • Water molecules exit the leaves through the stomata Transpiration- the process •Stomata open for gaseous exchange •More water vapour molecules in-between the spongy mesophyll cells than the outside air •Water molecules diffuses out of the leaves through the stomata •Loss of water creates water potential difference between xylem and mesophyll cells •Water moves out of xylem vessels through osmosis •Chain of water molecules pulled upwards with the assistance of the forces of cohesion and adhesion Factors affecting the rate of transpiration Factors Rate of transpiration Rate of transpiration will be fast if will be slow if http://passel.unl.edu/pages/animation.php?a=transpiration.swf Factors affecting the rate of transpiration Factors Rate of transpiration Rate of transpiration will be fast if will be slow if Humidity dry damp/ humid Temperature warm cold/ cool Light bright dim Wind windy still Quick check Are you able to: • 1) Define the term transpiration and explain that transpiration is a consequence of gaseous exchange in plants. • 2) Describe the factors that affect transpiration rate 1. Windier conditions increases transpiration rate because the boundary layer around the leaf is smaller. (T/F) 2. Transpiration rate is lower at night due to lower temperature. (T/F) 3. The water vapour concentration gradient is due to the difference in water vapour concentration between the atmosphere and the leaf. (T/F)