Transpiration and pressure flow Water and Nutrients Transpiration and pressure flow

32.3 Transpiration pulls water up xylem vessels Transpiration-cohesion-tension mechanism Water’s cohesion describes its ability to stick to itself Water’s adhesion describes its ability to stick to other surfaces; water adheres to the inner surface of xylem cells (Think of sucking soft drink up a straw) For the BioFlix Animation Transpiration, go to Animating and Video Files. Teaching Tips 1. The cohesive property of water allows some insects to walk or stand on a liquid water surface. The cohesion and adhesion of water is also the reason why we need to dry ourselves off after taking a shower, since water still clings to our skin and hair. 2. Demonstrate or ask students to recall what happens when a soda straw is lifted out of a beverage: some of the beverage still sticks to the straw. This is an example of adhesion. Copyright © 2009 Pearson Education, Inc.

Cohesion and adhesion in the xylem Xylem sap Mesophyll cells Air space within leaf Stoma 1 Outside air Adhesion Transpiration 4 Cell wall Water molecule Flow of water 2 Cohesion by hydrogen bonding Xylem cells Cohesion and adhesion in the xylem Figure 32.3 The flow of water up a tree. 3 Root hair Soil particle Water Water uptake from soil

32.4 Guard cells control transpiration open pores in leaves called stomata to allow CO2 to enter for photosynthesis Water evaporates from the surface of leaves through stomata Guard cells can regulate the amount of water lost from leaves by changing shape and closing the stomatal pore Teaching Tips 1. The change in shape of guard cells is due to internal fluid pressure, or turgor—important in many other organisms. Turgor helps maintain the shape of plant cells, gives structure to the hydrostatic skeletons of sea anemones and earthworms, and causes a penis to become firm upon erection. Before addressing guard cells, you may challenge your class to explain what leaves, earthworms, and an erect penis have in common. The answer is turgor. Copyright © 2009 Pearson Education, Inc.

H2O H2O H2O H2O H2O H2O K+ H2O H2O H2O H2O Stoma Guard cells Vacuole Figure 32.4 How guard cells control stomata. K+ Vacuole H2O H2O H2O H2O Stoma opening Stoma closing

32.4 Guard cells control transpiration Regulation factors: Open in the day, closed at night-triggered by sunlight Low CO2 concentration signals open Water availability Teaching Tips 1. The change in shape of guard cells is due to internal fluid pressure, or turgor—important in many other organisms. Turgor helps maintain the shape of plant cells, gives structure to the hydrostatic skeletons of sea anemones and earthworms, and causes a penis to become firm upon erection. Before addressing guard cells, you may challenge your class to explain what leaves, earthworms, and an erect penis have in common. The answer is turgor. Copyright © 2009 Pearson Education, Inc.

Phloem transports the products of photosynthesis throughout the plant 32.5 Phloem transports the products of photosynthesis throughout the plant Phloem sap - sucrose and other solutes such as ions, amino acids, and hormones Sugars are carried through phloem from sources to sinks Student Misconceptions and Concerns 1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction. Teaching Tips 1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner. Copyright © 2009 Pearson Education, Inc.

32.5 Phloem transports sugars A sugar source Leaves produce sugars via photosynthesis Roots and other storage organs produce sugar via breakdown of starch A sugar sink is a plant organ that is a net consumer of sugar or one that stores starch Growing organs use sugar in cellular respiration Roots and other organs store unused sugars as starch Student Misconceptions and Concerns 1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction. Teaching Tips 1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner. Copyright © 2009 Pearson Education, Inc.

32.5 Phloem transports sugars The pressure flow mechanism High solute concentration caused by the sugar in tubes causes water to rush in from nearby xylem cells Flow of water into tubes increases pressure at sources At sinks, sugars are unloaded from tubes and solute concentration decreases; water is lost and pressure is low The pressure gradient drives rapid movement of sugars from sources to sinks Student Misconceptions and Concerns 1. Although analogies are often useful, some of their particulars can be misleading. In many ways, the vascular tissues and movement of fluid through plants are unlike the circulatory system of vertebrates. Whereas vertebrates have a one-way flow of fluids propelled by a contracting heart through a contained tubular system, phloem sap, propelled instead by a pressure flow mechanism, can move in either direction. Teaching Tips 1. Many phloem saps other than maple syrup are used commercially. For example, phloem sap from rubber trees native to the Brazilian Amazon was once the major source of rubber. (Most rubber is now synthetically produced.) Pine oil, derived from pine tree resin, is the active ingredient in Pine-Sol cleaner. Copyright © 2009 Pearson Education, Inc.

High sugar concentration Phloem Xylem High water pressure Sugar Sugar 1 High water pressure Sugar Sugar source 2 Water Source cell Sieve plate Sugar sink Sink cell Figure 32.5B Pressure flow in plant phloem from a sugar source to a sugar sink (and the return of water to the source via xylem). 3 Sugar 4 Water Low sugar concentration Low water pressure